heat a montana home all winter with a half cord of wood

Paul, I am incredibly impressed! I live in Big Sky, Montana. Pretty cold here and we have 4000 sg ft(trying to downsize)and it takes us @ 3 cords to get through the winter. We have radiant heat as backup run by propane but if we keep a fire going all the time we use very little propane. I sell Montana farms and ranches for a living so my travel is our downfall. Girls don't keep the fire going all the time.

My experience with poplar in a conventional wood cookstove with a masonry chimney, is an enormous amount of creosote, even after a year of uncovered seasoning outdoors, so I avoid it completely.  I'm curious as to how a RMH works with poplar.  Is there a build up of creosote?

S. G. Botsford wrote:
I don't see a half cord as being impossible.  I'm in Alberta near Edmonton.  We have a similar climate to the plains area of Montana -- what Montana gains by being south of us, they lose due to higher elevation.  We run a heating season of about 10,000 degree F days per year.

We have a 2500 square foot house that is mostly heated with a moderate efficiency (80%) airtight steel stove, and a low efficiency century old cast iron wood/coal range.  (we do not burn coal in it.)  We burn about 3 cords a year.  


Paul is gaining a factor of 2 in efficiency by using a rocket mass heater. Montana isn't as dark as Alberta in the winter.  Longer winter days give him another, what 20-30%.

Wood energy is directly proportional to dry weight.  Hardwoods tend to be denser than softwoods, but larch or tamarack is more dense than poplar.  Spruce and poplar is about the same.

Drying time is important.  I now have covered storage for 16 cords.  I figure 4 cords a year, but usually don't burn that much unless it is a bitter winter.  

I burn mostly poplar.  Not a lot of heat per cord, compared to other hardwoods, but it's fast to cut and fast to split.

Buzz Tatom wrote:Paul, I am incredibly impressed! I live in Big Sky, Montana. Pretty cold here and we have 4000 sg ft(trying to downsize)and it takes us @ 3 cords to get through the winter. We have radiant heat as backup run by propane but if we keep a fire going all the time we use very little propane. I sell Montana farms and ranches for a living so my travel is our downfall. Girls don't keep the fire going all the time.

I think what you just said is that you have a conventional wood stove, and you use it to cut propane costs.   So, if you heated exclusively off of wood, you might be more in the 10 cord range?

Don Dufresne wrote:  I'm curious as to how a RMH works with poplar.  Is there a build up of creosote?

Rocket mass heaters don't have creosote.  A rocket mass heater tries to create a "chimney fire" every burn.  The chimney (or "heat riser") looks spotlessly clean every inspection.

I’ve noticed in these threads that sometimes people talk past each other, without really understanding (or wanting to understand) where a person is coming from. Sometimes we have a paradigm (world view) and mode of thinking that puts our heads into a box, and we tend to have no desire to lift the lid and look outside at the surrounding world.

This issue is compounded by the printed forum structure, where rational people can’t just sit around in a room, with favorite drink in hand, feet propped up beside the RMH, look each other in the face, and rationally discuss the issues at hand. The forum structure is also susceptible to drive-by shootings, by the types of people mentioned above.

In addition, “people don’t always say what they mean, or mean what they say.” (I learned this in a sales class, once upon a time.)

Before providing my thoughts, and attempting to shed some light on a few of the RMH posts, let me first disqualify myself. That way, paradigm deficient people who read this far, can just move on. There’s nothing to see here.  

I am a complete newbie to RMH’s. I have Paul’s DVD set, and I follow some of the threads in order to acquire knowledge and build my database for future use. I also like to see what issues people are struggling with as they get into these projects. I currently do not have a way to begin an RMH project, because I live in a small apartment inside a medium size city. My biggest challenge at the moment is to find a way to relocate, while remaining gainfully employed, to my parcel of land located a long way from here.

Frankly, I'm getting kinda sick of proving shit.

Amen, Paul! I have been in that situation a lot of times in life, especially while working inside large cubicle farms (i.e., large companies), with a lot of cubicle rats running around trying to partake of the master’s scraps.

