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Concrete slab desireable for radiant flooring? - Page 6

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Posted by Gary on November 6, 2005, 3:34 pm

There is an example of an over the subfloor radiant floor system (with
picture) on the Tauton online discussion forum right now, along with
some discussion of Warmboard, Quick Trak, ...

Go to http://www.taunton.com/thetauntonpress/forums.asp
Then "Breaktime", pick "Messages", find the "Energy" section, and look
for "radiant floor".

"Build It Yourself" Solar Projects

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Posted by DoHop on November 5, 2005, 9:11 pm
About to install radiant in a concrete slab house renovation.  Have
done several months of internet research and discussion with a variety
of suppliers.  All the plumbing here is in the slab with no subfloor, a
real pain in the neck!

The contractor telling you concrete as the only way to go is wrong, as
others in this thread have been gradually pointing out .  Concrete has
the advantage of mass, and in all radiant systems you don't think in
terms of quick thermostat corrections, so the mass is OK.  It would
take complicated comparison calculations that I don't believe have been
made yet (Department of Energy is doing extensive research on such
matters.), in the meanwhile I understand concrete needs to be fed
around 120 degrees [at the boiler], whereas the subflooring method is
85.  There are four methods, including the one new to me in the thread
of routing channels in conventional subfloor; you must have aluminum
fins around the tubing, so I'd like to actually see this method in
execution.  The plywood subfloor with aluminum bonded to the top is the
most expensive, $/ sq foot (www.warmboard.com), a new plastic system,
$.30 - 4.50 (www.FlorHeat.com), and a kit with fins, you cut your own
subfloor into 8" strips --why ship something heavy you can get at Home
Depot, approx $.50 (www.Radiantmax.com).

With reference to solar hot water: except in the sunny South, you have
to regard it as a supplement, with boiler backup.  Double coil heat
exchanger boiler (European) is the way to go.  Finally, I'm making sure
I have state of the art digital control over my system, both to run it
and measure its performance.  The only one I've found is a European
"SMT400"  (Approx $00) at www.thermomax.com, where I plan to purchase
most of my solar system.  I believe that you need a high efficiency
European boiler, too, otherwise the fuel cost is going to be too high.
I'm opting for the Monitor MZ 25C, although I haven't yet decided
whether I want my DHW on demand, which is a different model.  Be sure
you separate DHW from the so called "dirty water" for the radiant
system.  The boiler choice is more critical than the solar system.

Maybe I'll start a thread on my solar installation.  I plan to be
state of the art, both electrical and hot water.  I am starting the
purchasing week after next.

Posted by Iain McClatchie on November 6, 2005, 6:05 am
 DH> Maybe I'll start a thread on my solar installation.

Please do.  Frankly, I'd prefer if you put it on a blog
so you can post pictures.  Downside: when you go to sell your house,
the potential buyers might see how it went together... I have a feeling
houses are a bit like sausage in this way.

Details of your control system would be best appreciated, since
that's what I'm most nervous about.  The actual how-big-are-the-
panels calculations are more obvious.  You've also done better
research than I into the radiant flooring thing.  I'd be very
in details in how the installation went.

Posted by DoHop on November 6, 2005, 9:06 pm
 Good idea...will do.

Posted by Ron Rosenfeld on November 5, 2005, 9:34 pm

We have both.  Well, not quite.  We have an area -- a porch that we
converted to a four season room -- where we have the PEX tube over plywood
covered with lightweight concrete.  The flooring is tile.

It works really well.  The only thing to be careful of is to not lay down
the flooring until after the concrete is completely dry.  The concrete
manufacturer will have information regarding this.  FOLLOW the
instructions.  Also, there are instructions about when to turn on the heat.
If you turn it on too soon, the channels will expand, and your system will
forever make noise as the tubes move around (so our plumber tells us).  But
after a while, you want to turn it on to help with the drying out process.

I don't think the "feeling of the floor" will be determined by whatever
flooring you lay down above the concrete.

We also have areas with plywood over very deep joists -- I can't recall if
they are 11" or 14".  The PEX is stapled to the underside of the plywood
subfloor and then the bottom of the bay is insulated.  So this entire air
space is heated and, since heat rises, the overlying floor is warm.  It
also feels pretty good.  Subjectively, I prefer the concrete.  Objectively,
I'm not sure.  The basement stays warm; sometimes too warm.  Also, our cold
water pipes that run to the kitchen are partially in the bays underneath.
As a consequence of that, and also of the warm basement, it can take quite
a while to get good cold water in the kitchen.  That is a real
disadvantage, but perhaps a different design could have compensated.

Good luck.

-- ron  (off the grid in Downeast Maine)

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