! Are you interested in building a rocket mass heater? What is holding you back?

Glenn Herbert wrote:Erika, if you built a batchbox style RMH, you could have a window in the door for fire viewing. Do remember that an RMH, unlike a woodstove, will not be burning all day, but for an hour or two per day in most situations.

Isn't a batchbox style less efficient in fuel usage than a j-tube?

Judith, I believe Big AL was Allen Lumley.  
"For the good of the craft!"

Rico Loma wrote:Judith, I believe Big AL was Allen Lumley.  
"For the good of the craft!"

that was him!!!
and 'BOOM SQUISH' ?
he had such enthusiasm!

Hi Erika;
No, a J-Tube is not more efficient than a Batchbox.
In fact, it is the same efficiency, but a Batchbox burns hotter and for significantly longer.
They can heat a much larger mass.
They are also safer, with no openings directly into the fire.
A J-Tube and unsupervised children can lead to toys and other items being dropped into the fire.
Cats love heat, long bushy tails, and an open J-Tube could make things warmer than the kitty intended!

J-Tubes are excellent for sitting and enjoying the fire while adding wood every 30-45 minutes.
Batchboxes are for busy people who have things to do, including leaving for work all day.
Either choice is 100% better than using a metal box stove.

Once you heat with bricks (or cob), you will never have a metal box stove again.

M Ljin wrote:Non-permie family veto. Also worry about pipes freezing without a hot-air system.

I don't think anyone installing a RMH would remove the existing heating system(s). A RMH can simply be operated so that almost all of the heating comes from the efficient burning of wood. Any existing heating system can be left with the thermostat set around 40*F or whatever is suitable to prevent freezing in the absence of RMH operation...

A quick thanks to all who have participated so far on this thread. Sharing ideas, questions and concerns is what makes a public forum valuable.

It appears that the single biggest reason that contributors have mentioned as to the reason for not building an RMH is the concern for uninsurability of their home. For a new home build this becomes more of an issue when a building permit is closed and the local county creates the home profile for real estate tax purposes indicating that the primary heat source for the home is a wood stove. If this is the case for concern, when planning the build, having another source of heat that can be viewed by the local authorities and insurance companies as the primary heat source would get around this. It also provides a means of keeping the pipes from freezing if you will be away from home for multiple days. For existing construction with a different primary heat source, this is much less of an issue. I’ve never experienced an insurance company demanding to walk-through my home to see what is going on inside. So, this really becomes personal choice whether or not to allow a potential concern to drive your decision-making of what you do in your home. I can tell you that going on my 3rd heating season with my batch box design RMH (assuming the person follows the build design that many of us have adopted for a double-skin RHM with the guidance provided for a “proven design” as Peter van den Berg would say) a batch box RMH is safer than any metal box stove and as safe if not safer than any standard method of heating a home. Of course, this decision is one for each person to make, I’m not trying to tell you what to do.

It would appear that the next biggest reason is perhaps confusion over the various designs and their benefits/challenges in being able to compare them, leading to avoidance to proceed. My observation over the past few years of researching then building my own batch box is that you have to really invest time to read Permies Donkeys (Proboards) forum and any other resource you can find, and most importantly, ask lots of questions there are lots of great people ready to help you get started. Unfortunately, there is no single, easily accessible source that fully walks a newbie through the technology options, general nomenclature used, the benefits and use-cases of each and a general guide to building. So, the profile of a successful RMH builder is someone who is unafraid to tackle a somewhat complex project and construction skills that they may not currently possess.

Other reasons were also mentioned, including the existing home structure being insufficient to support the weight of a RMH and no reasonable alternate place to locate, like a basement. My goal with this thread is simply to get people talking to perhaps spark interest and ideas to incorporate this wonderful old world means of wood heat but doing so in a much more efficient manner. Keep the conversation going!

Glen, I think its extremely unwise to have a heat source in your home that insurance has not signed off on regardless of whether your home is new or an existing build.  Imagine John and Jane Doe install an RMH without telling their insurer and  have an electrical fire that destroys their house.  We both know the RMH had NOTHING to do with the electrical fire, but the insurance adjustor will come to once the fire is out and see they had a non approved heat source.  Insurers are just looking for a reason to invalidate a claim so they dont have to pay and the Does have given them one. They have lost their home and their means of rebuilding it despite having made their insurance premiums. Now imagine they  still have a mortgage they are stuck making mortgage payments  for the next 20 or so years for a house that does nt exist.  They are likely facing bankruptcy.  

