Radiant stone wall????

S Ebels

I'm thinking out loud here in the office with my Son-in-law and trying to come up with ways to make up a BTU shortfall in their new great room. About 70% of the load will be panel rads but due to very limited wall space and other considerations we have no other place for a rad. There is however, a stone (fake) fireplace approx. 16' tall in one corner of the room. I was just thinking what if......... we tubed behind the stone and turned the fireplace into a giant panel rad. We have some extra loops on existing Climate Panel manifolds so we could use the 5/16" tube spaced very tight and run it the same temp and reset as the floor panels.

Has anyone done something close to this. Do you think we'd have problems down the road with the stone or mortar cracking? I'm thinking I could get around 30-40 btu's a sq ft.

Whaddyah think?

Ted_9

I think you should do it and tell us what happens


PATRIOT HEATING & COOLING, INC.

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hr

Sure

it will be a big flywheel however and a bit tough to control the output.

Guesstimate the mass (weight) and calculate how many btus to raise it to say 80 F or more to turn it into an emitter.

Then of course the BTUs you load into it would come back out. It's basically a thick concrete slab turned on it's side

This is the concept behind the Rumsford and the soapstone fireplaces that store the heat in the mass in and around them.

hot rod

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S Ebels

Lot's of mass

Somehow I knew a person that has made radiant dogs and desks would chime in on this.

The high mass won't be a problem at least for overshoot. The panel rads will have TRV's on them to deal with rising room temps. The other side of the coin is that it'll take a long time to come up to temp when the room experiences a sudden increase in heat loss.

I'm trying to find some kind of data that would give me a clue as to the output of such an irregular surface. My gut tells me it will be different than a flat slab or wall. Maybe not as much as I think. If I would be able to raise it to 85-90*, do you think it would hit 40 btu's per sq.ft.?

I'm also tossing around what size of tube to run under the cement. 5/16", 3/8" or 1/2"? The small tube could be run very close together keeping the surface very uniform temp. The bigger tube sizes offer less flow resistance. I'm kind of leaning toward the 5/16" as it will present the same head as the rest of the loops on the Climate Panel manifold and simplify balancing.

Steve_OH

What kind of stone?

The thermal conductivity of stone varies quite a bit. The lowest value I have here in my references is for limestone, at 4 BTU/hr/sq ft/in/°F, and the highest is for granite, at 28 BTU/hr/sq ft/in/°F. For the granite, you'd need to maintain a thermal gradient of about 1.4°F/in to get 40 BTU/hr/sq ft; this is probably fine. But for the limestone, you'd need 10°F/in, which is probably asking for trouble: if the stone were 8" thick, for example, you'd need the back side to be 80° warmer than the front. Even if you could maintain that kind of gradient, it would surely wreak havoc on the mortar joints as the system warmed up and cooled down.

-Steve

S Ebels

This will be

Manufactured stone which is made out of a cement product. It's the kind you see the fireplace shops using in peoples houses. From what I understand, a metal mesh is nailed/stapled to the sub surface wood, OSB or plywood. Then a layer of cement/mortar is troweled over the mesh. Next comes the bonding layer of cement, to which the fake stones adhere. After placing the stones and allowing them to set, the gaps between them are filled with mortar. The maximum thickness will be from 3-5" depending on what exact type of "stone" they go with. So basically, it should act the same as regular cement.

BTW, the inside of the chase for the B-vent flue behind the stones will be R-19 batts. Also this will be constant circ with water temps reset according to O/D conditions.

Weezbo

That sounds like it would work.

as it is a fake fire place alreadydoes it have a hearth? i think you could load the heck out of it....and if it is stone whats a new scratch coat from time to time? so What if it cracks a bit...? mortas cheap:)

Steve_OH

Okay, so the conductivity will probably be more or less the same as that of concrete (around 8 BTU/hr/sq ft/in/°F), which means a gradient of 5°F/in. That's about halfway between "no problem at all" and "can't possibly work."

If you think about it, they use the same kind of stuff on the outsides of houses, and over the course of a hot summer day you build up similar gradients there, so you're probably safe.

