Posted By JohnyH on 22 Oct 2010 12:48 PM
For Dana1

If you were going to put R20 under the basement slab, wouldn't it be prudent to put pex tubing in? I don't know the cost but it could be utilized at a later time you don't have to use it but you could!

John

What would you use it for? If you have R40+ walls and a low heat-loss passive solar-tempered envelope design, using the slab as radiation for a heating system would be simply a waste.  It would cost more up front, be difficult to control, and provide no additional comfort.  The temp required for heating (even under design conditions) wouldn't be more than a couple of degrees above room temp- to bare feet it would feel about the same as an unheated slab.

Putting a length of PEX in the slab for hot water preheat stills makes sense (which I think I stated in a previous post.)  The slab is basically the passive solar heat buffer for the house, running at about room temp, which would be 25-35 degrees above the wintertime incoming water temps in Ogden.

While we are arguing passive vs active solar vs insulation.
 I would argue one of the easiest things to incorporate is solar air heaters. Low hassle, usable heat gain, low night time losses, low summer heat gain.
 
I vote for efficient design, Insulation, passive solar+ solar airheaters, and solar DHW, and efficient electrical appliances .     At some point, the biggest energy hogs in the house are electrical losses. My background electrical usage costs twice the monthly Heating bill. The thing that will save me the most money is reducing electrical usage.
Cheers,
Eric

Agreed- thermal air panels are simple & effective, and as cheap as it gets in the active-solar game. In sunny UT the uptake will be quite good, and as long as the thermal mass of the interior is high enough and insulation/infiltration losses low enough they could supply a decent fraction of the heat of even an R20-insulated building (but not so much that you could dispense with a heating system.)

What you don't get with thermal air panels (as compared to a hydronic solar setup) it thermal storage insulated from the conditioned space to be returned when the heat load is higher- you rely entirely on the thermal mass of the house. But 4-5" of concrete slab inside the insulation (including insulated from the dirt below), is a very reasonable amount of thermal mass to work with.

Thanks for the comments, I really want to make the right decisions with the design, this forum is a great help!

John