Burned up Fisher wood stove gasket

I’m new to wood stoves. When we got this place about a year ago, the gasket (is that even the right word) in our Fisher Grandpa (or Grandma?) Bear stove stuck down a couple inches. I’ve watched it slowly burn up over the season. It no longer seals, meaning smoke pours into the house.

Is this normal? Was something improperly installed, or am I running it too hot? Any guidance on how to fix it would be greatly appreciated.

 

Looks like the wrong size pipe.

 

Yeah I can see what you’re saying. Maybe it’s going from an 8” to 6”? I can survive without the stove this time of year, so at least I have 6 months to figure it out.

 

Stove outlet is likely 8" dia. Looks like you possibly have a SS liner (good thing). Wondering if the liner is 7"? Somewhat oddball size these days as 6" is more standard. Also curious if the liner goes all the way to termination? Can you measure the stove outlet diameter? Good luck and let us know what you find after looking closer.

 

Have you removed the Insert to address the issues yet?

There are no gaskets used on your Insert. (If this is a full size Insert, the model is “Fisher Fireplace Insert”, no Bear name given. The full size Insert uses Grandma doors, many are marked inside with GM/L and GM/R. They are Grandma width but much deeper. There was a Cub, Panda and Polar Bear. Grandma and Grandpa are freestanding stoves from the Fireplace Series)

There is no damper control where it should be at slot on right side of faceplate. There should be a lever with the same spring as door handles with notches on lever to adjust damper opening. There should be no pipe sticking down through the outlet. There must be a direct connected liner all the way to the top. Depending on where this is, if jurisdiction adopted the International Codes, the liner cannot be reduced in size from the 8 inch outlet. NFPA 211 allows 1 inch reduction, ICC allows no reduction.

Two ways to connect with damper in place are notching stainless flue adapter for damper rod or mounting a “Boot” on Insert top to connect liner. Boots are available with an angle if required.

With no damper, a baffle plate is required for efficiency and preventing temperature spikes up exhaust.

You will need to check clearance to combustible framing members to chimney exterior. An interior chimney requires 2 inches clearance, exterior chimney requires 1 inch to framing members. If framing members are in contact, 12 inches solid masonry is required from inner flue surface to chimney exterior. If you do not have proper clearance, an insulated liner is required.

Any stove or Insert benefits from an insulated liner. Many times it is required, since air cooling of an exposed liner in the existing flue cools rapidly as flue gas rise. Flue must remain above 250*f all the way to top while smoke is present. Chances are yours is not, reducing draft from not enough temperature differential from inside liner to out. This allows smoke to leak out without producing the correct vacuum in stove or chimney.

No smoke should come into home, even with a leak into stove or vent. Hot rising gases moving up the chimney creates a low pressure area in chimney flue and stove. This allows the higher atmospheric air pressure outside of the stove to PUSH into air intakes. Any leaks allow the higher pressure outside of stove or vent system to push in, not leak out. You have incorrect draft, negative pressure in home, or other issues causing smoke leakage inside.

 

Is the smoke coming out around the pipe ?

 

Coaly do you know off hand the measurements needed for a baffle for this insert? I have the same one, but use it as a free-standing stove.

 

I’ll have an update with pics in a day or two. Our cabin is in a remote area, and it took a MONTHS for a wood stove professional to come out. It turns out that a couple things failed, and we need a new liner. The existing liner was there for a long time, and the house used to be a rental, so I suspect there had been some abuse. One of the things that they did was cut a baffle, and they got the size wrong the first time. But the liner replacement has trumped any of the other issues for now. I’ll post more as I learn it.

 

I really appreciate the information. I’ve realized that this is far above my expertise level, so I called the only local professional. In hindsight it would’ve been more practical to fly you out to Washington State first class and had you look at this, paying you handsomely for your time. The wood stove people finally looked at it this week, and are sending me pictures and a quote.

On a side note, are you close at all to Kutztown? My mother is from there, and I always considered it a home away from home. I still have many relatives there.

 

Kutztown folk festival is a blast!

 

That’s a question that depends on the chimney, pipe configuration and your use.

First make a cardboard template. Set it on the brick retainers at rear. Raise the front until you have the same square inch opening area as chimney square inch area. This is what you will be doing as you lengthen the plate more towards the front, keeping the same smoke outlet area. The minimum area is the same as chimney. A straight up insulated chimney allows this reduced to 6 inch diameter flue very well. The more resistance added to the system, the more you will drop the plate at front increasing chimney temperature.

