Masonry OWB build.

[paragonbuilders]

Hello!
My name is Dan Larrivee and I'm from CT.
I've been reading on this site for a while and what a lot of great info!
I used to own a Central Boiler OWB and loved the constant fire and that the mess was outdoors but I always thought there must be a more efficient way.
I am going to build a refractory box for my fathers CB and hope to improve his efficiency considerably.
I'll post pics and info when I get to it.

Now to my new idea!
I bought a 1700 farmhouse that I'm fixing up slowly. With the additions that were done in the 60's it is 3500 sq. ft.
Also I am building a 30 x 42 garage/shop that I will be heating as well. I just hauled home 40 cord of logs so fire wood will not be an issue.

I already have insulated 1" lines run from the house to the garage. My plan is to build what looks like an outdoor fireplace on the back of my garage out of cinderblock with insulation and then a refractory firebox modeled after the seton/greenwood boilers. I think I like the new greenwood frontier style with the crossfire tubes. I'm also considering fire tubes in place of the water tubes. I'm not sure yet. I think it can be done rather cost effectively and that it wood look really cool. I'll attach a rough sketch I made of the rear of my garage. With it against the back of my garage I can access the heat exchanger from inside the garage and attach pipes thereby minimizing cold exposure. I would make the hx so it could slide into its chamber and come out for easy cleaning or repair. Then I would face the entire thing with stone.

I would love to hear some comments on the idea.

Dan

 

[stee6043]

If you have lots of spare time this sounds like an excellent project. If you value your time you'll probably never be able to build one for less than you could buy one. Even if your time was worth less than minimum wage if I had to guess. But there are lots of things us guys do that never make fiscal sense.

Is it too late to run another set of pex lines? If you read more here you'll probably find that single 1" lines may not be enough to move the kind of heat you're going to want to move with 3500+ square feet to heat.

Welcome to the forum and share pics!

 

[leon]

Dont waste your time or money,

you can fill your fathers CB firebox half full or more with standard
firebrick and have a better burn with less wood and less wood
burning overall.

In your case and proposed design I doubt seriously your insurer
would approve of this, nor would the plumbing inspector approve it
in your locality because it will not have been tested by a certified
plumbing appliance testing laboratory.


There is much more efficient way and it involves much less money
work or expense without laboring to build a masonry heat exchanger.

You can obtain thermal mass the easy way.


IN MY CASE I filled my 31 year old indoor wood and coal boiler half full
of fire brick after I laid down a 12 by 12 piece of angle iron to cover half
the grates reducing the the firebox to 12" by 12" by 36" to increase the draft
as I have an 8 by 12 chimney which is too big for my boiler with its 8 inch
diameter flue.

There is no reason you cannot fill it with standard firebrick like I did.

It will probably take a pallet of standard firebrick to fill it half full but believe me
it is worth every penny you spend on the firebrick because it soaks up the heat
from the fire and slowly release the heat back in the water jacket and
you will be out a lot less money, time, effort for your trouble.



I would rather see you purchase a Harmon SF360 (42 gallons) with your effort and
you can install a small wood door to throw wood into the shed by the
boiler and then shut the door afterwards. You can add storage by purchasing
an insulated tank from New Horizons (490 gallons) to increase the amount of thermal
mass of water 12 times and store heat in the firebrick to aid in the heating of the shed
or the home.

I like the Harmon wood and coal boiler design because of the firebox and the flue gas path in it.
you can also burn coal in it too as it is hydrotested.

The other thing is you have to have a chimney that is higher than the peak
of your shed to have a good draft anyway and a forced draft is only as good as
the height of the chimney pipe. .

I want you to succeed, not make mistakes. increasing thermal mass simply takes advantage
of one part of themal dynamics.

 

[DaveBP]

Welcome to the forum, Dan.

You'll hear a lot of different viewpoints from posters here. With a distinct tendency toward gassifying boilers and high efficiency. (Don't ask how efficiency is defined if you want a short answer).

