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Old 02-25-13, 08:20 PM   #21
Mikesolar
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Yes, I will chime on the solar and floor heat. I would rather see the whole floor on one zone with two inputs near the manifolds. The reason is pretty simple....often the solar will produce temps that will be too hot for the floor and it will be both uncomfortable to stand on and it may crack at a spot where the heated and unheated concrete meet.

If an antiscald thermostatic valve was used (simplest way), or a motorized 3-way valve (could be run off an arduino and outdoor sensor) then the floor could get the right temp at all times of the year and still be direct from the solar without a HX.

A buffer tank could be put in if you want but it may not be necessary OR you might want to do some DHW as well in which a HX will be necessary.

Lots to figure out. I'm not keen on LPG unless it is way cheaper than it is here. Otherwise I would just go electric as a backup (or a heat pump). Any combustion product has a lot of drawbacks.

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Old 02-26-13, 09:27 PM   #22
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Thanks to everyone for the replies.

Regarding Roth panels, found a local distributor right here in Rochester, but they only sell to contractors and wouldn't quote me any prices or sell it to me directly. Maybe I'll have to become a contractor! Does anyone have any rough estimates per sq ft. for the product?

Regarding insulation on top/below slab. Is it possible to quantify the difference between putting the heat on top of my current uninsulated slab vs in the slab with insulation underneath? I assume I'll be able to get ~2x the amount of insulation by digging down than I can give putting it on top of the existing slab (celing height is already only 7'4" to bottom of floor joists). Does this result in 2x less heat going into the room and instead going to heat the earth? Is it a linear relationship? Or is the R value not as crucial above a certain number and the reason to put the heat into the slab direcly is for the ability to hold the heat for long periods?

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If someone were living in a challenging latitude like Michigan, for instance, and/or had only a code house, or lower, the results could be very disappointing.
I'm at 44' latitude, which I would assume falls into the 'challenging' realm? My house is constructed of only 2x4s for the main walls, though I've got a wood basement with 2x6. I do plan on insulating them, considering getting spray foam done, which I would assume is about as good as I can get. Are you suggesting that trying to heat the space with solar would be just too much to attempt?

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How thick is the cement floor?
It's ~4" thick and a PITA to break apart with only a hammer drill and chisel/mallet!

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Well the heat your not getting into the floor your paying for its replacement.
My goal was never to completely heat the basement with the radiant, just to increase the comfort level by bringing the floor temperature up. I've got forced air down there now, but trying to heat the basement with vents in the ceiling is pretty ineffective. I was figuring if I could avoid having to run the furnace more by putting radiant in the floor, I'd be happy.

Or, maybe just properly insulating the space (floor and walls) would make things more comfortable with the heat I have now? Still lots of research to do!

thanks again for all the feedback/ideas!
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Old 02-26-13, 09:35 PM   #23
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I've done this 100s of times. If you can put up with a 7ft basement, simply put the 2" of XPS foam on the existing floor with a 6x6 wire mesh on top and the tubing (make sure it is an O2 barrier tube) , then put min 3" of cement down. It is the easiest way.

If the height is an issue, then there is little option but to break up the concrete. Solar is a bigger subject with many options but the floor comes first as you need a place for any size tank....lol

Closed cell foam is great and one of the few things I would do to insulate a basement wall. Fiberglas is not recommended, at least by me.

Last edited by Mikesolar; 02-26-13 at 09:38 PM..
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Old 03-01-13, 10:03 AM   #24
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Originally Posted by Mikesolar View Post
I've done this 100s of times. If you can put up with a 7ft basement, simply put the 2" of XPS foam on the existing floor with a 6x6 wire mesh on top and the tubing (make sure it is an O2 barrier tube) , then put min 3" of cement down. It is the easiest way.

If the height is an issue, then there is little option but to break up the concrete. Solar is a bigger subject with many options but the floor comes first as you need a place for any size tank....lol
Is the reason for the concrete (either new or on top of the existing) to help hold any heat that's been put in? To spread out the heat/prevent hot spots? Does it basically replace the need for a storage tank if I'm doing solar as the source of heat?
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Old 03-12-13, 01:39 PM   #25
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Default Solar heated basement floor: Awesome

Because your floor is relatively small and is not going to be your primary heat source, I'd probably not get all super wiggy about the performance overall, especially if you heat the water with solar. If I were doing this project I'd put my money and effort into harvesting and storing as much solar heated water as is practical and then sip that energy as needed. This would require more collectors/storage tanks but then you can use any extra energy for domestic hot water or even add a heat exchanger to supplement your forced air system.

1" foam on the slab and stuck to the walls* (spray foam your sill boxes too while you're at it) would make the space at least somewhat decoupled from the "outside" but if you approach it from this angle (more solar!!) then your losses to the less than insulated slab would be not as painful as if you were paying for fossil fuel on an ongoing basis.

*my advice to all homeowners and builders: no fiberglass insulation anywhere in a basement ever! Here's a graphic I put in all my energy evaluation reports

Good luck!
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Old 03-27-13, 01:31 PM   #26
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Default FYI: Basement alternatives to radiant heating

Hi,
Just wanted to contribute a few thoughts regarding the cost/benefit of radiant heating. The tearing up of the floor, putting down foam, pex etc. is an ideal. I've worked with customers that don't have that kind of money, patience whatever and have had great success warming up basements by doing two simple things.
1. Get the heat down to the floor. Often around here, the heating ducts in the basement poke out of the ceiling. The heat just stays high in this situation. Extending the duct into the wall to come out a foot or so above the concrete floor is the key. Best results come when there is concrete or the tile is the flooring since it can absorb the heat.
2. When insulating the walls. Go with 2" high density EPS attached right to the concrete (there are plastic anchors that are made for this, just requires hammerdrilling a narrow 2" deep hole in the concrete walls) or you can glue it. Next, put up a radiant barrier. You can get mylar stuff on-line or if you are really on a budget, just glue industrial sized aluminum foil to the foam using white glue. After the insulation you frame a thin wall against the foam to compensate for loss of floor space. (I use 2.5" steel studs and channel. A new wall is preferable to furring strips because foundation walls are rarely plumb and you need space for electrical and plumbing) The dead air space created by the thin wall allows the radiant heat in the basement to return to the wall surface making it feel warm.
These two things by themselves have turned formerly cold basements into cozy caves without tearing out the concrete.
I would suggest a relatively inexpensive experiment. If your heating ducts are coming out of the ceiling, extend them into the wall and out at floor and see how much difference that makes. It might be enough to give the feeling of comfort to the feet and you've saved yourself a ton of money and hassles.
YMMV.


Last edited by nascenta; 03-27-13 at 01:45 PM.. Reason: Clarified a point.
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