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International Journal of Ventilation ISSN 1473-3315 Volume 12 No 2 September 2013
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101
The Effects of Ventilation in Homes on Health
P. Wargocki
International Centre for Indoor Environment and Energy, DTU Civil Engineering,
Technical University of Denmark
Abstract
It is estimated that people in the developed world spend more than 85-90% of their time indoors. Of this,
most is spent in homes. To minimize health risks from pollutants occurring in homes, exposures should be
controlled. The most effective way to achieve this is to control sources of pollutants and to reduce emissions.
Often, especially in existing buildings, this strategy is difficult to implement, in which case exposures are
controlled by providing sufficient, presumably clean, outdoor ventilation air to dilute and remove the
contaminants.
The present paper attempts to find out how much ventilation is needed in existing homes to reduce health
risks. This is achieved by reviewing the published scientific literature investigating the association between
measured ventilation rates and the measured and observed health problems.
The paper concludes that, generally, there are very few studies on this issue and many of them suffer from
deficient experimental design, as well as a lack of proper characterization of actual exposures occurring
indoors. Based on the available data, in the reviewed studies, it seems likely that health risks may occur
when ventilation rates are below 0.4 air changes per hour in existing homes. No data were found indicating
that buildings having dedicated natural ventilation systems perform less well than the dwellings in which
mechanical ventilation systems are installed. Newly installed mechanical ventilation systems were observed
to improve health conditions. In homes with existing ventilation systems this positive effect was less evident,
probably due to poor performance of the system (too low ventilation rates and/or poor maintenance).
Studies are recommended in which exposures are much better characterized (by for example measuring the
pollutants indicated by the WHO Guidelines for Indoor Air Quality and improving ventilation
measurements). Exposures should also be controlled using different ventilation methods for comparison.
Future studies should also advance the understanding of how ventilation systems should be operated to
achieve optimal performance. These data would create further input and support to the guidelines for
ventilation based on health developed currently in the framework of the HealthVent project
(www.healthvent.eu).
Key words: ventilation, ventilation rate, ventilation system, housing, homes, health, pollutants.
1. Introduction
1.1 Background
How much ventilation is needed indoors and which
requirements should be used to design ventilation?
These two questions have been high on the research
agenda for years. They can be readdressed again
especially when strict requirements for energy use in
buildings are implemented and when there is a need
to make buildings tight and energy efficient (EPBD,
2010) so that the quality of life is not compromised
(e.g., Fisk et al., 2011; Wargocki, 2011).
Undoubtedly human responses should be used to
define ventilation requirements. However, it is
relevant to ask whether comfort requirement should
be used, as has been the case for years in many
ventilation standards and guidelines (EN15251,
2007; ASHRAE, 2010; ECA, 1992), or if ventilation
requirements should be based on health outcomes. It
may be argued that both are the same thing if the
World Health Organization’s (WHO) definition of
health is considered (1948). Still the link between
comfort and health is not clearly established and it is
not certain whether ensuring comfort requirements
will abate health risks and vice versa.
P Wargocki
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102
Ventilation modifies exposures occurring indoors.
It cannot reduce the emissions. It is used to dilute
and remove the pollutants occurring indoors. For
some pollutants the effectiveness of ventilation can
be quite high, and for some pollutants it can be
rather low. Ventilation can also bring the outdoor
pollutants that are otherwise not present indoors.
Consequently, ventilation requirements should be
defined based on the exposures occurring indoors.
The ventilation requirement can be estimated based
on the emission rates of pollutants, so that the
pollutants occurring indoors are at levels without
concern for human health and comfort. The
problem is that there are very limited data on the
relationship between pollutants occurring indoors,
their concentrations and health (WHO, 2010). Even
if the data for all pollutants were available, it
would be difficult to take into account all possible
interactions between pollutants, reactions occurring
between pollutants and all potential
transformations.
A pragmatic approach for setting ventilation
requirements can be proposed by observing, in real
buildings, whether there is an elevated risk for
health and comfort complaints in the case when the
ventilation rate is at or below a certain level; this
approach is now being exercised by the HealthVent
project (Wargocki et al., 2012). The disadvantage of
this approach is that buildings can differ between
each other in terms of exposures and pollutants
occurring indoors, as well as by other factors which
are difficult to control, such as temperatures,
moisture level and relative humidity (RH), noise,
light, surroundings, etc. They all potentially can
have an impact on human response and can obscure
the relationship with ventilation. Furthermore,
different buildings can be populated by different
people and thus the experimental observations from
these buildings may not be representative for the
general population.
Several studies have been carried out to investigate
the relationship between ventilation and human
responses both in the laboratory and as field studies.
Summaries and critical assessments can be found in
many reviews published previously (e.g., Mendell,
1993; Godish and Spengler, 1996; Seppänen et al.,
1999; Seppänen et al., 2002; Wargocki et al., 2002;
Davies et al., 2004; Angell et al., 2005; Richardson
et al., 2005; Grimsrud, 2006; Bonnefoy, 2007; Li et
al., 2007; Bone et al., 2010; Sundell et al., 2011).
An important limitation of the previous studies on
ventilation and health is that they have each used
different methods to characterize ventilation and
human response outcome. This makes it very
difficult to compare the results obtained in these
different studies. In some studies proxies for
ventilation were used, such as the concentration of
carbon dioxide (CO2), as well as proxies for human
response outcomes, such as the concentration and
prevalence of house dust mite (HDM) allergens
because there is consistent evidence that the
prevalence of HDM allergens increases the risk of
asthma. Another predicament is that when the
performance of different ventilation systems were
compared in different buildings there was
insufficient control for potentially disturbing factors
such as differences in exposures to air pollutants. In
spite of these limitations the previous studies
provide direct data on the importance of ventilation
for human health and comfort.
The present work tries to recapitalize on the results
of these past studies and reviews, particularly with
regard to the importance of ventilation for health in
residential buildings.