Paul is addressing, as he said, a particular target audience. These are the people, maybe like me at this point in time, who are just wanting to make some rough practical decisions, and then get on with the job at hand. Should I invest time and money into constructing an RMH? What are the benefits of an RMH over other possibilities? Roughly speaking, how much wood can I save? How much less wood do I have to cut? Roughly speaking, is it best to use one type of wood over another? If I do things differently, what are my expected results? And, so forth.

These people do not need to get into an anal situation of having “paralysis over analysis.” They are not asking Ivory Tower questions that need an f’ing PhD egg head to answer. And they damn sure don’t need UL tested bullshit.

Paul has done an excellent job of building, experimenting, and testing this stuff. He knows more about this shit than just about anyone. So, when he speaks, one should listen very carefully, before needlessly flapping one’s jaw.

Then we have the scientist/engineer personality types who enter the picture (Steve Boyd, M Johnson, and Creighton Samuiels), throwing fancy terms around, and it appears they are throwing a little cold water onto the discussion.

Quickly, before I get chastised, I must explain myself here. I am an engineer. I’ve spent a career crunching numbers. I take high level theory and creatively boil it down to practical use, to create products for customers. Unfortunately, as far as RMH's go, I am not a heat transfer or thermodynamics type engineer.

However, I understand what the scientist/engineer mindset is, and how these guys are thinking. I can read what these guys say, and have a good chuckle over it. Sometimes, I can sense they are saying some things in a “tongue in cheek” fashion. That’s because I come out of a background where lots of these types of goobers (like me) hang out. Other people, who don’t understand where they’re coming from, might tend to get offended.

So, we all need to calm down, sit around the RMH, drink a tall one, or maybe have a shot of whiskey (or two), and sing Kum bah yah.

It turns out that BOTH Paul AND these guys mentioned above are correct, as far as what each is trying to accomplish.

Paul has clearly stated what he is trying to accomplish. His work could easily be published in the popular press. However, it might not be so easily published in a scientific or engineering journal.

The reason is that he might not have, scientifically speaking, gained enough control over the variables that go into the experiment (e.g., wood type, density, moisture content, volume vs. weight, type of construction, materials, dimensions, etc., etc., ad nausea). Thus, from a strictly science viewpoint, there would be a “risk” of comparing apples to oranges, when interpreting between test results.

However, a thinking engineer/scientist type, would look at his “high level” results, and see such huge differences in the outcomes, that he or she would say “further testing and research is definitely warranted” from a scientific viewpoint.

As a matter of fact, Paul’s (and others) comparative results are so large, the average person should not waist time getting bogged down in arguments over scientific minutia (unless that is your hobby). Just get on with it, ignore these finer discussion points, and just build the damn RMH. You have enough evidence, based on Paul (and others) work to safely proceed forward. You will learn what works best for you, under your particular circumstances, and you can learn, experiment, and make adjustments over time.

If you want to measure in terms of “cords of wood” versus “weight density” or some other narrowly defined term, that’s fine. At the level you’re working at, any refinement would just get lost in the noise.

On the other hand, if someone is thinking of starting a business to sell RMHs, and/or looking at the engineering science behind the construction of RMHs to guide engineers on developing new features and types of RMHs BEFORE they are actually constructed, then you will eventually be dragged into a more scientific way to do development and testing. You will need to objectively account for all variables and unknowns, clearly state your “engineering assumptions,” and speak to each other in a funny language. You will be concerned with the types of questions/comments that Boyd, et. al., are making in these posts.

Both points of view (practical vs. scientific, high level vs. a-hole analytical) are valid! So, let’s not get our collective panties in a wad.

Both points of view will, in the long run, get to the same result (at least as far as most of the practical questions being asked in the posts).

However, Paul, et. al., are going to get there sooner.

Science and engineering can then come in and provide the missing details.

Hope I don't regret putting out an opinion on this topic but.... so let's say a person lives in the northwest. he typically buys a cord of wood found locally and generally it is consistent to other cords that person may buy over time, with respect to type, density, and volume, hence, general weight. In my area, my wood pile has looked pretty much the same for years now. Same wood types, same densities, same in about all respects. I would venture to say that is the case for about everywhere in the world. I would expect the same logic to hold true in Montana.

