Adding secondary burn to a Lopi FL wood burning insert

[s0ulP@tch]

(broken link removed to https://drive.google.com/file/d/1PW0PhlwDRqP1_2iKuwtOvNtG10QpLGAe/view?usp=drivesdk) for reference

I’m retrofitting my old Lopi FL from the 80s and want to add a secondary burn and chimney liner. Any comments from the forum are most welcome. Outside surfaces will be painted with fireplace paint after modifications.

So far I’ve used a wire wheel to get the rust off the outside of the body - doors, trim panels, and the blower assembly will be done next. I also started drilling the hole for the 1” secondary burn pipes. They will be angled up to rest just under the brick baffle (which isn’t installed in these pictures - the support is shown in the first pic).


Here’s a picture of the burner layout. The coupler will go against the inside wall. The 3” nipple will go through the inner wall, convection cavity , and outer wall. The pipe outside is black steel, and everything inside (including the 3” nipple) is 304 stainless. The burners are gas fireplace burners I found on Amazon - the are welded 304 stainless with 1/2” threads and are pre-drilled with burn holes along the 12” upright pipes of the “H” (facing down in this pic). A close nipple and full bore ball valve will control airflow from the outside (not shown).


For the pipe, I’m thinking about removing the damper and putting in a 8” to 6” reducer, then attaching a 6” flexible 304 stainless liner to that. Any issues with reducing the pipe diameter? I figured it would be more efficient with the secondary burn and require less air.

 

[begreen]

The secondary burn system will require more draft, so reducing to 6" could be detrimental. How tall will the insulated liner be?

 

[s0ulP@tch]

This is in the basement, so 30-35’ to the top of the chimney.

 

[bholler]

This is in the basement, so 30-35’ to the top of the chimney.

If it really is 30 to 35' you do not want to remove the damper. Sizing the liner for secondary combustion is pretty complicated. You need the proper combination of volume and velocity to make it work.

 

[s0ulP@tch]

Wouldn’t the air intakes (primary ones below the doors, air wash above them, and secondary burn ball valve) control the airflow as much as a damper?
I’m also not sure how I’d install a vertical stove pipe without removing the current damper.

 

[bholler]

View attachment 267762Wouldn’t the air intakes (primary ones below the doors, air wash above them, and secondary burn ball valve) control the airflow as much as a damper?
I’m also not sure how I’d install a vertical stove pipe without removing the current damper.

With that much height you will need the damper to limit draft. A box will need to be fabricated for it

 

[s0ulP@tch]

Ok thanks. So should I just put in the secondary burn system and skip the flexible liner? I understand that sweeping the chimney will require pulling the whole thing out.
And I know the “right” answer is to buy a newer stove. Not in the budget this year.

 

[bholler]

Ok thanks. So should I just put in the secondary burn system and skip the flexible liner? I understand that sweeping the chimney will require pulling the whole thing out.
And I know the “right” answer is to buy a newer stove. Not in the budget this year.

The liner is absolutely required for use and it needs to be insulated.

 

[s0ulP@tch]

Any suggestions on how to attach one while keeping the damper? This older model didn’t use a chimney liner - installation instructions just tell you to shove it in place and open the masonry damper.

 

[bholler]

Any suggestions on how to attach one while keeping the damper?

Like I said a box will need to be fabricated for the top of the stove.

 

[s0ulP@tch]

Ok. That’s the first mention of fabricating an adapter, hence my extra questions

appreciate the input.

 

[CharlieTuna]

Ok. That’s the first mention of fabricating an adapter, hence my extra questions

appreciate the input.

Any update on the project?

 

[s0ulP@tch]

I installed it as I had originally intended. Yes I know it’s not ideal for heating, draft, or creosote buildup in the masonry chimney, but it’ll work for now. Honestly it burns pretty well - once the pipes are hot I can turn down the primary draft to ~1/5 open and have the ball valve 3/4 open. Most of the fire is then burning from the tubes. I’ll get some pics posted.

I got this installed just before Christmas, and I’m almost out of wood (I will have burned maybe 1.5 cords of dry hardwood, my entire stack), so it’ll be a short burning season anyway. I will probably pull it out this summer and adjust it some, likely adding a third burner. I want to add the liner as well, and I’ll probably cut out the damper to do that. All of Lopi’s new stoves, including their inserts with more volume, have 6” flue collars and only have a damper as a baffle bypass. Otherwise they’re wide open on top and airflow is controlled entirely by the main draft intake. So to get this connected to a liner I’d cut off the damper and reduce to 6” and install sheet metal plate and ceramic fiber wool to insulate the chimney around the liner to prevent more air leakage into the house.

