~$900 Small Masonry Heater Proposal

[bholler]

I don't remember it was a private seller. I bought 3 for $80 (including shipping)

Yes but even if he does have some more the value of them is about $120. And I am sorry but loading wood starting a fire and cleaning ashes out of a 12x12 door would not make me happy at all. I think your general idea is a good one I just think you need a bigger door and I dont think you can do it for $900 at all

 

[byQ]

I checked the internal size of the small masonry heater doors @ Northstone Heat Supply. There smallest one has a 10" x 13" opening - so smaller than the 12" x 12" opening on the clean-out door. The hot seller that most mason's use is the one with a 410mm x 410 mm opening. This equals a 16" opening (so you lose 2" on each side of the converted clean-out door).

These masonry heater have small fireboxes. Hierony how is your clean-out door working? And how big is the internal opening?

 

[bholler]

I checked the internal size of the small masonry heaters doors @ Northstone Heat Supply. There smallest one has a 10" x 13" opening - so smaller than the 12" x 12" opening on the clean-out door. The hot seller that most mason's use is the one with a 410mm x 410 mm opening. This equals a 16" opening (so you lose 2" on each side of the converted clean-out door).

Yes that 2" would make a big difference. I am sure you could do it with that 12x12 door but I would not be happy with it. And yes I know that most masonry heaters have pretty small fireboxes. I have seen plenty of them and worked on plenty. I haven't built one but I am no stranger to them at all. And I dont see how you could build one for $900 even with scrounging allot of the parts. Unless of course you start buying in large enough quantities.

 

[byQ]

That is your personal preference to have medium to large door. I have a large door on my masonry heater but would have been fine with a small one. I guess the kit could have the option of having a fancy door but the price really jumps.

$900 might be a little optimistic. I forgot about the hollow metal frame that goes around the door. There are cast iron glass doors from China but you have to order big quantities, like 100. They are in the $75 range but that is probably before shipping.

 

[bholler]

Again I really do like your general idea I just think that the goal of $900 will be very difficult to hit.

 

[byQ]

$900 is without profit and without shipping costs. The kit would need to be picked up or delivered in my general area (Southern Idaho). $900 is the cost it would cost me if I built a small MH for myself. Well, really I could do it cheaper than $900. Because the outer materials would be free - river rock. Clay bricks for the flue surround - free. And I don't think 300 firebrick are needed. And usually the flue/pipe isn't included in the cost but I included it.

But if you were to run a business and you got 100 orders how would the $900 hold up? It probably wouldn't. Those clean-out doors are probably going to cost at least $100. And at some point you're going to have to buy new firebrick.

 

[electrathon]

nope there are lots of prefab masonry fireplaces out there

How do thay do that? Do you get a box of bricks and a pattern? Do they precut all the angle cuts? Pre build the fireplace (like a kit log cabin) and then pull it back apart? It seems like most houses are different and there would be so many variables.

 

[bholler]

How do thay do that?

lots of different ways but normally precast refractory panels you put together then build the surround around that core. There are also precut brick ones and a few other variations they are pretty much all modified rumford boxes. Yes there is variation but that doesnt effect the firebox if you are starting from scratch. we have retro fitted a few but that doesnt work out very often.

 

[St. Coemgen]

For what it is worth, The Missouri Department of Natural Resources has a nice little document how to build a masonry heater, with design plans:

(broken link removed to http://dnr.mo.gov/pubs/pub781.pdf)

As an Expat living in Europe, I can tell you masonry heaters are quite common here. There are even workshops on "how to" near where I now live, such as :

http://www.stovemaster.com/html_en/articles_7.html

One thing to think about, when DIY building a masonry oven, is to consider avoiding the typical "boxy" look. Masonry ovens can be most any shape you wish, and with consideration for different surfacing options (rather than just brick) including plaster, tiled, stone, etc, they can really become a dynamic part to your interior design. Just some examples:

https://uk.pinterest.com/orchardcroft/kemence-kalyha-hungarian-wood-burning-ovens/

Many of the masonry heaters here, for example, have a built in sitting spot. This lets one sit by the oven, often with one's back to the stove (if built correctly, they are never too hot to the touch at that spot). And if you have a wife, that is then where you may find her at most times.