I ask you is the risk worth the reward?

thomas rubino wrote:Hi Erika;
No, a J-Tube is not more efficient than a Batchbox.
In fact, it is the same efficiency, but a Batchbox burns hotter and for significantly longer.
They can heat a much larger mass.
They are also safer, with no openings directly into the fire.
A J-Tube and unsupervised children can lead to toys and other items being dropped into the fire.
Cats love heat, long bushy tails, and an open J-Tube could make things warmer than the kitty intended!

J-Tubes are excellent for sitting and enjoying the fire while adding wood every 30-45 minutes.
Batchboxes are for busy people who have things to do, including leaving for work all day.
Either choice is 100% better than using a metal box stove.

Once you heat with bricks (or cob), you will never have a metal box stove again.

That's good info.  Somehow I had it backwards in my head.  And I do have cats, so that's an important consideration.

I'm still a bit confused, what is a batchbox?

Mark Reed wrote:I'm still a bit confused, what is a batchbox?

Great question Mark. It is so easy for those who understand the terminology to just assume everyone is on the same page. The pictures will help to tell the story if you scroll up a few posts to the one from Thomas Rubino. He is showing both J-tube and batchbox versions of rocket mass heaters. The J-tube design has an open vertical wood feed tube that you place a few pieces of wood into the tube vertically and and the wood essentially burns from the bottom and drops into the tube as it burns. The batchbox utilizes a larger combustion chamber which you load a "batch" of wood filling the "box" (combustion chamber) and it burns the entire batch requiring no feeding or need to continuously tend. If I can find a picture of mine with a batch ready to fire up I'll post it to help tell the story. As Thomas mentioned in his post above, the J-tube will need your participation to continually feed it since the wood load is pretty small per burn whereas the batchbox can take a good load of wood, the door is closed and you can go about your business. There are further differences in the way that a batch box performs versus a j-tube but I'll stop there and wait for any follow-up questions. I hope this helps to answer your question.

Jeff Marchand wrote:Glen, I think its extremely unwise to have a heat source in your home that insurance has not signed off on regardless of whether your home is new or an existing build.

I respect your opinion Jeff and happy that you shared it. This really comes down to a personal choice. We are hyper focused on safety since we live hours away from the nearest hospital and emergency services in our area have a response time that is marginal at best. Regardless, our risk/reward assessment for our way of life highly favors the many benefits of a batch box RMH. For the population of folks who have a similar approach it is a fantastic way to heat. For those who see the risk as too high they should stick with whatever helps them feel safe.

Mark Reed wrote:I'm still a bit confused, what is a batchbox?

Mark, here is a batch box filled with wood. As you can see you don't use large logs and you fill the box fully. In this case, this is a follow-up 2nd burn with coals in the bottom that ignite the wood. Easy peasy...

A bit of health and limited finances.   Second limit is I am concentrating on solar first.  Beyond that I would actually like to do rockets in 4 buildings potentially.

1.  My house.  Passive solar mostly with some active active.  Since I started adding active solar, 3 of the last 5 years in northern WY at a bit over 4000 ft elevation I have run without heating the house at all.  But not at a temperature most people would consider acceptable.  Coldest ever the upstairs got down to 42 degrees for one day.(I was gone several days and didn't have time to light heater and it was 36 below out that day and really gray)  Mostly running just over 50 degrees.  And lighting the propane heater when it reaches 50.  My single biggest problem is how tight this house is.  To run the clothes drier something must be opened or it backdrafts either the heater or the water heater.  The house is extremely high mass so changing its temperature is a major undertaking.  Concern over air leaking in when heater off is another part.  Would need major dampers.  Guessing ideal would be J tube here.  Best would be done in the basement and bring the chimney up thru the floor where the current propane heater is located.  Exit would be thru a existing roof jack where the propane goes out now.  When the house was built planning for a wood stove as an option means all the piping going thru the roof is 10" properly UL listed stuff.  Just inside it necks down to 4" for the propane heater currently.  Other big problem is the destruction of storage space along that basement wall.  20 feet of super usable storage would have to be eliminated.  For the house have active solar with 33" x 154" worth of double pane glass.  Have 44" x 152" of double pane glass salvaged this last summer to add to that collector so I can more than double it.  Then on another part of the front wall I have 160"x 48" worth of glass for another collector for solar thermal air.  Also have 53"x58" double pane for a solar thermal hot water box on the goals too.  Till I get that much in and see where I am, I will continue to study rocket here with no action.  Hope is I can get the house so it gets to warm on sunny days in the winter.  Then use geothermal water with no heat pump to air condition the house and act as battery for any long runs of cold gray days.  But would still like the backup of a RMH.  Part of the future solar goals may help with ventilation though because I need a HRV system when on pure solar.  Propane stove dries the house out and never a problem but sealed tighted on pure solar have some moisture problems to solve.  Working on building an HRV core and that would probably solve air in for heater too.


