Masonry heaters

Hi guys,

I’ve been planning out heating options for the new house, and I’m gathering info on masonry heaters. I know some of you use them and I’d like to hear your experience, and what design you went with. My floorplan is open in the public areas, with a second story loft area, so radiant heat will work much better than convection - hot air would rise to the upper floor ceiling.

Hydronic (radiant) heat is another option, and seems to complement the masonry heater, especially for far away rooms not in line-of-sight to the masonry. I would use an outdoor wood boiler for this, I don’t think I can do it all with the masonry heater. Plus I like separate systems for redundancy, and we can fire the boiler in summertime for additional hot water needs.

I’d like to incorporate cooking functions if possible, via a stovetop and oven. I really like Kristijan’s setup with the bypass valves. Summer cooking in particular should NOT be heating up the masonry, just directly piped out the chimney. Reposting his video tour:

This thread has a bit of discussion around thermal mass and wood stoves:

This site has a lot of excellent design info on a masonry heater / rocket stove hybrid:

This is a new area for me, but I’m very aware of how thermals work… As are most of you fine folks. Hit me with your thoughts!


Your on the right track, masonry heaters rock. Clasical wood fired stoves are ok, but usualy they get super hot fast, then when the fire burns out they get cold fast too… incorporating some mass in is a gamechanger. It smoothes the output. For the first time ever we can leave for a day or two and return to a warm house. The place where we lived before, l had to set the alarm at about 2 in the night to fill up the boiler so that our babys were warm, zero thermal acumulation…
In our case, we maintain a smoldering “pilot flame” all the time. When you want to cook, throw a ring out and wake the fire, if the draft is good it takes just a few seconds to start roaring. Most of the time the exess heat from cooking acumulated in the bricks is enaugh, even in winter. We rarely let the stove to actualy burn past idle for warmth.

Tips l learned:

  • install big fireplace doors. Throwing in a thick round log spares you a lot of work and time. Myne are l think 10x10" or something like that and is way better thain the tiny doors the clasical stoves have.

  • go with a thiner cooktop plate, l got l think 8mm and it takes time for it to heat up and it gives a lot of heat off when you stop cooking. Both plates togerher weigh probably 80 pounds, maybe more. 6, or maybee even 5mm shuld be fine.

  • l laser cut the rings in the plate. Think about your style of cooking, usual pot sizes… and plan out the ring pattern carefuly. I got 2 small rings and one big+ small inside, but l spaced them a bit too close. If you throw a big pan on the big ring, it gets tight if you want a nother pot or two on the small rings.

  • heat expansion, hugely important in all stages of the build! I got most right, only messed up one part next to the oven and it formed a crack. No big deal at all but better to avoid.
    Same applyes to the cooking plate. If the dilitation gaps are not placed well, the whole plate buckles up some wich greatly decreases cooking efficiancy (less contact). We usualy cook without the rings, over the fire, but still… l need tk fix that some day. Only takes an angle grinder and a couple of minutes of work. But l too am joining JOs favourite sport discipline, procastinating :smile:


Well, if you are building a new house you only get one chance to do this right because other than a stand alone wood stove you will be incorporating it into your structure. I used structural steel channel iron to build my firebox with the flanges turned out and boxed in to act as ducts through which the heat from the iron is pumped with a fan. A convoluted smoke path channels the combustion up and back through several tiers made of more steel encased in concrete and the whole thing is encased with a floor to ceiling field stone. I also have two grids in the back of the stove which heat water that is thermosyphoned into storage tanks behind the stove and pumped though my floors. I have to heat a lot of space and burn a fair amount of wood but I quit feeding it at 7 pm and with outside temps in the teens we will still be right around 58 to 60F in the morning. You can’t have too much thermal mass. I have pictures of this thing somewhere here but couldn’t find them.


I like this one of Kirk Mobert’s for small spaces like a shop.


Hi ChrisKy,
You will need to lay out your square footage and a ground floor plan to get any good advices.
Let me explain.
We have lived for the past 27 years in a four cornered 30 foot by 40 foot ground floor 1200 square foot house. Seven semi-open plan rooms.
Before remodeling by us this had a central located wood stove and chimney. So would have had four cold corners no matter how hot fired.
Remodeling we re-located the woodstove into the coldest NW corner. No more cold corner there. We re-located the outside kitchen-mud entry door in the NE corner. Cold corner there doesn’t matter. The two bedrooms wanting to be cooler anyway at the remaining SE and SW corners.
Yeah, about 4,000 pounds of floors and walls thermal-mass in the wood stove corner. Needs 3X more at least for true overnight carry over. That old livingroom NW corner ceiling is 9 foot tall. Heat that room to 80-85F in the winter. Glass front woodstoves have radiating out throughout that room. Very cozy. The hot ceiling air flow settles down at ~75-72F into the dining room and kitchen. Then at ~72-68F thru the central small common hallway into bathroom; and two ways teeing off into the bedrooms at ~65F.
Return air flow is out of the children’s bedroom back into the living room.
Basically just like a spur-gear drive system. Only thermal flow.
Wife has aways though I could retrofit the kitchen to use her old antique kitchen wood stove. Hmmm. Not really. These need an open wall. A new modern insulated wood burning kitchen stove, sure.
And for sure for hard use summer food canning she’d need a third outside porch stove.
Either inside stove could then make domestic hot water.
For summer hot water a roof mounted heating system would make much, much more sense.
Fuel feeding and maintaining more than one woodburner gets odious.
Fuel wood sizing is a big factor too as Kristijan said.

