How does humidity affect roasting? How does the humidity affect the length of time required to reach a good light roast in a gas fired roaster.
I believe heat and humidity play a key role in the role of energy transference in the roaster. I roast (professionally)in a very dry climate and find it easier (more forgiving) to roast in a climate that generally has a more humidity.

Here is a link to a conversation about heating and humidity that hopefully will help answer your question.

I think the 3rd answer is the most appropriate in its relation to heat transfer and "other" objects in a room (i.e. Coffee beans).

How air humidity affects how much time is needed for heating the air?