2.  My shop.  Current heat is mostly solar with some coal stoker/wood.  Want to add a geothermal battery out the west wall and down the hill to hold the shop above freezing on it so the solar is starting from a warmer bottom base temperature.  Dream system would be all on solar beyond that.  Still thinking some heat would be need in quick bursts for a day or 2 at a time will be needed so more backup plan here.  Biggest hold up here is effort to clear the space.  Big pieces of steel etc in the way.  Rough guess about 6 ton of stuff to move off that wall and get stored elsewhere.  Probably 3 to 6 days effort just to make the hole in current storage space. Concrete floor and concrete block  wall to 8 foot high.  So stove itself would be simple.  Earth berm outside so getting to the back wall to go out through the 2x6 framed wall just about concrete height would be easy.  Best guess would be want a bigger batch box here with the pipe folded back on itself vertically up the wall.  While I have 40 feet of back wall even clearing 20 feet of it is work.  Other goal here possible would be a used oil burner stove.  From recent glass salvage got (6)  44" square double panes to add to solar thermal air on one end of the building and on the other corner of the building is a 51" wide area beside big doors and I got way more than I need of single pane windows in wood frames that just happen to be 51" so more solar there.

Have roughly 50 feet of 8" brand new stove pipe gathered.  4 barrels gathered.  Have great clay for dirt but would have to haul in sand for cobb.  So I am nibbling towards potential goals.

3.  Is the neighbors shop tool room.  Interior block wall with concrete floor and roof jack accessible at one end.  Still think RMH would be ideal for this location and I am still trying to talk him into it.  He belongs to the build a big fire and choke it to death thinking and convincing him that creosote is not a problem is so far a losing battle.  Likely to win this battle have to get one running to demonstrate.

4.  Want to gather enough material to do both a RMH and solar thermal air on one of the fair grounds buildings for Demo purposes.  The one building would be easy to implement both in.  And done properly wouldn't hardly affect any of that buildings uses.   Would be a matter of gathering enough materials, finding volunteers and talking the fair board into allowing it to happen.  Concrete block wall and floor with windows air paths in and out  and stove jacks could go thru.

Jeff, your post is on target.
Sure, we all have a choice to lie to a home insurance agent.  Some folks think that's a good game to play, but I can't do that. Financial suicide, in my opinion. Of course I believe an RMH is safer and better. However, my agent sticks with the company policy, and no discussion with me.  

Still working on a rocket water heater project, have already installed some pex lines inside, it's designed to lower wood burning in general.  
Will let y'all know how it works out

Rico Loma wrote:Jeff, your post is on target.
Sure, we all have a choice to lie to a home insurance agent.  Some folks think that's a good game to play, but I can't do that. Financial suicide, in my opinion. Of course I believe an RMH is safer and better. However, my agent sticks with the company policy, and no discussion with me.

I guess different areas have different approaches with writing insurance policies. I probably change insurance companies every 2 years so I can play their rate increase game and keep my premiums as low as possible. I have never had an insurance agent ask if I have any wood burners in the home or even anything about how I am heating my house. So, I've never made any deceptive statements about my property and to be very clear am not I recommending that anyone do so. If insurability of your home by adding an RMH is a concern than I'm all for reducing stress and just shelve the idea and find some other fun projects to pursue.

I would like to implement a RMH into an elevated yurt. The yurt is located on a hill with a slight grade and is held up by a wood reinforced platform. Parts of the yurt are nearly 2'-3' above the ground level.

I plan to make a thread about this with pictures and more details but I'd just like to know if this is even possible. I guess it would have to be on the exterior of the yurt to avoid the weight issue and also fire danger?

Any thoughts or links would be appreciated.

