Mama Bear with through masonry wall lined chimney

[pontiacgta2002]

Hello, I'm trying to see what the clearances are for non-combustible walls. I looked through the manuals and all relate to clearances of combustible walls. I have used the stove for years but just now really learning how it works. As it sits now the stoves top plate is 8" from masonry wall. The rear legs are 10" from wall on brick hearth. Front legs are 18" from the front edge of hearth. 6" pipe going through 10” thimble wrapped in insulation into a 6" flexible single wall corrugated pipe. The chimney pipe is in a terracotta brick chimney with granular cement insulation. I noticed last night that the masonry wall was hot and could not touch it directly behind the stove. The masonry seems to be attached to fire rated drywall. It has a hallow sound when tapped on. What should the distance from the top plate to wall be from the masonry wall?


I don’t see any type of UL label or plate. The SN is FS01-16265

 

[pen]

Unfortunately, that brick shouldn't be straight against any drywall, fire rated or not. For it to be a proper heat shield it would need to have air be able to circulate from the bottom up through the top, and be placed 1 inch way from the combustible wall behind it. Also, at that point, the distance to that heat shield (brick wall) could be reduced to 12 inches. Technically, if there are combustibles in that wall right behind the stove, then it's supposed to be 36 inches away, even though it's brick (surprisingly, brick is not a good insulator).

Here's a more detailed explanation of what I just mentioned https://www.hearth.com/econtent/index.php/articles/stove_wall_clear

The next question is how close are the combustibles (in particular the studs) to the crock as it passes through that brick?

What's back there should look something like this

I feel your pain, I found this when I opened mine up because of the advice of a good member here years ago.

I had no where near the 12 inches around that crock to combustibles needed. I wound up removing the combustibles, putting in a header in, and building a brick surround




One advantage that I have though is that my stove does have solid concrete behind it, I simply had to worry about my pass through with that crock.


Good luck and good on you for checking into things.

pen

 

[coaly]

Reduced clearance with 3 1/2" solid brick against a combustible is able to reduce by 33%. 1 inch airspace behind brick makes it 66%
That would be 24" compared to 12" with 1 inch air space.

Clearance to a non-combustible wall (that you may not have) such as in a fireplace or solid masonry wall is not in manual. Fisher recommended minimum of 3 inches to prevent overheating side and back sheets preventing warpage.

It would be interesting to see what's behind that brick. Is it a single flue chimney? Or possibly wider making it non-combustible behind it? You need to find out for sure.

The clearance to the book shelf is 36 inches.

 

[pen]

Reduced clearance with 3 1/2" solid brick against a combustible is able to reduce by 33%. 1 inch airspace behind brick makes it 66%
That would be 24" compared to 12" with 1 inch air space.

Thanks for clearing that up, my apologies for saying 36 above there.

 

[pontiacgta2002]

Pen,

Thanks for the information. I plan to tear down the exterior chimney this spring, this will allow me to see what’s going on behind the brick in the house. The chimney sits on the north end of the house and gets little sun to dry it out after rains. The bricks are flaking apart and some have cracks in them. I plan to install or have installed double or triple walled SS pipe out and up. This will allow me to have a tee on the bottom for an easier cleaning. I have to pull the stove away from wall currently to vacuum out all the debris completely. For now I could place a temp hearth to extend it further into the room allowing me to pull the stove away from the wall to obtain the proper distance. I could use single wall pipe to do this or a double wall pipe insulated to fit through the thimble as it’s a 9” thimble ID. This will make me feel better and allow me to run the stove through this winter.

Another question for you guy’s, should I load the wood above the fire brick or even with it? I only have a single row of fire brick along the sides of the stove. There are no retainers for a second row.

 

[pontiacgta2002]

Coaly,

Thanks for your information also. I will plan to pull the stove away from the brick wall to get the 24" clearance. The book shelf is not 36" but will be when i pull the stove out further. Until I saw the manual that I found on this site, I had no idea about what clearances it needed. This is a great site for this Fisher stove. I was thinking about replacing it with a lopi in a few years for the efficiency gain. Time will tell.....

 

[coaly]

Without the manual you would need to go by the generic clearance given for all unlisted appliances in NFPA 211. That's where the reduced clearance with UL approved heat shielding comes from too.

I don't think it matters much if you load it above the brick. It's not like the glowing coal pile at the bottom that would be in direct contact with the side sheet for long periods. It gets more air front and center too, so the upper sides are not the hottest area. They see much more heat around the flue pipe on the back. (where there is no brick)
A baffle inside directs a lot of heat to the stove top and the back runs cooler too - That was the reason I made a baffle in my Mama Bear. My stove was in the middle of the kitchen about 5 feet from the fridge. Milk went sour in the door overnight so I set up a UL stove pad behind it propped against a portable drying rack. That cured the milk issue, but the stove board was in the way. So I figured why not direct the heat inside the stove to prevent so much radiation from going rearward? Worked great, and I noticed with the first fire a huge reduction in smoke. Then I remembered Fisher started putting baffles in the double doors in the 80's to comply with the new smoke regulations that were slated to become stricter from '85 to 1988. So I inadvertently designed the same type baffle as what they called the Smoke Shelf Baffle in the Fireplace Series. Don't know why they never added them to the Bear Series single doors, but it sure works.

I'm thinking of replacing my '03 Pontiac Grand Am with a BMW, but I'm afraid of the results too.