[Exeric]

Even if your site looks good for solar heating from a solar insolation perspective with the simplest form of it, utilizing roof heat, it may not be. Like I said, the average high temp where I live now is 53F on the shortest day of the year. I need a 27 degree temp rise to give me a good reserve in which to supply the house with warm air over a couple of hours. The simpler forms of solar heating without heat storage will be the cheapest and easiest to implement. However, if your site is not adequate in the heart of winter then you should probably go with solar PV instead, or a solar heating system that gives a higher temperature like dedicated solar panels of either warm air or warm water construction.

There's one exception. In the southwest of this country you have very high insolation values because those regions are generally considered high plains, or high desert areas. At high altitudes there is not as much atmosphere so it can get fairly cold depending on where you are. The cold air at high altitude is most what makes it cold. But they also don't get a lot of cloud cover and precipitation, and because the air is thinner and doesn't absorb as many infrared photons for a given outside temperature in winter your solar heating panel or roof will get hotter for a given temperature there than other places, like California.