If you decide to try it, you might want to use a mixing valve to moderate the temperature of the water. Then gradually crank up the heat over the course of a few days until you get the heat output you want, or until you start hearing funny sounds coming from the wall, whichever comes first.... In any case, using some aluminum to distribute the heat over the back of the stone will likely help quite a bit.

-Steve

hr

The output of any radiant panel

is driven by the delta T between the surface temperature of the panel and the surrounding temperatures.

I have seen the number used vary from 1.7- 2 output/ degree difference.

So... If the surface of the radiant panel is 82°and the room temperature is at 68°F expect @ 28 BTU/sq. foot output. If you use the 2°number.

I'm not quite sure how manufactures can sell 40° BTU/ sq ft output numbers unless they drive the surface beyond a comfortable 82° (for walked on floors). Or use an air temperature of 65°. This would get you close to the 40 BTU number thrown around the industry.

Personally I think a realistic number would be more like 30 BTU/ ft. max from a "comfortable" radiant floor with a "comfortable" room temperature


The higher BTU/ ft numbers may work in a commercial slab application with wide tube space, higher surface temperatures and cooler air temperatures, but I question 40 BTU/ sq. ft. in a home.

I agree with Steve the weaker link will be getting the heat from the tube to the mass. The transfer plates in good contact with the stone would accelerate the transfer, spread the heat more evenly, and probably require less supply temperature. All in all more controlable.

Still the weight of that mass is unchanged and any temperature over room temperature it will continue to give off some heat. It's not at all unlike the solar gain a slab see on a sunny day that gets hard to control.

Of course you could dump cold incoming domestic water through it to drop the temperature quickly. Get free "quote unquote" DHW preheat. And free radiant cooling! (ala the internet hucksters

I'd still like to see you give it a try, also. Sounds like an unique application to solve a supplemental heat problem. A good RPA showcase entry and magazine article in the works!

We want pictures!!

hot rod

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jerry scharf_2

I love it

Steve,

I think it's a perfect setup. The hearth is supposed to be a place of warmth, and you get to make it so. As I hoped, you said the rads have TRV. This means that the stone produces a percentage of the heat and the rads cover the rest of the steady state and pickup. With any luck, the rads are in a different part of the room than the hearth.

I haven't thought it through all the way, but if you bedded the transfer plates into thinset with some bend over anchors to hold them in place till it sets, it might do the trick for good contact. As for cracking, with outdoor reset and constant circulation, this should not be a problem. It will certainly want a different temp than the rads.

As for output, 40 seems like possible but a bit optimistic. As Hot Rod said, the surface is going to have to be fairly warm to get this. It's not the problem it would be for a floor, but you still don't want it at 95.

You may really need to work carefully with the insulation. If they are in your neck of the woods, it would be ideal to have as little thermal bridging to the exterior wall as possible.

jerry

c.t.kay

it works, put a product like dura rock on the surface in strips, then put the tubing between the strips, put a circuit setter or a thermostatic valve with a remote sensor on on the supply line.this method also works well in mud set shower pans and in tile shower walls.

S Ebels

Looks like

We're going to go for it. Talked it over with the kids and it sounded like good fun to them. We're also going to go with radiant floor and 3 wall combo in the sunroom. Lot's of glass, 55 btu's/sq.ft. heat loss, no room for a panel rad. This one is going to be fun!!

Tom_38

radiant wall

S ebels
I did two of them last year both of them were to make up some extra btu's that I couldnt get out of the floor
I used Wirsbo Transfer plates. I had the insulation contractor spray foam the back side of the fireplace,then the contractor installed plywood to attatch the Wirsbo plates. we ran 2 250 foot loops of 1/2" Wirsbo. Then we installed them on the low temp loop used Wirsbo Telestats with out end switches so they could come on when any zone called for heat if required ( like a wild loop) the house has 8 zones so in the cold one is always calling and the stone fireplace always gets some heat.. Works Very well

Tom

S Ebels

T Bradd

Can you give me any idea what the temps were? What did the surface temp of the fireplace run and what actual water temp was being supplied it?

Thanks

Steve