1.2 Objective
The main objective of the present work was to
prepare a state-of-the-art report on ventilation and
health in homes. In particular, the following
research questions were addressed: (i) Does a
relationship exist between health and ventilation in
residential buildings?; (ii) What is the potential
reason for the observed relationship?; (iii) Which
health problems are related to ventilation?; (iv) Are
there any differences in prevalence of health
symptoms in residential buildings having different
ventilation systems?; (v) Are there any differences
in the prevalence of health problems among
different population groups?; and (vi) Does
ventilation itself contribute to the pollution of
indoor air in residential buildings?
2. Method
2.1 Approach
To address these research questions the following
approach was implemented: (i) hypotheses and
search terms were defined; (ii) a literature search
was performed; (iii) abstracts of all identified papers
and reports were screened; (iv) literature was
grouped as follows: literature providing information
on ventilation and its proxies, and health and its
proxies; literature providing information on
exposure ventilation and its proxies, but not on
International Journal of Ventilation ISSN 1473-3315 Volume 12 No 2 September 2013
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103
health and its proxies; surveys and reviews; and
literature not relevant for the objective of the present
work; (v) reference lists in surveys and reviews
were screened to identify whether there were any
other papers that were missed in the literature
search, and if so they were included; and (vi) papers
providing information on ventilation and health,
addressing the objective, were reviewed and used to
form conclusions.
2.2 Literature Survey
Scientific literature on the association between
ventilation and health in nonindustrial residential
indoor environments was gathered by searching
through the following databases: MEDLINE by
National Library of Medicine; Cambridge Scientific
Abstracts (including Mechanical Engineering
Abstracts, Environmental Sciences and Pollution
Management Search sub-files, Biological Sciences
Search sub-files, TOXLINE, ERIC, Computer and
Information System Abstracts) and AIRBASE by
the Air Infiltration and Ventilation Centre (AIVC).
In addition, the Proceedings of Indoor Air, Healthy
Buildings, RoomVent, AIVC and CLIMA
congresses taking place in the last 10 years, i.e.
since 1999 were also surveyed.
The term “ventilation” was considered as both the
ventilation rate, i.e. amount of outdoor air supplied
to indoor spaces, and as the ventilation system, i.e.,
the way the air is supplied to indoor spaces – using
natural or mechanical forces, or combined, with or
without air-conditioning (AC). Proxies for
ventilation were also accepted including
concentration of CO2. Information on condensation
on windows was collected as a proxy for elevated
RH and low ventilation rate, but no specific term
was created for relative humidity in order not to
obscure the search. Health was considered to
follow the basic definition of the World Health
Organization (WHO, 1948): health is a state of
complete physical, mental and social well-being
and not merely the absence of disease or infirmity.
Proxies for health were also accepted, i.e.
pollutants for which there are documented effects
on health such as concentration of HDM allergens,
radon, etc. Nonindustrial residential indoor
environments were considered to represent all
kinds of housing: dwellings, row houses and
detached houses.
Only papers including records in each of the three
search categories were selected (as a source of
search records, keyword indexes of the international
conferences Indoor Air ’90, ’93 and ’99, and
Healthy Buildings ’97 and ’00 were used): (1) the
category “ventilation” including different records
pertaining to ventilation rates, e.g., air change rate,
air supply rate, etc., as well as ventilation systems,
e.g., infiltration, dedicated natural ventilation,
mechanical ventilation, etc.; (2) the category
“environment” including different records
pertaining to nonindustrial residential indoor
environments, e.g., dwellings, houses, etc.; and (3)
the category “health” including different records
pertaining to health, e.g. symptoms, diseases,
allergy, asthma, etc.; comfort and productivity were
not included.
3. Results
More than 140 papers and reports were identified
through the literature search. Among these, 34
documents were considered to provide information
relevant for the objective of the present work; their
details are given in Table 1. As many as 20 reviews
and surveys were identified on the topic of
ventilation and health. More than 60 papers were
irrelevant for the present work.
3.1 Asthma and Allergy Symptoms
Several studies, in some cases with large cohorts,
have been carried out to observe whether there is an
association between ventilation and asthma and
allergy symptoms. The results are inconsistent.
In studies with children, low ventilation rates were
strongly associated with increased risk of having
self-reported asthma and allergy symptoms (at least
2 out of 3 symptoms such as wheezing, eczema and
rhinitis) when conditions in homes of children with
symptoms (cases) and children without symptoms
(controls) were compared (Bornehag et al., 2005;
Hägerhed-Engman et al., 2009). The odds ratios
(indicating the risk) for wheezing and rhinitis were
significantly lower among infants in homes where
heat recovery ventilators were installed; similarly
there were reduced CO2 levels compared with
homes with placebo units without such a system
(Kovesi et al., 2009). Nocturnal chest tightness in
adults, a symptom of problems with the respiratory
system as a consequence of asthma, was associated
with higher CO2 levels indicating lower ventilation
rates in homes (Norbäck et al., 1995). Improper
ventilation defined as a ventilation problem was
associated with elevated risk of asthma (Ezratty et
al., 2003).
P Wargocki
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Table 1. Short summary of studies considered relevant for the purpose of the present work;
AC=air conditioning; PM=particulate matter; GLM=general linear model; RR=response rate;
SBS=Sick Building Syndrome; HDM=house dust mites; RH=relative humidity; PFT=perfluorocarbon tracer;
SARS=severe acute respiratory syndrome; CFD=computational fluid dynamics.
Reference Results Design Buildings Population Ventilation
rate Ventilation
type Health
endpoints
Bell et al.
2009
Presence of AC
reduced PM
exposure and
associated
health effects
Cross-
sectional,
analysis
through GLM
Houses (ca.
