Optimize fireplace in new home?

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ragnarok

New Member
Sep 7, 2021
7
missouri
Hi, we purchased our first home recently, and are looking into learning about fireplace operation and how to optimize what we have here. Its a 1970 built home with a big stone fireplace. It has an ash dump chute that goes down into the basement, and I can see cinder blocks going up through the attic and then out a stone chimney, so its a pretty substantial chunk of masonry. The actual burning area has a metal "shell" and air spaces around the back and side of the shell with a fan (to help distribute heat I assume?). The fan sucks air in from one side, and it blows out from the other side and the top. There are even 4 pipes (see picture) right below the damper to help get the air really hot before it comes out the top vent. There arent currently any doors or screen.

I've read that old fireplaces arent very efficient, and its often better to place a "fireplace insert" in it. Is this metal shell with venting and fan basically a built in fireplace insert though (minus doors)? There aren't any doors currently, and I'm betting it'll be hard to custom fit some, but I'm also considering taking up welding and will need a project so I'm not opposed to making some!

Do I have a good base here to build from here and make doors, or is it a lost cause and be better off (besides saving time not having to make custom doors) buying an insert? Any other improvements that could be done? The ash chute runs opens to the basement, but the back of it runs down by the carport, so Im also considering adding an outside air vent to that maybe? I'll also be sure to have the chimney cleaned before using.

Thanks for any tips for what we should do with this!

overview.jpeg damperpipes.jpeg sidevent.jpeg
 

kennyp2339

Minister of Fire
Feb 16, 2014
6,099
07462
Those pipes are a basic crude heat exchanger to extract to some heat that would be going up the chimney, the efficiency of a fire place is pretty poor, generally you loose more heat then whats produced since its an open hole in the house wire circulation in the form of heat going up the flue, the air that gets sent up has to be made up from somewhere, so it comes in from the outside through small cracks, poor insulated walls and windows.
People install inserts (its a wood stove designed to fit into tighter masonry clearances) to regain the heat loss, inserts today are air tight and tested stoves, the produce more heat then what they take out and generally have an efficiency of 70%, that means out of 100% of the burn, 70% of the heat being produced is getting transferred into the living space
If you decide to go that route, you'll have some work, an insulated liner, cutting out the old heat exchanger tubes and light masonry work would be needed, but the savings in the long term cover the initial costs associated on the install.
 

EbS-P

Minister of Fire
Jan 19, 2019
1,458
SE North Carolina
I think what you do to it depends on your wants and budget. Do you want to heat with it full time? Supplemental or just a pretty fire to look at 16 times a year?

Inserts are the most efficient. If you have a tall enough opening you can do a hearth mounted stove same efficiency as an insert.

The two sided look in unique. it makes altering it more of a challenge. Doors won’t make it more efficient

An insert is basically a black metal box on the side so they are not super attractive from the side but a two sided surround could be custom fabricated. What you have is average or above average for the 1970s. Feed it enough dry wood it might keep the room livable during a power outage. Get your self a Dutch oven and you could be eating hot meals too.


evan
 

ragnarok

New Member
Sep 7, 2021
7
missouri
Those pipes are a basic crude heat exchanger to extract to some heat that would be going up the chimney, the efficiency of a fire place is pretty poor, generally you loose more heat then whats produced since its an open hole in the house wire circulation in the form of heat going up the flue, the air that gets sent up has to be made up from somewhere, so it comes in from the outside through small cracks, poor insulated walls and windows.

It has an adjustable damper, so you can control how much airflow goes to the chimney. If I install sealed doors and an outside air source, shouldnt I be in the same ballpark as an insert, since it already has venting around it? Even if I got 40% or something instead of 70% (perhaps due to rudimentary heat exchanger design) I would be happy. I just don't want to do all the work custom making doors and still have "negative" results and end up even colder with a fire. But with a sealed box and the ability to control the air coming in, the air going out, and the airflow around it, I should have something decent going, right?


I think what you do to it depends on your wants and budget. Do you want to heat with it full time? Supplemental or just a pretty fire to look at 16 times a year?


