Adding secondary burn to a Lopi FL wood burning insert

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coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,273
NE PA
I don't think those gas burner tubes are going to take much heat at all if they are normal thickness tubes.

A burner tube has lots of cold air and gas moving through it. The portion before the holes is called mixing tube where the air and fuel mix. The blue flames ignite above burner and the burner tube stays cool. Retired gas man here that always heated his house with wood and coal.

I've built secondary combustion tubes with half inch black iron, but you could use stainless if you want. Schedule 40 is the minimum gauge I would use. If you have a welder, my best attempt was with a double steel baffle plate. 2 plate steel baffles with about 1/2 inch space between them. Welded to spacer around perimeter. A flange on top for air inlet connection and holes drilled in rows in the bottom plate. I used the number and size of holes that was on the floor model at Home Depot. It was a top vent stove and I ran the black iron up the stack and out the side of pipe without modifying the stove. Took care of the baffle, preheating air and admitting air.

Search keyword "Boot" for the connector to bolt to stove top and notch for damper rod.
I don't see how you could seal the Insert to hearth face good enough for the proper low pressure in firebox needed for differential pressure from inside and outside of the firebox.
 

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New Member
Nov 26, 2020
34
Oregon
I’ve seen those burner baffles and they look cool! I don’t have a welder or good fabrication equipment so I went this route. Everything inside the fire box is stainless including the burners, which were manufactured for gas fireplaces. The 1” main pipe is sch 40, and the burners are probably sch 10. So far they’ve held up quite well. The pipe outside the stove is sch 40 black steel to cut down on costs. It should hold up fine since it will never have contact with flames.
Here are the burners I bought. There’s no wood fume/air mixture happening in the pipes - they get preheated by the fire and spit out hot air into the firebox, igniting the gasses.
Amazon product
As mentioned before I plan to put a chimney liner on it later to increase draft. I’ll seal up around the top of the masonry fireplace with sheet metal and ceramic fiber insulation or rock wool since I know the 2” insulation behind the trim panels won’t seal perfectly, although it’s so far doing a decent job - plenty of suction once the chimney heats up after 25-30 min. Start the next video around 5:45 for a good demonstration of what I intend. I’d have to cut out the old damper and remove some bricks to get a 6” liner installed. Has anyone here done something similar? I’d still use the trim panels with 2” fiberglass insulation behind them as they’re installed now.

It was noted earlier that the fire looks just like any other fire in an old stove. I’ve done burns in this stove without using the pipes and it’s obvious to me there’s a lot of combustion from these tubes. The burns last longer and provide more heat (admittedly anecdotal). The space between the burners typically has flames fed by the main intake, which is why I’d like to add a 3rd burner so I can reduce the primary draft even more and have the entire underside of the baffle covered by burners.

I appreciate all the ideas! Good to hear other routes people have taken. This was a budget build and so far I’m happy with the results.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
I’ve seen those burner baffles and they look cool! I don’t have a welder or good fabrication equipment so I went this route. Everything inside the fire box is stainless including the burners, which were manufactured for gas fireplaces. The 1” main pipe is sch 40, and the burners are probably sch 10. So far they’ve held up quite well. The pipe outside the stove is sch 40 black steel to cut down on costs. It should hold up fine since it will never have contact with flames.
Here are the burners I bought. There’s no wood fume/air mixture happening in the pipes - they get preheated by the fire and spit out hot air into the firebox, igniting the gasses.
Amazon product
As mentioned before I plan to put a chimney liner on it later to increase draft. I’ll seal up around the top of the masonry fireplace with sheet metal and ceramic fiber insulation or rock wool since I know the 2” insulation behind the trim panels won’t seal perfectly, although it’s so far doing a decent job - plenty of suction once the chimney heats up after 25-30 min. Start the next video around 5:45 for a good demonstration of what I intend. I’d have to cut out the old damper and remove some bricks to get a 6” liner installed. Has anyone here done something similar? I’d still use the trim panels with 2” fiberglass insulation behind them as they’re installed now.

It was noted earlier that the fire looks just like any other fire in an old stove. I’ve done burns in this stove without using the pipes and it’s obvious to me there’s a lot of combustion from these tubes. The burns last longer and provide more heat (admittedly anecdotal). The space between the burners typically has flames fed by the main intake, which is why I’d like to add a 3rd burner so I can reduce the primary draft even more and have the entire underside of the baffle covered by burners.