55,000
households)
Elderly (>65
years old);
55,000
households
N/A N/A, only
whether AC
present or
absent (from
registers)
Mortality and
PM10;
cardiovascular
and respiratory
hospitalizations
and PM2.5
Bornehag et
al. 2005
Hägerhed-
Engman et
al. 2009
Lower
ventilation
rates associated
with the risk of
being the case
(having asthma
and allergy
symptoms)
Case-control 390 houses 198 cases
and 202
controls
(from cohort
of 14,077)
Measured
with PFT
method;
median
0.34 h-1
(cases)
0.38 h-1
(controls)
With
mechanical
system
present and
absent
Self-estimated
asthma/allergy
symptoms:
wheezing,
eczema and
rhinitis
Clausen et
al. 2011
Toftum et al.
2011
Bekö et al.
2010
Ventilation rate
not associated
with being case
Case-base Houses Children,
200 cases
(with
asthma and
allergy
symptoms)
and 293
bases among
which 15
were cases
(from cohort
of 11,082)
0.46 h-1 for
cases and
bases
estimated
with CO2
measurements
With
mechanical
system
present and
absent
Self-assessed
asthma and
allergy
symptoms
(wheezing,
eczema and
rhinitis)
Coelho et al.
2005
Poorly
maintained
ventilation
systems (dirty
filters, blocked
vents)
associated with
health
complaints
Cross-
sectional
Collective
social
habitat
Elderly (60-
95 years
old), 96
persons
N/A Mechanical Health
complaints
Deger et al.
2010
Increased risk
of asthma for
children
leaving along
streets with
highly dense
traffic and on
ground floor
Cross-
sectional
Homes Children
(n=980 out
of 7980)
N/A Only
building
factors
registered;
whether
adequate
asthma
control
Asthma
Drinka et al.
1996
Presence of
recirculation
increased risk
of attack rates
of Influenza A
Cross-
sectional
4 nursing
homes
Elderly
(n=690)
N/A Mechanical
with 0%,
30% and
70%
recirculation
Influenza A
Table continues on next page.
International Journal of Ventilation ISSN 1473-3315 Volume 12 No 2 September 2013
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Table 1. (continued).
Reference Results Design Buildings Population Ventilation
rate Ventilation
type Health
endpoints
Emenius et
al. 2004
No association
between
whole-house
ventilation and
being a case
(but with RH
and
condensation
on windows
markers of
poor
ventilation)
Case-control Homes Children
181 cases
and 359
controls
from 4089
BAMSE
cohort)
Average
0.68±0.32 h-1,
69% >0.5 h-1
with PFT
method
With
mechanical
system
present and
absent,
mechanical
(exhaust
only)
Self-assessed
recurrent
wheezi
ng
Engvall et
al. 2003
Presence of
mechanical
ventilation
system reduced
ocular and
nasal
symptoms
Cross-
sectional
231 multi-
family
buildings
3241 of
4815
inhabitants
(RR=77%)
N/A With
mechanical
system
present and
absent
Self-assessed
ocular, nasal,
dermal and
respiratory
symptoms
Engvall et
al. 2005
Reduced
ventilation
caused the air
to be perceived
as poor and
stuffy but had
no effects on
SBS symptoms
1-year cross-
over
intervention
Multifamily
building
44 people 0.5-0.8 h-1 vs.
25-30%
reduced to
0.4-0.5 h-1
Mechanical SBS symptoms
Ezratty et al.
2003
Asthma
attacks,
headache and
migraine
associated with
poor
ventilation but
can also be
caused by other
factors
Cross
sectional
3373
households
in 8
European
towns
(LARES
survey)
8519
residents
N/A With forced
ventilation
system
present and
absent
Self-assessed
health
problems
Gustafsson
et al. 1996
Children
symptoms not
associated with
type of system;
mothers’
complaints of
poor air quality
and mucous
membrane
symptoms
related with
condensation
on windows
Cross-
sectional
Homes 638 children N/A With
mechanical
system
present and
absent l
Self-assessed
allergic
symptoms
Harving et
al., 1993
Reduced
ventilation rate
increased
concentration
of HDM
because of
higher RH
Cross-
sectional
Homes 96 families
with at least
1 asthmatic
<0.25h-1 vs.
0.25-0.5h-1
vs. >0.5 h-1
measured
with PFT
With
mechanical
system
present and
absent
Medical
diagnosis of
asthma; skin
prick test
Harving et
al. 1994
Increased
ventilation
rates reduced
HDM and RH
Case-control Houses 53 asthmatic
patients (of
which 23
controls)
0.4 to 1.5 h-1
measured
with PFT
Mechanical N/A (measured
HDM as a
proxy)
Table continues on next page.
P Wargocki
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Table 1. (continued).
Reference Results Design Buildings Population Ventilation
rate Ventilation
type Health
endpoints
Howieson et
al. 2003
Installation of
mechanical
ventilation
system with
heat recovery
improved
health
conditions
(reduced HDM
and RH)
Case- control Houses 68
asthmatics
<15 years
old, 32 +17
in active
groups
(cases) and
19 as
controls
N/A Mechanical Health
symptoms and
self-recorder
peak flow
(lung
functions)
Jacobs et al.
2009
Increased in
lead poisoning,
asthma and
obesity
associated with
increased use
of AC
Cross-
sectional,
longitudinal
Houses 2 national
cohorts
N/A N/A
(national
register of
changes in
use of AC
from 1970s
to 2000s)
National
register of
health
Jones et al.
1999
Building
factors were
not associated
with case status
Case-control Houses Children,
100
asthmatics
from 11,000
matched by
age and
gender
N/A N/A
(heating
methods
(incl. ducted
heating) and
other factors
related to
IAQ)
Doctor-
confirmed
asthma,
wheeze and
hay fever
Kishi et al.
2009
Mechanical
ventilation not
associated with
risks of sick
housing
syndrome
Cross-
sectional
2297
detached
houses of
5589
(RR=41.1%)
Residents N/A With
mechanical
system
present and
absent
Self-assessed
sick housing
syndrome
symptoms
Kovesi et al.
