[tcoppi]

Burning natural gas is among the cheapest forms of heating we have, and it works 24/7/365 and at all latitudes. Solar heating using a slab as a heat reserve requires re-engineering houses completely and may be impossible in a lot of places that don't get a lot of sun during the coldest months.

[NotSammyHagar]

sure, nat gas works great where lines go to your house. I was at a house in the seattle area last weekend (a well developed metropolis) where people had propane. Solar goes everywhere, but depends on good weather to be useful.