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Concrete slab desireable for radiant flooring? - Page 3

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Posted by Iain McClatchie on November 5, 2005, 3:39 am
Gary> The alternative that we are probably going to use is:
Gary> Subfloor is plywood.  On TOP of the plywood, a 2nd layer
Gary> of plywood that is the same thickness as the PEX is laid
Gary> down.  The 2nd layer has grooves to accept the PEX
Gary> tubing, which is installed with aluminum spreader plates.

Is this called "warmboard"?  I've seen this in a high-end house
during a contractor's tour (seriously high end -- 20+ foot ceilings
everywhere, had to be 8000+ ft^2).  I understand the stuff is
$/ft^2.  That's quite a lot for us.

We live on the San Francisco peninsula (California), a little up
the hill (first floor will be at 860' elevation) from Silicon Valley.
My simulations show the house will need to pump ~ 10
BTU/ft^2/hour through the floor on a cold day.

The extra 10 C (18 F) is a serious issue, of course, as it wipes
out ~ 20% of our expensive storage capacity.  I thought it would
also make the collectors less efficient (since they have to
operate at higher inlet temperatures), but the published curves
(SRCC) don't show a significant difference.  We're using glazed
flat-plates, either SunEarth or Heliodyne.

We *also* plan to have a fan coil, but for displacement
ventilation, not heating.  That is, the fan coil output will be at
75-80 F, not warm enough to heat the house.  It's job is to heat
the fresh air being blown into the house through very low-
velocity ceiling diffusers.

Gary> There are several outfits that make precut panels with the
Gary> PEX grooves in them, or you can make them on the site.

How much does it cost to make them on-site?

I grew up in an Eichler with radiant (copper tubing) in the slab.
Nice even heat was never a problem, but we never turned things
off when we went on vacation.  Stagnant air was definitely a

I'll take a look at your link later.  Thanks.

Posted by Solar Flare on November 5, 2005, 12:53 pm
What happens when the next owner (or yourself) have to replace the flooring and
put nails at a guess?

Posted by Gary on November 5, 2005, 3:23 pm
 Solar Flare wrote:

That would not be a smart thing to do :-)

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Posted by Philip Lewis on November 5, 2005, 7:37 pm

That's where you hand the new owner the house documentation, with
pictures of the wireing in the walls (before the wallboard/plaster is
installed) the pictures of the floor water tubes, etc...

I kinda like the idea of an extra layer of engineered wood placed in
there with routed groves for the tubeing... no idea how well it'd work
though, or how easy/tough it'd be to do though.

I'd like to retrofit my heating system to radiant floor vrs
radiators...  I have access to the joists from below, so the retrofit
won't be horrible.

I'm thinking insulation (no, not *more* insulation... *any*
insulation) might be a better first step though. ;)

be safe.
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Posted by Iain McClatchie on November 6, 2005, 5:52 am

SF> What happens when the next owner (or yourself) have to
SF> replace the flooring and put nails at a guess?

Yep.  That's not the major reason I'm shy of the idea, but
perhaps it should be.

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