The longer you make the plate, the closer to the front it gets. This depends on your use. If you want maximum heat in a large area, only cover about 1/2 or less of the firebox length. If you want to extend burn time, make it longer toward front. It will also not have as much tilt upward towards the front, the deeper or longer it is.

Here is what this changes; the firebox design is a diagonal flow design. In at bottom, diagonal across firebox, out exhaust. The deeper the baffle plate, the more this makes the design a S Flow. The more S flow, the longer the burn with more even output. This means you get more of a cigarette burn. The exhaust gasses have to move toward the intake to get out, slowing it down. Off gassing doesn’t take place all at once in the entire firebox. You fill the box more to the top so the air coming in the front has to burn front to rear. This only heats the wood close to the burn zone creating a longer burn with less off gassing all at once. More even output. The Insert being deeper and narrow is a good candidate for this type burn.

Draft determines how deep or long the baffle can be. Most just guess, and make the baffle support adjustable sitting on brick wedges. The stronger the draft, the closer to front you can get at the minimum smoke space area. If it tends to roll smoke in opening doors, drop the plate slightly to increase draft. This allows more heat out, to increase differential temperature as well as decrease firebox resistance.

Always think of the chimney creating low pressure area in stove, measured as draft, and everything else takes it away. There are tables and formulas giving how much resistance each pipe fitting, straight pipe, spark screen adds. The highest resistance is always the air intake. And of course the flue damper can add variable resistance when needed in an over drafting case.

No one can tell you what size or angle since every vent system drafts differently. Altitude and atmospheric conditions change it, as well as negative pressures in the home. The main thing is determine how much you want to change the flow for duration of burn vs. high output btu. (Notice most newer secondary burn stoves come up close to the front door making a deeper S) Then raise and lower to adjust for each system’s draft. A very flat baffle is the most S you can get. Not all chimney systems will allow it.

Always use a pipe thermometer keeping inner flue temps above 250* f to the top while smoke is present. A magnetic thermometer reads about 1/2 actual inside flue gas temp, so 250 on thermometer is actually 500 cooling back to 250* as it exits, hence the burn zone on thermometer starting at 250*f.

You will find any baffle is better than none, taking away the temperature spikes, and making any stove more controllable.

 

No, couple hours north. But we go there for the accent “don’t cha kno”?

 

Thanks for the info. Unfortunately, it looks like I am retiring the fisher. Had the chimney inspected again this year. I still waiting on the report. But the sweep told me I have stage 3 creosote build up. He also said that the mortar in my terra cotta chimney is failing and that it is a hazard. I’m not so worried about me, but so have my little girls and wife in the house. I’m gonna see if I can get a SS liner down the flu, and get a newer stove….
Odd thing about the creosote is that I maybe used the stove 6 weekends last winter, which is not a lot considering people here burn 8 months straight. Can that much creosote build up that badly with such limited use? Should I get a second opinion? OP, sorry If it seems I am hijacking the thread.

 

The Insert was being used without a liner directly connected to it, all the way to the top??

A full liner is required with ANY Insert.

Yes, it can form rapidly depending on the diameter of the fireplace chimney flue. As I mentioned above, flue gas must satay above 250*f when smoke is present. When allowed to expand into a larger area of a larger flue made for a open fireplace, temperature drops drastically. Hence the reason for the liner code being the same size as appliance outlet.

 

Coaly I used it as a free standing stove. Stove pipe going into a thimble. Terracotta liner all the way up. You actually give me some guidance on the set up.

 

Ok, normally an Insert is using a chimney made for an open fireplace that has a larger flue. That’s fine.

Perhaps the stage 3 hard coating has been there and not removed the last time it was cleaned? If the joints are leaking bad, the cold air mixing with flue gases will lower the flue temp allowing water vapor to condense on flue walls.

 

Understood, I had a BK insert installed in the fireplace on the main floor, so I am familiar with that. I don’t know that the flu in question was ever used much. When I get the new inspection report, would you mind if I pM you? I do not want to clog up the OPS thread with my issues. I am also going to get a second opinion from another company. Last year, the guy couldn’t legally tell me it was ok to use for liability purposes, but definitely alluded to the fact it was ok.
This new tech was a hard “NO” when asked. I am also questioning his knowledge a bit because I was asking about a block off plate for the insert upstairs, and he had no clue what I was talking about. I don’t want to give up the stove if I don’t have to, but It’s not even a question if it puts the family at a risk.