Hi Tyler;
What style of RMH were you thinking of building?
Weight is an issue, but it can be mitigated with some strategically placed pier blocks.
To protect your wooden floor, you lay clay bricks flat to support 1/2" of cement board, to build on. This removes heat issues from the wood, and it allows air to ventilate around the mass.

thomas rubino wrote:What style of RMH were you thinking of building?

Hey Thomas, I'm really just a newbie when it comes to RMHs. I understand the concept but I couldn't even tell you which type I have planned to build. Hopefully after I make a thread some of you can toss out some ideas.

Glenn that is good news, I'm glad you have so many companies to choose from. Another cool thing about NM!

Ga is so complicated with regulations,  a lot has to do with an astounding 159 counties here.  And we aren't a bigly state. So fiefdoms exist, and crony systems abound, and our state secretary rules over all that mess, including the insurance regulations.  Makes me laugh, just to keep from crying.
State offices often have bizarre powers, it seems to me, with other issues,  like voting rolls and power bills. Ga power customers were forced to pay IN ADVANCE for nuclear plants, very corrupt outcome for the common man...

"The Georgia reactors came online Monday — seven years late at a cost of $35 billion, more than double the initial $14 billion estimate. The United States just finished what could be its last big nuclear build"
.Apr 30, 2024"

Hence my move to stay with one insurer that is available, etc

All of the above that others have explained- insurance, fear of fire, fear of increased paperwork, cost to have built, staying up to code...

What I would need is to see someone near me go through the process or have someone mentor me through everything.  I am not a builder and don't understand them. I would need help with the paperwork part of things too, not just the building.  I foresee myself buying a more efficient wood stove in the next few years, and would love to do something more efficient.

I met someone who burned down a cabin with one.  I also met someone who had one in her beautiful round home and she told everyone how amazing it is.  So, I have heard good and bad reports on them over the years.  I would love to find something more efficient than a wood stove. I'm hoping to just build more of a hearth than is already around the stove for more even heating.

Hi Jolene,
You have plenty of good reasons to be hesitant about RMHs.
But I do want to mention your two examples: love at first light and OMG, I burned my cabin down.

All RMHs are homeowner-built.
Quality control is in the hands of the homeowner or their designated competent person performing the build.
In the early days of RMH development, when J-Tubes were the most well-known, there were a lot of funky builds happening.
J-Tubes are so simple to make that anyone could build one, but not all folks are created equal.
Some are so very much smarter than the innovators that they make... improvements...
Cruising YouTube showed many questionably "improved" builds that the builder was super proud of, and they would be posting follow-up photos and results for years to come...
And you never hear from them again, we started jokingly referring to these questionable builds as " Flaming Units Of Death."
However, then you have the folks who can follow directions as stated, and not make "improvements."
This is no doubt how the lady with the round house acquired hers.

Built to specifications, an RMH is safer than any box stove made.

If a cabin with a RMH burned down, somebody did something very wrong, which can happen with any heat source. A properly built RMH poses much less fire danger than any other kind of wood burner.

I love the idea of a rocket mass heater to use wildfire fuel thinnings and orchard prunings from my property for heating instead of over harvested and laborious or expensive to acquire hardwood. I also hate how any energy I might buy, including wood for heat, tends to come with paying people with environmental values and practices I oppose.

My reasons for not having built one yet are many. My wife is skeptical of it as a priority over other homestead projects that I am more qualified to undertake on my own. The one local person I know who has built one also has told me he doesn’t use his much anymore because in our mild climate (rarely below 25f, but cool and rainy from Nov-April) it tends to easily overheat his house for hours. He does have a cob house that holds a ton of heat and makes his alternate wood stove more efficient as well, but this did take some wind out of my RMH building sails. We also have a top of the line woodstove that came with our house (purchased 2020), and I think my wife would be much more inclined to let me build a hearth around it for thermal mass than to build an RMH. Even so, to do list will have to be cut down before I get to any such project. I should get to that now!

Ben Zumeta wrote:I love the idea of a rocket mass heater to use wildfire fuel thinnings and orchard prunings from my property for heating instead of over harvested and laborious or expensive to acquire hardwood. I also hate how any energy I might buy, including wood for heat, tends to come with paying people with environmental values and practices I oppose.

My reasons for not having built one yet are many. My wife is skeptical of it as a priority over other homestead projects that I am more qualified to undertake on my own. The one local person I know who has built one also has told me he doesn’t use his much anymore because in our mild climate (rarely below 25f, but cool and rainy from Nov-April) it tends to easily overheat his house for hours. He does have a cob house that holds a ton of heat and makes his alternate wood stove more efficient as well, but this did take some wind out of my RMH building sails. We also have a top of the line woodstove that came with our house (purchased 2020), and I think my wife would be much more inclined to let me build a hearth around it for thermal mass than to build an RMH. Even so, to do list will have to be cut down before I get to any such project. I should get to that now!