This is a temporary stove. We are probably going to rip out the entire chimney stack in a few years and build a batch box rocket mass heater instead.

let the hate roll

 

[s0ulP@tch]

I’ve tuned my air controls so I can heat my entire 1961 1900sqft 2-story house with a full load + a log or two after the main fire has burned down enough to add a bit more fuel. Winter days have been at the high 40s during the day and between 28 and 35 or so at night. We burned through a lot of wood over Christmas break while we kept the upstairs 78 degrees and learned how not to burn efficiently in this stove. We now get upstairs to peak at 68-70 and are super comfy. When we replace the house’s original doors and windows heat retention should get a little better.

New gaskets on the doors & glass. I need to replace one pane eventually - the small crack lets in a minimal amount of air.

 

[Turbo_B]

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.

 

[s0ulP@tch]

I’ll take some good pictures this week. I tried uploading a video but it must be too big or a bad format or something.

One of the new pumice bricks broke already, but I had another spare. It was probably the heat of the direct fire on cheap brick. I’ll check out the vermiculite board - it would be nice to have something that seals up the baffle better since the bricks I have seem to walk a bit as they expand and contract, opening small gaps in the baffle. I did take some of the old broken bricks and placed them on the ledges beneath the baffle to better insulate the fire box, not sure it helps any.

 

[Turbo_B]

This is what I used to replace my hard firebrick. So far it seems to be fine - but it only has about one cord of wood burned under it.

Vermiculite Board

 

[Hoytman]

There were three posts above that I disagreed with. You've obviously been able to do what you wanted and it looks nice. You've proven it can be done. Not as complicated as some would have you believe. Good for you!

 

[s0ulP@tch]

Some pics of burning this morning. Air intakes are tuned as I mentioned in previous posts. The first pic really shows the burners in action.

 

[Turbo_B]

Looking good!

Perhaps more info than you want this morning - My old Suburban and my Appalachian stove both had rectangular outlets with no flue connector. I picked up these for my stoves and have been working well. Connecting these to a proper flue liner helps keep the heat in the room and really improved the draft on my old stoves.
Flue pipe adapter

 

[s0ulP@tch]

Looking good!

Perhaps more info than you want this morning - My old Suburban and my Appalachian stove both had rectangular outlets with no flue connector. I picked up these for my stoves and have been working well. Connecting these to a proper flue liner helps keep the heat in the room and really improved the draft on my old stoves.
Flue pipe adapter

My stove has a 8” round opening, so I should be able to just use a round 8” > 6” reducer after cutting off the damper. Next season I’ll do some upgrades like adding a third burner and hopefully a chimney liner. You aren’t the only one who’s mentioned how much better these burn with a liner

 

[bholler]

I installed it as I had originally intended. Yes I know it’s not ideal for heating, draft, or creosote buildup in the masonry chimney, but it’ll work for now. Honestly it burns pretty well - once the pipes are hot I can turn down the primary draft to ~1/5 open and have the ball valve 3/4 open. Most of the fire is then burning from the tubes. I’ll get some pics posted.

I got this installed just before Christmas, and I’m almost out of wood (I will have burned maybe 1.5 cords of dry hardwood, my entire stack), so it’ll be a short burning season anyway. I will probably pull it out this summer and adjust it some, likely adding a third burner. I want to add the liner as well, and I’ll probably cut out the damper to do that. All of Lopi’s new stoves, including their inserts with more volume, have 6” flue collars and only have a damper as a baffle bypass. Otherwise they’re wide open on top and airflow is controlled entirely by the main draft intake. So to get this connected to a liner I’d cut off the damper and reduce to 6” and install sheet metal plate and ceramic fiber wool to insulate the chimney around the liner to prevent more air leakage into the house.

This is a temporary stove. We are probably going to rip out the entire chimney stack in a few years and build a batch box rocket mass heater instead.

let the hate roll

The requirement for a liner has much more to do with your safety than performance. Codes don't care much about performance they are in place to help keep people safe. Ignore them if you want but you are doing something we have seen end badly many many times. And do not cut that damper out I really think you will regret that if you do with the height of your chimney. I have been doing this a long time and installed hundreds of stoves and inserts. You want that damper.

 

[s0ulP@tch]

The requirement for a liner has much more to do with your safety than performance. Codes don't care much about performance they are in place to help keep people safe. Ignore them if you want but you are doing something we have seen end badly many many times.

Yep, well understood. The plan is to get the chimney swept before next fall (we also had it inspected this year before we burned anything) and get a liner installed to improve both safety and performance. I have no desire for a chimney fire.

 

[bholler]

There were three posts above that I disagreed with. You've obviously been able to do what you wanted and it looks nice. You've proven it can be done. Not as complicated as some would have you believe. Good for you!

You are assuming there is a benifit to this system and that it will hold up. The pictures of the fire I see look pretty much like the fire in any old stove with a baffle installed. But I see no problem with trying a secondary combustion system. There is a big problem with running a slammer

 

[bholler]

Yep, well understood. The plan is to get the chimney swept before next fall (we also had it inspected this year before we burned anything) and get a liner installed to improve both safety and performance. I have no desire for a chimney fire.

You can have multiple chimney fires in one year especially with a slammer.