We have an electric furnace in the house, and don't mind running it, so the goal definately isnt to go 100% fireplace heat. Although in winter I see myself making a fire several times a week, so I'd like to get a bit of usable heat out of it and not suck all the heat out of the house.

The two sided look in unique. it makes altering it more of a challenge. Doors won’t make it more efficient


Are you saying doors wont make it more efficient assuming I leave the side open? I do plan on adding a wall with ceramic glass on the side if I decide to add gasketed doors to the front of this thing. At that point I would have a sealed box (with outside air routed in from the ash dump chamber?) with venting around it. That would help a bit with efficiency wouldnt it? What is it that an insert would have going for it over the custom built enclosure? A better heat exchanger? Or would the size of the burning chamber also be a factor? I could build the enclosure a bit smaller if that would help.

Would it be stupid to buy a fireplace insert and then cut a hole in the side and reseal it with ceramic glass? I guess it would depend on the design, but it seems like it might be possible to find one that would be feasible for. I still like the idea of custom building my own enclosure for some reason though. I won't get 70% efficiency, but if I could get to even something like 40% efficiency with good planning I'd be happy as long as its putting out some usable heat.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,077
central pa
It has an adjustable damper, so you can control how much airflow goes to the chimney. If I install sealed doors and an outside air source, shouldnt I be in the same ballpark as an insert, since it already has venting around it? Even if I got 40% or something instead of 70% (perhaps due to rudimentary heat exchanger design) I would be happy. I just don't want to do all the work custom making doors and still have "negative" results and end up even colder with a fire. But with a sealed box and the ability to control the air coming in, the air going out, and the airflow around it, I should have something decent going, right?





We have an electric furnace in the house, and don't mind running it, so the goal definately isnt to go 100% fireplace heat. Although in winter I see myself making a fire several times a week, so I'd like to get a bit of usable heat out of it and not suck all the heat out of the house.




Are you saying doors wont make it more efficient assuming I leave the side open? I do plan on adding a wall with ceramic glass on the side if I decide to add gasketed doors to the front of this thing. At that point I would have a sealed box (with outside air routed in from the ash dump chamber?) with venting around it. That would help a bit with efficiency wouldnt it? What is it that an insert would have going for it over the custom built enclosure? A better heat exchanger? Or would the size of the burning chamber also be a factor? I could build the enclosure a bit smaller if that would help.

Would it be stupid to buy a fireplace insert and then cut a hole in the side and reseal it with ceramic glass? I guess it would depend on the design, but it seems like it might be possible to find one that would be feasible for. I still like the idea of custom building my own enclosure for some reason though. I won't get 70% efficiency, but if I could get to even something like 40% efficiency with good planning I'd be happy as long as its putting out some usable heat.
First even the best set of doors available might get you to 20% at absolute best. There just is no way to get efficency out of a fireplace like that.

Even if you did control the incoming air enough to get an efficient burn when it goes into the massively oversized flue for that amount of incoming air it would cool rapidly forming huge amounts of creosote.

And yes cutting a hole in the side of an insert is a stupid idea and would void the listing warranty etc of that unit as well as hurting the efficiency because the firebox temps would be significantly lower.

In addition to all of that any glass you put in that doesn't have a properly designed air wash system is going to be black in no time at all requiring cleaning every fire.
 

ragnarok

New Member
Sep 7, 2021
7
missouri
First even the best set of doors available might get you to 20% at absolute best. There just is no way to get efficency out of a fireplace like that.
Why is that? Is it the size of the enclosure? I could make it smaller if thats more efficient.

I understand a why a commercially designed insert would have several multiples of efficiency better than an open fireplace with no venting around it. But I'm having a hard time understanding why if you take the time to seal it and vent around the shell and tweak it that you're still looking at efficiency less than a third of an insert. Whats the secret sauce that makes an insert over 3x more efficient despite any efforts?

Thanks for the tips on watching out for increasing creosote build up as I tweak things, and considering airflow over the ceramic glass!
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,077
central pa
Why is that? Is it the size of the enclosure? I could make it smaller if thats more efficient.

I understand a why a commercially designed insert would have several multiples of efficiency better than an open fireplace with no venting around it. But I'm having a hard time understanding why if you take the time to seal it and vent around the shell and tweak it that you're still looking at efficiency less than a third of an insert. Whats the secret sauce that makes an insert over 3x more efficient?

