Subscribe or Renew Membership Subscribe Renew

build your own fireplace insert...

ponytl's picture

I have given alot of thought to this... and i see no reason I can't build one just as good if not better than a purchased unit...  i know i'd use thicker steel... have more mass... have more ways to get the stored heat from that mass... maybe incorporate a small boiler so that i could pipe the heat to more remote areas... have more options on cleanouts.... ect...

i see no difference in this than if i laid all the bricks on a masonary fireplace... so if you will skip all the "UL" listing stuff and "insurance"  and inspectors ect...  if insurance wouldn't cover dumb azzzz homeowner mistakes then they would not pay half the claims they do...

just input or advice... or tell me i'm a dumb azzz ...



(post #85063, reply #1 of 19)

You are on the right track....if you are a good welder and can weld well enough on vertical or overhead joints.

In 1978, I built one simply because back then inserts were so new here in Texas, that few people knew about them.  I used 1/4" steel plate for the bottom and sides, and then use 3" wide channel iron on the back and the inward tilted back wall.  My fireplace has an opening of 48" and 32" high, so any insert I could find simply wasted the firebox space.  It lasted until 3 years ago when the original damper just rusted out and fell into the metal insert's  poured fireclay floor.  I used the slowest speed from a central heating furnace to blow air into the room through the side of the firebox and around the hot steel firebox.  I also added as many fins to the side to bring out the heat as much or better than the heavy Channel Iron I used for the back wall.  The center of the house, floor level, fireplace has a hollow space beside the brick and mortar structure where I had a 20x25" hinged filter grill in the living room/dining room to quieten the noise of the blower and to pull the heat being pushed into the den, through the kitchen and back into the LR/DR area...

I based my design on a commerical design called a "Fuego".  The only reason I quit using it was I was concern as to what the fireplace mason had put behind the original damper assembly....  Here's a link to that design...  Just be ready to do some welding in the firebox inside the house and do a lot of talking to your spouse about how those welding sparks won't hurt anything that's covered with a damp sheet.... ;>)


(post #85063, reply #2 of 19)

Let us know how it goes after you finish.

Built entire fireplace and 'inserts' from scratch, no problems since 1972. .

1/8" floor plate canopy above, not in direct contact with flame.  Anything metal in contact with ashes is stainless pipe (well, it is SS now, after I had to replace anything in contact with the ashes after first 15 years. Where there is direct ash and hot coals area is 4" of firebrick in back of SS.

Basically built a waterwall with 1/2" to 2" black iron pipe above the ash level - circulate water thru the pipes with 1/4 HP B&G pump, circulate the hot water thru 2 old full sized 1970's chrysler A/C heat exchangers in ducting. 

Welding black iron pipe with no leaks is a challenge welding, was quite a learning curve for me - no problem with mild steel though.

Heated 5300 sq ft house with wood this way for 30 some years (till DW said she was too old to cut and split 8 cords a year), WSHP now (diy naturally, whole 'nuther story).

Tried tempered glass doors on FP for first 10 years or so, too mcuh of a pain to keep clean, plus they do anneal and crack after about 6-8 years of continuous fires. Have steel doors now with artistic perforations.

Unfortunately for last 15 or so years in WA state any wood burning appliance has to be 'certified' (meaning the state gets a big cut of the inflated cost).  You can build your own Rumsford, etc. here if you join the state association. PE license no use for this to bypass 'one size fits all' law.   

(post #85063, reply #4 of 19)

I have plenty of room... will have full access to front & back...have plenty of steel...  at least 1000 fire bricks... alot of stainless... and  several nes sets of doors that went to inserts....I'm a little fuzzy on where to transfer the wood fire heat to the water...  i have several new 2 ton a/c A coils that look like they'd be fine to pump water through... slip em into a air handler... or just into existing ductwork...

( i have maintained my office building that has hot water for heat for the 7 years i've owned it... simple 24v honeywell valves tied into the thermostats that control the hot water flow... simple fined coils with a blower & duct work... must be 50 of them in the building... all have 2 sets of coils one for chilled one for hot...) so i kinda have a clue on this part

 I'm not sure of the water temps this would generate... but i'd like to keep it in the range that i could use pex for most of the runs once i got away from the heat source..

do i pump it through an old hot water tank so i have a holding tank? maybe use a water heater as back up and a storage tank?

the "water wall" is my main question...  is this just above where the fire is?  pretty sure i could build something like  2 capped  24" long 3" black pipes on each side with as many 1" pipes as i could get between them... pretty easy to hole saw into the sides of the big pipe and weld as many 3/4" pipes between them as i could fit... ladder style... with a bung on each side  for in and out....  as long as i stay above ash level rust is not as much of an issue? 

I know you have addressed some of this before... but thanks  for any more insight you can provide...


(post #85063, reply #5 of 19)

water temps this would generate

When the kids were teens (25 yers ago) it was their job to start a fire when they got home from school.