2009
Installation of
mechanical
ventilation
reduced rhinitis
and wheeze
(and RH) and
had no effect
on health
centre
encounters and
hospitalizations
Placebo-
controlled
intervention
51 houses of
68 selected
Inuit infants
in 37 homes
with placebo
and 14 in
homes with
active
ventilation
units
CO2
measured and
averaged 900
ppm with
system and
1,400 ppm
without
Mechanical Self-assessed
respiratory
symptoms and
health centre
encounters
Leech et al.
2004
Self-assessed
throat
irritation,
cough, fatigue
and irritability
reduced for
cases
Case-control Cases = 52
houses with
energy
efficient
ventilation
and best
construction
practices;
Controls=53
houses in
the same
price range
Occupants,
128 cases
and 149
controls
N/A Mechanical
ventilation
system
Self-estimated
health
symptoms
Li et al.
2005
CFD modelling
of wind
pressure
predicted
ventilation rate
and virus
spread between
flats
Simulation by
CFD; no
measurements
Multi-flat
blocks
N/A N/A With
mechanical
system
absent
SARS
infection rate
Table continues on next page.
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Table 1. (continued).
Reference Results Design Buildings Population Ventilation
rate Ventilation
type Health
endpoints
Marmor
1978
Risk of
mortality
doubled during
heat waves in
homes w/o AC
Cross-
sectional,
retrospective
Nursing
home
6930
residents
N/A N/A ( with
or w/o AC)
Mortality rate
Norbäck et
al. 1995
At high CO2
the prevalence
of nocturnal
breathlessness
(a symptom of
asthma) was
higher
Cross-
sectional
88 homes
(51% flats
and 40%
single
family
houses)
Adult
residents
CO2
measured
averaged
1,020 ppm
(natural) and
850 ppm
(mechanical)
With
mechanical
system
present and
absent
Self-assessed
questionnaire
and clinical
examination of
asthma/atopy
Øie et al.
1999
Low air change
rates increased
risk of
bronchial
obstruction
Case-control Homes 172 cases
from Oslo
Birth cohort
and 172
matched
controls
Above and
below 0.5h-1,
measured
with PFT
(also quartiles
6.9, 11.5 and
17.6 L/s per
person)
With
mechanical
system
present and
absent
Bronchial
obstruction
Palonen et
al. 2008
Air was
perceived
stuffy with
natural
ventilation and
it was noisy
with
mechanical;
natural and
exhaust
ventilation
caused
fluctuating
temperatures
and cold floors
Cross-
sectional
102 single
family
houses
210 adults
and 152
children
0.3h-1
(natural); 0.34
h-1 (exhaust)
and 0.4 h-1
(mechanical);
measured
PFT method
and in
exhaust
With
mechanical
system
present and
absent,
mechanical
(exhaust
only)
Self-assessed
perceptions
Rogot et al.
1992
Risk of death
42% lower in
homes with
AC
Cross-
sectional,
retrospective
Homes n=72,740 N/A N/A (with or
w/o AC)
Mortality rate
Ruotsalainen
et al. 1991
More
symptoms in
dwellings than
in houses;
More
symptoms in
houses with
natural
ventilation and
in dwellings
with
mechanical
ventilation
Cross-
sectional
242
dwellings
and houses
473
occupants
(RR=93.1%)
Houses
0.45h-1;
dwellings
0.64h-1
With
mechanical
system
present and
absent
Self-assessed
perceptions
and SBS
symptoms
Sundell
1994
Low air
changes rates
promoted
infestation of
HDM
Cross-
sectional
29 homes N/A 0.1h-1 to
0.8 h-1
measured
with PFT
N/A N/A (HDM, a
proxy for
allergic
symptoms)
Table continues on next page.
P Wargocki
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108
Table 1. (continued).
Reference Results Design Buildings Population Ventilation
rate Ventilation
type Health
endpoints
Warner et al.
2000
Installation of
mechanical
ventilation
reduced HDM
and RH but no
effects on
health
Intervention,
12 months
40 houses 27 children
and 13
adults
Aimed at
0.4-0.5 h-1
With
mechanical
system
present and
absent
(mechanical
intensified
with vacuum
cleaning)
Self-assessed
asthma and
allergy
symptoms;
Measured lung
functions and
bronchial hypo
responsiveness
Willers et al.
2006
No
associations
between health
outcomes and
sufficient
ventilation
Cross-
sectional
Homes 647 children
at age of 4
from 3,000
birth cohort
on asthma
and allergy
N/A Assessment
of whether
ventilation in
kitchen (with
gas cooking)
sufficient or
not
Blood samples,
self-assessed
respiratory and
allergic
symptoms
Wong et al.
2004
Prevalence of
symptoms was
higher in
dwellings with
AC
Cross-
sectional
3 residential
dwellings
Generally
adults, 105
in naturally
ventilated
and 58 in
naturally
ventilated
with AC
CO2 up to
1,600 ppm in
naturally
ventilated
with AC vs.
550-600 ppm
without AC
No
mechanical
ventilation
system (with
and w/o AC)
Self-assessed
SBS symptoms
Wright et al.
2009
Installation of
mechanical
ventilation
system
improved
evening peak
expiratory flow
(not morning),
reduced RH
but not HDM
Placebo-
controlled
intervention
Homes 120 adults
with asthma
N/A, aimed to
provide
0.5 h-1
With
mechanical
system
present and
absent
Peak
expiratory flow
Xu et al.
2010
Exhaled breath
condensate
nitrate
concentration
reduced ph
improved and
peak expiratory
flow improved
when
mechanical
ventilation
units with air
cleaner
operated
Cross-over
intervention
Homes 30 children
diagnosed
with asthma
CO2 averaged
1500 ppm
w/o system
and
800-900 ppm
with system
With and
w/o unit
with
mechanical
ventilation
system with
air cleaner
Exhaled breath
condensate and
peak expiratory
flow
Yu et al.
