What do you want the gh for? You can grow tropical plants year round in San Diego. I once lived there! Cardiff to be exact. With a year round average temp of 69.5 degrees are looking to raise the temp and humidity a bit?

I'm in inland el cajon. It can get into the 40's here. Alot of what I grow are tropical waterlilies and some fish. I kept a pond heated last winter but its too expensive. Also my wife kept a heated area for her sulcata tortise so I want an area for him. Energy is too expensive to keep doing this.

nomadh wrote:
It seems that in San Diego I should be able to keep a greenhouse a nice warm temp all year without power.
Unless you have something for storing heat like barrels of water and insulate the greenhouse with a solar pool cover the greenhouse will eventually take on the outside temperture if it stays low for any lenght of time.
Greenhouses do heat up in the day time well above the outside temperture but that heat is quickly lost if not stored. Also in the summer without ventilation the tempertures can exceed 120 degrees or more. Natural ventilation is not enough unless you remove the sidewalls and have roof vents and a very good shade cloth.
You also will need some way to circulate the air for the health of the plants and the tortise.
Do you plan on using solar fans?
With good insulation and heat storage you should be able to gain 5 or 6 degrees which would be ok as long as you don't go below 40 outside.

Yes I plan on lots of water for lilies and fish. And in the summer many of the windows will just be left open. I want to use the solar plans I say in mother earth news. East wall and east side of roof overshooting the south facing windows so in summer when the sun is overhead the overhang will shade it but in the winter when the sun is low it will shine in through the southfacing windows.
I hope I can get more than 5 or 6 degrees. I'm hoping for 20 at night.