do you cover the screen at all with foil or plexi glass, not the whole thing i do about 1/2 to 3/4 youll have to play around with it for a little bit to get it right pluse it will help with humidity but make sure it dont get to high either .and if you dont have a thermostate and it gets to hot put a peice of that reptile astro turf stuff then your substrait over it. hope this helps out .may not work for you but it works for me i have a cold basement.
you can also try an irrredeciet or what ever they are called there cheaper than che's and work pretty good for ambient temps.