2004
SARS
infection rates
matched virus
concentrations
predicted by
simulations
using plumes
and wind flows
Simulations,
no field
measurements
High-rise
dwellings
N/A N/A N/A SARS
infection rates
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Contrary to the above no association was observed
between ventilation rates in homes of children with
asthma and allergy symptoms (cases) and children
with and without symptoms (bases) in a study which
used a similar approach to that of Bornehag et al.
(2005) described above (Clausen et al., 2011).
Clausen et al. used a case-base design rather than
case-control design and they also used CO2
measurements to estimate ventilation rates rather
than a PFT method used by Bornehag et al. (2005).
This could, among other factors, contribute to the
different results obtained in both studies which
otherwise had the same protocols for registering
symptoms. Also, no association between ventilation
rate and self-estimated asthma and allergy
symptoms was observed when the odds ratios for
cases and controls were compared in a study of
Emenius et al. (2004) in which the PFT method was
used for ventilation rate measurements. In this study
RH and window-pane condensation (a marker of
elevated humidity) were however associated with
the elevated risk of symptoms.
Data on the presence and type of ventilation system
and increased risk of self-estimated asthma and
allergy symptoms have also shown to be
inconsistent. After installation of mechanical
ventilation with heat-recovery in homes where no
such system was previously present, the risk for
symptoms was reduced both for infants (Kovesi et
al., 2009) and adolescents (Howieson et al., 2003),
but not for the adults and children with asthma
(Warner et al., 2000). In the latter study the levels of
RH and HDM allergens were, however, reduced.
Homes judged to have sufficient or not sufficient
kitchen ventilation were not a risk factor for
respiratory and allergic symptoms among children
(Willers et al., 2006). Neither were the houses with
characteristics likely to affect indoor air quality,
other than ventilation (Jones et al., 1999), a study
that actually did not look specifically at the effect of
ventilation. Gustafsson et al. (1996) showed that
heating and ventilation systems were not associated
with allergy symptoms in children.
Ventilation rate and ventilation system type were in
some studies associated with exposures and markers
of exposures likely to cause allergic symptoms. One
of these markers is the concentration of HDM
allergens. Any methods and remedial actions
reducing this allergen can be considered as effective
methods for improving health conditions. Several
studies showed that increased ventilation rate
reduced the concentration of HDM allergens
(Harving et al., 1993; 1994; Sundell, 1994). Also
installation of a new mechanical ventilation system
in homes which did not previously have this system,
reduced the concentration of HDM allergens
(Warner et al., 2000). This was most likely because
the ventilation rates were increased. In these studies
no direct measurements of symptoms or complaints
among building occupants were made. In some
studies increased ventilation rate reduced RH, which
was often observed and documented by lack of
condensation on window panes. Also proliferation
of HDM allergens depends on moisture level and is
inhibited when the relative humidity is low. Because
both elevated RH and window-pane condensation
are indicators of potential dampness problems in
homes, which are considered to be strong risk
factors for health problems (Bornehag et al., 2001;
2004), these data suggest indirectly that increased
ventilation rate can reduce health problems by
reducing the moisture level in homes.
3.2 Building-Related Symptoms and Complaints
The presence of mechanical ventilation systems in
homes was associated with reduced self-estimated
health symptoms, typical of sick building syndrome
symptoms among adults, compared with homes
without mechanical ventilation (Engvall et al., 2003;
Leech et al., 2004; Palonen et al., 2004), probably
because of higher ventilation rates. This is implied
by Ruotsalainen et al. (1991) who showed that the
presence of mechanical ventilation was associated
with a lower prevalence of symptoms when the air
change rates were higher. Kishi et al. (2009) found
no relationship between the existence and operation
of mechanical ventilation systems and the risk of
building-related symptoms. Maintenance of the
mechanical ventilation system could cause the
inconsistency between the results from different
studies. For example, Coehlo et al. (2005) showed
that mechanical ventilation systems in homes having
dirty filters, blocked vents, etc. were associated with
increased rates of health complaints of elderly
people. Also noise generated by the mechanical
ventilation system could contribute to complaints
and cause the association between mechanical
ventilation systems and health complaints to be
inconsistent (Palonen et al., 2008).
Generally, no studies were found directly
associating ventilation rates in homes with self-
estimated building related symptoms. Indirectly
Wong et al. (2004) showed that houses where AC is
used increase the risk of health symptoms; these
houses were usually sealed and had much lower
ventilation rates. Indirect evidence on the
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association between ventilation and health was also
suggested in studies showing that increased
ventilation rate lowered the perceptions of poor air
quality and stuffy air (Engvall et al., 2005; Palonen
et al., 2008), under the assumption that these
perceptions are markers of a health risk.
3.3 Respiratory Tract/Lung Functions and
Bronchial Obstruction
Reduced ventilation rates were associated with the
risk of bronchial obstruction but only when homes
had verified dampness problems and plasticizer
containing surfaces (Øie et al., 1999). Increased
ventilation rates following installation of new
mechanical ventilation systems with heat recovery
in homes without such a system was associated with
improved lung functions (Wright et al., 2009; Xu et
al., 2010). In the study of Xu et al. the effect could
not be separated from the effect of an air cleaner
installed together with the system. No effect on lung
functions was observed by Warner et al. (2000) after
new mechanical ventilation systems were installed
in homes without such a system, although
ventilation rates were increased. In their study the
installation of mechanical ventilation systems
reduced levels of RH and HDM allergens.
Installation of heat recovery ventilators in homes of
infants, previously without such systems, brought
levels of CO2 down to 900 ppm compared with
placebo units installed in other homes where CO2
levels were 1400 ppm. Levels of RH were also
reduced but did not affect health centre encounters
and hospitalizations due to respiratory problems
(Kovesi et al., 2009). Actually, no hospitalizations
occurred during the study. Since the population of
homes where interventions were made was small it
was unlikely to expect that a rather small change in
ventilation would have a strong effect on respiratory
problems that can be demonstrated by the effect on
hospitalizations.
