Got a Grandma Bear - Weighing my options on chimney

[BamaRama]

Picked up a Grandma Bear with straight doors and no UL label with an 8" flue out the back. Need help/advise/opinions please.

There's a back-story to my question, so here goes....

I have a Majestic Thulman L36A Fireplace (Zero Clearance 8") in a house I've been living in for about 15 years. The house has an A frame great room and the chimney going out the ridge of the A frame with a big wooden chase that I couldnt access without roping up. When I bought the house, it had a Little Buck insert in the fireplace, so i slide it out to inspect. The firebrick were cracked and the side plates (whatever you call them) that screw onto the sides were melted. So I sold the insert and installed ventless gas logs and closed off the flue (right or wrong). Then I had the house reroofed and the roofers did away with everything above the roof line and roofed over the chimney.

So, I took the paneling off the inside to see what is left and found some disturbing things. Paper backed insulation has fallen on the chimney, a wooden frame holding it in place in only one place, the roofers didn't cap the chimney like I told them to, and the patch job on the underlayment is subpar. Took lots of pics.

I am open to suggestions on how to make this work if it's possible/feasable. Should I try to use this fireplace with the stove, If so, how? I can fix the clearance issues and will use an elbow to go out of the roof just below the peak.

Should I tear it out and start over with a hearth and black pipe and salvage the Class A triple wall to go through the roof?

Thanks in advance for you comments.

David

 

[Grisu]

Welcome to the forum!

That looks like a tough case; I see a multitude of issues and it will take quite a bit of work to make that stove a safe installation using the fireplace and chimney. Thus: Have you thought about ripping the whole fireplace and chase out, finish the wall, make a nice hearth there and then install a stove with proper stove pipe (preferably double-wall straight up through the roof or a rear-vent stove with a horizontal section going out the back connecting to proper class A chimney through the wall)? You will gain some space in the room, it will probably not be more work than getting the current setup fixed, it will be much easier to get a safe installation, and look like it was designed that way instead of a cheap fix.

I would also suggest to rethink your stove choice. A modern EPA-approved stove will give you more heat from the same amount of wood, a nice fire view, often closer clearances, only needs a 6" chimney (most models), comes with warranty, and is less polluting.

 

[BamaRama]

Thank you for you thoughts Grisu. Everything on this house is a tough case LOL. Ripping the whole thing out is one of my options, but I had not thought of running horizontal through the wall. I would still need to take it through the eve at about 25 feet high, so that's no small endeavor. And opening the space up is a consideration.

If i decide to use the existing fireplace, getting another ceiling box installed while inside the chase wouldn't be easy and the floor hearth would need to be ripped out and replaced. The bricks are too high to run the flue into the fireplace.

Whatever I do is going to be a lot of work.

I lurked around on the forum before I got the Fisher. One of the reasons i went with it is because it doesn't have or need a fan. And I plan on adding the baffle and damper so It hopefully I can run it efficiently.

 

[coaly]

Moved to Classic Forum where it will get more traffic since it is an installation question for any non-listed stove and not Fisher specific.

If this chimney is triple wall using air circulation only without insulation around inner flue, (thermal siphon) it was not recommended by Fisher since the inner flue liner stays too cool. Page 2 in the manual here;
https://www.hearth.com/images/uploads/Fisher_Manual.pdf

 

[BamaRama]

triple wall using air circulation only without insulation around inner flue, (thermal siphon)

I think that's what it is. When I was inside the chase, I was able to stick my finger down in between both pipes if that means anything. And i can't see insulation in the picture... if that means anything...

 

[bholler]

That chimney system is also not rated to handle the temperatures it need to for a woodstove

 

[Grisu]

That chimney system is also not rated to handle the temperatures it need to for a woodstove

That's what I thought.