So it matters little if you buy wood that is very dense and I buy wood that is less dense. If I conduct a test using my wood compared to wood I previously used, likely it will provide a valid test. If I wanted to compare it to wood another person in a different locale has, it might not weigh the same. So as long as Paul is using his wood and comparing it to his wood, his testing is valid. If he wants to compare his results to wood found in another region, the results may differ. BUT, the basis for this test is that Paul has stated he wants to see if he can get through a Montana winter on X amount of "his" wood, not compare the results to somebody else's wood. Trying to alter the basis for Paul's test is outside the parameter's that Paul has set for his test.

Just sayin...

paul, dont worry bout them always someone wanting you/me to prove. wish i could see[im blind] how it works sounds like you save on heating thats whats they afraid of.                                                                                     russs2

Thanks, Paul.  That's always been a question for me.  Pretty amazing.

paul wheaton wrote:

Don Dufresne wrote:  I'm curious as to how a RMH works with poplar.  Is there a build up of creosote?

Rocket mass heaters don't have creosote.  A rocket mass heater tries to create a "chimney fire" every burn.  The chimney (or "heat riser") looks spotlessly clean every inspection.

Our temps have not gotten above freezing for quite a while.   The forecast for the next ten days is nothing above freezing - in fact, some lows below zero.

Went to bed last night and the temperature inside was 70 and this morning it was 65.

If you look at our firewood rack in the first post, you will see seven full cells and two half cells.  We filled it six days ago (tuesday) and we are now down to three full cells.  So during this cold time, we have been burning about one full cell per day of wood.   Using one full cell per day, we would go through a half cord of wood in 42.7 days.  

Only watched the filling of it since the whole pebble idea was intriguing and more accessible for me and only happened upon it from a YouTube search.

Thank you for the link.

This discussion has broken my silence from simply reading posts, for over a year now, to actually saying something.

For the last seven days, we used 5.75 cells.  That is 8.625 cubic feet.  At this rate, a half cord of wood would last 7.4 weeks at temperatures that don't get above freezing.  Since we do see a lot of days with above freezing temps, we should be able to stretch that quite a bit.

The forecast says that friday will get to about -14.

The average temperatures for missoula:

month	high	low
november	42	25
december	31	17
january	33	18
february	39	21
march	50	28

So we are currently going through the coldest part of the montana winter.  I'm not sure if we will end up with less than half a cord for the winter, but it looks safe to bet that it will be less than a cord.  

And I think that if we put drapes on the windows and optimized the rocket mass heater a bit we could get well below a half cord.

Paul, I'm super impressed. Having lived most of my adult life heating houses with wood, I find it amazing that a rmh is doing such a good job on wood consumption as compared to a standard wood stove.

And I think that if we put drapes on the windows and optimized the rocket mass heater a bit we could get well below a half cord.

Maybe radiant drapes like mylar emergency blankets. They do also also work to reflect the heat out in the summer. With a radiant mass heater it is the radiant heat that needs to be preserved. If it feals cold on the side facing the window but warm on the back you need a radiant shield to bounce the heat back.

I think an enclosed porch for the front door would probably help a lot too.

We had a bit of a fire in the morning yesterday.   Not all that much, really.

Outdoor temp this morning around 10 or 11.  Indoor temp of 64.

To show everyone the efficiency of our yesterday finished RMH, i decided to collect all ashes over the winter, because people here in Portugal fetch shovels of ashes out of theur chimneys each week.

Today will be the big test.  

It is about 15 outside right now.  It was 62 inside this morning.   It is supposed to get below zero tonight at 6pm and keep dropping until it gets to -15 tomorrow morning.

Last night when it was zero outside, it was way too warm inside.  The thermometer said it was 74, but it felt much warmer.  So we shut the fire down.

This morning it is 65 inside and -10 outside.