3.4 Infectious Diseases
No studies have been found that directly associate
infectious diseases with the ventilation rate or type
of ventilation system in homes. However, the design
of ventilation systems should avoid mixing of return
air with supply air and assure proper air distribution,
considering that increased recirculation of air in
nursing homes was associated with an increased risk
of attack rates of Influenza A among the elderly
(Drinka et al., 1996). Also air distribution played an
important role in the spread of SARS (Yu et al.,
2004; Li et al., 2005).
3.5 Other Outcomes
Studies with other health outcomes than those listed
above have also been found including mortality,
cardiovascular hospitalizations, obesity and lead
poisoning. None of them was directly associated
with either ventilation rate, ventilation system type,
or the maintenance of ventilation systems in homes.
These are mentioned here only because the data
provide some indirect evidence.
Use of central AC in homes has been shown to
reduce exposure to particulate matter (PM) mainly
from outdoor traffic, and was associated with
reduced cardiovascular and respiratory
hospitalizations, as well as mortality among the
elderly (Bell et al., 2009). The data on both AC and
health outcomes were obtained from the local
community registers and it is difficult to judge
whether proximity to PM sources outdoors was
included in the models. Nevertheless, it can be
hypothesized that reducing exposures to outdoor
sources, by e.g. sealing houses, which is usually the
case when central AC are used, may have a positive
effect on health. This is somewhat confirmed by
studies of Deger et al. (2010), who showed that
children living along streets with highly dense
traffic have an increased risk of asthma, particularly
for children living on the ground floor and having
no adequate control of pollution causing asthma.
Proper filtration of outdoor air would thus be
important. Sealing houses can, at the same time,
reduce the outdoor air supply rate which may be
detrimental for health as well.
The data from two national longitudinal studies in
the US on house characteristics show that increased
use of AC, resulting in most cases in lowered
ventilation rates as a response to energy saving, was
associated with obesity and lead poisoning (Jacobs
et al., 2009). It must be emphasized though that
many other factors could also contribute to the
observed association including changes in lifestyle,
nutrition, etc. AC has also been shown, in many
studies, to reduce mortality for elderly during hot
weather (Marmor, 1978; Rogot et al., 1992). This is
most likely due to control of indoor temperature by
cooling, but may also be caused by reduced
exposure to outdoor air pollutants occurring during
hot weather because AC is often associated with
sealing houses.
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4. Discussion
The present data provide important reference
material to the project HealthVent defining health-
based ventilation guidelines for Europe
(HEALTHVENT.eu) (Wargocki et al., 2012). The
guidelines will have two parts, one prescribing rates
at which ventilation is supplied to reduce health
risks among the population exposed in buildings,
and on prescribing how to achieve compliance,
proper design, operation and maintenance of
ventilation systems. Both aspects are addressed in
the reviewed studies.
4.1 Ventilation Rate in Homes and Health
The results of studies on ventilation and health risks
in homes suggest that increased ventilation rates,
also demonstrated by reduced concentration of CO2,
generally reduce health problems; only in a few
cases were no effect or reverse effect observed.
To observe which level of ventilation rate can be
considered to protect people in homes against
negative health effects Figures 1 and 2 were created.
Figure 1 shows that increasing ventilation rate
consistently reduced the concentration of HDM
allergens in houses. The effect was significant over
a large range of ventilation rates, from about 0.1 to
1.4 h-1, suggesting that there can be a dose–response
relationship, i.e. a lower concentration of HDM
allergens when ventilation rate is increased. Lung
functions were seen to be improved by ventilation
rates above 0.5 h-1, but the data are only from one
study so it would be imprudent to form
recommendations based only on these results. For
self-reported asthma and allergy symptoms the
results seem to be equivocal and only one study
shows that increased ventilation rate reduced the
risk of asthma/allergy; in two studies no statistically
significant effect was observed. Figure 2 shows that
lowering CO2 levels, i.e. increasing ventilation rate,
reduced significantly symptoms of asthma and
allergy. No effects of increased ventilation rate on
SBS symptoms were shown, and sometimes
symptoms increased with increased ventilation rate
(Figure 1). Only one study showed that reduced
CO2, i.e. increased ventilation rate, reduced
symptoms (Figure 2). These results suggest that this
health outcome may not be very sensitive to changes
in ventilation in homes, although SBS symptoms are
clearly associated with changes in ventilation rates
Figure 1. Ventilation rate in homes and health; black bars show the studies in which increase in ventilation rate
caused statistically significant reduction in health outcomes; empty bars show that health outcome has not been
statistically significantly changed in the indicated range of air change rates, while grey bars show that increasing
ventilation rates increased significantly health problems.
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6
Borne hagetal(2005)
Engvalletal.(2005)
Harvingetal.(1994)
Palonenetal.(2008)
Ruotsalainenetal.(1991)
Warneretal.(2000)
Emeniusetal.(2004)
Harvingetal.(1993)
Sundell(1994)
Øieetal(1999)
Clausenetal.(2011)
Airchangerate(h
‐1
)
(lung functions)
(housedustmites)
(housedustmites)
(asthma &aller gy)
(house dustmites)
(SBS symptoms)
(SBS symptoms)
(housedust mites)
(SBSsymptoms)
(asthmaandallergy)
(asthmaandallergy)
P Wargocki
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112
in offices (Seppänen et al., 1999; Wargocki et al.,
2002; Sundell et al., 2011).
Taking only the studies in which significant effects
of ventilation rate on health were observed, the
minimum ventilation rate in homes at which no
health risk exist seems to be about 0.4 h-1 (Figure 1).
