I grow in an unheated but insulated back room in my house with a 400wMH light. The walls of the 28"x28" space are lined with something called "ice blanket" which is a flat white closed-cell insulating foam sheet about 3/8" thick. It costs a couple bucks a foot, but a foot is 48" wide. It took me 12' to line the three walls,the floor, and the removable 4th wall.

I just came off a week of +/- single digit (f) weather. The temp/Rh and co2 in the room are computer monitored. Light goes 18/6 with the 6 dark hours in the middle of the night. Temp never dropped below 58f and never rose above 68f.

I've had my bud cycle going in the same sort of weather, and looking back over the weather log (avg day temp +23f, night going down to +9f), with a bud finishing period of 8 hours light, the temp never got above 62 nor below 48.

So depending on the size of the room you've got and what you plan to do to line the grow area walls, 1kva of MH light could keep it plenty warm enough.
rodekyll Reviewed by rodekyll on . 1000 watt hps/mh so am getten this light 1000 wat hps and mh douse any one how how much heat it gives off would it be enuff to keep the plants worm if in a sealed room in winter Rating: 5