exactly and anything can give off heat. i.e. water heater... oven, heaters all kinds of shit....they dont even scan in the daylight hours because of the sun will heat a house the fuck up.
if you dont combat the hot air you are exhausting of course it will show/give off heat
air cooling lights will help. hell even liquid coolings, but thas not practical right now.... well at least not for me. if you are that worried, line your grow room with poly shield or something of the like. remember when installing to overlap with duct tape.