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Hydro/Wind/Wood/Geothermal And other types of alternative energy

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Old 09-20-2014, 09:52 AM
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Default How much wood?

We want to start building on our 40 ac in WI next summer, so we're advancing from pipe dreams to serious plans.

We're going to go with an earth berm construction burrowed into the side of a hill. I want to go with an in-floor, circulating hot water system using a wood burning boiler. House sq footage in the range of 1800 +/- 200 sq ft.

Any ideas/experience with how much wood it'll take to keep us cozy from Oct - April each year?
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Old 09-20-2014, 11:56 AM
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We want to start building on our 40 ac in WI next summer, so we're advancing from pipe dreams to serious plans.

We're going to go with an earth berm construction burrowed into the side of a hill. I want to go with an in-floor, circulating hot water system using a wood burning boiler. House sq footage in the range of 1800 +/- 200 sq ft.

Any ideas/experience with how much wood it'll take to keep us cozy from Oct - April each year?
Congrats Doc on the plans.
I have never seen an earth berm house---but it should hold a temp fairly well.(No drafts)
I am going to say 6-8 cords?? Maybe less depending on how warm you want to stay?

A question? Will this system also heat water for you?
Its an idea?
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Old 09-20-2014, 02:29 PM
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I used to size residential HVAC systems many years ago. This was before computers and programs but had a work sheet that I used but don't have any more. But the general rule of thumb for a standard construction home was cubic feet x 5 to give the BTU's needed.

So at 1800 square feet x 8' ceilings to get your cubic area you have 14400 cubic feet. That times 5 gives you 72,000 BTU. That will help size your boiler. Of course being partly earthen construction would take less heat.

I wouldn't know how to figure the amount of wood needed. But if you look at some manufacturers sites, and look at their boilers in the 80,000 - 90,000 BTU range, they might have something showing the amount of wood used.
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Old 09-20-2014, 09:08 PM
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I think this is one of those questions that's impossible to answer accurately.

There are too many unknown variables

I imagine the dealers of those heating systems in your area can give you a better answer than most folks here

If the house is set in a hill, make sure your chimney is as high as you can get it, to keep smoke away from the house, and to prevent downdrafts
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Old 09-20-2014, 10:06 PM
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Here's a table that lists how many MBTU (million BTU) are contained in a cord of various species of wood.

You should expect some variability based on the efficiency of your wood burner, but I expect this will get you a reasonable first order approximation. If you read the method used to calculate these figures, it seems he's made some conservative assumptions.


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Old 09-21-2014, 09:27 AM
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Thanks for the reference, Cnynrat. Amazing the stuff you can find on line.

An underground house doesn't have to deal too much with loss of heat via convection (air leaks), but more loss of heat thru radiation- although it never has to equilibrate with outside temps <55*F essentially. I'm thinking it would take only half the fuel as a conventional construction, particularly since we're wasting less energy by heating the water instead of the air directly.

I ask the question because I have absolutely no clue how much wood it takes to heat a conventional house. I use a cord each winter here just in my fireplace. But it's terribly inefficient- the fools that originally installed it place the granite lentil blocking the top vent of the double walled fire box. Pretty stupid.
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Old 09-21-2014, 11:26 AM
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Just for reference sake - our house is 1325 sq ft. 1/2 of it is very old double board construction that is not insulated. The other 1/2 is an addition that is more conventional construction which is insulated. Full basement - all new windows and doors withing the past 8 years. We have a good older air tight wood stove which is located on the first floor at one end of the house in the newer section. We use just about 5 full cord per winter here in NW Penna. The stove will run constantly from about the middle of November through the end of March and about half the time a month before and after that.
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Old 09-21-2014, 09:30 PM
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Congrats Doc on the plans.
I have never seen an earth berm house---but it should hold a temp fairly well.(No drafts)
I am going to say 6-8 cords?? Maybe less depending on how warm you want to stay?

A question? Will this system also heat water for you?
Its an idea?
I read my question and it sounded kindof dumb.
What I should have ask--will you be able to use the heatd water for washing/bathing etc?

