Originally Posted by Astroboy
How does uninsulated and unheated garage stay above freezing when it's cold outside at 19 degrees?
Do you think this is mostly the residual heat from the warmer days before, or the solar heat that it soaks in during the day (has it been very sunny)?
I think it has to do with the fairly constant temperature of the earth (soil). The underlying soil doesn't drop to the level of the air temperature. So, you are using that heat to keep your enclosed garage at a temperature higher than the outside temp. If you have a concrete floor, it is also radiating out the heat it has absorbed from the earth.
(Same premise as using geothermal--just takes advantage of the relatively stable 55 degree or so temperature of the earth a few feet below the surface.)
Obviously, the better insulated and air tight the structure is, the better is is able to retain the heat given off by the soil below it.