Methods to measure humidity of the air in a furnace in which the temperature is around 800°C?

The problem with measuring the humidity of the air in a high-temperature furnace is that the humidity sensor can only stand less than 200°C. So a pipe and pump will be required to pump the air out and cool it to a temperature that the humidity sensor can work at. The problem is, condensed water vapour on the pipe and in the equipment will cause the measurement to be inaccurate. I would appreciate it if anyone has experience on this and can give some advice on the best method.