That said, efficiency is not necessarily everyone's highest priority. Looking at all those OWBs out there (burning two or three times more wood than required) makes it pretty obvious. Or all those V-8 pickups that only ever carry their single commuter to work and back.Or all those Harleys that get a thousand miles/year or less on them. We all do things that are not as efficient as somebody else's rig. That doesn't mean we can't enjoy them more than any other choice we could have made.

If you enjoy reading online, spend time on this forum (and some of the others here @ hearth.com) and learn to use the search function to hunt down topics of interest to you. You'll learn a lot and be inspired to try stuff you may never have thought of. Lot of wild projects have been described here (with pictures!). I've done lots of whacky stuff over the years, some successful and some not so much. Learned from most of them. Your proposal sounds like a great project. Keep coming back for more feedback as it progresses (and sketches always make our replies easier and clearer).


Whatever you end up doing.... cut, split, stack and top-cover that firewood now. Do that first.
No matter what you use to burn it in, it will burn more efficiently if it is very dry.

See, there's that efficiency thing again.

 

[paragonbuilders]

If you have lots of spare time this sounds like an excellent project. If you value your time you'll probably never be able to build one for less than you could buy one. Even if your time was worth less than minimum wage if I had to guess. But there are lots of things us guys do that never make fiscal sense.

Is it too late to run another set of pex lines? If you read more here you'll probably find that single 1" lines may not be enough to move the kind of heat you're going to want to move with 3500+ square feet to heat.

Welcome to the forum and share pics!

I love to try new things and experiment. I'm not worried about "wasting time" because the process is half the fun.
I realize it would be better with more volume, I was planning on putting storage in the house to help even out the demand. Do you think that would do the trick?

Thanks for the welcome.
Dan

 

[paragonbuilders]

Dont waste your time or money,

you can fill your fathers CB firebox half full or more with standard
firebrick and have a better burn with less wood and less wood
burning overall.

In your case and proposed design I doubt seriously your insurer
would approve of this, nor would the plumbing inspector approve it
in your locality because it will not have been tested by a certified
plumbing appliance testing laboratory.


There is much more efficient way and it involves much less money
work or expense without laboring to build a masonry heat exchanger.

You can obtain thermal mass the easy way.


IN MY CASE I filled my 31 year old indoor wood and coal boiler half full
of fire brick after I laid down a 12 by 12 piece of angle iron to cover half
the grates reducing the the firebox to 12" by 12" by 36" to increase the draft
as I have an 8 by 12 chimney which is too big for my boiler with its 8 inch
diameter flue.

There is no reason you cannot fill it with standard firebrick like I did.

It will probably take a pallet of standard firebrick to fill it half full but believe me
it is worth every penny you spend on the firebrick because it soaks up the heat
from the fire and slowly release the heat back in the water jacket and
you will be out a lot less money, time, effort for your trouble.



I would rather see you purchase a Harmon SF360 (42 gallons) with your effort and
you can install a small wood door to throw wood into the shed by the
boiler and then shut the door afterwards. You can add storage by purchasing
an insulated tank from New Horizons (490 gallons) to increase the amount of thermal
mass of water 12 times and store heat in the firebrick to aid in the heating of the shed
or the home.

I like the Harmon wood and coal boiler design because of the firebox and the flue gas path in it.
you can also burn coal in it too as it is hydrotested.

The other thing is you have to have a chimney that is higher than the peak
of your shed to have a good draft anyway and a forced draft is only as good as
the height of the chimney pipe. .

I want you to succeed, not make mistakes. increasing thermal mass simply takes advantage
of one part of themal dynamics.

I'm open to different ideas but whatever I do it will be outside. And I love to build things so it will be fun for me. Mistakes are ok to me.... That's how we learn.
I'm not looking to get thermal mass from the masonry. In fact I will be insulating the firebox from the masonry. It will just be the skin like the metal siding on the typical owb just better looking and stronger.
Dan

 

[paragonbuilders]

Welcome to the forum, Dan.