I appreciate all the ideas! Good to hear other routes people have taken. This was a budget build and so far I’m happy with the results.
Please do not follow the advice in that video he asked lots of questions then argued against the answers and proceeded to ignore advice and code
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
How would one seal off the chimney stack? I’m open to advice.
The best way is by fabricating a sheet metal plate with insulation above it. But many just use insulation. But the is for performance not safety. The fact he insists insulation isn't needed on the liner even though he has been shown it clearly is needed is a safety issue. The fact his stove is to far back and he can't completely close the air is another issue
 

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New Member
Nov 26, 2020
34
Oregon
The best way is by fabricating a sheet metal plate with insulation above it. But many just use insulation. But the is for performance not safety. The fact he insists insulation isn't needed on the liner even though he has been shown it clearly is needed is a safety issue. The fact his stove is to far back and he can't completely close the air is another issue
Ok, so insulated liner and a sheet metal plate with insulation. Thanks.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
Ok, so insulated liner and a sheet metal plate with insulation. Thanks.
And place the stove so you can actually operate the controls. I think that one is pretty clear but I guess not to everyone.
 

[email protected]

New Member
Nov 26, 2020
34
Oregon
Not sure to whom you’re referring by “everyone“ or how one would install this so that the controls aren’t reachable. I can’t imagine how one would install it sideways. Controls are all on the front of the stove. I installed it per the manual from the manufacturer. The only additional thing is the ball valve for the burn pipes, and that is out front as well. It’s all pretty clear from earlier posts, including pictures...
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
Not sure to whom you’re referring by “everyone“ or how one would install this so that the controls aren’t reachable. I can’t imagine how one would install it sideways. Controls are all on the front of the stove. I installed it per the manual from the manufacturer. The only additional thing is the ball valve for the burn pipes, and that is out front as well. It’s all pretty clear from earlier posts, including pictures...
I was referring to the video you posted as a reference which is a very poorly done install.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
Aluminum relfects 95% of radiant heat. I would use aluminum for that.
Galvanized works just as well. But aluminum is fine. It really depends which you have easy access to
 

CharlieTuna

New Member
Jan 10, 2021
52
PA
I've built secondary combustion tubes with half inch black iron, but you could use stainless if you want. Schedule 40 is the minimum gauge I would use. If you have a welder, my best attempt was with a double steel baffle plate. 2 plate steel baffles with about 1/2 inch space between them. Welded to spacer around perimeter. A flange on top for air inlet connection and holes drilled in rows in the bottom plate. I used the number and size of holes that was on the floor model at Home Depot. It was a top vent stove and I ran the black iron up the stack and out the side of pipe without modifying the stove. Took care of the baffle, preheating air and admitting air.

Do you have any pics of this?

Did you base this on another design you saw?

Did you use something to insulate above the baffle plate?

Any issues with running the airpipe out the exhaust pipe? I would think by narrowing the exhaust opening it speeds the gas past it up the pipe, but that may be contrary to the manufacturers specs. Is that a good idea?
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,273
NE PA
Do you have any pics of this?

Did you base this on another design you saw?

Did you use something to insulate above the baffle plate?

Any issues with running the airpipe out the exhaust pipe? I would think by narrowing the exhaust opening it speeds the gas past it up the pipe, but that may be contrary to the manufacturers specs. Is that a good idea?
Pictures, no. This was well before I had a digital camera. I was traveling through Amish country in a '99 Land Rover I got in 2000, so that's about the time I came home and built it. I didn't have a phone until 2018!

I repair and rebuild steam equipment and worked on them around a few Amish farms. This put me in contact with a few stove and water heater builders. D S Machine makes models with this type baffle / secondary burn design.
It's nothing new.

I described in post #5 back in 2015 here; https://www.hearth.com/talk/threads/grandma-bear-retrofit-with-secondary-air.140515/#post-1982755

No insulation above baffle. That wasn't heard of until years later. We only had firebrick or furnace cement to make refractory parts back then.

I simply bolted a 3/4 pipe flange on the top plate with one large hole centered on the plate and used one 45* elbow coming off the plate extending vertical up the outlet. 90* out the side of pipe. I double nutted with electric clamp nuts to pipe.
This worked well in a Grandma Bear stove but had no glass doors to view combustion. I set neighbors and friends up with Fisher stoves since retiring from the gas business getting them alternate heat sources. The others I've supplied have the trademarked Smoke Shelf Baffle that was used in the double door stoves that I adapted to the single door Bear Series that never had factory baffles.

Dwell time in the pipe was not a big concern since the hottest part of the stove is the baffle plate. Being a hollow plate there is plenty of time to heat the incoming air within the baffle. I use 5/16 for all baffle plates to prevent warping. That was the material stove tops were made of, so it was plentiful for Fisher to use for their baffles.

Don't know what you mean by contrary to manufacturers specs. I only deal with Fisher Stoves that went out of business in 1988 due to not being able to pass the stricter EPA laws coming into existence. Only baffles were designed back then to reduce particulate, but could not pass the last stage of the stricter requirements. So many manufacturers went out of business. These are the stoves I retrofit and are still going strong. Unfortunately only the last models built offered glass doors, and none had glass in the single door deep design that actually fits firewood and burns better than a wider stove for fire viewing.
 