To the OP: Usually you would drop a high-temp rated liner down there to make the flue compliant with a stove but since your flue is already 8" wide you would need to downsize the liner. That may cause smoke and draft problems with the Grandma Bear. Not to mention that you need to find the right ceiling box for your current system and you still need to make sure you have at least 2" clearance around the pipe which is currently not the case. Another option would be to change the whole chimney system but then it may not fit on your fireplace anymore. Plus, a building inspector may not like it as the system would probably not be approved for your fireplace and you cannot guarantee that only the stove will be used on that flue in the future. In any case, you will also need to extend the hearth and lower it to make the pipe fit under the lintel. Honestly, I don't see how that is any easier than just ripping out the whole system, put drywall up on the wall and extend the hearth to the back to fit a stove there.

Even with baffle and damper the Grandma Bear won't be as efficient as a modern stove. Plus, no freestanding stove "needs" a blower; old smokedragon or new EPA-stove alike. Maybe you are mixing that up with fireplace inserts. Ceiling fans will certainly help in that room, but that is also true for any stove.

 

[BamaRama]

After studying on this for the last few days and the much appreciated replies, I think the best option will be to rip it out and start over. I don't want to do anything that will take away from the what little value the house has or cause a problem down the road when I sell it.

The Grandma bear is preferred in because I have it. Maybe I should have considered all of this before I bought it but it was a bargain so I'm going to try to make it work. Can't afford to get a new stove and replace the chimney / hearth. Maybe the new plan should be to install the accommodation for a rear outlet wood heater and upgrade the heater at a later date.

I'm not seeing an option in the manual for a horizontal pipe out the back of the Grandma Bear. I need to determine if running horizontal (with clearance) per the attached drawing will be a problem. I found the clearance chart. Can those reduction levels accumulate by using two methods of wall protection, thus reducing the horizontal run? Is it possible to 45 out the back and 45 into the thimble? How will be the best way to run out the back through the wall?

Also wondering how the roof transition will work out. My house, referring to the diagram, is rotated 90* and the 23" eaves are on a 12-12 pitch. I've seen 6-12 12 flashing but not sure if it will work.

Thanks again.

 

[coaly]

There is no option to connect to the back because the stoves were made in different configurations with top, side and rear vents for different installations. Rear vent (III) models require double wall connector pipe inside as well. (as per manual)
A 6 inch stainless liner will work fine in a Class A All Fuel Chimney with no smoke roll in problems, even adding a baffle. Codes do not technically allow pipe or flue reduction from the outlet size of appliance. The double door Fisher line was designed for open door burning with screen in place, so they were designed with the larger 8 inch outlet to prevent smoke roll in at top of door opening. With a correctly drafting chimney, a 6 inch flue works very well and is very common. The firebox size of yours is smaller than a Papa bear that was designed with 6 inch. If you ever go with a newer stove it will likely require 6 inch as well.

Here's a video with baffle added and connected to a 6 inch flue;

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

That was posted by a member here; https://www.hearth.com/talk/threads/cant-seem-to-figure-out.119184/page-2#post-1617042

 

[BamaRama]

Thanks for you thoughts and the video Coaly. I had read about the 6 inch pipe in some of your earlier posts. It's definitely a consideration.

I guess my earlier post should have been "'I'm not seeing an option in the manual for an extended horizontal pipe out the back of the Grandma Bear."

I'm thinking that extending the horizontal run to get get clearance from back wall will affect draft, which leads to the follow-on question about reducing clearance. Clearance is 44" for the back wall. I want to position it as close to wall as I can and still have a safe installation. Using the NFP chart, I can go with a 66% reduction and get to 29". Will this be too long for a horizontal run?

 

[coaly]

Grandma top and rear outlet minimum to combustible back wall is 36. As with any unlisted appliance you can get a 66% reduction with proper heat shield. (Does not include Canada) As long as the pipe is pitched upward at least 1/4 inch per foot you're fine.

You probably quoted the rear outlet Grandma requiring 44 in manual. That is a mistake on page 8 of the unlisted first manual. That can't happen with manuals that become part of the UL Listing today. They somehow printed 36 to pipe and added 8 inches for pipe diameter totaling 44 inches from stove to rear wall ! Notice on rear outlet Grandpa on page 10 it is the correct 36 inches to stove. (28 to pipe) I don't know how many people noticed that, but it doesn't make sense.