I'm sure I'm not the first one to think about this but it just dawned on me that there should be fairly simple ways to turn RMHs into Assbackward Turbo Mass Coolers in hot times of the year? Anyone doing work with this yet?

I think where I live it could be as simple as pulling air backward and out the door inside with a small fan overnight. I imagine that eliminating condensation damage would be the main concern.

Les Frijo wrote:I'm sure I'm not the first one to think about this but it just dawned on me that there should be fairly simple ways to turn RMHs into Assbackward Turbo Mass Coolers in hot times of the year? Anyone doing work with this yet?

I think where I live it could be as simple as pulling air backward and out the door inside with a small fan overnight. I imagine that eliminating condensation damage would be the main concern.

They are doing this at Wheaton Labs--it was in the Low Tech Things movie. I forgot how it worked but I believe they just opened the windows at night and it worked that way.

M Ljin wrote:

Les Frijo wrote:I'm sure I'm not the first one to think about this but it just dawned on me that there should be fairly simple ways to turn RMHs into Assbackward Turbo Mass Coolers in hot times of the year? Anyone doing work with this yet?

I think where I live it could be as simple as pulling air backward and out the door inside with a small fan overnight. I imagine that eliminating condensation damage would be the main concern.

They are doing this at Wheaton Labs--it was in the Low Tech Things movie. I forgot how it worked but I believe they just opened the windows at night and it worked that way.

Oh yes. Even more simple. Probably a combination of both would double the cooling of the mass being cooled from Inside and outside.

I'd love to build one and try it out. Still looking for the place to do it. The longer I wait the better they seem to get too. Thank you scientists!

Hey Les;
You can forget the "Turbo" portion, but it sounds good though.
Yes, they will stay cool in a dark, insulated space.
Let the sun shine on them for an hour, and they are no longer cool.
If the room they are in is poorly insulated and it's 90°F+ outside, your mass isn't going to help.

If you have a source of nice cool air and blow it into your mass, it may provide some cooling.
Depending on the humidity levels where you live, a swamp cooler will provide better cooling.
RMHs heat. ( Rocket Mass Heater)
RMCs (Rocket Mass Coolers) have not been innovated yet...
We encourage experimentation, start a thread and toss some ideas out.

Thanks Thomas,
The sun effect is a good thing to remember no matter heater or cooler.

Here where I am in the northern midwest United States of America, it is usually too humid when it's too hot. Swamp coolers can't be relied on. It's pretty much expensive air conditioning or whatever cooling you can get with windows open overnight. Possibly making it even more humid inside and never getting near as cool as outside.

Any system here would have to have some sort of cooling coil and condensation trap to be really helpful but if you didn't open windows at times of high humidity it might be pretty good at keeping the place cool and less humid. Maybe offset some of the mass of the hot house itself if pulling air inside the mass.

I'll try and wrap my head around some stuff and start another thread. Back to the Rocket Mass Heaters!

Thanks.

If you are in a mild climate, you really don't want a big high-mass heater. A small heater with minimal mass around it would be optimal. If you already have a modern relatively efficient wood stove, it probably doesn't make sense to scrap that and build a new RMH. I would do as you suggested and add a bunch of masonry around but not touching the existing stove.

Ben Zumeta wrote:... We also have a top of the line woodstove that came with our house (purchased 2020), and I think my wife would be much more inclined to let me build a hearth around it for thermal mass than to build an RMH. Even so, to do list will have to be cut down before I get to any such project. I should get to that now!

Thermal mass inside your insulation envelope can go a long way to evening out the "too hot" followed by "too cold" issue with woodstoves. We have "decorative" bricks (as opposed to structural) around our basement wood stove, but the concrete slab it's on has no insulation and it really shows.

I believe if one is building an RMH, there are ways to insulate under it?

We're hoping to build a "Masonry Heater" in my son's planned home. It will be as close to a Rocket Mass Heater as we can get, although we do want at least basic water boiling, soup making capacity integral as well, but here "Masonry Heater" is an accepted term, whereas "Rocket" will scare the volunteer fire department.