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fbelec

Minister of Fire
Nov 23, 2005
3,045
Massachusetts
the first picture in post 19 is spooky. looks like a skull
 

swh73

New Member
Sep 27, 2021
2
Troy Michigan
Winter is fast approaching an I should of been thinking of this months ago but I did not. I have been running the stove for years without a liner. I will be adding one. I have a lot of draft problems and the smoke backs up in the house. I will weld up a box to install over top of the damper so I can attach the liner to it. I am so curious about the pipe you installed in yours. Is that adding more air into the box? I always seen to have a need for more air in mine. sometimes I leave the door open just a little.
 

[email protected]

New Member
Nov 26, 2020
34
Oregon
Yes, this adds more air into the firebox, or at least a new way for air to be fed in. There are primary air inlets below the door, airwash above it, and now the burn tubes. Most Lopi wood stoves follow the same design, but they combine the air controls into one handle. Because this was a retrofit I thought the easiest way to get it to work was to just add another inlet. I don't mind - it makes the stove look a little steampunk >>

When I turned on the reburn tubes I typically turned down the primary and secondary air inlets so most of what was burned was the smoke coming off the charred wood. I imagine adding a liner would have dramatically helped the way it operated, but honestly it did pretty well as it was. Once the masonry chimney got warm it drafted decently.

This system has been decommissioned, though. Sold it on Craigslist along with the liner kit I had purchased to improve draft, but we decided to remove the entire masonry stack to get back some more room in our living room upstairs (this stove was installed in the finished basement fireplace, which shared the same masonry stack as the upstairs fireplace; different flues). A 3'x5' open fireplace that was never used was just a waste of space. We're planning to build an alcove downstairs for a new Lopi Evergreen II and install a Class A chimney through the opening the old masonry left. Still get wood heat, but in a smaller, more efficient package with less floor real estate taken up in the house. I figure if I can heat the entire house in January on an inefficient draft in a slammer, the Evergreen II should do just as well.

Thread detailing the alcove build is here.
 
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swh73

New Member
Sep 27, 2021
2
Troy Michigan
Yes, this adds more air into the firebox, or at least a new way for air to be fed in. There are primary air inlets below the door, airwash above it, and now the burn tubes. Most Lopi wood stoves follow the same design, but they combine the air controls into one handle. Because this was a retrofit I thought the easiest way to get it to work was to just add another inlet. I don't mind - it makes the stove look a little steampunk >>

When I turned on the reburn tubes I typically turned down the primary and secondary air inlets so most of what was burned was the smoke coming off the charred wood. I imagine adding a liner would have dramatically helped the way it operated, but honestly it did pretty well as it was. Once the masonry chimney got warm it drafted decently.

This system has been decommissioned, though. Sold it on Craigslist along with the liner kit I had purchased to improve draft, but we decided to remove the entire masonry stack to get back some more room in our living room upstairs (this stove was installed in the finished basement fireplace, which shared the same masonry stack as the upstairs fireplace; different flues). A 3'x5' open fireplace that was never used was just a waste of space. We're planning to build an alcove downstairs for a new Lopi Evergreen II and install a Class A chimney through the opening the old masonry left. Still get wood heat, but in a smaller, more efficient package with less floor real estate taken up in the house. I figure if I can heat the entire house in January on an inefficient draft in a slammer, the Evergreen II should do just as well.

Thread detailing the alcove build is here.
I saw the new one you had drawings for. I may play with the unit I have to add more air. I have heard of people adding outside air so Im not pulling air out of the house.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
Winter is fast approaching an I should of been thinking of this months ago but I did not. I have been running the stove for years without a liner. I will be adding one. I have a lot of draft problems and the smoke backs up in the house. I will weld up a box to install over top of the damper so I can attach the liner to it. I am so curious about the pipe you installed in yours. Is that adding more air into the box? I always seen to have a need for more air in mine. sometimes I leave the door open just a little.
When you hook it up to a liner you probably won't need more air anymore. It will operate very differently when it actually has decent draft. I would hold off on any additional modifications untill it is installed properly
 

Blazzinghot

Member
Dec 5, 2019
149
New Plymouth, Idaho
awesome! any pics of it in operation?

I tried the firebrick baffle, then bought 1.5" thick vermiculite board and got a better secondary burn in my old Suburban.
I am just wondering how you know you were getting a better secondary burn from the vermiculite board over the bricks. How could you tell the difference? I put bricks in my Country Striker but have the board and insulation in my shop but have not used it?
 

Blazzinghot

Member
Dec 5, 2019
149
New Plymouth, Idaho
I noticed you stated you purchased the stainless tubes on Amazon but did not know they came already welded together. I was picturing in my mind a bunch of stainless tubes that you have to put together and drill holes in. But this certainly saved on some work. this is a very non-invasive way to install secondary burners. Just one hole in the side of the stove. I have done this with two holes on the back of the stove which has worked well for me. This should save on firewood and give you longer burn times. Thanks for sharing the pictures and how you did installed the secondary burners.
 
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