 

[hierony]

Sorry about the delay, the notifications don't seem to carry through.

Anyhow, my heater door works just fine--and it's only 8" wide. It's probably similar to some tiny long stoves in firebox width. You have to keep in mind @bholler that this isn't a metal wood stove & you don't run it like one. You start from a cold/warm heater, fill up the firebox, light it/get it going, close the door, and walk away or just watch & let it burn down. This once, maybe twice, a day. You don't need to poke the fire, you don't need to add wood--in other words, you don't need to put your hand into a burning fire. And believe me, if you open the door after it's started burning (even during the coal phase) you won't be able to get your hand even close to inside without welding gloves, which honestly wouldn't help much/for long. It's not like you need to chuck 10" wide pieces into the thing--4 to 6" are preferable for good burns and can be gently placed...

Masonry heaters have their own classification/definitions within International code. Look in the International Residential Code, Chapter 10, Section R1002--Masonry Heaters ((broken link removed to http://premiumaccess.iccsafe.org/document/code/362/6125042)). You can find ASTM-1602 around if you look thoroughly enough (mostly definitions, sketches, and clearances, plus a stipulation to build by/under an experienced stove mason). They are EPA exempt due to how clean they burn (always excess air but not too much like a fireplace). If you follow the standards & get everything inspected, you should be good to go in terms of insurance & such. These are massive heaters built of brick & stone--the surface (min 8" thick walls) gets to maybe 110-130 F (ie, NOT burning temp).

My door:
I need to get a better handle yet. I was wrong about the threads--it's 1/4-20 (very common). I'll also redo the door gasket--use 3mm silica wick from a vap shop, embed in a nice layer of high-temp silicone. Should make the door close & seal better. I've obviously overheated it some, but only to dull red w/ lights off--I was setting the wood too close to the door... The back side of the door has threaded holes, so I might get a 1" or so hole milled in the thing & put in a tiny view port of ceramic glass.

@byQ you could get a 1/4" rod, thread one portion, file/grind a flat section on the other end so a key would hold your handle. I like your idea of a metal knob--my wood handle keeps getting a little charred... I might also suggest using brick plugs for the cleanout ports--the metal ones cost some & make a hot spot where you might otherwise like to put your back. The Stovemaster website has some images of these (linked by St. Coemgen). Got anybody interested yet?

 

[bholler]

You have to keep in mind @bholler that this isn't a metal wood stove & you don't run it like one. You start from a cold/warm heater, fill up the firebox, light it/get it going, close the door, and walk away or just watch & let it burn down. This once, maybe twice, a day. You don't need to poke the fire, you don't need to add wood--in other words, you don't need to put your hand into a burning fire. And believe me, if you open the door after it's started burning (even during the coal phase) you won't be able to get your hand even close to inside without welding gloves, which honestly wouldn't help much/for long. It's not like you need to chuck 10" wide pieces into the thing--4 to 6" are preferable for good burns and can be gently placed...

Yes I am fully aware of how they work and how they are run. I have not built one but I have worked on many and have a few friends and colleges who have them. And I would not want to load through a 12x12 door I don't care if it is hot or cold it would be a pita. And no you don't poke the wood in a wood stove either. And by the time I load wood it is just coals and the stove is not that hot either. I am not saying you could not do it with a door that small I am saying I would not like to do it and I am sure many others would feel the same.

 

[byQ]

Your door is the same brand as the clean-out doors I have. I'm glad it is working. I like the looks of that little arched door. My sister wants a small masonry heater. She wants to build it, too. I'll help her with planning, and will be watching over her shoulder/giving advice.

Regarding burning, I noticed that same thing - once the heater was warmed up it was easy to start a fire.

 

[mellow]

Maybe @John Ackerly or one of the Green Heat crew will chime in, they got a new employee that is building these things left and right in canada and abroad.

 

[begreen]

Yes I am fully aware of how they work and how they are run. I have not built one but I have worked on many and have a few friends and colleges who have them. And I would not want to load through a 12x12 door I don't care if it is hot or cold it would be a pita. And no you don't poke the wood in a wood stove either. And by the time I load wood it is just coals and the stove is not that hot either. I am not saying you could not do it with a door that small I am saying I would not like to do it and I am sure many others would feel the same.

