Wall shield and hat channel?

[14erjohn]

First of all, this forum has been an invaluable source of information for me to plan my woodstove installation - many thanks!

I'm planning to install a wall shield of durock and tile with a 1" air space from the drywall. Is one layer of durock adequate or is 2 better? I can get 4'x8' sheets of durock so no joints required for the size shield I'm building.

Also, and this may be a dumb question... I found a few lengths of metal hat channel at Home Depot to use for spacers. Does it go flange side to the wall? I'm assuming so but since the studs are vertical and I want the hat channel to be vertical, only one flange will be solidly attached to a stud. I thought I could use drywall anchors for the other flange, or should I even worry about it?

Thanks!

John

Jotul Castine (on a pallet in the living room)

 

[begreen]

The simplest thing to use for spacers is 2 strips (3"wide x the height of the shield) of the 1/2" durock on top of each other to build it out to 1". That makes a firm flat foundation for the wallshield durock. You can use the screws designed for the product. Just don't place a support strip directly behind the stove pipe and you should be fine. Leave a 1" gap at the bottom and top to allow for ventilation behind the shield.

You'll want to be sure this is the cement based durock, there is another durock brand underlayment that is much lighter. I think it has styrofoam pellets or something like that mixed in. That's not what you want. Normally this comes in about 3x5 sheets. Another brand that is ok is wonderboard.

 

[14erjohn]

The simplest thing to use for spacers is 2 strips (3"wide x the height of the shield) of the 1/2" durock on top of each other to build it out to 1". That makes a firm flat foundation for the wallshield durock. You can use the screws designed for the product. Just don't place a support strip directly behind the stove pipe and you should be fine. Leave a 1" gap at the bottom and top to allow for ventilation behind the shield.

You'll want to be sure this is the cement based durock, there is another durock brand underlayment that is much lighter. I think it has styrofoam pellets or something like that mixed in. That's not what you want. Normally this comes in about 3x5 sheets. Another brand that is ok is wonderboard.

Thanks - I've read about using durock strips as spacers, but I already have the hat channel. Just wondering if anyone has had direct experience using it.

Trust me, this is the real cement-based durock... I can get it in both 3x5 and 4x8 sheets at one of our area Home Depots. Easier to work with the smaller sheets but with the large sheets I can avoid joints.

Any opinion on 1 versus 2 layers of durock for a wall shield? Assuming 16" centers for whatever spacers I use...

 

[begreen]

I've only seen it done with 1 layer, but no harm using two if it's well supported. It isn't going to flex like a floor, in a way it's more like hanging tile wall art.

 

[Jags]

For the hat channel, the "legs" are screwed to the wall, leaving the "flat" surface to screw the rock to. That is assuming you are using the 2 leg style. __/----__

(yep, I could screw up a stick man).

 

[Flame Job]

I have a question regarding whether or not you need drywall to start this process. I am building new construction, and I know exactly where the hearth is going. Should I still finish the wall with drywall and then start the process as oultined in this post, or is there a way for me to skip the drywall and save even more space? Can cement board be attached to the wall studs, or is that a problem? In essence, I want to be able to have my stove as close as possible to the back wall, and have the back wall as thin as possible. Thanks much for your advice.

 

[Jags]

I have a question regarding whether or not you need drywall to start this process. I am building new construction, and I know exactly where the hearth is going. Should I still finish the wall with drywall and then start the process as oultined in this post, or is there a way for me to skip the drywall and save even more space? Can cement board be attached to the wall studs, or is that a problem? In essence, I want to be able to have my stove as close as possible to the back wall, and have the back wall as thin as possible. Thanks much for your advice.

My suggestion would be to stick with the drywall and the minimum clearance distances as stated in the owners manual.

 

[Flame Job]

But isn't the clearance in the owner's manual the distance to a combustable surface? Isn't the point of this post coming up with a safe way to better that clearance by insulating the combustables?