Sorry about that---I have never seen one of these systems work--look forward to your progress.
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Old 09-22-2014, 09:06 AM
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Thanks Coaltrain for the input. That gives me a ballpark figure to keep me interested. The advertisements say wood boilers reduce heating costs by more than 50%, and the in ground construction should reduce it by another 50%. So it shouldn't cost me anything then, right? In fact, if I go a step further and insulate it well, they should owe me money!

Anne- yes the water heating system can be integrated with the heating. When I was a kid and we heated with coal. There was a separate little boiler for hot water. We used scrap lumber in that one. When I was four, I decided I was adult enough to handle the hatchet and promptly took a chunk of my finger off. Fools learn from their mistakes, so by now I have a rather large knowledge base at my disposal, and still getting larger on a regular basis.
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Old 09-22-2014, 10:01 AM
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We have a really big house 4500sf and use a taylor outdoor water stove and in floor system. I use about 10 cords . Temps are usually around 0 to +5 at night
It's an old taylor and not the newer gasification models which use a lot less wood. If I had money I would replace with newer one like that. They are very efficient use a lot less wood.

Here's an example

http://www.centralboiler.com/e-classic.html

And the hearth forum has lots of good info.
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Old 09-22-2014, 11:43 AM
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You guys seem to use a lot more wood then me. Though I will admit my measurement system may not be as accurate as some of you.

My house is about 1300 square feet, with what I'd call just ok insulation. I use a 1970s Yotul stove with no blower. I place a fan behind it on the floor to help circulate the air. I also use cottonwood, which is a very poor firewood, but that's what we have. I do use some oak or hard elm for my overnight wood when I can get it.

Now to the measurement system. I know what a cord is suppose to be, 4x4x8. But I've always gone by the pickup load, which around here, and when I was in Arkansas, most people said a level pickup load of split wood was a 1/2 cord. Of course that's a full sized 8' bed on the pickup.

Here I haul all my wood up unsplit, and then split over the winter. But however it comes out I will probably haul up 6 heaping pickup loads of wood which will get me through the winter. And that is a short bed truck, not 8'. So in my case, 6 pickup loads should work out to about 3 cords of low end fast burning cottonwood.

Now I am guessing a bit here. In the past we cut for my house and my daughter and son in law's house. Their house is about 1800 sq ft. They used the wood heat to supplement their propane heat. We always tried to get 12 loads of wood, and that seemed to be enough. I'm kind of guessing I was using half of it. This winter I will know for sure because having my new barn means I now keep my wood at my place instead of all of it in their barn.
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Old 09-22-2014, 01:06 PM
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I think your calculations for your cord is pretty close. I get my firewood from a local guy now cut/split/delivered since I can't do it anymore. He also calls a level 8' pickup bed a 1/2 cord. I have a wood shed that I measured out to hold 3.5 cord so using that as a guide the pick-up rule is pretty close.

We have only hardwoods here - I wouldn't dare burn anything else due to creosote buildup and chimney fire danger. It is a mix of red oak, hard maple, and cherry. A lot of times the trees would have been standing dead for a few years - getting it cut/split/delivered in the spring seems to season it perfectly for use that following winter.

Just for an example - our wood is cut to 18" lengths and split 4 ways which gives a chunck about 8" on the long end. We will use 9 pieces for a whole day and another 3 pieces if we have to run the stove and feed it overnight. Most night we can leave it go out except for last winter when we ran it 24/7 most of January and February.

I estimate this to be about 4.5 cord:



And this being close to 6 cord:



Also there is a commercial outfit in the next town that sells firewood using a firewood processor. They have measured their wood to comply with the law - here is their list:

6' pick-up bed - 1/3 cord
8' pick-up bed - 1/2 cord
single axle dump truck - 2 cord
tri-axle dump truck - 5.5 cord

For all these it is measured as thrown in - not stacked.
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Old 09-22-2014, 04:52 PM
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I wish I could get more hardwood, I wouldn't have to cut so much since it would last much longer. Cottonwood won't give me a creosote problem, but it burns fast so you need more wood. Actually if you were having a fire in a fireplace just for atmosphere cottonwood would be great because it tends to give you plenty of flame and no popping or sparks. So basically it's good to look at, but not as good if you're trying to heat with it.

