Hi everyone, I have a maybe dumb question I wanted to run by folks. I am in the processes of building an ICF house in Portland, OR. It will be a well insulated, tight house with good doors and windows. We will also have a pretty thick concrete roof. We will do hydronic heating and cooling with bare concrete floors on both levels. I don't think standard geothermal system will work for us, we don't have enough space for a ground loop, and can't afford to dig wells. Here is my question: ---Could I put hydronic tubing in our roof concrete, and use it as a source for a water to water heat pump?--- I know it won't be as efficient as a true geothermal heat pump, because the roof won't be a nice constant temperature. I think it is closer to an air to water heat pump, where I am just using a large concrete heat sink to get heat from the air instead of a fan and coil. It seems like there are a few nice parts to this idea: - No noisy fan outside - Pretty big area, like 300square meters - We could put black roofing on the roof, to get a little heat from sunlight when it is cold. - There would be a lot of thermal mass there, so it could even out between day and night. What do folks think? Have you heard of people doing that before? Also, we will have a backup wood gasification system we can fire up when it gets really cold. Thanks for the replies, Scott

Roof is not a good choice in my opinion. You are going to have two temp extremes right next to each other. I am assuming in your area you have an abundance of ground water do to low elevation and close to large masses of water, so you could do pump and dump. But you are also in a temp area without much extremes so air to air seems like the best option.