What is the proposed design? Compacted gravel and then ...?

Posted By manitoban on 12 Jul 2012 01:52 AM
Great replies, I appreciate the input. One clarification that most are missing is that I was intending to put the pex ABOVE the thermal mass and separate it by a V.B. and 2" of rigid foam. In this situation it wouldn't be any different than staple up under an upper floor (low mass). I have that setup in my current house along with pex in the slab in my basement and I actually like the staple up more. A well sealed V.B. should take care of any radon or moisture issues...and I'm pretty much sitting on shale rock with no clay to speak of. So I take it crushed stone or compacted sand would be two cheaper alternatives that would be stable enough to replace concrete? Again this is more about me trying to save money on a concrete floor that has no function "as I see it" rather than trying to perfect my radiant heating system. I already accept the cost of the wooden floor above so that money is already accounted forand will be spent regardless. i suppose the original question would have been better posted in a foundation discussion forum somewhere!

Badger. What are you refering to as "class 5"?

Thanks!

I really don't see any reason to put the tubing above the concrete (or sand). RADIANT tubing depends on surface temperature and emission AREA for any efficiency. What you are going to make is a convector but with out the convection. The insulative value of the air it sits in will slow the heat transfer and to get any heat out of it, you will have to have a much higher temp than you would in a mass that can remove the heat at the right rate (30C vs maybe 50C). You will also have to circulate the water for a longer period of time during the day, and if you are trying to be energy conserving, that is a few more watts.

I read that as putting insulation and vapor barrier between the tubing and concrete/sand/gravel, not suspended-tube radiant.

Above-the-subfloor radiant (WarmBoard style) is very responsive and has good output with low-temp water. His original description was:

"...2" of XPS foamboard with pex pipes layed on top between 1x6 boards glued directly to the foam board, topped off by a 3/4" finished wood floor."

That reads as tubing fully in contact with the finish-flooring. I'd add thin-metal heat-spreaders to reduce the temperature striping at the tubing contact which would also lower the water temp requirements.

Dana finally nailed it "Warmboard style" but the home made version of course!
I must admit after reading post after post suggestiing thermal mass you guys have convinced me to at least explore the possibilities. To follow through if I did plant the pex in 6" of crushed stone above the insulation and the V.B. how would one finish a floor like that?

Posted By manitoban on 13 Jul 2012 07:59 PM
Dana finally nailed it "Warmboard style" but the home made version of course!
I must admit after reading post after post suggestiing thermal mass you guys have convinced me to at least explore the possibilities. To follow through if I did plant the pex in 6" of crushed stone above the insulation and the V.B. how would one finish a floor like that?

honestly, if you must put it in something other than concrete, make it a sand bed. I have a lot of tubing in place and the rule of thumb is to always keep it away from sharp objects and that includes things that can, over time, through expansion create a hole in the tube. Think of that rope slowly rubbing on the rock that eventually works its way through (I'm from N.S. so pardon nautical reference). I have seen it happen.

If you are trying to do a warmboard equiv., that is fine but you won't be saving any money or energy and depending on the water temps, you may not like the sounds coming from it.

Better check with your local codes before you go any deeper. Some area codes require a concrete slab because of termites and rodent control or other reasons. Subterranean termites are a huge problem in Arizona as are voles and other tunneling rodents species that would tunnel right through and make a home in your basement.