Glenn Herbert wrote:If you are in a mild climate, you really don't want a big high-mass heater. A small heater with minimal mass around it would be optimal. If you already have a modern relatively efficient wood stove, it probably doesn't make sense to scrap that and build a new RMH. I would do as you suggested and add a bunch of masonry around but not touching the existing stove.

Thanks for the confirmation. I do try to always burn a hot, clean burning fire based on what I have learned largely on this forum about RMHs. Particularly, I try to create thermosiphons of oxygen rich air over hot coals and get the chimney and stove to the high end of safe (450-600f) before throttling airflow. Doing with more thermal mass would be much better. Any ideas on conveying the wood stove heat to thermal mass more effectively?

Les Frijo wrote:
I'm sure I'm not the first one to think about this but it just dawned on me that there should be fairly simple ways to turn RMHs into Assbackward Turbo Mass Coolers in hot times of the year? Anyone doing work with this yet?

I think where I live it could be as simple as pulling air backward and out the door inside with a small fan overnight. I imagine that eliminating condensation damage would be the main concern.

It might be worthwhile to read John Hait's 1982 book 'Passive Annual Heat Storage'  to consider the speed at which heat travels through mass exposed to airflow, and the actual mass required to store any appreciable amount of heat/cool, as well as the methods of storage and retrieval.

Tommy Bolin wrote:

Les Frijo wrote:
I'm sure I'm not the first one to think about this but it just dawned on me that there should be fairly simple ways to turn RMHs into Assbackward Turbo Mass Coolers in hot times of the year? Anyone doing work with this yet?

I think where I live it could be as simple as pulling air backward and out the door inside with a small fan overnight. I imagine that eliminating condensation damage would be the main concern.

It might be worthwhile to read John Hait's 1982 book 'Passive Annual Heat Storage'  to consider the speed at which heat travels through mass exposed to airflow, and the actual mass required to store any appreciable amount of heat/cool, as well as the methods of storage and retrieval.

Hi Tommy, Thank you for the recommendation. Sounds like just what I'm looking for.

I found it right away and hope it's ok to post the link here...

https://archive.org/details/passive-annual-heat-storage-improving-the-design-of-earth-shelters-john-hait

YES I am interested, since 2017. Thought we would be building one in 2020/2021.
Here are some things holding us back:

. Status of our house build. It has taken years longer than anticipated.

. Not sure whether we will need it for heating our house more than a couple times a year, and if that is the case we would rather invest the time and money to build an outdoor RMH instead of one for our house. We are building an earthship-inspired tire bale home, and other folks who have similar houses have said that they only use their wood stove a couple times a year. Our house currently does get cold enough to need heat, but we will be enclosing the “porch” (like the greenhouse part of an earthship) and that will be our main winter heater, and we won’t really know what we are dealing with for temperature control until that is in.

. Building on permit — we want to get our occupancy permit as soon as possible (after living in a tiny pop up camper for 6 years), so we will be getting occupancy before glazing the porch//greenhouse. We also don’t want to battle for permitting the stove, and plan to put it in after having occupancy.

. Like many others, we are unsure about how to do it. I am just starting up my deep dig into RMH after 3-4 years of focusing elsewhere. One advantage we have over others with this hesitation is that over the last 6 years we have done so much other stuff that we had no idea how to do. My hub and I are both pretty handy with conventional building but little about our house is conventional. Through the years of this build, I find that we fret about the next mysterious unknown part of the build while executing the current tasks. It has caused a decent amount of our delay in getting this house done, because even though we are pretty confident by nature, we mull each new thing around and plan it one way, then another way, learn everything we can from others’ experiences, try to find someone local with experience to help, usually fail and have to do it ourselves, then find that once we get into it it really isn’t that bad. I am guessing this will be the case with RMH.

. Our delays have helped us in many ways. There are several parts of the house that I can look back on with relief that we didn’t do it the way we first thought of. If our house hadn’t been so delayed, we would have conventional septic. Our delays in building gave me the time to go round & round with the regulators until, by the time we were ready to plumb our septic, we had an approved permit for vermiculture septic, perhaps the first permit in the country. I think this delay has also helped us with RMH thinking. In 2017-2020 I was planning on a J-tube and bench between our sleeping and living areas. My hub was resistant because he loves fire and wants to see the fire. Now I think a batch box & bell would work so much better for our situation and location, and I hadn’t stumbled upon any of that info last time I was looking into it. I think we can make a wide tall bell that can make up much of the wall between those areas, and we can build the rest of the wall around it. And we can have our beautiful viewable fire.