I'm enjoying seeing how this works out.  If I may ask, and you may have mentioned it earlier and I missed it, how many square feet and how well insulated is the house you are heating?

I have no idea how well insulated it is.  Standard double-wide el-cheapo-lame-o insulation I expect.

I think we have speculated in the past that this place is about 1400 square feet.  Maybe a little less.

I'm not sure how variable your winters are on a year to year basis, for temperature, but here we had two winters in a row that were exceptionally mild (part of the oceanic Super El Nino that happened), but this year... it has been colder than the past few years.  Temps as low as -24F for several days, and -10 F for more than a week on either side of it.  

The reason that I say that, is that if your part of Montana has great variability year to year, than you might be able to heat this winter with a less than a cord, but a milder winter with less than half, and on a really extreme winter just over a cord.  Regardless, the proof is that the RMH is massively more efficient than a conventional stove.  

Also, without getting too involved in the contention earlier in the thread, around here when someone is buying a cord of wood, or saying that they burn say '3 cords a winter', it is almost always part of the conversation as to whether this is pine (killed by bugs, and thus dried and seasoned already in the bush), or birch, or fir, or poplar, or balsam, or alder... or whatever, and, if it was not dead wood, then how it was seasoned.  A cord of seasoned birch (or doug fir) goes for a much higher price than a cord of pine or a cord of dry dead poplar, not only because it is not as common or easy to get, but because it is denser, and burns longer, and because the seller should be spending time curing it and drying it.  A cord is not a cord.  A cord of birch is not the same as a cord of pine or a cord of doug fir by weight or BTU's or by any performance in a woodstove or RMH, and at least around here the conversation would involve that knowledge.  It might not be what you wanted the thread to be about, but I don't think that the people were trying to create controversy, or deserve to be slammed for bringing up a different angle of observing that part of the experiment.  

I'm glad that you are running this experiment and doing it in a not very efficient space.  It proves a lot, just in and of itself... but if you enclose your porch, put insulated curtains, add more mass near your RMH barrel, build your stratification area, then your experiment will have to start completely fresh, as any of those will change your experiment greatly... or not...  The stated 'heat a Montana home all winter on a half cord of wood' still holds true.     Great work, Paul!

paul wheaton wrote:I have no idea how well insulated it is.  Standard double-wide el-cheapo-lame-o insulation I expect.

I think we have speculated in the past that this place is about 1400 square feet.  Maybe a little less.

Thanks Paul.  This additional info gives more meat to the experiment for me.  

Next season put a wood stove in there and see how MUCH wood you CAN burn! In the name of science! Jk don't do it, feeble attempt at humor😀 keep up the good work

It is ten below outside right now.

Last night i went to bed and it was 69 in the house and the fire had been out for a couple of hours.  This morning I got up and felt it was a bit chilly, but got a bunch of things done and .... checked the thermometer ...  60!  That's way too cold!   Now that I think about it I do feel rather chilled!

I thought I would come here and write a note before building a fire.  

Hi Jocelyn, how is the experiment coming along? Any update on how much wood has been used since mid-December?

Jocelyn told me two days ago that we are at 0.38 cords so far.

Paul, I was curious to more exact sizing of your pebble bench and pebble sizing. I am sorry if I somehow missed these details, I was considering doing pebble bench or bell masonry and I'm trying to figure cost difference. It seems it's easier as far as flue hookups for a mass duct vs a bell. But maybe you have some more input? If you could build another in a similar environment do you think you'd make another pebble bench or would you try a bell?

Jon McLain wrote:Paul, I was curious to more exact sizing of your pebble bench and pebble sizing. I am sorry if I somehow missed these details, I was considering doing pebble bench or bell masonry and I'm trying to figure cost difference. It seems it's easier as far as flue hookups for a mass duct vs a bell. But maybe you have some more input? If you could build another in a similar environment do you think you'd make another pebble bench or would you try a bell?

Jon,

I think your question would be best in a thread all its own.  Although details about this rocket mass heater might be best in this thread:  https://permies.com/t/48515/pebble-style-rmh-fisher-price

It has been a very cold winter.   High temps during the day rarely get above freezing.   A LOT of days with lows below freezing.  

