How do you build an air heated concrete slab?
I am looking to build a bungalow in a moderate climate. Temperatures range from about 30 to 65 in the winter and about 45 to 75 in the summer. The house will be south facing with lots of south facing windows with tile and concrete floors. I expect this will produce enough heat to keep the house comfortable with out any gas or electric heating. The plan is to prevent the sun entering in the summer and allow it to shine in in the winter. I estimate sun would begin entering about 10 am and finish about 3. I would like to distribute the heat more evenly and have uniformly warm floors. I would like to pull the warm air from the peak of the house and using a fan pump it into a hollow space under the concrete floor. I am hoping by the time the evening comes the concrete space would start releasing its heat and as air flows through the floor would warm the entire house as well as travel through the floor to warm the tile. First would this set up work for a one level house in this type of climate? If so how thick should i make the concrete floor between the empty air space and the tile? Does it make a difference if the bulk of the concrete (thermal) mass is below the airspace or between the airspace and the tile? Thanks for any advice you may have!
What you are proposing here of using warm air collecting high up on your ceiling to heat the floors is a great concept but the rewards for your efforts would be minimal. I say that because the air at the cieling would certainly be warmer than at floor level, but not so much so that mechanically diverting it into your slab would provide noticeable savings or comfort. and putting air tubes in floors comes with significant challenges, you can read more here -
Radiant floor options - comparing liquid hydronic radiant, electric wires, and air tubes
As for distributing heat to the floor - hydronic under floor tubing as well as engineered air heated radiant floors are pumping or blowing super-heated air or liquid through floors, whereas the air at your ceiling is only slightly higher in temperature than the air at the floor. so by the time you divert it down through ducts to the floor, then try to run it through ducts in the floor, the temperature would fall off very quickly and you would see next to no benefits I would imagine.
Instead, if you were you to install a ceiling fan to pull warm air down from the ceiling, it would increase the absorption rate of heat into concrete slightly, and perhaps even more than were you to run it through tubes. And that would be a far more simple manoever and much cheaper with about the same benefits likely.
Important to note - this is not to rip on your idea here, the way I came to the conclusion that the benefits are not worth the effort is because I had the exact same thought 20 years ago when building my house and after calculating it I found it was not sensible undertaking. But I love the thinking that got you there.
There are lots of ther innovative passive solar energy efficient building techniques you can find in our building guide pages that may help, and good luck with your build!