Son once threw in about 2 bushels of plywood scraps (before it was illegal to even burn scrap wood here) - resulting steam melted the solder out of the Cu pipes in the basement - downstream of about 15 feet of iron pipe!

AC coils work great for the duct exchanger.

Just grabbed the camera, but battery dead, will post a couple of detailed pix later of inside of fireplace.

Pix attached is a couple of years ago when one of the pipes developed a pinhole and had to pull a few pipes to repair - can see on the back wall of the F/B 3/4" pipes in manifold, similar on front wall and over the fire. 

Edited 12/29/2008 8:09 am ET by junkhound

(post #85063, reply #6 of 19)

""....resulting steam melted the solder out of the Cu pipes in the basement - downstream of about 15 feet of iron pipe!""

Interesting cautionary note contained in that.

I have seen more than one old stove with the fire box blown out from a steam explosion caused by lack of adequate water supply.

When I added hot water coils to a stove we used copper pipes with high temp solder (on the advice of an old timer we knew who had survived his injuries as a result a stove explosion) because if the temps got too high the sweated fittings parted and the pressure released prior to an explosion, either that or add a pressure/temp release valve in the line as close as possible to the stove box.

They can't get your Goat if you don't tell them where it is hidden.

Life is Good

(post #85063, reply #11 of 19)

thats is a great pic :)    

in dealing with race engines localized hot spots were a common issue... where even with water circulating you'd get steam pockets...  the higher you could pressurize it the less of this you would have...    there was always the balance of restricting or slowing down the flow enough that you would take away/remove the heat... and not slow'n it down so much that it had time to become vapor...

so i assume the same idea would hold true here


thanks for that great pic...


(post #85063, reply #13 of 19)

I'm thinking too, that you want a couple of good pop-off vaves to keep from building too much pressure on this system! ;)

There was a place here with an old pressure tank or hot water tank about 3' diam and 12' long. I had done some work on the house one year and recommended that they replace it. Just plain looked scary.

They said no, we'll wait 'till it starts leaking.

Couple years later, they had another contractor working around it to make a finished room from the utility area. They dropped tools to go to lunch, and about two minutes later, the whole end of the tank blew out, pushing a 3' step ladder through a wall. The electrician had been standing on that ladder a few minutes before that!

The owner was sitting and reading his paper on the deck above this, so he got the surprise of his life!



Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!



Oh Well,

We did the best we could...

(post #85063, reply #7 of 19)

The Fuego insert has a fibox inside an outer shell as shown if you click the link provided.  The firbox "floats" inside the outerbox (mine on rods to minimize conduction i suppose.  I think my brothers fuego inner box rested on triangles instead.)  I think you would want to put any water jacket against the outside of the back wall and top of the inner box but there really isn't any reason you couldn't surround the entire inner box.  You might even need the extra pipe to keep enough volume of water around the box.  I would be afraid of mine turning to steam.  My fuego is hotter than hades in July.

BTW, I clean my ceramic "glass" doors with ordinary window cleaner, newspaper and the ash in the box.  Just spray the glass and then the paper.  Dip the paper in the ash and it comes right off.


(post #85063, reply #8 of 19)

I don't see why you couldn't build your own insert. it is basically a wood stove that is thrown into a masonry fireplace.

Some basics on comparables.
The Fuego mentioend is a dual wall 12 ga metal

A Fisher used to be 1/4" plate

The All-Nighter was 5/16" plate

Jotul's and others are cast iron.

The ones made from plate steel are normally lined with firebrick to help keep them from warping and burning thru over time.

I know a guy here who made a bunch of them from curved boiler plate that I think was 3/16". If any of them ever warped, it doesn't show given that it is already curved.



Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!



Oh Well,

We did the best we could...

(post #85063, reply #10 of 19)

wow thanks for the great idea... i have a 44" dia.. 1/4"  steel tank  thats about 6-7 ft long... i think i might have just found  foundation for my steel fireplace...

it's not really an insert  since  i only have a stone harth at this point...

what i do have is full access to both sides... the back side is my workout room  with a full steam room and a full dry sauna... the front side is my den...  I'm thinking now that i might want to load and clean it from the back side... 

i was wondering about the steam issue... i wouldn't want it to be a pressurized system...   with a little basic plumbing and a couple 24v valves... i could have it open more zones as the water temp got hotter giving me more water volume to keep the temps down...

now what i really want is to tie this into a few solar panels  for  during the day... the roof this will be vented through is a flat bur... this part of the building was a freezer... so it's slab...12" of cork...slab... roof is decked in T&G 2x6 topped with 12" of cork... and then the BUR... it's a 80x 85ft almost flat roof... never shaded...  ceilings are about 15ft...  this 80 x 85  is divided in half... half being my garage workshop... other half has my gameroom... 60 seat stadium style theater...  den... workout room... and a guest suite...  (all sprinklered just in case :) )   I have been eye'n the area under the  seats of the theater... i could build a large hot water storage tank  that would fit. each platform is 14" higher than the last...   all open as i built box trusses all the way across for each rise... so after 3 rises i have about  38" clear under that landing the next one i have 52"...  not sure on the gallons  but 48" wide x 30 or so inches deep... i think you'd want clearance above it... and i can make it up to about 14ft long give'n me plenty of room on each end...   

solar by day... wood by night... if i insulated the tank well  not sure how long it would hold temps...  even with it be'n inside the heated space...backkfill around the wood burner with sand for mass maybe?... kick'n myself for not run't tubes in all the concrete i put down in this place... small boiler for back up or just a large  water heater...

 i know i'm over think'n this... and i don't have to do it all at once...  but i do need to build the firebox so i can finish up the den area...

thanks for the input...


