Garn Framing Question

[rvtgr8]

I posted this over at Garn, but did not get a response. Thought I might try it here.

Slowly but surely my project is starting to take shape. On the Hearth Forum I have followed the progress of several Garn installs and I have noted with some interest that the steel studs that people are using do not seem to meet the requirements in my install manual. Commonly, the sheetrock will not fit (5/8") when placed on a 3.5" stud and so they go for a smaller size stud or thinner sheetrock. From the pictures and the stories, it also becomes obvious that the gauge of the steel is not 18, but more likely the lighter 25 gauge sold at big box stores. I am not saying that they are doing it wrong. These are competent heating guys and I would not presume to criticize. But it raises a question. Some of these guys have the studs mounted right up against the unit without any protection for heat loss through the studs. Is it essential to place a thin layer of rock wool between the studs and the tank. If so it will exacerbate the thickness problem and the stud sizing. Do you have to use 5'8 rock if you can use something else that is non-flammable like concrete board or Hardi backer board? That might be thinner but harder to tape for fire purposes. Will that impact warranty? Right now, I am looking at pictures of installs that have the metal studs up front and on the end, but wood studs on the side and I am not sure that is kosher.

My original plan is to insulate with vermiculite inside steel (18 ga.) framed walls with 5/8" sheetrock, but if I could use alternate materials that I have on hand such as OSB on side framing, wood studs on the sides, concrete board in place of sheetrock, etc.it would make things easier for me. I have no intention of sacrificing safety for economy, but if there are solutions of equal value then I am all ears. Any thoughts?

 

[foxt]

For what it is worth, here's one man's recent experience with his first GARN install. I had the same questions when I built my enclosure several months ago, noticing the inconsistencies between what the GARN documents call for and what seemed to be common practice from reading the forums. I would love to hear from Dectra on this, or from folks who have had the chance to observe the long term performance of these enclosures ...

I went with what seems to be the most common approach, I stick framed a structure large enough for the GARN and storage of wood, etc. The GARN was planned for a back corner. I stick framed a sidewall and ceiling, and sheetrocked/taped the GARN-facing sides of the four surfaces (3 walls and ceiling) with 5/8 firecode.

As far as the front wall goes, I used 2.5" steel studs and spaced them such that I could get 5/8 firecode between them and the flange of combustion area collar. That also gave me a thermal break between the studs and the tank. I know some folks use sheet metal for the front surface, and I would have loved to do that but I don't have the skills.

I didn't have access to the volume of vermiculite that I needed, so I never even considered that. I would want to hear from folks who have done that before I tried it myself. I used fiberglass for insulation, and if I had it to do over again I would have used rockwool. No one in the area stocked rockwool and I would have had a long wait, and I decided it wasn't worth it. Given the better performance of rockwool at higher temps, I do wonder now what impact that would have had on my standby losses, and I hate the thought that there was something relatively simple I could have done to reduce those losses.

What do you mean by "OSB on side framing"?

 

[rvtgr8]

Thanks for the reply Fox. I love the whole Garn experience. It is like a good movie, "I laughed, I cried, I got the popcorn..." The framing question comes from my reading about standby loss as I am plumbing in the project. I guess I am intrigued by the creativity of this "framing" because each install is just so unique. I really have in mind a small loading area with ceramic tile floor to ceiling so I can keep it clean and have it look nice as well. The backer board would be a great surface for the tile. Dectra and the boys over at Garn are somewhat unclear on some of these points, but they sure make a great boiler.

Robert

 

[foxt]

Robert,
The GARN is indeed a great boiler. I know you've had a rough start, but when all is said and done, you'll be happy. Were you thinking of tiling the front wall? That indeed would look sweet. Depending upon what ambient temps your space will experience, what type/size tile you would use, etc, I'd be concerned about movement of the backer/tile interface. Hardi or something similar would be fine, but I'd do what I could to provide for some elasticity in the bond - modified thinset or a membrane like Ditra under the thinset might do the trick.
Compared to sheetrock, tile is "forever", and you probably already thought about this, I'd also make sure I provided for access to everything on that front wall - electric elements (even if you don't have them installed), cleanouts, drain, etc. And you're right to be planning for standby loss well ahead of doing anything - it kills me to think about the amount of wood I am burning (and therefore the amount of felling, cutting, splitting, stacking, etc) that isn't making it into the house. Only thing that would make me feel worse is if I was burning oil ...

Tom

 

[Jim K in PA]

Robert - as has been discussed in a couple of other threads, 5/8 rock is not necessary on the front wall, since there is no benefit. The GARN air collar is designed to use 3.5" studs with 1/2" sheetrock, but mine has a bowed front wall that makes slipping the sheetrock under the collar just about impossible. I think Toms (foxt) approach using the 2.5" stud with a thermal break behind and the 1/2 or 5/8 rock in front would be plenty. If you decided to tile the front wall, then consider using durock or wonderboard or some other cementitios front substrate to tile over instead of the gypsum.