We are now at 0.50 cords of wood.  

(source)

We are past the average coldest part of winter.  December and January are our coldest months.  I suspect that at about mid march we won't need to heat anymore.  Three and a half months down, including the two coldest months, and one and a half months to go, and no coldest months.

This morning the temperature was zero.   The forecast for the next week shows a lot of days with temperatures above freezing.

Maybe we can finish this winter at about 0.6 cords of wood.

At this moment, we are at 0.56 cords of wood for the winter.  

paul wheaton wrote:At this moment, we are at 0.56 cords of wood for the winter.  

I have burned more than that, and I have a propane furnace as well as a woodstove, and I live about 10 degrees or so closer to the equator than you do.

paul wheaton wrote:At this moment, we are at 0.56 cords of wood for the winter.  

We did burn one more fire since that point.  One load into the wood feed is about 1/8th of a cubby which is   0.1875 cubic feet or 0.00146 cords.

The bottom line is that we are still at 0.56 cords of wood for the winter.   And we haven't had a fire in a week.   A lot of that is because we have more people staying here and more cooking.  

I think there is a good chance that we are done for the winter.  So maybe that's it.  



0.56 cords of wood for the winter



I think we can get that down to 0.25 cords of wood if we do the following:

- curtains and window quilts and really good stuff to really insulate those windows when it is dark outside

- put in an enclosed porch on the front door.  So there is less cod air exchange happening when people come and go.  

- switch the stainless barrel on the rocket mass heater for mild steel.  

- add some stratification chambers to the mass so it isn't such a straight shot outside.

- reduce the size of the roof exhaust from 8 inches to 4 inches so when there is not a fire, there is less heat escaping at that point

- improve general lighting:  incandescent light much closer to where people spend time

- reduce the use of the bathroom fans and the kitchen fan.  Replace that use with air cleaners and dehumidifiers.

- make more lap blankets available at chairs and couches.

- put in a few dog bed heaters with rugs at the foot of couches and chairs.  

- allow lower temps in the house if that is what people are comfortable with.  Hopefully, the lighting and dog bed heaters make people think the house is too warm at 65.


Here are a few things we did toward the end of the experiment that I think made enough of a difference that we should do it earlier on the next time:

- We started this test with three or four windows open about a quarter of an inch.   In fact, we didn't really notice it until some of the rooms were uncomfortably cold when it got below zero outside and we figured it out.  Then the windows had ice on them and were quite frozen.  So we had to wait until it warmed up enough that we could close the windows all the way.  

-  We started off with one of those heat activated fans on top of the barrel.  Later I grabbed a second one from the office and put it up there too.  In january I put a box fan on the mass and ran it at its lowest setting whenever i was running a fire.  I felt like that harvested more heat that might have been going out the roof.  

- we started using a dehumidifier.  We dry our clothes on clothes racks instead of in the dryer for lots of reasons.  This plus cooking added a lot of humidity to the air.  When combined with the cooler temperatures and trying to run bathroom/kitchen fans less often the dehumidifer did a lot to reduce or eliminated molds.  

- around january we made an effort to use bathroom fans and the kitchen fan less often to keep heat in more.  

- fill the cubbies a bit tighter with wood near the end.   At first, the cubbies were packed with bigger wood with gaps at the top.   Toward the end, we would fill the gaps with stuff closer to kindling.  When you measure a cord of wood, you don't have the cubbies forcing big air gaps in, so the cubbies system skewed the numbers about 10% in the beginning.   Toward the end, we were packing the cubbies tighter which is probably closer to the truth of it all.



I think that if we started doing some of the smarter things at the beginning of the test that we ended up doing at the end of the test, we would have finished with about 0.4 cords of wood.  

I think it is fair to say that for this year we comfortably heated a 3 bedroom montana home with a rocket mass heater with a half cord of wood.  Not only is "0.56" close enough to simply call it a half cord, but if our improvements at the end of the test were done at the beginning, we would have easily come in at less than a half cord.

Here is a video summary: