Sorry took so long here, but I have a lot of reading material to sort through to give you a proper answer. There is a product out the is supposed to help with sealing in the heat, it is a foil covering, I would guess somewhat similar to Mylar but a bit of an up grade. Easy grow foils from the UK. It is availiable in Canada and the USA now. Check out easy-grow.co.uk and the one you would be interested in is the lightite version. That one is also a thermal barrier. Any well insulated room should be okay, but this should help and make shure you are safe.