Think of your true needs as seasonally LARGE. Shoulders seasons, Medium. And summer, small.
A small commuter car cannot haul the whole fam-damly, dog(s) and all.
Need a medium for that. And that medium sedan/SW/Ute/SUV cannot loads haul and tow like a true truck-truck. Need a true large truck for that. Commute it that!? Not long term.

Back to the square footage and floor plan . . . the new to us 2100 square foot retirement house has a centrally located wood stove mounted in at least 20,000-30,000 pounds of rock thermal mass . . . and that whole house with very good insulation through-out. It will easily overnight carry over good heat. But . . . two corners rooms go too cold all of the time. I have to use one Cadet wall heater and one portable oil electric heaters to moderate them to useable. Not ideal at all. Will be working on that.

Steve Unruh


Ha, glad to hear I’m not the only one :smile:

When it comes to long term convinient heating I would go hydronic, with at least a 500 gallon storage tank, including solar to have free hot tap water out of heating season. I use a 1000 gallon storage tank and if I don’t light a fire one day I can make up for it the next and still maintain 70F indoors at all times.

But, but - it depends. Outdoor boilers is not a thing over here. Ideally, in my opinion, if you already have brick chimney an indoor boiler is superior. You get the best out of two worlds - apart from the storage tank capacity - you get additional thermal mass in the chimney bricks, the boiler itself and piping. Heat losses that would otherwise only benfit the crows. Also, a super efficient boiler and a lot of insulation wouldn’t be as important.
But, but - I’ve learned you may have insurance issues across the pond when it comes to indoor boilers and indoor everything requires space. Also, I don’t remember if you have an existing chimney. If you decide to go for and outdoor boiler I would recommend to at least try fit the storage tank indoors.
A boiler setup requires a separate kitchen cocking stove though, but can then be simple. Early fall and late spring I find we often manage a chilly morning just by lighting a few sticks for the porridge and coffee pot - shortening the boiler season.


Anyplace that requires a building permit requires some sort of approved heating system, meaning forced air, hot water boiler or electric baseboard. once those bases are covered and you can usually have a permitted wood burning apparatus of some kind as long as it meets codes and is approved. Insurance companies often have a different point of view. Outdoor wood burners are usually allowed by insurance companies where wood stoves are not, but knowing several people who have them, not one would go that route again. Not nearly as efficient as advertised. Russian type masonry heaters are safe and extremely efficient but I imagine that do to their rarity here, most building departments would have trouble approving them and you would have to jump through a lot of hoops for a permit unless they could be convinced that it was just a fireplace. Then you would probably have to figure out how to get a triple wall flue into it somehow. Just speculation on my part.


Tom is right. Michigan Residential Building Code requires a heating system capable of maintaining 65 degrees F unattended before alternative attended heating systems can be approved.


tcholton717 and don_mannes are right. But, that being said, rocket mass heaters have ‘gone viral’ in this country. Supposedly you can diy build a home heating system in one day and with $50, if you really know what you are doing. There is a fierce ongoing debate where permaculture type people are pitted against building inspectors. Basically the inspectors will not approve any heating device that is not Underwriter Laboratories (UL) approved.
You can read about all this on the internet in very many places. I have read books called The Hand Sculpted House, and Rocket Mass Heaters. It always seems that they tell you NOT to tell any inspectors or code enforcement people.


There is a large and growing population in the US that are more and more inclined by the DAY to not tell any branch of government (federal, state or local) what they are doing at or in their home, their vehicle and more. Out of sight out of mind, just had a conversation with my dad the other day on how hard it is to even find a house for sale today that has a wood burning stove and his advise was buy the house that works for my needs and when the paper work is signed off cut a hole in the damn roof and put it in! Any permit or county law be damned, heat the house and keep the family inside warm or what is the purpose owning of owning the thing! I envy many other states that still embrace wood stoving where big mass wood burners are used to there maximum efficiency. As Steve has said before and from my experience growing up a wood stove makes a home. And damn do I miss it


I kind of agree, just put the durn thing in. But be durn carefull, house fires, carbon monoxide poisoning and other bad things happen. It’s my understanding that there are quite a few of those masonry stove builders up in Oregon, Ernie and Erica Wisner for example. I would try to team up with some of them.


Hi Chris, I really like masonry heaters but don’t forget that your house will already have several tonnes of mass in the slab, drywall and ceramics. Don’t be afraid to build a house that requires very little heat. Spend your money on the insulation and triple pane windows you won’t regret it at all. Code minimums are what builders convinced the governing bodies to water things down to not best practices. If you search up the “pretty good house” group they lay out the basics for a well insulated well sealed house. A high internal mass well insulated home would only need a simple wood stove and won’t cool down overnight. Our house went without power for 22 hours this winter and only lost 2 degrees Celsius with no heat. We did run radiant piping in the slab in case we want to add an outdoor or indoor wood boiler but at this point the heat pump heats the house wonderfully for not all that much. I do miss wood heat though.


