My wife and I are planning on building a house in Maine, and I'm interested in using a rubble trench foundation, but I'm wondering about how one insulates the floor so that it does not feel cold. We are considering in floor heat as well if that makes a difference. I'll definitely be looking into the FHB article on rubble trenches as well.

Ben,
Glad to have gotten into your thread while your new house is in the planning stages. Yes by all means use radiant heat in the floor. Use geothermal hvac heat exchanger, the only system which returns more energy that it takes to run it. The heat exchanger coil(s) can be buried, stuck in a well(s) or in a pond. What does your property have to offer ?
deralte (aka Emmett)

Thanks for the reply Emmett. The site is partially wooded, but the uimmediate site for the house is relatively open with few smaller trees to clear. I like the rubble trench idea because for one it seems to be less expensive, but also more stable in the long run as well as being a bit less invasive. I'm curious about the actual process though, If the house doesn't have a basement, and the floor is above greade which I assume it would be with a rubble trench. How does one insulate so that the radiant is not lost through the floor? I've been thinking about Geothermal for a while, and have begun to look into at most likely using a well or wells since I'd prefer not to trench and run pipe horizontally. Do you have experience with these systems?

Ben,
You have several choices in separating the generated heat from the heat loss into the ground below. Even those floors which are radiant concrete slab on grade get a positive heat exchange by putting a plastic sheet moisture barrier on sand covered with 4" of rigid foam on top of which goes your tubing pylons tied into the rebar mesh for strength. . If the idea of a concrete floor (can be made to look like stone if you wish)does not appeal then a conventional joist system (works with fabricated joists too) with two inches of rigid foam and a mylar outer skin goes underneath the joists or tji's.
blow in about 4-6" of low expansion foam. your inlet tubing boards go on top (with or without subfloor underneath) . Prior to mounting your subfloor/tubing boards rough in your plumbing on top of the blown in insulation. The stadler-vega plumbng system is easy to install and you have no glue fumes to inhale. (google em up).
Put either a hardwood (nail carefully) or glueless laminate floor on top of your tubing and it is a snap to keep it at 78 or so degrees year round.
Yes I have a list of preferred vendors which I could email to you if desired. No I am not being compensated by any of them.
deralte

Emmett,

I too would like to know more about heat exchangers in northern climates. (New Hampshire)

I am pondering a closed loop system in a river. I am getting conflicting answers on the practicality of this. Some say "no problem" and others say the very small differential temperatures lead to icing problems.

Any first hand experience, or know a solid source for specific information?

Thanks - but I don't want to hi-jack this thread...

Pete

Pete,
Sri bout the delay in responding but just returning from playing with the buffalo on the dakota plains.
Think a moment about the concept and efficiency of a geothermal system. You are attempting to normalize your thermal point of contact to be nearly the same temp year round. This minimizes the amount of energy required to set your house at a living heating/cooling temp. The farther north you go (but below the artic circle) you will find a termal mass which is about 55 or so degrees year round. If your water exchanger is forced to work from a base of thirty something degrees you have a gain over sub zero air to air systems but still requires a lot of energy to get up to seventy something. Your northern climate may not be the best place to think water.

Thanks, Emmett.

Pete

my parents put geothermal into a lake here in central ontario, and they have been very happy with it. yes, there are problems with icing up on the pipes, but they wired the pipes to a bunch of steel reinforcing mesh and concrete blocks to keep it all down...
As I understood the installation, it was a matter of how long the pipe is in the lake.
One of the best things for my folks is the summertime air conditioning the system provides.... ontario can get quite hot and humid in the summer and fall.