This is the lowest ventilation rate at which no
increased health risk was observed in the reviewed
literature. This level is close to the requirements of,
e.g. Danish Building Regulations (BR10, 2010) set
at 0.5 h-1, as well as the measured ventilation rates
in US residencies, which is from 0.5 to 0.7 h-1
(Pandian et al., 1998). Taking the studies in which
significant effects of CO2 on health were observed,
the maximum level of CO2 in homes at which no
health risk was observed seem to be about 900 ppm
(Figure 2).
4.2 Ventilation System in Homes and Health
Present results show consistently that newly
installed mechanical ventilation systems reduced
health risks in homes. The reason for this is most
likely that outdoor air supply rates were also
increased when the system was installed, and the
system when new was not a source of pollution.
Furthermore, the installation of a mechanical
ventilation system could also contribute to fixing
other problems in homes which could, if existing,
contribute to health problems, such as e.g. leaky
roof, unsealed ceilings, etc.
Present results show also that there was less evident
effect on health in buildings with already existing
mechanical ventilation systems. Mechanical
ventilation systems can become strong pollution
sources as a result of their poor maintenance, as e.g.
shown in a recently published study in 299 Dutch
homes (Dijken et al., 2011). Although there is a
wealth of data showing that dirty filters and dirty
ventilation systems contribute to elevated health
risks (e.g., Sieber et al., 1996; Seppänen et al., 2002;
Mendell et al., 2003; 2008), these data are mainly
from offices. On the other hand the present survey
found no studies which associated the maintenance
of ventilation systems in homes with health. Only
the study of Coehlo et al. (2005) showed association
between improper operation of the system (blocked
vents, switched-off fans, etc.) and elevated health
complaints. Poor performance of ventilation systems
could also contribute to less evident effects on
health in buildings with existing mechanical
ventilation systems. Mechanical ventilation systems
should be properly designed, balanced and operated
because, as shown by Palonen et al. (2005), they can
become a source of nuisance, e.g. due to increased
noise levels indoors. This result was confirmed
recently by Bogers et al. (2011).
No studies were found which associated dedicated
natural ventilation systems and hybrid systems with
health.
4.3 Source Control and Filtration
Increasing ventilation rates reduces the
concentration of HDM allergens. These results may
also suggest that ventilation modifies moisture
levels, thus it is modifying conditions which are
Figure 2. Concentration of CO2 in homes and health; black bars show the studies in which reduction of CO2
(i.e. increase in ventilation rate) caused statistically significant reduction in health outcomes.
0 200 400 600 800 1000 1200 1400 1600 1800
Wongetal.(2004)
Norbac ketal.(1995)
Xuetal.(2009)
Kovesietal.(2009)
Carbondioxideconce ntr at ion(ppm)
(asthma &allergy )
(asthma&allergy)
(SBSsymptoms)
(asthmaandalle rgy)
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promoting the proliferation of HDM. Most of the
studies on the association between HDM allergens
and ventilation were performed in Nordic countries
and in the UK, where increased ventilation rates
during cold periods reduce RH in homes, thereby
inhibiting the growth of mites. Reduction of
moisture has also many other benefits for health, as
moisture is generally known to be a marker of
elevated health risk in homes (Bornehag et al.,
2001).
Too low RH can also cause problems and could be
one of the reasons why Ruotsalainen et al. (1991)
observed in Finland that increased ventilation rate
caused an increase of SBS symptoms, such as
dryness, nasal problems and itching. Their study
was actually performed from November to April so
it is likely that RH was quite low, although
measured to be on average approximately 36%.
Moisture can also be controlled by creating barriers
in the building structure and/or local exhaust in
laundries, bathrooms and kitchens, as well as by the
banning of drying of laundry in spaces where people
live.
Ventilation air can also transport outdoor pollutants
(particles, pollens, etc.) into indoor spaces. This is
suggested by studies of Bell et al. (2009) who
showed that the use of AC reduced health effects
related with PM from outdoors because houses were
sealed. These results show the connection between
indoor and outdoor environment and the need for
reducing exposures to particles entraining indoors.
This should rather be achieved by, e.g. efficient
filtration, than by sealing homes, i.e. reducing
ventilation rates, which can also be detrimental for
health. The risk of elevated health effects due to
exposure to particles will depend on the location of
houses (urban, rural), proximity to outdoor sources,
etc. Again, reviewed studies have not sufficiently
documented these factors so it is difficult to assess
their impact on the presented results.
4.4 Populations Studied
Among all studies reviewed in the present report,
thirteen studies concerned health risks for children,
twelve for adults and five for the elderly. They have
thus reasonably well addressed different population
groups.
All studies that did not show association between
ventilation system type and ventilation rate and self-
reported asthma and allergy symptoms were carried
out with children. In most cases the prevalence of
asthma and allergy is based on parental reports (self-
assessments). Perhaps this caused inconsistent
results. Verification of parental reports with
objective methods would be useful.
All studies in which there was no association
between ventilation type and/or ventilation rate, and
self-reported SBS symptoms concerned adults.
In the case of exposure of the elderly none of the
studies showed direct association between
ventilation type and or ventilation rate and health
outcome.
4.5 Limitations
There are numerous confounding factors that could
influence and disturb the observed associations.
They include among others: study design,
controlling and measuring of ventilation rates,
differences in source strength; interactions between
sources and ventilation rates; dose-response effects
that are likely to be log-linear; ventilation systems
as sources of pollution, multifactorial genesis of
health problems, climatic differences, different
thresholds of effects for people and location of the
study, as well as different methods by which health
outcomes were measured.
Quality of data plays an important role when
forming conclusions on ventilation and health. No
attempt however was made in the present report to
grade the studies according to their quality as
regards experimental design, measurements and
analysis of results.
If such a grading had been based on the study
design, case-base, case-control and placebo-
controlled interventions with double blinding would
be ranked high while cross-sectional studies and
longitudinal observations would be ranked quite
low. In the former, many of the confounding factors
are controlled experimentally while in the latter the
control can only be made by adjusting the statistical
models for the factors likely to obscure the
association.