It’s not so much hiding things from building departments. If you have a mortgage then your lender will require you have homeowners insurance and if you have a fire, even if it’s from some cause other than the heater, for instance an electric fire, your insurance company will still not cover it because you have a unapproved and unreported piece of equipment. Then the bank will sue you for the balance of what you owe them and you are in a deep pile of do-do.


Yes exactly TomH.
Best to appear to be conventional and in-compliance.
Expanded off the good Sovietism adaptation of, “They pretend to pay us - so we pretend to work.” They demand compliances, so I will give them a limited show.

I’ve learned to keep the main house somewhat “conventional”, and what can be seen and on-demand inspected; in more; versus less, compliances.
Now it is the out-buildings that I’ve learned to keep detached, space distanced, off-mortgage, off-homeowners insurances so then they can be all my own ideas and ideals. And I will fight them on this. And I will only comply with the taxman on these. They now use Drones. Counting and calculating the roof-tops square footages. Ha! If I had the soils, slopes, and drainage I’d be sorely tempted to go mostly underground on my outbuilding shop. Here PNW wetside that would draw in the Drugs cops, then.

Give her the house is a Great technique for keeping domestic peace too. Domestic harmony? Ohhh. Thats a no-talk subject, eh.


So, … After going through this whole train of thought in my mind several times, and now seeing it on this forum, I come to the conclusion that a solar furnace is the way to go whenever possible.


Only problem with the solar air heaters is how difficult it’s proven to get that absorbed quickly by the house mass to avoid over heating. The nice thing about using water as the transfer vehicle is you can store it easily and transfer it slowly to a slab or radiator.


They do the same fly over reconnoitering here Steve. They probably use drones now to. They fly over the whole county after the leaves drop and they make and place overlays on last years maps to see if anything has been added to a property. They should be so diligent with their other responsibilities.


I built a sort of combo masonry stove / outdoor boiler. There is probably 2000 lbs of concrete and for sure 4000 lbs of water (500 gallons). Depending on conditions, the water temperature continues to rise after the fire is burned out. The rest of the time, I do believe the masonry is still contributing heat to the water, though not dramatically obvious. Inside the house, we have installed a heat exchanger into the plenum. Yes it requires electricity to run the setup with pumps and blower, but quite minimal.


Chris i really like the concept of a masonary heater though the closest i have come to one is a Tarm wood gasification boiler. A few lessons i learned the hard way with that system. First the cold water in the jacket of the boiler makes it almost impossible to start. When the boiler temp was below 140F it would literally put out paper and cardboard. My solution was to use an on demand oil boiler to pre heat the tarm wood boiler.
It also had a bad drafting you have to be very careful to run the blower before opening the door or you can easily get a fireball of explosive gas my best friend made that mistake and luckly only lost his eyelashes to the flames.
There is a Russian wood gasification boiler design that i like the looks of much better.
That system uses a hot water radiator to pull the heat out of the boiler to a storage tank my Tarm had a 700 gallon tank and that would hold my house on baseboard for 12 hours in NH. With radiant floors you will get much lower operating temperatures and more heat storage in the same volume of water as you get about 40 degrees F of additional useable heat.
I have a farm house built in 1900 now on the farm and it has 2 chimneys that start in the basement and pass through 2 floors with 9 foot ceilings plus an attic. These chimneys are so long that i have a hard time establishing a good draft when it is above freezing. This makes me a little nervous about a mansonary heater i would definitely want to talk to someone who had run them about spring and fall when you don’t need alot of heat and the draft might be marginal. I know it was very easy to get smoke in the house with the Tarm wood boiler.
Honestly as much as i love wood the Tarm boilers are crazy expensive and i think all the brick or stone work for a masonary heater would also be too expensive for me to consider at the moment. There are incentives in the Inflation Reduction Act pass by Congress last year for both heat pumps and solar panels. I would look long and hard at a ground loop geothermal heat pump backed up with a thermalmass storage tank that is heated as an opportunity load off solar panels. I would back the entire system up with a generator powered by a wood gasification system probably easiest with a PTO driven generator and a wood gas tractor. That would take advantage of the tax credits for radiant heating and geothermal and or solar and it would allow you the safety of a wood gasification system to power and heat your entire home.
Those are my thoughts after spending many hours reading about it. I really do love wood heating and the concept of a masonary heater but i had some cold start and smoke issues with the Tarm and these long chimneys on normal wood stoves. Just enough to make me nervous i guess.
Oh i forgot to mention the biggest advantage to the 700 gallon thermal mass at my last house was that i had a coil in it for endless hot water from my wood or oil boilers. I would have to heat the tank about once a summer to get all my hot water it was insulated to R50 and built outside under my deck.


Dan, do your 1900 era long chimneys go straight up without kinks and bends in them and are they made with individual bricks without clay liners? I have remodled old houses with chimneys that I would be scared to hook a wood burner to.