The later manuals for Model III require double wall out the back of all rear vented stoves in through the wall installations.

 

[BamaRama]

Wow, that helps unravel the mystery of the difference in the stoves that justified the clearance differences. The difference is in the manual, not the stove. That was bugging me.
I also noticed that the manual for the newer stoves gives more technical details on the installation. Is there anything in the new stove manual regarding installation that is not a good idea on the old stove?

So by my calculation, i can go 24" with a 66% heat shield. That's getting more to towards where I want it sit.

 

[coaly]

There was no manual at first, and many people asked for one. The PA fabricator wrote it and they were then given with all the I and II models. The stoves were tested by different labs across the country, but areas of states didn't recognize other areas testing labs as the sales area grew. In 1978 UL became the standard testing lab accepted nationwide. It was then that UL tested each model and calculated minimum clearances. They have movable walls around the stove with thermocouples to measure surface temperature calculated above ambient air temp. A manufacturer can try for a certain clearance, but it's up to UL what the final clearance is, then printed on the UL tag and manual. So the later manuals for each model take into consideration heat shields back and bottom for wall clearance and floor protection. Any stove without a UL tag, pre UL or missing for any reason is considered unlisted, so you use the section in NFPA 211 for unlisted stove clearances. That is where you will find the 66% reduction along with the criteria of what is considered an approved shielding method. The articles linked below put that into layman's terms.
66% of 36 inches is 23.76 so subtracting that 66% from 36 gives you 12 1/4 inch minimum from stove to combustible. That is measured to the combustible wall, not heat shield.

These two articles give you the details;
https://www.hearth.com/econtent/index.php/articles/wood_stove_clearances_installing_it_safely
https://www.hearth.com/econtent/index.php/articles/stove_wall_clear

 

[BamaRama]

Thanks for the info Coaly. Very helpful to get me on the right track here. Thanks for straightening me out on the clearance math. Since the legs on my stove are about 3" and the floor is combustible, according to the first link, my only option will be 4" blocks covered with sheet metal. To get 18" on all sides the pad would need to be 61.5 X 64.

How long are the legs supposed to be on a Grandma? Is 3" right? Seems pretty stumpy to me. EDIT.... Looks like I may have bought a hack job. Overall height doesn't check out.

 

[coaly]

Many were cut down so the rear vent was low enough to pipe into an existing fireplace. On the brick hearth or cement that was fine. Floor protection is calculated for different leg lengths. (Standards in manufacture also included in NFPA 211) Over 6 which is what yours should be, and under 6 requiring more floor protection.

Your front leg length (angle iron corner) should be 25 inches and rear should be 31 inches according to original drawing. (Grandma I and II) Some customers asked for higher or lower and could have them special ordered that way. So it doesn't always mean it was hacked......

You can always get a piece of 1 1/2 angle iron and cut to leg length desired and put it over the existing short piece and bolt it if you don't have a welder. With a welder, the rear legs are very easy to change. The front normally has the hinge plates welded to the angle iron making it more difficult to replace the fronts. (There are some from the Dunn Brothers in VA and W VA that welded hinge plates to the stove face with longer special bent hinge plates. They are easy to change legs front and rear).

 

[BamaRama]

It looks like I'll be adding leg length. Unless I'm off track again, it's the difference between using the standard solid masonry bricks laid flat or finding hollow blocks that are a full 4".

So I envision the appropriate amount of bricks laid flat and side-by-side, end-on-end until pad is big enough, then covered with 24 gauge sheet metal with hemmed sides to keep the bricks in place. Is this right?

What would work best to cover the pad? Flagstone, sandstone are in abundance here and can get it wholesale.

 

[coaly]

I put 24 gauge sheet metal on floor, then 1/2 inch cement board. Then a brick pad. Mortar under and between bricks if it's permanent.
Here's my temporary pad in a log cabin that stays cold under it. I add a bottom shield to all the Fisher's I burn about an inch and a half away from bottom. That makes the most difference directly under stove. It goes from uncomfortably warm without the shield to cool with it.



