green house heat

I'm only using my green house to store trees right now. It's still too cold to start plants in. They say we will get snow again tonight. I was wondering if I could not get a pond pump to use with a solar pool heater. The solar heater could heat the 2 tanks of water I have, and the pump could pump it from one tank to the next. The hot water could heat the house? Just wondering. A cheap pool heater is under 50€. I could even get a solar pump.