A. Do not take off the coat unless asked to 'get more comfortable'. But then it could be a trick question: They ask you to get comfortable, and you take off your coat. Which means you are NOT comfortable in with the coat on?
B. If you are a bit too uncomfy in the coat, and (say) sweating (I hope due to the heat), be frank and polite and ask if it would be ok with them if you took off the coat.
Hehe: One of my interviews was supposed to last for an hour or so. I was all dressed up. The people interviewing me had just returned from a jobsite (this was for a construction firm). And all of a sudden, I was the best-dressed person in the room! After the initial pleasentaries were exchanged, I told them directly that since the job I was interviewing for was a field job, it should not matter whether I interviewed with my coat on or off. They agreed readily