You'll hear a lot of different viewpoints from posters here. With a distinct tendency toward gassifying boilers and high efficiency. (Don't ask how efficiency is defined if you want a short answer).

That said, efficiency is not necessarily everyone's highest priority. Looking at all those OWBs out there (burning two or three times more wood than required) makes it pretty obvious. Or all those V-8 pickups that only ever carry their single commuter to work and back.Or all those Harleys that get a thousand miles/year or less on them. We all do things that are not as efficient as somebody else's rig. That doesn't mean we can't enjoy them more than any other choice we could have made.

If you enjoy reading online, spend time on this forum (and some of the others here @ hearth.com) and learn to use the search function to hunt down topics of interest to you. You'll learn a lot and be inspired to try stuff you may never have thought of. Lot of wild projects have been described here (with pictures!). I've done lots of whacky stuff over the years, some successful and some not so much. Learned from most of them. Your proposal sounds like a great project. Keep coming back for more feedback as it progresses (and sketches always make our replies easier and clearer).


Whatever you end up doing.... cut, split, stack and top-cover that firewood now. Do that first.
No matter what you use to burn it in, it will burn more efficiently if it is very dry.

See, there's that efficiency thing again.

Thanks dave,
I'm definitely interested in efficiency, just doesn't have to be great for me. I'm happy with good. I considered building a true gasifier, but there is a lot of science behind getting it perfect, so I decided on the seton/ greenwood style. It's still way more efficient than a traditional owb, and I can build it rather easily.
That being said I'm open to thoughts and ideas that I haven't considered.

Dan

 

[456wood]

Im no expert but one thing to keep in mind with this type of build is the firebricks will absorb a lot of btus but if you dont get that heat into the heat exchangers it is lost. I think this is especially important if you burn with storage and let the fire die out. Would like to see pictures as you build. Have fun with it

 

[heaterman]

The problem with a CB or any other brand of typical OWB is that the firebox/combustion chamber is also the heat exchanger. This is why they have such poor actual efficiency. They can't generate high enough combustion temperatures to burn clean and they can't reduce the exhaust gas temperature far enough to be efficient. The basic design does not and can never work well in terms of burning clean or efficient. You basically have to isolate the combustion process from the heat exchange process to do both correctly and that always means a two stage burn.

Adding a bunch of brick in the combustion chamber may help a little with keeping temps up but you'll have even less sq ft of heat exchanger surface. The basic thing to remember is that the primary purpose of firebrick, cement or any refractory type material is to function as an insulator, not heat storage. The best storage medium (invented by God himself) is water. The challenge is to move the heat from the wood and wood gas to the water and do it cleanly.

 

[old wethead]

I agree that the outdoor wood burning is the preffered way to go...I was thinking of just getting a Harman wood boiler for example and building a shed outside and running pex lines to the house with storage and running that...not so much storage that the boiler is off for multiple dats but so you could get maybe 8 to 12 hrs between firings... shed would only have to be slightly larger that boiler so it will stay warm with heat off boiler...like an old box conainer off a truck or something...

 

[paragonbuilders]

So I had a rain day Thursday and decided to tackle my dads central boiler project.
I picked up 216 fire brick ( that's all they had) and a sheet of 1/2" hardie backer board, and headed to his house.
I shoveled out the fire chamber and scraped out as much creosote as I could. I was surprised how easy it scraped down to bare metal above where the ashes were. A little more elbow grease required at the bottom.
I removed the door and brought it in the shop and had my dad clean it.
After sweeping out as much dust as I could from the fire box, I cut a piece of the hardie backer to lay on the floor back as far as the large baffle. I did this for two reasons. First was extra insulation from the firebox floor which is part of the water jacket. The second was to keep any ash that worked its way through the firebrick off the steel to hopefully reduce corrosion.
Then I started stacking bricks. We dry stacked them for now until we are done experimenting. There is a 3" angle around the perimeter of the firebox and I stacked the side walls straight up at this point. The back I stacked just in front of the large baffle until I hit it. This effectively forces the gases to go up and over the sides and down the back side of the firebricks before going below the baffle and out the back to the flue. I thought this would help us maintain as much heat exchange area as possible. The fire bricks were all stacked to just above the top of the door opening. Here are some drawings of the fire box my dad made in Microsoft paint.

