Yep!!!! i have 3-60" VHO's under my canopy...they do produce heat,although i'm sure this isn't even close to the MH heat....when i open my canopy, a wave of warm air blows out of it everytime!!!!i don't have any fans or anything in my canopy...now that you mentioned it, i actually forgot to install them!! i planned on it and completely forgot..i don't have heat issues in the tank though..i may end up with them in the middle of summer...let me put it this way...if i had a fan or two in my canopy, i'm sure the heat wouldn't be any problem at all..it wouldn't be able to build up in there!!