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

In another thread, there were people who cast doubts on how little wood it would take to heat a three bedroom montana home.  

Frankly, I'm getting kinda sick of proving shit.  If nothing else, I have proven a lot of things, and the people that demand proof suddenly go quiet.  You would think they would have the decency to say "I am impressed - and I was wrong" - but they never say anything.  I wonder if they work for big oil or something.

At the same time, what can I say ... I am compelled to perpetually do experiments.  

So, this year's experiment is to see how much wood, exactly, do we use over a winter in the fisher price house.   A standard issue double wide with a pebble style rocket mass heater in it.  

I think a pebble style rocket mass heater is about 20% less efficient than a cob style rocket mass heater.   But pebble style has other perks.    People tend to not sit on this rocket mass heater - which is, by far, the most efficient form of heat.  But that's okay.  We'll get information about how warm the house is without that.   Further, this rocket mass heater has given up other forms of efficiency for the sake of being a bit more .... gilligan resilent.

The real deal ...  

We have some shelves near the door where we store some wood.  In the past it seems like we re-filled it about six or seven times in a winter.  See the attached pic.  For this experiment, we are going to use just the two rows of shelves shown.   There are seven full size "cells" and two half size "cells."   Using wood that is 15 inches long, a full size cell holds 1.5 cubic feet.  When this whole thing is full, that is 12 cubic feet.  There are 128 cubic feet in a cord.  

It was packed full yesterday morning.   Yesterday afternoon we ran the first fire for many days.  I think we ran a fire for about an hour and a half.   We were going to run it longer, but we forgot.   You can see how much wood we used.   We woke up this morning and the house is quite warm.   It got below freezing last night.  It is still below freezing right now.   Inside, the temperature is about 66 and I am thinking about starting a fire.  It is supposed to get to 55 today - and when it does, I suspect that the interior temperature will rise to 72 because the mass is still putting out heat.

In another thread, I said that we heated this house with about half a cord of wood.  But we didn't carefully measure it.  I thought we reloaded the firewood rack/shelf about six or seven times.  If it was six times that would be 72 cubic feet.  0.56 cords of wood.  

We currently don't have any insulative curtains or window quilts.   Maybe we should get some of those to make this a fair test.  

What kind of wood? Does it make a difference?

It can make a huge difference.

https://chimneysweeponline.com/howood.htm

We will be using pine, fir and larch.  They have much lower BTU per cord than, say, osage organge or hickory.  We are planting locust, oak and mulberry - but it will be a long time until we can use that.

I heat with wood and yes, the type of wood is critical. But I wonder... if you don't take into account the time/cost/impact to harvest, BTU per unit should not matter since BTU is related also to weight. IOW, it takes a hardwood a lot longer to grow and it stores more carbon. A pine grows super fast. So in terms of ecological impact of the actual burn as opposed to harvest, is it really about BTUs?

I too love doing things that people say you cannot, go Paul!

How many sq ft is the house? I'm not familiar with trailer construction... is it standard 2x4 construction with fiberglass bats for insulation?

Sounds reasonable to me since I already did it.  DW and I built up above Clancy, MT in 1982.  Built passive solar with attached greenhouse with a Jotul stove at the lowest level.  The half cord per year we burned was often slab wood with lots of bark.

There are many ways.

Why not build a house that can be heated largely with the heat supplied by occupants, cooking, doing laundry, ... ?

Eric Bee wrote:... IOW, it takes a hardwood a lot longer to grow and it stores more carbon. ...

That's not QUITE true.
hardwood has a particular cell structure
some hardwoods grow faster than softwoods
some hardwoods a lighter than softwoods

As an extreme example, BALSA is a hardwood
https://en.wikipedia.org/wiki/Ochroma

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.

For the last week or so, temps have been almost always below freezing.  Right now it is 15 degrees F outside.  Based on yesterday's forecast for today I thought I would wake up and it would be -2.   The hourly forecast says that we will hit -2 in a few hours.  

I did the longest burn of the winter yesterday.   I had been neglecting the house temperature all winter and when I would build fires, I would tend to forget to keep the fire going when we would get up to 70 or so.  Yesterday I was determined to get the indoor temp up to 75, but I kept forgetting and the fire would go out.  So I technically had three fires yesterday.  I think that during the time that I was awake, there was a fire about as much time as there was not.  When I went to bed the fire had been out for a couple of hours and the house temp was 72 - the highest I had seen all day.  I woke up this morning and it is currently 68.