 

[paragonbuilders]

We attached a piece of hardie board to the door also since we had some left to help protect it from the extra heat. We will see how it holds up. It cracked after a day so I parted on a coat of stovo to help protect it.

The first fire was exciting. About five splits and a few smaller pieces and I had the fire roaring in about five minutes. The boiler temp was at 130 degrees. I was wondering if it would draft naturally and it seemed to be just fine. After 20 min I checked on it. Up to 145 degrees. I opened the door to a nice fire. Top bricks were just under 600 degrees. I pulled the clean out cap and the flue temp was at 296 degrees. Here are a few pictures.

 

[paragonbuilders]

Now the idea is to see how much efficiency we can squeeze out of it. So we are thinking a high alumina board on top off the fire brick tight to the back with a 6" space in front near the door. And add some combustion air at the top somehow. Any ideas or thoughts would be great.
Also we are adding a tjernlund ad-1 draft inducer to the chimney to help draft while loading, possibly on start up, and also possibly during burn if needed. It comes with a rheostat to set speed.
What I'm trying to figure out is how to check how the fire is responding to our modifications without opening the door. Any ideas?

 

[leon]

Fill the firebox half full of firebrick or more to within four inches of the rear baffle height
with NO MORTAR and you will see a huge increase in the boilers ability to store heat as well as have
a hot fire and have reduced smoke in the process before you fo anything else.

You will not need the draft inducer or the fire backer board once you add more firebrick

You need to add section of stove pipe with barometric damper setting the counterweight
at maximum that is all you need.

I would also put a layer of firebrick on the floor of the boiler as well.

 

[paragonbuilders]

Hi Leon.
What do you mean fill the fire box half full? Halfway to the top? Or more layers up the back wall?
Why no mortar?
The draft inducer was mostly to keep smoke fom coming out door when loading. If I need it for more its there.
What does te barometric damper do?
I did put a layer of fire brick on the floor.
I'm not sure that my goal is to store heat in the brick. My intention was to allow a hotter fire to achieve more complete combustion before crossing the path of the water jacket. We all know how inefficient these central boilers are.
I was going to install the fire board to keep the heat more condensed in the firebox allowing even higher temps. Right now the baffles of the water jacket are directly above the fire sucking heat before complete combustion I believe.
Do you think that I don't need it?

 

[leon]

1. Fill the fireboxes actual volume half full or more is what I mean and what I did.

I filled my boiler half full exactly to the point below the flue which makes the
rectangal of firebrick 12" by 12" by 32" in size.

fill the firebox by starting at the back and stop at the half way point and then start at
the next layer and continue until the fire brick layers are 4 inches below the the rear baffle then stop.

test fire it and see how the temps are with the water temperature and then you will be asssured that
you can add more firebrick to the mass with zero issues and you will have more heat and less smoke
after you add a barometric damper.


NOW you have to understand that the barometric damper must be installed horizontally after the the flue exits
the boiler in order to operate properly. The natural draft will be aided by the barometric damper simply by the
pressure gradient/vacuum created by the combustion process within the boiler. This also reduces the need for a huge smoldering fire which wastes fuel as well.


No mortar is needed because the fire will heat every exposed inch and
also enter every exposed edge of brick and absorb it and shed it back
when the fire slows down.

2. the barometric damper permits the entrance of an exterior draft at the
exit point of the boiler which is what is done with with oil fired boilers- I have one on my oil boiler and as it shares
a common chimney with my wood and coal burner the amount of draft I obtain by the use the damper is excellent but I have to
add a chimney extension.

3. you neither need the backer board or desire it because it defeats the exposure of the water jacket to the hearth.

4. you want to store the heat in the brick to maintain a hotter firebox temperature and as an aid in natural draft.

 

[paragonbuilders]

interesting. Have you done any testing to show how efficiency has improved? Do you have fire brick walls on the sides as well? I am looking to squeeze as much efficiency out of it as I can while learning so when I build mine I'm more prepared. From what I've learned it is important to keep the fire isolated from the heat exchange until the combustion process is complete. Then pass the hot gas over the exchanger, in this case along the water jacket, before exiting the flue. By placing the fire board above the firebrick I am enclosing the fire as best I can to keep temps up then it will exit and flow along the upper baffles then down the sides to get below the large baffle and then up and out the flue.
Already I have a smokeless fire within 4-5 min. with natural draft.
Soon we will have an I idea if we are using less wood.

 

[leon]

My boiler has water on the sides and top of the boiler and it only has 25 gallons of water in it.
so it heats up quickly with wood and coal fires. The issue is poor draft in my case.

My firebrick is loose stacked all the way up to the flue as I mentioned, I have not brickeds the walls
but probably will if i am unable to replace this boiler this year.


You do not need the fireboard, you can eliminate completely it as you already have a smokeless
stack when burning which is what you want to have anyway.

I will strongly suggest that you install more firebrick without mortar as I did and your father will be
very happy and the fire box will be fine.


If you purchase a small OWB for your own use and do the same things to it with the mortared and
loose firebrick and barometric damper you will not need a masonry heater

 

[maple1]

Barometric dampers do not increase draft - they decrease or limit it.

 

[paragonbuilders]

If the fire isn't hot enough then I'm not getting complete combustion whether or not the smoke appears smokeless. I'm going to have my boiler tech friend come over and check efficiency for me. Then when I tweak things further we have a point of reference.
Thanks maple1 for the info. I've never seen one on a wood burning appliance.

Also I'm not building a masonry heater. I'm building an outdoor boiler out of masonry instead of steel. The masonry will be insulated from the firebox and heat exchanger. It is not intended to hold any heat.

 

[leon]

Barometric dampers do not increase draft - they decrease or limit it.

Hello Maple1,

I have to disagree with you as my wood and coal boiler is starved for draft without it because the
chimney is too short/does not clear my roof line enough. When the oil boiler is not running the
barometric damper aids in my boilers combustion so after 32 years of using a barmotric damper
for both units I can honestly say they work for me and always have increased my draft for my
wood and coal boiler.

 

[maple1]

Barometric dampers limit draft to your furnace. They provide an alternate path for the draw in the chimney to draw air from - that is, with a barometric damper, the chimney will pull at least some air from your basement (or the outdoors, or the shed, or wherever the unit is setting) rather than pull all of it through your furnace/boiler. Any amount of air the baro pulls from your basement is that much less air it will pull through your furnace/boiler. If you adjust the barometric damper so that it is always closed (noted above as setting the counterweight to maximum), you will have the same effect as having no barometric damper at all - until you have large surges in chimney draft (say from wind gusts) that will pull the damper open a bit, which serves to limit the draft the furnace/boiler sees. They in no way increase draft to your furnace/boiler.

That's my story & I'm sticking to it - always open to more feedback from others though.

 

[bmblank]

There's no way a bathymetric damper can increase draft, unless the air going in thru the damper is of a greater temperature than that of the flue. In other words, the boiler room temp would be in the 500°F range... Not likely.
This is not to say a boiler will not burn better with one. Its very possible it fixes some unknown problem the fire was having.

 

[paragonbuilders]

Well so much for building my boiler. At least for this year. I found a greenwood 200 that is one year old for $3200. It still looks brand new! Needs the hx cleaned and its ready to go. Boy is it heavy. About 3000 pounds. Now to figure out what to do for storage....