I'm pretty sure the door on the Jotul 118 is smaller than 12 x 12. More like 9 x 11 I would guess. Folks have been heating with them for a long time. But the 118's door is proportional to the firebox behind it. Not sure on byQ's masonry stove.

ByQ, what is the firebox size behind the door? Is it a long rectangular box like the F118's firebox or is it much wider than the 12x12 door?

 

[bholler]

I'm pretty sure the door on the Jotul 118 is smaller than 12 x 12

My cawley door was only a little bigger than 12 x 12 and that was the only thing about the stove I disliked. Infact it was one of the main reasons I got rid of it.

 

[begreen]

Tons of splits have gone through doors that small in countless cigar burners and side loaders.

 

[bholler]

Tons of splits have gone through doors that small in countless cigar burners and side loaders.

yes I know it can be done i have done it and didnt like it

 

[byQ]

On the plans I have the firebox is wider than it is deep. On hierony's heater the door looks to fit the firebox like the door on the little Jotul - that is the firebox is deeper than it is wide.

Here is the small contraflows firebox. Let's calculate the width of the pictured firebox. The math, two 9" bricks = 18" - 2(2.5" brick width) = ~13" wide firebox. So a 12" opening should be okay on this small heater.

 

[byQ]

Here is the opening before the door is installed. The door is going to be bigger than the firebox opening - by a few inches on each side.



And here is the door in place - I'm guessing a 15" or 16" door.

 

[bholler]

Here is the small contraflows firebox. Let's calculate the width of the pictured firebox. The math, two 9" bricks = 18" - 2(2.5" brick width) = ~13" wide firebox. So a 12" opening should be okay on this small heater.

I am curious how much space will a firebox that size heat? I know how these heaters work and I know they are pretty efficient but you just cant fit that many btus into a box that size. But yes if your firebox is going to be that small you really cant go much bigger so the 12x12 would work fine.

 

[byQ]

I'm not sure of the btus. But if btus are proportional to volume of the entire heater than this small heater would be,
3' wide x 2' deep x 6' tall = 35 ft3.

And the big heater would be,
4' wide x 3' deep x 7' tall = 84ft3

So the bigger one has about 2.5 times the volume. The small heater would probably have to be fired twice a day in most houses.

 

[bholler]

I'm not sure of the btus. But if btus are proportional to volume of the entire heater than this small heater would be

The volume of the firebox is what determines the btu capability of the heater the mass of it just determines how much heat it will store and release over time. That small box looks to be about 1.5 cubic feet which if you packed it totally full of oak at 10% mc (which then could not burn because you would have no way to get air to it) you would have 486337 btus available. Which means if you are saying 2 burns a day you are only talking about 40,000 btu output.

 

[begreen]

Depending on the house 40K btus is pretty good, especially if it's continuous unlike the cycling of a conventional stove.

 

[hierony]

From my reading of the sporadic tidbits on masonry heaters, the N. American version is usually designed for a nominal 50 lb load. I'd guess a typical actual load from 40-60 lbs, depending on wood density. With a smaller heater (like mine) it might be fired twice a day, or just once a day for larger heaters. One can also use 1.5 loads (reloading the heater with half a load once the first full load is down to a few coals) for a potential total of 3 loads a day. Depending on how the heater works, one can also do 1/2 or 3/4 loads too (useful during shoulder season).

If you need more than 30-40k btus, you're house is probably giant and you could afford to install a multistory heater with multiple fireboxes to increase output. 'Cause you must be rich in the first place to actually own such a place...

Also in the lit is the story of an ill-functioning masonry heater. The owner had a "professional" rebuild it but that person bypassed all the heat channels, in essence making it into a fireplace (requiring another rebuild from a real stove mason). Claiming familiarity with masonry heaters doesn't make one actually knowledgeable...

 

[bholler]

Depending on the house 40K btus is pretty good, especially if it's continuous unlike the cycling of a conventional stove.

Well yes that is why I asked what size house it would heat but that 40,000 is based on an absolutely full firebox which is not possible and 100% efficiency which is also not possible. So the real number would be much much lower.