Masonry Heater Report

[Prof]

I thought I should provide a little update about my first year living with a masonry heater. As I posted previously, Alex Chernov designed the heater, which was then built by a local mason. In general, the build went off without a major hitch. Alex provided excellent support for the local guy doing the work and later to me as I started operating it.

I would say that the heater was our primary source of heat, with the occasional fire in the wood stove in the basement during the colder days--probably not needed, but my wife likes the house in the mid 70s. We didn't use the furnace at all, outside of testing it every couple months just to make sure it worked.

We fired the heater twice a day--in the morning and evening. We used 40-50 lbs at each firing. I initially expected to do a fair amount of cooking on the stove top of the heater, but this didn't get all that hot. Don't get me wrong, I wouldn't put my hand on it, but in a typical firing, it didn't get much above 500F and it took a while to get there. So we used this to heat water or make some soup, but not much stove-top cooking. Ironically, the oven, which I did not expect to use that much became the most useful element of the heater--we cooked 90-95% of our dinners in the oven from November-April. This included our Thanksgiving turkey and pies! There was a learning curve here, as the temps in the oven easily reached 700 F with it going past the point of my ability to measure it frequently (My IR gun only goes to 750 F). So we bought some foundry gloves that made grabbing a 700+ degree roaster a bit safer. Once we learned how to cook at high heat, the food was amazing. In fact, my wife is looking forward to cold weather this year for this reason.

The heat was great, and the heater was a joy to lean against. The cats were basically glued to the thing. The exterior of the heater would get to about 160F with it getting about 200F right above the firebox. When I cleaned the heater last week, there was virtually nothing in the pipe. There was some fly ash and soot in the cleanouts of the heater, but probably only around a quart or so.

 

[Simonkenton]

Great report! What a great heater. I wanted to put a Tulikivi in my house but wound up with a fireplace instead.
Your heater looks great! You have a great eye for design, as your heater rock work looks just like my fireplace pictured to the left.

 

[Prof]

Great report! What a great heater. I wanted to put a Tulikivi in my house but wound up with a fireplace instead.
Your heater looks great! You have a great eye for design, as your heater rock work looks just like my fireplace pictured to the left.

Thanks!

 

[begreen]

Thanks for sharing. That looks like a job well done. How large a space are you heating with the stove?

 

[Prof]

Thanks for sharing. That looks like a job well done. How large a space are you heating with the stove?

about 1600 sf

 

[Adahn]

That's a beautiful piece of work.

 

[Prof]

That's a beautiful piece of work.

Thanks!

 

[maple1]

What kind of flue temps would you be seeing? Or were they measured?

 

[kennyp2339]

How much wood do you think you went through cord wise? would it be fair to say between 3.5 to 4 cords total since you filled it up twice a day at 50lbs a clip?

 

[Prof]

What kind of flue temps would you be seeing? Or were they measured?

No real way to measure flue temps by a standard probe thermometer. The flue gases go through the oven and exceed my IR thermometer 's range (over 700F). The fire in the heater is fairly consistent in its properties and never really looks like a run-away stove. Sorry I can't answer your question more precisely.

 

[Prof]

How much wood do you think you went through cord wise? would it be fair to say between 3.5 to 4 cords total since you filled it up twice a day at 50lbs a clip?

That's a pretty good estimate on the year, since in the shoulder season I'm only firing once a day or even every other day. I'm going to pay a little more attention this year since we are more settled into the house. Last year I had several stacks of various sizes spread about. Two loads in the heater seemed like the equivalent of loading my PE summit 4X with decent loads. We used the summit to heat the place (from the basement) during construction. Once the insulation was in the summit did a good job of keeping the place warm, even from the basement.

 

[maple1]

No real way to measure flue temps by a standard probe thermometer. The flue gases go through the oven and exceed my IR thermometer 's range (over 700F). The fire in the heater is fairly consistent in its properties and never really looks like a run-away stove. Sorry I can't answer your question more precisely.

But the gases must exit the stove somehow? Can't really tell in the pics.

 

[electrathon]

This heater looks great. Very pretty and functional. I am curious how long will the unit last when being used as a primary heat source? How long till the mortar and inside bricks crack and loosen? I see people burning out stoves in a handful of years, will it outlast most stoves?

 

[Prof]

But the gases must exit the stove somehow? Can't really tell in the pics.

Goes through the top of the heater into a class A chimney. The class A starts on the second floor--about 4 ft up. I can't bring myself to drill a hole in a class A chimney, especially since there was no real creosote in there to speak of and the general rule of masonry heaters is that you don't have to worry about it. I'll still clean mine every year, at least until a get a few seasons under my belt.

 

[Prof]

This heater looks great. Very pretty and functional. I am curious how long will the unit last when being used as a primary heat source? How long till the mortar and inside bricks crack and loosen? I see people burning out stoves in a handful of years, will it outlast most stoves?

