you got a bright idear there i think it could possibly work.

Sounds like a good plan. Fridge doors are doubled paned which will keep in a lot of heat. I don’t know if flood lamps will put out enough heat, you might have to put in a propane heater to keep the house warm enough in winter. Depending on what you plan to grow, many things don’t need heat at all to survive winter but tomatoes and other warm loving plants will.

Since the doors act as insulators from the heat in the freezer case, they will do just fine to hold heat in during winter.
Part of the idea behind a greenhouse is that if properly bult, there is no need to add much extra heat, even in winter.
Without knowing where you live, it is hard to say if supplemental heat will be needed. One way to accomplish this in a more green manner than burning a hydrocarbon fuel, is to use heat storage items in your greenhouse.
Siting the greenhouse so that the maximum sun gain can heat up not just the air inside, but re-cycled old barrels, plastic or metal, filled with water (and a bit of bleach to keep the gunk down) sealed up, and outsides painted black or dark green. If you use these as the “legs” to rest your benches or flats on, you can save more costs there as well.
The concept is for the barrels to absorb the heat as well during the day, and at night, as they cool, the give off the heat back into the green house.
might help you oput a bit.
Good luck and well done for wanting to go green!
Kay

I’m impressed with your idea, and the above answer about passive solar heat, with the barrels and such, is a great idea. I have two concerns, the first is the wieght of the doors, but as long as your welded frame can withstand it…and the second is the heat issue…where do you live? Are you planning on actively growing in the winter or just starting seeds for spring? I live in Eastern Washingnton and have yet to see a green house here that didn’t have some source of heat during the fridgid months. Some things to consider. It’s a great idea though. Where are you getting all these glass fridge doors?

you would be better of making the frame with timber, if it is made with a single angled flat roof, it would be easier to construct.

a lot depends on what size glass you can get.

depending where you live and what you want to grow will determine the heating you need.

the doors will hold heat better than the rest of the building unless your greenhouse is insulated, therefore, i say yes