How to calculate thermal exchange rate of Air?

The heat capacity of humid air is approximately given by:

C p =1.005+1.82H

where 1.005 kJ/kg°C is the heat capacity of dry air, 1.82 kJ/kg°C the heat capacity of water vapor, and H is the absolute humidity in kg water vapor per kg dry air in the mixture. So the specific heat capacity of humid air is greater than dry air and humid air will take more energy to heat by a given amount.

But the difference is quite small. I think 100% RH at 25C is only about 2% water, and if you need to heat the room the temperature, and therefore the water content, is presumably even lower. Taking the 2% water content only increases the specific heat by about 3.6%.

Are you looking for the Specific Heat Capacity of humid air?...

You are forgetting about other, more important, heat transfer mechanisms like conduction and convection. In most practical situations, these will dominate over radiation.

If there are measurements or calculations to show how much they change (if any) depending on the amount of water vapor in the air? I'd take that as well.

But I was looking for how much the air would be warmed by IR radiation, and then that heat would be transferred by conduction and convection.

Seems as tho if I knew what amount of IR radiation would be absorbed by a sample of air that was 1% water vapor, that I would just double that to estimate it for 2% water vapor?