So this is about how much wood we use to get through the winter.  If you look at the "firewood rack" in the first post, you will see two shelves full of firewood.  I think we have burned that much.  Maybe a little more.  So,  let's say 14 cubic feet.  0.11 cords of wood so far this winter.

Jocelyn has been carefully tracking our wood use, so she will have the exact numbers.  

I have ideas about how to improve the efficiency of this.   I am tempted to open it up next summer and make something closer to a stratification chamber.  

8 inch system CSA:   50.24
6 inch system CSA:   28.26
this system woodfeed CSA:  32.66

So the system we are running is probably closer to a 6 inch system than an 8 inch system.

Jocelyn sent me the official count:   0.167 cords of wood used so far this winter.

And this has been with keeping the house "comfortable".  We've had it over 75 for a few burns.   Morning temp is usually around 67.   We've had some days where it didn't get above freezing and rather than having a fire every other day, there was one time when I let two days pass (just out of laziness) and when I got up in the morning it was 59!   59 is probably a pretty normal morning temperature for conventional wood stoves (maybe even a lot lower than that) but I'm rooting for something more comfortable.  I guess I want to finish this year's experiment and say "we burned one tenth the wood and we were more comfortable too."

It is 74 degrees in here now.  This is just way too warm for wintertime.  I'm shutting down the fire.  It didn't get below zero this morning. Apparently it is currently 14 degrees.  It is supposed to dip below zero tomorrow morning.

The extended forecast says we won't go above freezing in the next nine days and beyond.

So after that last post, we didn't have any more fires in the rocket mass heater.  So the last fire was yesterday at 10am and the house was at about 74 degrees.  

Got up this morning around 6 and it is 9 degrees outside and 62 inside.

Just a curiosity of mine (and I think you have probably been asked this many times already), but, why do you have the outside of the mass sided with wood? After all, it is insulative and seems like it would tend to restrict the transfer of heat from the mass to the house somewhat. Which leads me to a question I have been pondering regarding my RMS. I come home from work and build a fire. This is about 3AM. I go to bed about 5-ish and have a fire going. By the time I get up, the fire is out of course, but I keep wondering if there is anything I can do to prevent so much heat loss from going out the stove pipe with the air that is going out through it it after the fire has gone out. Other than waking up and covering the hole, because if I wake up I am going to throw more wood on, not plug the opening. Anyone have any suggestions on how to reduce the heat loss out the stove pipe once the fire has gone out?

andy careaga wrote:Just a curiosity of mine (and I think you have probably been asked this many times already), but, why do you have the outside of the mass sided with wood?

This is a pebble style rocket mass heater.   There are holes along the bottom and just under the granite top.  It works a little different from a cob style.

I keep wondering if there is anything I can do to prevent so much heat loss from going out the stove pipe

Is this a rocket mass heater we are talking about?

I think Andy is trying to deal with the mass drafting heat up the stack after the fire is out.
The standard solution is covering the air intake,but he wants to avoid getting up at night to do this.

So, maybe a spring loaded or weighted flap over the air intake. Or a plug that goes over the end of the fuel,getting lower as it does.
If you can get a good idea of when the fire burns out,it could be a timed device.
There is an argument that says, if we are going to spend resources automating draft control ,why not automate fueling instead? An auger for fuel pellets,or wood chips, or a   oil dropper.

paul wheaton wrote:It can make a huge difference.


We will be using pine, fir and larch.  They have much lower BTU per cord than, say, osage organge or hickory.  We are planting locust, oak and mulberry - but it will be a long time until we can use that.

Hey Paul, long time fan of permies.com by the way, I don't find time to comment as much as I'd like ( just had to get that off my chest). I was wondering, and I'm sure you've considered it, what you think of coppiced wood growing systems for fuel? Coppice meaning heavy pruning varieties that regrow from the trunk. It seems more appropriate for RMH due to the higher burn temps (higher surface area), faster usable fuel crop, less processing involved, etc. I imagine you could fit quite a bit more 1-2" diameter sticks into those "cells" than those split logs. Also I believe you can coppice locust, oak and mulberry. Please let me know what you think.

Side note; Thanks for being so frequent in updating such experiments, many of these topics I'm very interested in.