(post #85063, reply #12 of 19)

Out in idaho, my SIL rented an earth sheltered house that had a smaller version of that kind of setup. There was a large water tank for the flywheel, set up higher than the wood stove, IIRC, with pipes plumbed through the water jacket so that heated water rising would do a natural convection cycle with no pump. Colder water at bottom of tank would run down into the water jacket, and rising heated water spilled over to the tank. There were connections left for plans once upon a time for adding solar too, but that had never happened.

There was a thermostat activated zone pump to run this water thru the base board heaters. It was built before PEX in slab radiant. The domestic hot water came from this system somehow too.

even in extreme cold, they could be gone for three days and still have the place above 50°F, and I think most of the heat loss was a couple of cheap lousy sliding glass doors.
It was a really cheap place to live in, energy wise.

Only problem was that when the fire died, that shoestring plumbing system would make gurgling, burping noises, right on the other side of the bedroom wall



Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!



Oh Well,

We did the best we could...

(post #85063, reply #14 of 19)

(post #85063, reply #3 of 19)

I started with general tempered glass bi-folding doors, but I couldn't get it air tight enough.  Plus when on small log and flame was against one of the door panels, it sounded like a .22 going off, not to mention the shattered beads of glass everywhere and a fire going with no way to stop sparks.... ;>(

Then, I found these doors that are built like a tank and had spin drafts that could cut down airflow to the fire almost to the point of suffocation...

The glass panels are ceramic glass and can take a flame up against the glass.  Because they are so large, on overnight slow burns, they really coat over and turn black.  But, a little spray oven cleaner after they cool, and an hour of waiting, they come clean like new.

Please post pictures of your process.  Using one of those disposable camera, but always putting it inside a ziploc bag keeps it handy and clean...


(post #85063, reply #9 of 19)

You aren't a dumbazzz.  But this is probably one of those 'high effort -- high reward' type deals.

I'm more fond of 'low effort -- high reward.' 

How will you make it EPA compliant tho? Some stoves are catalytic, more are 'non -catalytic' --ours having a network of baffles that reburns exhaust...


(post #85063, reply #15 of 19)

photos attached

Have fun, and don't get to dirty fixing a leak 15 years from now <G>

If you have lots of SS pipe, that would be the way to go, I only had about 30  ft of SS without having to go out and pay big $$ for more. Probably 170 plus ft of pipe on the whole assembly not including the HE in the ducts. .

Edited 12/30/2008 11:24 am ET by junkhound

fireplace.jpg78.89 KB

(post #85063, reply #16 of 19)

You can always weld up a copy of an existing design, but it's a challenge to get everything working, IMHO.

Here's some info on water heating from a woodstove:

(post #85063, reply #17 of 19)

thanks for the link...

I'm thinking a honeycomb... kinda thing... as one option...  more a boiler kinda sorta...

basic idea at this point is to have the walls of the firebox be a water jacket much like the water jacket of an engine block...  i have some 3/8" thick  3" x 12" steel tube... enough i think to make the sides and smoke shelf....

I'm try'n to design something fail safe and i think that means little or no pressure... simple pop off valve vented out the roof from the highest point of the water jacket should do... as long as i build it where it can run dry... ie... be able to have a fire with no water in the jacket and still be fine.... like the 100% drain back of some solar collectors to keep them from freeze damage...

like everyone you want to keep as much of the heat you produce and still keep a hot enough burn to keep it clean...

thanks again for the link....



(post #85063, reply #18 of 19)

One more design caution.

It is possible to design a situation where you are absorbing so much heat through the water jacket or water piping that your stove never produces really clean burning temperatures.
You can cool the flue gasses to the point they condense in your flue pipe, danger of creosote buildup is high under those circumstances. Be careful not to take to much heat from the entry to the flue.

They can't get your Goat if you don't tell them where it is hidden.

Life is Good

(post #85063, reply #19 of 19)

Yes, it's pretty much a bad idea to combine the firebox and the heat exchanger. The most efficient designs use a hot firebox insulated with firebrick, etc., and feed the output gases into a heat exchanger. The firebox needs to run at 1000F or more, while the heat exchanger obviously stays below 212F.

Also, if you cool the flue gases too much, you'll get creosote condensation in the chimney, which will start a chimney fire if not cleaned frequently. That's why even high-efficiency woodstoves send a certain amount of heat up the stack.