Thanks for the tips on watching out for increasing creosote build up as I tweak things!
An insert is engineered and tested to work with a much smaller amount of air in and out. They also have a carefully designed secondary combustion system and a heat exchange system designed to work with the whole system. In addition they have a much smaller liner hooked to them and running out the top of the chimney. Like I said you may possibly be able to make the fireplace burn much more efficiently. But if you do you will have a creosote factory on your hands with the large flue.
 

ragnarok

New Member
Sep 7, 2021
7
missouri
An insert is engineered and tested to work with a much smaller amount of air in and out. They also have a carefully designed secondary combustion system and a heat exchange system designed to work with the whole system. In addition they have a much smaller liner hooked to them and running out the top of the chimney. Like I said you may possibly be able to make the fireplace burn much more efficiently. But if you do you will have a creosote factory on your hands with the large flue.
I'm not opposed to installing a liner up the chimney. It sounds like if i do a good job that will be on the to do list.

Honestly it sounds like a fun project for me to study wood stove design and try to replicate as much as I can. I wonder if its possible to replicate the secondary combustion by tweaking the outside air delivery to certain locations with piping.

I think the hardest part would be changing the heat exchanger setup to something more efficient, since I don't have access to the area behind the fireplace except through a small vent.

Obviously this is all too much work for most people to bother with, and buying an insert would save massive amounts of time. But if I can keep the form factor I have and get some of those gains, I have plenty of time to tweak things.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,077
central pa
I'm not opposed to installing a liner up the chimney. It sounds like if i do a good job that will be on the to do list.

Honestly it sounds like a fun project for me to study wood stove design and try to replicate as much as I can. I wonder if its possible to replicate the secondary combustion by tweaking the outside air delivery to certain locations with piping.

I think the hardest part would be changing the heat exchanger setup to something more efficient, since I don't have access to the area behind the fireplace except through a small vent.

Obviously this is all too much work for most people to bother with, and buying an insert would save massive amounts of time. But if I can keep the form factor I have and get some of those gains, I have plenty of time to tweak things.
How would you size the liner? How would you even install it with the heat exchanger tubes in the way?
 

ragnarok

New Member
Sep 7, 2021
7
missouri
How would you size the liner?

I'm not sure. Is it based on the size of the enclosure and how much wood you'll be burning at a time on average? Surely theres some kind of guideline for that?

How would you even install it with the heat exchanger tubes in the way?
Good question! Seems like it might be difficult. Does this mean an insert isnt even really an option unless I do some demolition? More reason to just try to optimize what I have perhaps. I don't really mind cleaning the chimney regularly.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,077
central pa
I'm not sure. Is it based on the size of the enclosure and how much wood you'll be burning at a time on average? Surely theres some kind of guideline for that?


Good question! Seems like it might be difficult. Does this mean an insert isnt even really an option unless I do some demolition? More reason to just try to optimize what I have perhaps. I don't really mind cleaning the chimney regularly.
There are guidelines for open fireplaces yes. For stoves which is basically what you are trying to design I am sure there is an equation for intake air volume vs firebox size etc. But I have no idea what that is. You do realize how much you would end up spending on all of that ceramic glass a properly sized liner etc etc right? You won't be far from what an insert with a smaller liner costs honestly.


And yes to install an insert you would at minimum need to cut those tubes out of the way
 

ragnarok

New Member
Sep 7, 2021
7
missouri
There are guidelines for open fireplaces yes. For stoves which is basically what you are trying to design I am sure there is an equation for intake air volume vs firebox size etc. But I have no idea what that is. You do realize how much you would end up spending on all of that ceramic glass a properly sized liner etc etc right? You won't be far from what an insert with a smaller liner costs honestly.


And yes to install an insert you would at minimum need to cut those tubes out of the way
Yea, the enclosure I'm thinking of would have 3 panels of ceramic glass about 12"x20". One for the side and 2 for the front doors. In nerceram thats about $300. I'd probably spend another $400 buying enough 1/4" sheet steel. Throw in a bit more for gasket material, hinges and stuff and Im imaging supples cost about $800 total.