Along the lines of coppicing fuel. Anybody have any thoughts on coppiced mountain alder. I burned it in my RMH the other day and it seemed to burn well and it grows fast! Great pebble stove by the way Paul, keep pushing the efficiency on people and maybe one day they will get it.

Brian McCune wrote: what you think of coppiced wood growing systems for fuel?

Daniel Ray wrote:Along the lines of coppicing fuel. Anybody have any thoughts on coppiced mountain alder.

Brian and Daniel, I found a recent thread that may work better for your questions. The "energy crops" forum in general is a good place to search and see if anyone has considered alder in your region.

https://permies.com/t/53988/Fuel-wood-whats-grow

Along the lines of coppicing fuel. Anybody have any thoughts on coppiced mountain alder. I burned it in my RMH the other day and it seemed to burn well and it grows fast!  

I think It should be pointe out that fuel wood for a RMH is the inverse of what is used for a box heater. The main reason hard woods are prefered is they burn slower with less volatiles making high flames and produce more radiant heat from the burning carbon.
RMH on the other hand is burning volatiles and storing the flame heat in the mass to be radiated later. Therefor the ideal fuel for RMH is high in volatiles and low in ash and high non volatizing carbon is undesirable. Observing the burn characteristics of wood I have available The popular which is considered undesirable because it burns so hot and fast should be best for RMH and it leaves very little ash.  The certified stove i am using right now has secondary draft tubes under the smoke shelf to burn the wood smoke. For it to work properly I need to operate it with light weight volatile wood with high flames until the secondary air tubes and smoke shelf is hot enough for secondary combustion.
I can load it up with hard wood for a longer burn after it is up to temperature but I have noticed that when active flames stop the smoke shelf cools down and secondary combustion is not complete the smell of unburned hydrocarbons is much stronger when I go up the hill to get more wood.
So I think the wood Paul is burning in this experiment is probably close to ideal for RMH and ideal for his availability

I know that this kind of complaint is a bit late, but a better metric for judging the heat energy of firewood is by seasoned weight.  Hardwood or soft, the available btu's per pound are almost identical, whereas the btu's by volume vary significantly by species of wood, by stacking method, and by the growth conditions of the tree during it's first 20-30 years.  Personally, I don't doubt at all that a RMH can heat a home on a fifth of the wood compared to a pre-EPA cert woodstove; because my post EPA woodstove can come pretty close, and the calculations that I have run with "available btus" per pound of wood should make this possible.  The operating efficiency of older woodstoves aren't the only problem that contributes to needing greater amounts of wood.  In my own experiences, even a very efficient (if not as efficient as a rocket mass heater) EPA cert woodstove has trouble meeting the tested efficiency percentages because they often produce too much heat for a smaller space, resulting in an over-heated wife opening the kitchen door for relief.  Those woodstoves are most efficient near their max BTU/hour output, basically roaring, and a "low smolder" is very bad; both for efficiency & air quality.  I've sort-of solved this problem with my own house, by using an old-fashioned trick of building tight bundles of sticks tied together with twine.  I use less poundage, but have enough combustible surface area to sustain a hot, efficient burn; that is reduced to loose charcoals in about a half-hour or less.  The mass of the steel woodstove does get hot to the touch, but not as hot as a full, or even half full, load of cordwood.  I use this trick during the cool nights of spring & fall without driving my wife out of the house.  On warmer (but still cold) winter days (I live in Kentucky, a temperate winter zone, so this might not work for you); I might do this trick twice, once in the early morning to knock off the chill, and again as the sun sets.  

This old fashioned trick has a name that is now considered a hateful thing to say to a homosexual, so I won't repeat that here.

Thank you for the data. I will have to think on this some more I reckon.

Here's another question I have been pondering. When I first built this RMH, the research I did led me to think that a 7"x7" firebox/tunnel would be a good idea since I had 8" dia stove pipe from the previous wood stove. I have been wondering lately if I would have been better off building a 6"x6" firebox, that maybe it would provide a better long term burn using a smaller amount of wood. Anyone have any thoughts on this? Maybe other benefits to using a smaller firebox I am unaware of?

I stopped burning yesterday morning.  

Outside temp is about 10.  Inside temp this morning is 63.  

For a while I was sitting on the couch and putting my bare feet against the wood of the rmh to feel the lovely warmth.

I made bread last night.   After kneading, I put the dough in a bowl and set it on the warm bricks of the closed off wood feed.   Massive rise in about 40 minutes.

