Not idle, but not hard work either.
I think the problem is that I have it sitting in front of one my tube mono block amplifiers. They are relatively small amplifiers, but they do put out a significant amount of heat. You're probably thinking: "yes, stupid, that is probably the problem", but, because it seems like other who have done the upgrade have had overheating problems, I was just concerned that I had not done the upgrade properly.
I am still worried - it was just so easy to do (I followed Phillipma1957's excellent breakdown). I have not had any problems... yet.