Radiant wall retrofit??

[Mike Fromme]

Anyone retrofit radiant to the backside of existing Sheetrock wall?

I've got a few rooms I'd like to play around with radiant walls with. The rooms currently have fan convectors which work fine with 180 supply temps. Predictably they get a little cold on design days when storage temps drop.

It's a cape style addition so I have acces to the back side of the knee walls. So I figured why not add some radiant wall to help keep the rooms temps a little more stable.


The question is how to attach the transfer plates (joist trak) to the back side of the Sheetrock without affecting the finished side?

Probably some sort of blocking or maybe plywood between the plates and Sheetrock attached to the studs...any other ideas?

 

[peakbagger]

I have the Siegenthaler book open and he shows insulating the wall cavity with fiberglass, then installing OSB in place of drywall, then installs strips of isoboard foam on top of the OSB, leaving a channel for the heat transfer plates then install the plates and then the tubing and then screws drywall on top through to the OSB. This adds thickness to the wall (and also gets bridging of the studs. He really pushes that every inch of material between the tube and the room means having to run a higher loop temp and the higher chance that the heat goes elsewhere. You could do a similar concept by pushing it back into the stud cavities but its a lot of work which would be costly with a contractor but a DIY might be willing to work it. Running the tubing would be a nightmare due all the studs you have to drill through. I expect going with 2x4 walls with foam insulation with Johns concept on top might be the ticket instead of the common 2x6 walls required by most energy codes.

 

[Mike Fromme]

This will be supplemental heating for the room, so I don't need an ideal assembly. Which means whatever I do has to be done from the backside... Just doesn't make sense to redo the walls; even DIY.

My vision is to take the normal radiant floor assembly, rotate it 90 degree and put it on the back of the wall. I won't have to do any drilling to run the tubing. I'll run the tubing on top of the joists to the end of the wall and pull loops up into each stud cavity... Where I will somehow attach the joist trak to the back of the Sheetrock.


I'm thinking the easiest way will be to glue the joist trak to the back of the wall with sillicone adhesive. Which will hopefully be strong enough to hold while I install the tubing. Once the tubing is in place I'll take 2x4 blocking and notch the flat side to fit over the tubing and use that to hold the trak in place tight to the Sheetrock. And then insulate with rigid foam attached to the 2x4.

 

[sportbikerider78]

If I was you, I wouldn't worry too much about getting a close contact with the back of the sheet rock. You're not going to get squat for surface area contact with radiant tubing.so not much conduction. I'd just focus on sealing off the area well and insulating.

 

[Bad LP]

With all that screwing around to do it 65% is there a reason you just don't go with panels? I'll bet it's going to be cheaper in the end.

 

[Mike Fromme]

I don't really want a radiator in the rooms. More in the way of furniture, ugly and more to clean. Plus I want to see how well radiant walls work for future houses.

The knee walls are 5.5' x 20' in each room... So maybe 20 plates and 300' of tubing, a few pieces of insulation and a couple spun copper manifolds. No mixing valves or balancing valves, pumps etc. So ~$300 per room. Less if I used stamped plates.

 

[lazycoyote]

Here's a video that shows a radiant wall install:

Sent from my ONE A2001 using Tapatalk

 

[Bob Rohr]

The radiant panels from Roth would be ideal for that. they are foam panels with aluminum layer and groover 6" oc. I would use foam adhesive or silicone to get the best conductive transfer. You want the entire sheetrock area to be a "radiator"

i di a wall in myna office from the back side with those aluminum transfer plates from Radiant Engineering. Getting the tube in the track or panels is a bit tricky without piping any sheetrock nails. insert the tubing first.

Use 3/8 tube as it bends tighter an works easier. Upon or Mr Pex is the most supple tube, keep it warmed up for easy shaping.

Radiant walls are an excellent way to radiant heat. you can run much warmer temperature than floors, about double the output in BTU/ sq. ft.

 

[Mike Fromme]

Had a little time to get started.

4' tracks were to long. So I cut them in half... Three feet would have been ideal but a waste of material. Used 1/2" hePEX which was very easy to work with. 2' OC stud so I doubled up the loops in each bay. Ended up with a ~5" OC tube spacing.

I notched a couple 2x4's to hold the plates in place. And as Bob said it's much easier to put the tube in the plates first.


@Bob Rohr what water temps are you using?

 

[sportbikerider78]

Is there any BTU target for how much heat you want to get into the room? Just curious how you go about calculating this.

Very interesting. I didn't even know people did radiant walls.

 

[Bob Rohr]

My system runs on a outdoor reset control, so supply temperature varies with high limit at 128F.

Here is a short section from Idronics 6 on radiant ceiling and wall design, including formulas for predicting output.

 

[Mike Fromme]

Is there any BTU target for how much heat you want to get into the room? Just curious how you go about calculating this.

Very interesting. I didn't even know people did radiant walls.

I didn't do any fancy calculating. Just wanted to the room to be warmer when I let storage temps get low. The kickspace convector I have in the room is rated for ~8000 but with 180* water and less then half that at ~120. Which is not enough on colder days.

 

[Mike Fromme]

It's been a few weeks since I got one room done. Ended up changing how I did things. I cut a piece of foam insulation to fit between the studs, routed slots in the foam and snapped the joist trak into the foam. Then put that on the backside of the wall... It's working better then I could have hoped for. What was the coldest room in the house when storage got low is now the warmest.

I've had the convector switched off since I got the walls done so I'm saving some electricity as well

The surface temp of the wall has been around 80-90* depending on storage temp. Which is just about right to give that nice bone warming radiant feel when you walk into the room.

 

[maple1]

That's a neat looking project. Once in a while I have ideas bouncing around in my head about what we can do for infloor heat in our kitchen when the time comes to re-floor it (20 year old pine flooring is getting pretty ratty looking in spots). Might have to bounce around wall ideas too.

An problems getting the air out? Those high vertical loops had me picturing air traps.