Our house is a 1.5-story house + cellar. During the winter we run our central heating system by an oil-fired boiler. In the summer, when the hottest days in Helsinki may be 30 oC, we let the water circulate in the radiators while the oil burner has been switched off for several summer months.

Hot water for dishwashing is taken from a small electric boiler. If the circulating pump of the central heating system is stopped, tap water running through a copper pipe coil in the boiler in the cellar cools the boiler to 15 oC.
However, the circulating water running through the radiators heats in the interior up to 23 oC, when the room temperature is 25-26 oC and outside temp about 30 oC. Thus when the circulating water returns to the boiler, we get from the boiler coil lukewarm water at 23 oC from the warm side of the faucet. Quite suitable for washing hands. And the rooms cool down a few degrees only having the 100 W circulating pump running.

This proves that if a small-capacity heat pump would be included in the central heating system, large radiators would in the summertime keep the interior temp at a tolerable level at a minimal cost.

By the way, we also have our house surrounded by large birches that with their enormous evaporation capacity and large foliage contribute to our comfort.

Taisto Leinonen, M.Sc.
Helsinki, Finland

from a Simple Midwest Roofer