Garrett is here as part of the bootcamp.   I had him start the fire the last few days.  

Wood use continues to be hardly anything and the house is kept plenty warm.

what you think of coppiced wood growing systems for fuel?

For it.  Planted seeds.  Probably a great topic for another thread.

Daniel Ray wrote:Great pebble stove by the way Paul, keep pushing the efficiency on people and maybe one day they will get it.

Keep pushing it ....    

It turns out that my pushing it isn't doing much.  We kinda need a thousand people.  Or a 200 million dollar advertising campaign.   I spent a fair bit of yesterday being so psychotically angry in this space I was starting to see weird colors.   I keep seeing messages like "hey everybody, global warming is real, we gotta buy those light bulbs"  or "I'm going to standing rock to protest" ...     and it's as if all this work and all of the internet never existed.  

Sisyphus never got the rock to the top.

Creighton Samuiels wrote:a better metric for judging the heat energy of firewood is by seasoned weight.

Perhaps what you meant to say is "I think a better metric for judging the heat energy of firewood is by seasoned weight."

I have a different position.  Since I am doing the work, I am choosing to follow the universal standard format for measuring firewood:  the cord.  

because my post EPA woodstove

I think your post is not so much about this experiment as you would like to discuss the stove you have - which would be best in a different thread.

andy careaga wrote:Here's another question I have been pondering. When I first built this RMH, the research I did led me to think that a 7"x7" firebox/tunnel would be a good idea since I had 8" dia stove pipe from the previous wood stove. I have been wondering lately if I would have been better off building a 6"x6" firebox, that maybe it would provide a better long term burn using a smaller amount of wood. Anyone have any thoughts on this? Maybe other benefits to using a smaller firebox I am unaware of?

Have you seen DVD 2 and 3 of the new 4-DVD set?   That covers all the stories of this rmh.

I think the choice of an 8-inch system vs. 6-inch system would depend on the materials you will use for the core and the size of the space you wish to heat.

paul wheaton wrote:

Creighton Samuiels wrote:a better metric for judging the heat energy of firewood is by seasoned weight.

Perhaps what you meant to say is "I think a better metric for judging the heat energy of firewood is by seasoned weight."

I have a different position.  Since I am doing the work, I am choosing to follow the universal standard format for measuring firewood:  the cord.  

because my post EPA woodstove

I think your post is not so much about this experiment as you would like to discuss the stove you have - which would be best in a different thread.

Fair enough. This is your forum, after all.  Still interested in your data regardless, since it will be more rigorous than anything I might have.  Now returning to keeping my mouth shut mode in 3....2....1....

Paul, you say at the beginning of this thread that you are "... getting kinda sick of proving shit".  I, for one, don't think you will prove anything by measuring the volume of wood you are burning. Measuring and comparing the weight  of wood burnt would be only the only reasonable comparison given what we all know about the amount of energy contained in a given weight of wood/as opposed to volume.  Saying that as you are the one who is  "doing the work, I am choosing to follow the universal standard format for measuring firewood:  the cord"   contributes nothing to the discussion, or your own credibility. The cord is indeed a universal measurement of wood for when it is sold, but not as a measure of its calorific value - this is usually reflected in the price that is paid per cord.

Paul, so what are the characteristics of the house you are heating? How many rooms, square footage, construction type? I am using mine in a  7-room ranch style house, not counting the 2 bathrooms and my rocket mass heater can get it toasty enough that the furnace does not turn on but I doubt I am anywhere near matching the amount of wood you are using... or not using depending on your perspective. That is just going by the amount you said you used from the picture of the shelf. I think you are keeping your place a shade cooler than I do mine, when I am home anyway. And then I am confident there is quite a bit of energy lost out the chimney from the air flowing through it. And this RMH is my first effort also. I think one could characterize it as "generic" compared to one made by a person that gets to build them more frequently but it still makes me happy! It beats the tar out of the 4-5 cord woodstove that it replaced.

Steve Boyd wrote:Paul, you say at the beginning of this thread that you are "... getting kinda sick of proving shit".  I, for one, don't think you will prove anything by measuring the volume of wood you are burning. Measuring and comparing the weight  of wood burnt would be only the only reasonable comparison given what we all know about the amount of energy contained in a given weight of wood/as opposed to volume.  Saying that as you are the one who is  "doing the work, I am choosing to follow the universal standard format for measuring firewood:  the cord"   contributes nothing to the discussion, or your own credibility. The cord is indeed a universal measurement of wood for when it is sold, but not as a measure of its calorific value - this is usually reflected in the price that is paid per cord.