Same stove in my kitchen on cement board and tile which isn't enough protection. With shield and unheated basement, the floor in center stayed cold under it. I put felt on the brick bottoms to protect tile. They support weight on tile and make loading easier with it higher.

 

[BamaRama]

I had thought about the metal underneath because it is simple. But NFP says the top surface of the masonry is covered with sheet metal. That's why i am looking for a way to dress it up and make it look better.. .and not so slick. With the metal on top, you have to worry about flex and expansion causing a problem with the veneer. It appears the lower heat shield would alleviate that. I do intend on it being a permanent installation.

If I decide to add a bottom shield would it be okay to add enough leg length to have 6" between the shield and floor?

 

[coaly]

That's why I "top cover" the floor with metal first. I can understand preventing a glowing ember from falling through a crack and sheet metal protecting against that. But as far as on top and making an expansion joint between masonry layers, you're right, I wouldn't do that. Make sure R value is enough and embers can't reach the wood floor under it. I tape cement board joints with fiber mesh tape thin set as in tiling too.
Yes, as long as the legs are 6 inch minimum. The I drawings had no shields. There was a revision in 1977 showing an optional bottom shield with same legs. That's the design I make the shield from. Instead of drilling holes through legs, I put very small clamps on the legs and set the shield on them. The angle iron corners prevent the shield from moving laterally in any direction. I make it about 1/4 inch smaller to allow for expansion. The floor is warmer to the sides of the stove than under it. Without shielding, the floor is hottest at the center of stove.
The VI later had the bottom shield connected to the rear shield so the intake is below the ash fender and exhaust is up the back below the rear outlet. Shown at bottom of page 12.

 

[BamaRama]

Yeah I think the plan forward is to first get the old fireplace out and drop small a horizontal ceiling between the back wall and the first exposed beam. Then install a chimney support centered in the ceiling and come off of that with an offset to go out the roof. I'll use double wall black pipe at clearance to determine hearth pad size. What is the distance from the back of the stove to the back of the pipe on your stove? That's 6" pipe, right?

Would it function better to offset the black pipe and use a straight chimney? At this point, either way would work, just a matter of cost vs gain vs aesthetics. I had rather the ceiling box be in the center because straight pipe will look better. Then the chimney offset may be tricky with the lengths. It will be about a 40" run of chimney to the roof, then another 3 feet up.

 

[coaly]

6 inch single wall; measures 10 inches from stove back with 90* elbow.

 

[BamaRama]

Thanks Coaly. Gonna pick your brain here, sorry for any stupid questions. Using an 8" tee on back of the stove with a reducer to pipe, is it better to put the damper before or after the reducer, or does it matter?

 

[coaly]

It doesn't matter. Normally within the first full section of connector pipe.The chimney creates the low pressure area for atmospheric air pressure to push into the stove. The lowest pressure area is at the stove collar. The T, elbows, connector pipe length and reduced size all add resistance to flow. The damper is a variable resistance added in case it's needed. It doesn't "hold the heat in", it reduces draft, and velocity, slowing the incoming air. It just needs to be easily accessible.
With the reduced pipe and flue, (higher resistance to flow) you probably won't use it much with doors closed.

 

[BamaRama]

At this particular moment, to center the stove in the room, I'm figuring on putting an offset in the stove pipe and try to go with a straight chimney out the highest possible point on the left side of the 12/12 roof.

I want to use double wall stove pipe. I was looking at Duraplus chimney and DVL pipe but they don't offer an adapter. Got any ideas on this?

 

[coaly]

I think something like this installed into or over the stove collar, with the 6 inch end inside the double wall T may be what you're looking for. A drip free connection isn't necessary connected to the side of a T since any condensate is going straight down to the cap on bottom and won't leak out the side. When seated all the way into or over the connecting piece, the single wall will not be exposed.



(broken link removed to http://www.ebay.com/itm/6-to-7-5-8-Stainless-Steel-Fisher-Stove-Pipe-Reducer-/171421826373?pt=LH_DefaultDomain_0&var=&hash=item27e9897d45)