I suspect it will be more like a masonry fireplace in longevity. Stoves burn out mostly because of metal fatigue due to the heat swings. I'm sure some bricks might need replaced as time goes on, but when I asked this question to a couple people who built these things, one seemed serious when he said that the heater is a "generational thing." The designer said that the heater is actually stressed less when it is continuously fired (meaning at least one load per day). Apparently masonry heaters do best when they stay warm as opposed to cooling off and warming up. We really noticed this to be true when we cooked in the oven. Cooking in an oven that wasn't 200F at the start of the firing was not so easy (pizzas were fine, but not roasts, chickens, etc).

 

[maple1]

Goes through the top of the heater into a class A chimney. The class A starts on the second floor--about 4 ft up. I can't bring myself to drill a hole in a class A chimney, especially since there was no real creosote in there to speak of and the general rule of masonry heaters is that you don't have to worry about it. I'll still clean mine every year, at least until a get a few seasons under my belt.

Ah ok - so chimney right on top of stove more or less? Couldn't see the top part in the pics, or I wasn't looking at them right. Still curious how much heat it is scrubbing before the gas hits the chimney, but I guess not easy to measure. Very nice!

 

[kennyp2339]

Ah ok - so chimney right on top of stove more or less? Couldn't see the top part in the pics, or I wasn't looking at them right. Still curious how much heat it is scrubbing before the gas hits the chimney, but I guess not easy to measure. Very nice!

From what I understand is that a ton of heat is scrubbed before the gases hit the class a chimney pipe, the design of these units has a big "s" path or zig zag both horizontal and vertical, I would suspect temps would be somewhere in the 400's, which is fantastic considering that gas temps are probably near 1000 as they leave the fire box.
I really like these masonry heaters, I love the look and function of them.

 

[Mikefln]

That is awesome, if you don't mind can I PM you? I have a lot of questions.

 

[Prof]

That is awesome, if you don't mind can I PM you? I have a lot of questions.

Absolutely, I'd be happy to answer any questions that I can.

 

[Simonkenton]

I know the Tulikivi is designed with a fire box about 5 feet high. Engineers in Finland learned that a fire box of that height would produce the highest temps.
At the top of the fire box, the smoke and heat are channeled down to the bottom of the heater, towards the outside. Two flame/smoke paths go towards the outside of the heater.
Then, back up again go the smoke and gases, into the chimney. A single chimney goes out, and up.
This up and down path generates very high heat in the firebox, and transfers a maximum amount of heat into the masonry.

These are great heaters and I wish I had one! Had to settle for a Jotul.

 

[byQ]

This heater looks great. Very pretty and functional. I am curious how long will the unit last when being used as a primary heat source? How long till the mortar and inside bricks crack and loosen? I see people burning out stoves in a handful of years, will it outlast most stoves?

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Repair Detail 24 years later


This Finnish style contraflow masonry heater and cookstove were built in the Autumn of 1991 on the Lake St Pierre Archipelago, Quebec.
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Both heater and cookstove are connected to the same 8 x 12 inch chimney flue. The heater has been fired by the same person every day, often with 2 fires per day, every season for 24 years.
The cookstove has been used only occasionally.

The refractory core follows the 1984 Finnish Fireplace Construction Manual, i.e. the traditional Finnish model with sloped fire box ceiling and 3 inch wide throat. The side channel walls are in common clay brick, layed flat in clay mortar making the walls 4 inches thick.. The fire is fed with under air.




The fire box showing no spalling and minimal mortar loss from the joints. The fire box floor and base of the walls were originally lined by a row of skew cut refractory brick. Only one of these brick remains mortared in position, the other 7 have long since broken free and been discarded.
The grate was replaced last year.




Detail of the back right corner of the fire box. There is some cracking in the wall, but this probably happened years ago and is of little relevance.




View up through the fire box. One full brick, layed lengthways across the lintel, has cracked down the middle along its length, and from side to side across the middle. Three quarters of the brick have fallen, or been pulled away, while one quarter has remained in position.




The remaining piece of brick was removed and a new full brick layed onto the lintel.




New skew cut pieces of brick were cut and layed into position. They would brake free quite quickly if mortared in to place, and so are layed dry.
The function of these pieces is to help concentrate the embers on to the grate during the latter stages of the fire.

It can be seen that this heater has endured almost 25 years of continual seasonal use until needing to be repaired. The repairs made are minor and of little consequence. The condition of the fire box and throat is good. It can be supposed that the heater will be operational for many years to come.

Marcus Flynn

2015

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[Squirrely]

View attachment 199283

Those wedges are an excellent idea.
I did the same on my firebox with cast iron ones.
They work great and make the box easy to clean.



Greg

 

[Adahn]

Am I mistaken in saying that the firebox looks like a coal fired one?

 

[sportbikerider78]

Very cool. Soup to nuts, how much do these set you back if you don't do any of the labor?

 

[Squirrely]

Am I mistaken in saying that the firebox looks like a coal fired one?

You're right. It is.

I got the liners from the UK because they're not available in the US. For simplicity and economy, Morso uses many of the same parts in different models, so the liners fit perfectly.

Greg