I disagree.  "How many cords of wood do you bur?" is a very common question when people talk stoves.  Yes we can get into technical discussions if we want but the common person relates more to the cord.  In my opinion of course.

Keep up the good work Paul

Steve Boyd wrote: contributes nothing to the discussion, or your own credibility.

Perfect!  Then you do the test the way you think it should be done.  

andy careaga wrote:Paul, so what are the characteristics of the house you are heating? How many rooms, square footage, construction type?

We call this "the fisher price house".  It is a standard, 3-bedroom double-wide.  Small.

I am confident there is quite a bit of energy lost out the chimney from the air flowing through it.

I have been thinking a lot about the amount of exhaust of a batch box system that is burning far more wood at one time, but is using an 8-inch exhaust.   I wonder if this system, with its teeny tiny wood feed might be more efficient with a 4 inch exhaust pipe.  

I've also been thinking a lot about some sort of strategy for a stratification chamber.

M Johnson wrote:

Steve Boyd wrote:Paul, you say at the beginning of this thread that you are "... getting kinda sick of proving shit".  I, for one, don't think you will prove anything by measuring the volume of wood you are burning. Measuring and comparing the weight  of wood burnt would be only the only reasonable comparison given what we all know about the amount of energy contained in a given weight of wood/as opposed to volume.  Saying that as you are the one who is  "doing the work, I am choosing to follow the universal standard format for measuring firewood:  the cord"   contributes nothing to the discussion, or your own credibility. The cord is indeed a universal measurement of wood for when it is sold, but not as a measure of its calorific value - this is usually reflected in the price that is paid per cord.

I disagree.  "How many cords of wood do you bur?" is a very common question when people talk stoves.  Yes we can get into technical discussions if we want but the common person relates more to the cord.  In my opinion of course.

Keep up the good work Paul

Thanks M.  

There are certainly multiple audiences.   But I think the audience I am most trying to reach are the people that are currently considering heating with wood.  They make their decisions based on how mush wood they would bring in or buy.  And that wood is measured by the cord.

paul wheaton wrote:
I have a different position.  Since I am doing the work, I am choosing to follow the universal standard format for measuring firewood:  the cord.  

I saw this sentence and my first thought was that it was more than fair that you measured the efficiency of your stove by how much wood you had to cut for it. Especially for the homesteaders who grow and cut their own wood, the volume measurement of wood makes sense. They might not pull out a scale to  measure each log, but they'll remember each tree they cut or each wheelbarrow full of wood they split.

Casie Becker wrote:... more than fair that you measured the efficiency of your stove by how much wood you had to cut for it. Especially for the homesteaders who grow and cut their own wood

Exactly.   When people talk about wood heat, they talk about cords of wood.  

As for weight - I think knowing the weight is of little value unless you are regularly measuring moisture content and how punky the wood is.  

---

On a related note, we are burning through a LOT of wood this week.   But this has been a pretty cold week for our winters.  Lows of about 14 and highs of about 22.  Most of the winter will see high temps getting over freezing.

Steve Boyd wrote:Paul, you say at the beginning of this thread that you are "... getting kinda sick of proving shit".  I, for one, don't think you will prove anything by measuring the volume of wood you are burning. Measuring and comparing the weight  of wood burnt would be only the only reasonable comparison given what we all know about the amount of energy contained in a given weight of wood/as opposed to volume.  Saying that as you are the one who is  "doing the work, I am choosing to follow the universal standard format for measuring firewood:  the cord"   contributes nothing to the discussion, or your own credibility. The cord is indeed a universal measurement of wood for when it is sold, but not as a measure of its calorific value - this is usually reflected in the price that is paid per cord.

I think every single log should be thoroughly analyzed, weighed, it's caloric content should be measure by taking random core samples which should be UL tested, in a lab, by scientists.  

Then, and only then, can we truly know if there's a difference between burning 5 cords of wood, or 1/4 of a cord.  I mean, you never know.  That 1/4 of a cord could be really dense, high energy wood.



BTW, I think he will absolutely, positively, 100% prove something by showing the massive reduction in volume of wood burned over a season with a rocket stove as compared to a wood stove.  Just not to those pigheaded individuals who wish to challenge anything and everything...