Problem with sealing the connection between the top of my wood stove and stove pipe

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

dennwill1

New Member
Dec 29, 2020
6
State Road NC
I have a Fisher fireplace insert that was converted to a freestanding stove. The flue connection on top of the insert is less than 8 inches in diameter and so I had to slightly crimp an 8 inch pipe adapter and slide it the best I could down into the flue connection. Needless to say it is a pretty good fit, but not perfect. I took some Imperial 2000 degree stove and fireplace cement and mortar and applied it according to the instructions. It worked well for a few days, then started to crack and come apart allowing my stove to smoke out a bit around this connection. There has to be some better high temp sealing material. It is not a very big gap that I am trying to fill, just places where the crimp did not form exactly to the flue connection. Thanks, Dennis Williams State Road NC
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
I have a Fisher fireplace insert that was converted to a freestanding stove. The flue connection on top of the insert is less than 8 inches in diameter and so I had to slightly crimp an 8 inch pipe adapter and slide it the best I could down into the flue connection. Needless to say it is a pretty good fit, but not perfect. I took some Imperial 2000 degree stove and fireplace cement and mortar and applied it according to the instructions. It worked well for a few days, then started to crack and come apart allowing my stove to smoke out a bit around this connection. There has to be some better high temp sealing material. It is not a very big gap that I am trying to fill, just places where the crimp did not form exactly to the flue connection. Thanks, Dennis Williams State Road NC
What is your chimney setup? The pipe should be under vacuum so no smoke should leak out
 
  • Like
Reactions: Isaac Carlson

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
6 inch stove pipe straight up to ceiling to a ceiling box that adapts thru the ceiling and roof to double wall from ceiling out the roof. I installed a damper in the 6 inch pipe about 18 inches above the stove
Well reducing to 6" is part of the problem. What is your overall height?
 

dennwill1

New Member
Dec 29, 2020
6
State Road NC
Here are some pictures
 

Attachments

  • 100_0038.JPG
    100_0038.JPG
    136 KB · Views: 96
  • 100_0037.JPG
    100_0037.JPG
    58.9 KB · Views: 99
  • 100_0036.JPG
    100_0036.JPG
    98.7 KB · Views: 107
  • 100_0035.JPG
    100_0035.JPG
    147.5 KB · Views: 111

dennwill1

New Member
Dec 29, 2020
6
State Road NC
The setup works fine, This is not my first woodstove. I just need a better stove pipe cement , I think there must be something better out there than this Imperial. I have read comment from other users of this cement about it cracking and falling out of the joints as stoves and pipes heat and cool.
 

dennwill1

New Member
Dec 29, 2020
6
State Road NC
I would also like to know where to find correct information on what size gasket material I need to use for the doors on this Fisher unit. I bought it second hand and do not have any manuals etc on this unit.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
The setup works fine, This is not my first woodstove. I just need a better stove pipe cement , I think there must be something better out there than this Imperial. I have read comment from other users of this cement about it cracking and falling out of the joints as stoves and pipes heat and cool.
It doesn't work fine if you need to seal the pipe joints you don't have adequate draft.
 

kennyp2339

Minister of Fire
Feb 16, 2014
5,936
07462
@dennwill1 what @bholler is saying holds a lot of weight, the smoke pipe should be under its own vacuum and large enough to evacuate the exhaust gases produced by the stove, under certain conditions 6" pipe installed on a stove that requires a 8" chimney can work, but its a velocity factor vs total volume of what the chimney can handle, no stove pipe should ever need furnace cement to keep it from leaking gases into a living area.
The reasoning for him asking about total chimney height is to get a better idea about potential velocity, a 15ft chimney will have a different effect vs a 35ft chimney.
As far as clearances, nfpa requires unlisted wood stoves to have minimum protection of 36" all the way around, and a certain hearth thickness calculated in K factor, since this was an insert at one time, converted to a free standing stove, if it was ul listed (tag would be on the back of the stove) it is now considered unlisted because it was modified to be installed differently then initially designed (insurance & safety implications)
 

wagne223

New Member
Jul 10, 2019
40
North Florida
The setup works fine, This is not my first woodstove. I just need a better stove pipe cement , I think there must be something better out there than this Imperial. I have read comment from other users of this cement about it cracking and falling out of the joints as stoves and pipes heat and cool.
I can't help you on the stove cement question, but I would think finding a sealant that can withstand the expansion and contraction of a sheet metal pipe that cycles from 50 degrees to 600 degrees will be difficult. Plus the sealant would need to have a flash point over 2000 degrees in case you have a flue fire.

Below is a video that demonstrates why you should not need any sealant on your stove pipe.

 

wagne223

New Member
Jul 10, 2019
40
North Florida
I think you will be better served to seek out your draft issue then trying to find that sealant.
Could be chimney, or house not getting enough make up air.

The guys here are very smart when it comes to helping with these issues but you have to be open and listen to what they say.
 

Isaac Carlson

Minister of Fire
Nov 19, 2012
545
NW Wisconsin
1. Your pipe is reduced in diameter. That reduction pretty much cuts your draft in half.

2. Your key damper is choking the draft but the stove is still pushing against it. You need to close the air down more and open the key damper to balance your draft. It's worse when you have a big stove on a small pipe.

I'm not going to comment about clearances.
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,273
NE PA
I would also like to know where to find correct information on what size gasket material I need to use for the doors on this Fisher unit. I bought it second hand and do not have any manuals etc on this unit.

You have Series III doors that use flat gasket that fits in the door seal channel on stove front. The Imperial Cement you have is for that use. It is also for cementing joints on cast iron stoves. The outlet area gets too hot for cement. If there is any original cement in door seal channel, remove with wire wheel to bare metal since it makes the gasket material too thick. Any width that fits in seal channel is fine.

High temperature silicone may work longer, but is not the correct way to solve the problem at connection, and no sealant is required.

The problem is not enough heat in chimney to create the correct draft.

An 8 inch chimney diameter has more CAPACITY than 6. Almost twice as much. So the Insert was designed with an 8 inch outlet to allow enough heat up a larger existing fireplace flue. Continuing that size to the top is one way to cure the problem, but also uses much more heat up the stack than the smaller 6 inch. Reducing will not allow the full BTU output of the stove, but they are seldom used for maximum output anyway. A 6 inch pipe and chimney works in many cases, but can cause issues in installations where the chimney is too tall and cools too much, pipe configuration uses elbows that create resistance, or high single wall pipe allows excessive cooling before entering chimney. That’s why we need to know chimney height, and type.

You need to maintain 250*f. flue gas temp inside chimney flue to the top of chimney when smoke is present. This creates the draft required at stove outlet to allow air into stove. Below this critical temperature, water vapor from combustion condenses on flue walls and allows smoke particles to stick forming creosote.

Is the ceiling over 8 feet?

Do you have a magnetic pipe thermometer on the single wall pipe showing surface temperature? You need that so you know when and IF you can slow rising gasses with a flue damper.

Start with pipe damper open. Bring up to temperature, and control fire with intake dampers. The flue pipe damper is a variable resistance. It is used for control of an over drafting chimney by slowing the velocity of rising gasses. The damper should only be needed for open door burning with screen in place. If smoke exits any pipe joints there is a draft problem. The correct heat inside the chimney flue creates a low pressure area inside chimney, pipe and stove. This allows higher atmospheric air pressure to PUSH into stove intakes. Any leaks allow indoor air IN, not smoke out. The detrimental effects of a leak is cooling chimney.
 
Last edited:

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,273
NE PA
From a legal standpoint, just no.

This appliance was tested to UL testing criteria Listing no. MH11256. Manual page 6 requires installing into masonry fireplaces which meet construction requirements of NFPA 211 Code for chimneys, fireplaces and vents. It also requires hearth to extend 16 inches to the front of fireplace opening.

If no tag is affixed to this Insert it is not a UL Listed appliance. Modifying in any way loses the UL approval.

** North Carolina adopted the 2015 International Family of Codes and the Mechanical Code requires ALL appliances to be UL approved (Listed) for any new installation. **

This Code also does not allow any reduction of pipe or flue less than the outlet diameter.
(NFPA 211 did allow 1 inch reduction, but the code adopted has added no reduction is allowed.)

NFPA 211 has a section for unlisted appliances and reducing clearances that is physically safe to use. This is still safe, just not legal since no installation of unapproved appliances is now allowed. This was added to prevent installation of home made, untested stoves, but also stops installation of antiques and unlisted stoves before UL testing was done.

This is all for a new installation of appliance. It does not affect use of an existing appliance. So many install to NFPA 211 Standard and claim they were existing, since it's difficult to prove when an installation was done.

The floor protection is inadequate. 18 inch floor protection is now required in all directions, including front. This is due to radiant stoves heating the floor area, and logs falling out. This was designed as a convection heater at the rear, radiant heater at the front.

Clearance to rear would be 36 inches for a unlisted appliance, even though this was determined for radiant stoves compared to the double case around the back of this Insert. A blower under ash fender blowing into slot removes convected heat from air chamber keeping the back cool. The 36 inch requirement would still be required since no code can foresee all installation scenarios. Obviously this isn't going to get hot or radiate much to the rear, but the minimum clearance is still required.

That said, this is the best looking conversion I've seen. Most are tall and spindly, and just don't look right. This would be great in a basement rec room with cement wall and floor with a blower, and about 15 feet or so of insulated 6 inch chimney. Very efficient for an older stove !
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,273
NE PA
I should add, your draft is important in this model with glass doors. Every stove has a minimum requirement measured at stove collar where pressure is the lowest. The air intakes are the most resistance in the system. The rising hot gasses need to create enough vacuum in the stove to allow atmospheric air pressure to push into both the primary intakes on sides as well as air wash under door at slider intake adjustment. Normally start with side vents a few turns open and front sliders open. As it heats up, close side vents, forcing all air to enter front keeping glass clear. Weak draft or slowing too much with damper, or size restriction slows incoming air and will not keep glass clean. Opening front sliders to adjust flame and flue damper open should be adequate for over night burns. Only close flue damper partially if it continues to burn too fast. I'm sure that will not be needed with reduced pipe. (providing there is an adequate insulated chimney)