there are lots of posts and lots of diff opinions on heat and windows on a mac
its all your choice and it depends partly on how long you want to hold on to your hardware for - if you upgrade regularly maybe its no issue at all
in my own case i basically have decided - if you do a lot of work in windows and its heavylifting eg video/audio work or gaming, and its for long times eg hours rather than an hour here or there, then its wise to instal a manual fan app
on the imac i use smcfancontrol which works well
its an osx app but there is a "reboot trick" to get the fans to run at your own setting when in windows as well, search teh forum here for smcfancontrol
just my own opinion