I figure between what's on my pallet in the barn and on my covered deck by the house I have 2 loads split. I stack my unsplit in another shed. Here I will have 3 rows of unsplit stacked 8' long and 6' high, which should be between 4 and 5 pickup loads.

My plan it to add to this come late November after deer season, as long as it hasn't snowed so much I can't get down to cut some more.
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Old 09-22-2014, 05:29 PM
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Back when we lived off grid we had 2 heating wood stoves and a wood fired cook stove. All our firewood came from our property that had been logged a few years before we bought the place - very convenient! All hardwood tops. I would skid the tops and limbs in with my tractor and cut them up near the wood shed - then stacked the rounds in there. I split the wood as I needed it over winter - gave some exercise using only a maul. The red oak, maple, and cheery split easily especially when frozen.
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Old 09-22-2014, 07:31 PM
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I wish I could get more hardwood, I wouldn't have to cut so much since it would last much longer. Cottonwood won't give me a creosote problem, but it burns fast so you need more wood. Actually if you were having a fire in a fireplace just for atmosphere cottonwood would be great because it tends to give you plenty of flame and no popping or sparks. So basically it's good to look at, but not as good if you're trying to heat with it.

I figure between what's on my pallet in the barn and on my covered deck by the house I have 2 loads split. I stack my unsplit in another shed. Here I will have 3 rows of unsplit stacked 8' long and 6' high, which should be between 4 and 5 pickup loads.

My plan it to add to this come late November after deer season, as long as it hasn't snowed so much I can't get down to cut some more.

All we got around here is oak and hickory . Green hickory is best for the taylor .
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Old 09-22-2014, 07:52 PM
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Seldom used cotton wood---cold smokey fire.

MoF--why green hickory?
You'd have to have a blowtorch to get it started here----
Just asking--never used green for my woodburner afraid of the creosote build up.
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Old 09-22-2014, 10:37 PM
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Seldom used cotton wood---cold smokey fire.

MoF--why green hickory?
You'd have to have a blowtorch to get it started here----
Just asking--never used green for my woodburner afraid of the creosote build up.
A taylor water stove operates based on forced air into fire box.
When water is at right temp the fan doesn't run. And flame die down to nothing but hot coals waiting for fan to blow air in when way temp goes down.

Season wood burns to quickly. Green hickory last longer than. Any wood I have found. I load it once in morning and once in evening
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Old 09-22-2014, 10:54 PM
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All we got around here is oak and hickory . Green hickory is best for the taylor .
When I lived in Arkansas back in the 70s I sold quite a bit of firewood over the winter. Everyone wanted Red Oak which there was plenty of, but they also all wanted green wood. Give somebody dead wood and they'd complain.

One winter we pruned back some big standard apple trees so there was quite a bit of wood there. Green apple was about as good as oak if not better, and sure smelled good.

Quote:
Seldom used cotton wood---cold smokey fire.
Actually Annie cottonwood can give you a hot fire. The reason is because it burns fast, which gives a hotter fire. Doesn't give you a decent bed of coals, but I suspect that's because it burns fast.

I like the fact it lights easily so it's easy to get a fire going. But I sure wish I had more oak for overnight wood so I had a decent bed of coals in the morning if I don't get up overnight to throw another log on the fire.
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Old 09-23-2014, 12:25 AM
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A taylor water stove operates based on forced air into fire box.
When water is at right temp the fan doesn't run. And flame die down to nothing but hot coals waiting for fan to blow air in when way temp goes down.

Season wood burns to quickly. Green hickory last longer than. Any wood I have found. I load it once in morning and once in evening
Is the stove you are talking about an outside wood boiler? They are quite popular around here - nice in that you can burn just about anything in them and not worry about a chimney fire. Your using green hard wood makes sense then especially with the forced draft.
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Old 09-23-2014, 12:48 AM
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Is the stove you are talking about an outside wood boiler? They are quite popular around here - nice in that you can burn just about anything in them and not worry about a chimney fire. Your using green hard wood makes sense then especially with the forced draft.
Yeah it is. It is about. 25 yards from the house.
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