If such a grading had been based on the method of
ventilation measurements, the method using
perfluorocarbon as tracer (PFT method) would be
ranked high (although largely debated as regards its
accuracy in the scientific community) because it
accounts only for outdoor air supply rate, while
using CO2 would be ranked low because the
calculated ventilation rates provide information on
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total dilution including outdoor air and make-up air
(the air from other rooms in a house) rather than
only outdoor air supply rate (Bekö et al., 2009) as is
the case for PFT method.
If such a grading had been based on categorization
of the ventilation systems, the studies which
installed mechanical ventilation systems would be
ranked high compared with the buildings with
existing mechanical ventilation systems because of
their good maintenance and close to design
performance. Also studies in which categorization
of the system had been made through inspections
rather by examining registers or blue-prints would
be ranked high because they would use the actual
data rather than unverified information.
The grading could have also been made based on the
measurements of health outcomes. Many studies
used self-administered questionnaires and may be
ranked low compared to objective medical
measurements and/or diagnosis made by the doctors
which would be ranked high. However using
questionnaires is the most efficient, low-cost
method of collecting data, widely used in large
epidemiological studies of the type discussed in the
present report. Besides, there is some evidence on
the consistency between self-reports of health
problems and doctor-diagnosed health problems.
Even if objective medical measurements had been
used, the information on the thresholds at which
health effects are observed would be needed. These
can vary between people and in many cases are not
available. Also lack of the effect on objectively
measured health symptoms does not preclude the
effect on health, especially if the objective method is
not properly selected and not properly applied.
Consequently the studies in which self-reported and
doctor-diagnosed symptoms were used can be
ranked evenly.
It is worth noting that consistent observations
regarding associations between ventilation rate and
ventilation system and health stem generally from
the studies which would have been ranked high.
4.6 Implications for Future Work
Present results show that more evidence of the role
of ventilation for health is needed. Despite the
paramount importance of ventilation, especially
considering the impact on energy, it has not
received proper attention. The need for reducing
energy and future buildings being much tighter than
today will require that the proper ventilation of
homes, obtained by, e.g. mechanical systems with
heat recovery in cold periods and dedicated natural
ventilation systems in warm periods, will be the
essential part of the future building structure.
The performance of different ventilation solutions
and their impact on health should be better
understood. There is an obvious need for producing
guidelines as regards commissioning and
installation as well as maintenance of systems
supplying air to indoor spaces, not only for
mechanical systems but also for other systems.
Regular inspections of ventilation systems can be
forced, as it is done for example in Sweden
(Boverket, 2009); these inspections can actually
become a part of energy certification of buildings.
Future studies should try to answer the fundamental
question on how much ventilation is actually
needed. This question is only partially answered by
the present report due to limited data and the
limitations of different studies. A series of studies
on ventilation and health would be needed to answer
this question. They should take into account all
possible limitations and, what is probably most
important, should link ventilation to actual
exposures, admitting thus that ventilation is not a
mitigation measure and should not be used as such.
5. Conclusions
Ventilation rate in homes is associated with
health in particular with asthma, allergy, airway
obstruction and SBS symptoms. This
association is based on the limited evidence.
Ventilation rates above 0.4 h-1 or CO2 below
900 ppm in homes seem to protect against
health risks.
No specific ventilation system can be
recommended to provide minimum ventilation
rates.
Increasing ventilation rates in homes reduces
house dust mites known to cause allergic
symptoms, most likely because of reduced
moisture levels which inhibits their
proliferation.
Newly installed mechanical ventilation systems
nearly always reduced the risk of health
problems. This was not the case for buildings
with existing mechanical ventilation systems,
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most likely due to their poor maintenance, lack
of commissioning, regular checks and
inspections, etc.
Buildings in which air conditioning is installed
increase the risk of health problems probably
due to lowered ventilation rates (tightening and
sealing of buildings to reduce energy).
No differences were observed in the prevalence
of health problems between different age
groups, children, adults and elderly.
A series of studies on ventilation and health in
buildings with different ventilation systems
would be desirable.
6. Practical Implications
Required ventilation rates depend strongly on
exposures, i.e. with a high load of pollution more
ventilation is needed than if the loads are low. The
ventilation rates can be reduced by controlling
sources of pollution both being of outdoor origin
(e.g., particulate matter) and indoor origin (e.g.,
relative humidity (RH), particulate matter (PM),
house dust mite (HDM) allergens, emissions from
building products and appliances, anthropogenic
emissions). Future homes should secure proper
control of exposures to pollutants in order to reduce
health risks for occupants on one hand, and at the
same time they should secure that the energy needed
to support sufficient ventilation is as low as
possible. This control can be implemented by
different solutions including provision of sufficient
ventilation, which should be closely connected to
estimated exposures.
Different ventilation systems can be applied from
dedicated natural ventilation systems, hybrid
systems to mechanical ventilation systems with heat
recovery, all depending on the conditions which
promote application of one system over another.
Ventilation should not be considered to be the only
mitigation measure to control exposures but
complementary and supplementary to other
measures, such as, e.g. source control, air cleaning
and/or local exhausts. These measures are easy to
implement in newly constructed homes, and more
difficult but still possible to apply in existing homes
unless they are renovated or refurbished.
It is of utmost importance that systems securing
ventilation rates in homes are inspected for their
performance. Regular annual or bi-annual
inspections should be implemented and regulated so
that the proper operation and maintenance of
systems is ensured. They can become, e.g., a part of
energy audits, chimney sweep control, etc., or can
be performed completely separately.
Acknowledgments
Thanks are due to Velux A/S for supporting present
work. Thanks are due to Nuno da Silva, M.Sc. for
finding the literature and for creating the data base
with articles used to prepare the present paper.
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