 

[begreen]

The minimum clearances are to combustibles which in this case are the wall studs. It doesn't matter much if there is durock directly on the studs or drywall. If the stove permits, the clearances can be often be reduced by using an approved wall shield and double wall pipe.

There's no rule that the distance can't be larger. We've had people express concerns that their walls were uncomfortably hot with some stoves installed a minimal clearances. If there's no wall shield, I prefer to add a little to the minimum clearance just for peace of mind.

Another alternative is to pick a different stove that has tighter clearances. What stove are you considering FJ?

 

[Flame Job]

Right now, the Avalon Arbor is the top contender. I may look a bit more, but from what I have seen and read, it's the one. According to the owner's manual, with appropriate pipeshields, I can go as close as 11" between the connector and the combustable back wall. I just wonder if I can safely shave off some clearance if I go with the durarock and 1" air space.

 

[Jags]

But isn't the clearance in the owner's manual the distance to a combustable surface? Isn't the point of this post coming up with a safe way to better that clearance by insulating the combustables?

Flame Job, this is my own personal opinion, but when it comes to a box full O fire in my house, I prefer the KISS method. Keep it simple (stupid), follow the rules (owners manual and codes), and be a diligent wood burner.

Heat shields can be of use in certain installs, but I would not approach a new install with this intentionally planned to "better that clearance". Again, just my opinion and I am sure that others may feel differently.

 

[Flame Job]

I agree 100%, Jags. I want to be completely safe. My only thought is that if the surface we are measuring to is not drywall, but tile over cement board over an inch of air, doesn't that count for something?

 

[Jags]

I agree 100%, Jags. I want to be completely safe. My only thought is that if the surface we are measuring to is not drywall, but tile over cement board over an inch of air, doesn't that count for something?

It sure does, but I am not qualified to say "how much". And to state it simply, very few are. I do know a thing or 2 about fire ratings and fire walls, etc., but if my stove manual said "keep it xx distance from combustibles", thats what I would do. In my opinion, a heat shield should be an "extra" layer of protection on top of the stated distances. Unless it is engineered and tested from the factory for your stove, I would take any "firewall" or "heat shield" data with a little caution.

Lots (and I do mean LOTS) of things must be taken into consideration. How much heat transfer is those metal screws that end up screwing into those combustible walls going to affect things. How old is the drywall, what kind of paper was used (its a little different now than from years past). 1/2" durock or 5/8", single layer or two?? EVERYTHING makes a difference in an engineered firewall (which is what a heat shield is when used to reduce distance to combustibles)

There is some common knowledge data to support different configs of firewalls, using different components, but its FIRE in MY house. I will stick to the stove engineers tested data.

Jags opinion (man, did I just hear trumpets in the background )

 

[begreen]

The Arbor gets hot in back due to its cross-draft design. We considered the Lopi Leyden but the clearances were a deal breaker for our location. Compare it to the Jotul Oslo or Pacific Energy Alderlea T5 for clearances to see a major difference.

The manual does say that clearance can be reduced by using an NFPA211 wall shield, so this would be up to the inspector to approve. If you choose this route, you might want to contact Travis with your query and get a written answer for clearances with an NFPA 211 wall shield. Take that to the inspector and get his approval before starting.

 

[Jags]

Bingo BG - you da man

NFPA211 engineered, tested and approved. Now there's a shield I could stand behind for design. Being that the manual states this specifically, it should have been tested and approved at the factory. Now were cookin' with facts and the company should be able to give you figures on the difference this will make for clearance to combustibles. No guess work.

 

[Flame Job]

Gentlemen:

As usual, this forum us spot on. Thank you very much.

 

[Hogwildz]

BegReen, I think ya have the Wonderboard and " other" style of Durock mixed up. I have sheets of Wonderboard here, and it has the Styrofoam bb's in it.
Its not recommended for hearth use let alone a wall shield as far as I remember. Goose can answer about these products better than I. He researched them all for his hearth.