[masraum]

I think in theory it could be made to work (it's basically what AC does), but for that, you'd have to have a way to pump all of the air in the house over the radiators through a duct (ala Air Conditioning). Basically, you'd have to turn the radiators into a huge condenser, and I don't think the radiators would have the surface area that a real condenser does. I don't really think that's feasible. Then, there's the water problem that Taz's Master brought up. I think for them to really make a dent, you'd have to be able to cool them to subfreezing temps (like 0* or less) which again, doesn't seem possible (the condensed water would freeze and insulate them).

The closest thing to what you're talking about is geothermal heating and cooling where you use a huge radiator in the ground to heat your house in the winter and cool it in the summer, but I think you need a climate that doesn't have too much of an extreme (hot or cold) climate for that to work well.