So now we are in the mode of finishing up to get our occupancy permit (main hurdle: building the waterproof sloped shower floor on top of our road base underfloor to finalize our plumbing permit — the next thing that we have no experience in). We are probably at least a year and maybe more like 2 from building our RMH (if we decide we need one in our home), which is the perfect time to start diving in to research and planning for real, and the mulling-around phase of RMH thinking.

Right now we heat our construction space with a 30,000 btu propane unvented heater with controls 1-5, usually set at 1-2.5. That is with the house insulated and closed up, but without our greenhouse “furnace”. I think if we do build an RMH a 6” will suffice, even though using the calcs I found on one of the guru websites (don’t remember which at the moment) say we need a 9” based on external minimum temps. Our house performs really well with 6’ thick walls, and we are in NM with huge diurnal temp swings, so even though it can get down to 0F at the coldest, it isn’t often below freezing for a high.

Kimi! Great to learn more about y'all and the challenges you have worked through.  We are pleased to know that shower is perhaps your last piece of the plumbing puzzle.  
Your land in NM looks lovely, and it's a great choice for an innovative house.   You are indeed living in The Land of Enchantment

Life can be hard and cruel
Yet gracious
And the struggle is beautiful

When I moved to this farmstead in 2007 with 100 yr old brick house I was eager for a 'Kachel Ofen', masonry heater, as I has seen in Germany. But the mass likely was about 2 ton on a floor with crawl space under. Not easy to reinforce. That stopped me. question #1. btw, I'm 72.
Now reading here over Xmas holidays 2025 I see options. I would replace a woodburning stove "Bakers Choice" (cost C$3500 new today). I bought that stove planning on using for cooking/canning but rarely do. It throws a nice radiant heat but uses 150 cu ft wood a year. Wood here in ON costs C$300/50 cf picked up.

#2 Space to heat is 340 sf main room/kitchen 10ft ceilings. Total area on floor is 1460 ft connected by 5 ft wide hall. will main room be too hot?
I have NG furnace in basement, oversized, set at 15dC in winter  (60dF)Would likely keep, tho prefer to swap out for heat pump. Have 10Kw solar array with 20kwh battery.

#3 how much weight can 2x12" roughcut joists on 2 ft centers under wood floor carry? Masonry foundation walls are within 5 ft on two sides and 2 ft on other. Weight of stove on footprint 4x5ft (likely Shorty style)? Is only crawl space under that part of house so not easy to reinforce with posts. Wall behind current stove and RMH site is 8ft btw door openings.

Question #4 stopping me is how to heat the rooms not adjacent to mainroom, ie 3 bedrooms 270 sf and living room 240 sf? All have one exterior walls brick/plaster lathe construction.

#5 replacing cookstove with RMH means losing backup cooking appliance if lose power, How to build with a cooktop/oven/hot watertank?

Ian
I feel your pain when it comes to  the crawlspace issue. Our 105 year old house was free when we bought this land, as it had so many signs of age and neglect,repairs 90 % complete,  and the hardest were those involving spelunking.   With some ingenuity, you can still make this possible. Last year I helped a buddy cut through his wooden floor to install steel reinforced support, then rebuild the space, then build a jtube and bench design.  He never had to crawl

Others here are experts, not me, I would just say please research and find one rmh that works for you in the wilds of Ontario.  I am most impressed with Uncle Mud designs and building that specifically helps any homeowner-builders , tailoring to the site and climate.  Check his work.  

Do not despair, even the humble j tube
can be used for cooking and warming.  On the upscale side, please peruse the stoves of Matt Walker, two amazing folks here have documented builds with his designs, Burra Mallaca and Tony ullje.  Read those threads for effectiveness and aesthetics built into the project. If memory serves many of his are batch box style, better for Ontario winters.  
Predicting great success for your project!

Sorry, I should have typed
Tony Uljee
He built a large rmh in Ireland that is truly a work of art, well documented here on permies

I second Rico's comment about crawlspace access. Code even says that a masonry heater needs to be supported directly by masonry piers or foundation and not wood, so there is that to consider. Cutting out flooring to give easy access to build up from a crawlspace floor makes sense - you won't be wanting a wood floor under the heater in any case.

Heating rooms distant from the heater location could be tricky, and we can only advise usefully with a floor plan of some sort and/or good pictures.