I'm not really opposed to the cost of an off the shelf insert. But I think to get one that looks nice and keeps the open side, I'd probably have to have some company custom make it and I imagine that'd be alot of money. The fireplace is opening is 39" wide in the front, 16" wide opening on the side, and 25" tall. Its about 24" deep. Are you aware of any off the shelf units that have similar dimensions and would look nice from the side?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,077
central pa
Yea, the enclosure I'm thinking of would have 3 panels of ceramic glass about 12"x20". One for the side and 2 for the front doors. In nerceram thats about $300. I'd probably spend another $400 buying enough 1/4" sheet steel. Throw in a bit more for gasket material, hinges and stuff and Im imaging supples cost about $800 total.

I'm not really opposed to the cost of an off the shelf insert. But I think to get one that looks nice and keeps the open side, I'd probably have to have some company custom make it and I imagine that'd be alot of money. The fireplace is opening is 39" wide in the front, 16" wide on the side, and 25" tall. Its about 24" deep. Are you aware of any off the shelf units that have similar dimensions and would look nice from the side?
A company cannot legally custom make a stove for you now. And if they did it would most likely be in the 40 to 50% efficency range of old stoves no where near a modern one without lots of engineering and testing.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,077
central pa
Yea, the enclosure I'm thinking of would have 3 panels of ceramic glass about 12"x20". One for the side and 2 for the front doors. In nerceram thats about $300. I'd probably spend another $400 buying enough 1/4" sheet steel. Throw in a bit more for gasket material, hinges and stuff and Im imaging supples cost about $800 total.

I'm not really opposed to the cost of an off the shelf insert. But I think to get one that looks nice and keeps the open side, I'd probably have to have some company custom make it and I imagine that'd be alot of money. The fireplace is opening is 39" wide in the front, 16" wide opening on the side, and 25" tall. Its about 24" deep. Are you aware of any off the shelf units that have similar dimensions and would look nice from the side?
You also forgot to add in the cost of the liner. You will need a larger one so it will most likely exceed $1000
 

EbS-P

Minister of Fire
Jan 19, 2019
1,458
SE North Carolina
You wouldn’t ever think of modifying a corvette to plow a field. Sure you could and it would be quite the sight. And probably even get it insured. but it’s not running in your living room.

if it’s important find the UL listed appliance you like the best and another project to work on. If not get some nice doors and get ahead on your firewood.
Just some thoughts to provide some perspective.

Evan
 

EbS-P

Minister of Fire
Jan 19, 2019
1,458
SE North Carolina
I new there was one posted to a thread awhile ago.

no clue as to it’s availability

 

SpaceBus

Minister of Fire
Nov 18, 2018
6,254
Downeast Maine
I new there was one posted to a thread awhile ago.

no clue as to it’s availability

Decent output on that model if it could be found here.
 

ragnarok

New Member
Sep 7, 2021
7
missouri
I new there was one posted to a thread awhile ago.

no clue as to it’s availability

That looks really nice! It could definitely work, and if I could find one like that about 6-12" wider and fill the space it'd be hard to pass up. That ones already at about $4000 though, so probably looking at $5000+ if I could find one a bit bigger. Probably start eating into my efficiency by trying to find one excessively big, and better off just making a spacer for the 270 model you linked.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,077
central pa
That looks really nice! It could definitely work, and if I could find one like that about 6-12" wider and fill the space it'd be hard to pass up. That ones already at about $4000 though, so probably looking at $5000+ if I could find one a bit bigger. Probably start eating into my efficiency by trying to find one excessively big, and better off just making a spacer for the 270 model you linked.
I don't believe they are available in the US
 

Rob_Red

Feeling the Heat
Feb 2, 2021
307
Southern New England
If it were me I would put a regular insert in there and plate of the open side with something attractive, either a large interesting piece of stone or something metal and decorative.
 

kennyp2339

Minister of Fire
Feb 16, 2014
6,099
07462
Honestly for me, I'd keep the fireplace as is, just like you burn it 15 times a year, and would install a free standing wood stove some where else in the house to have my heat source, O'd buy a fill closing chimney cap, keep it closed shut unless I was going to make a fire.
 
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