Is burning wood for heat carbon neutral?

[allhandsworking]

[quote author="btuser" date="1307075733"]I'd have to say no. A lot of wood is just going to rot in place, therefor release the carbon anyway so look at it that way. Wood fermenting in a forest stew will produce methane which is a lot worse than CO2.[/quote
That's right and burning that local wood is displacing the fossil fuel that would have been burned! Most wood burners use standing dead, fallen, or trimmed timber that would have rotted or been transported to a land fill.

 

[allhandsworking]

Sorry redundant.

 

[tom in maine]

Interesting thread.
Burning wood is one hell of a lot more carbon neutral than any fossil fuel.

Here in Maine, in-growth per acre per year is about 1/2-1 cord.
It is not anywhere near as efficient as a solar thermal collector but it still is solar heat and it is what I consider the
"current" carbon cycle. It is not carbon that was sequestered millions of years ago that when released is going to contribute to
global warming.

As long as it is burned in something efficient and is produced in a sustainable way, it is a way station
for us as we transition to solar and/or zero energy buildings.

I will burn wood or pellets rather than fossil fuels anywhere I can.
It is not perfect, just better.

 

[Seasoned Oak]

The main problem I see with wood is not the emissions from the burning, which may well be the same as if the tree had died and then rotted, but the fact that once the tree is down, it is often hauled longish distances and then burned.

That is where I reckon the carbon emissions kick in ;-)

A lot of times it's not though. I just had a cord of oak dropped off that was cut less than a mile from my house. This years pine, is from the house across the street, last years was from the house next door to it, and next years is from the house on the other side. All of this wood was headed to the dump if I didn't take it. They are all trees which were cut down anyway, not cut for firewood. The only still standing trees I cut are already dead.

ditto on the re-purposed pine, 2/3 s on the wood i burn would have gone to the landfill. Oak floorboards ,floor joists,,wall studs,lathe boards ,most 100 years old or so.

 

[Dune]

Interesting thread.
Burning wood is one hell of a lot more carbon neutral than any fossil fuel.

Here in Maine, in-growth per acre per year is about 1/2-1 cord.
It is not anywhere near as efficient as a solar thermal collector but it still is solar heat and it is what I consider the
"current" carbon cycle. It is not carbon that was sequestered millions of years ago that when released is going to contribute to
global warming.

As long as it is burned in something efficient and is produced in a sustainable way, it is a way station
for us as we transition to solar and/or zero energy buildings.

I will burn wood or pellets rather than fossil fuels anywhere I can.
It is not perfect, just better.

Thanks.

 

[GaryGary]

if one can grow as much wood as one uses in a year, then the heat is carbon neutral. Insulation and stove efficiency can help make this happen. By using solar to supplement the wood heat, or wood to supplement solar heat. These new passive solar haus would be easy to heat with less than acre of wood lot, one 8 inch tree a year would do it. If you grew fast growing hybrid popular it would be interesting to see how much land would be needed compared to btus.

Well said.

And, an interesting question -- Just as a rough guess on the question:

The ref listed below says 5 tons of poplar per acre in the Ukraine (I'm sure we can do better

Taking a 2000 sqft house in a 6000 heating degree day climate (cold), and with R60 ceilings and floors, R30 walls, R4 windows, and 0.3 ACH infiltration, the yearly heat demand is about 39 million BTU, and of this about 17 million is met by internal heat gains (lights, bodies, dogs, ...) leaving 22 million BTU to be met with heating fuel. It could be less than this if some passive solar was used in the house design, but say no solar. Not sure that this home would meet Passive House Institute standards, but its a good efficient home.
http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

Could not find a value for heating value of poplar, but aspen is listed as 27 lbs/cf, 2290 lbs per cord, 14.7 million BTU/cord.
So, with an 80% efficient wood burner, it would take (22/14.7)/0.8 = 1.87 cords, or (1.87)(2290) = 4280 lbs of poplar(aspen) to heat the house.

With the 5 tons of poplar per acre, this would be less than half an acre -- as a very rough estimate.

Seems like a good strategy for a pretty close to zero net carbon home.

Gary


From: http://www.hemphasis.net/Paper/paper_files/hempvtree.htm
"In Ukraine, poplar wood grown for pulp produces 5.1 tons/acre/yr, and dry stems of hemp produce 3.24-4.05 tons/acre/yr. This is 4-5 times more than indigenous forests in Ukraine, and approaches the increment of the most productive plantations of fast growing poplars. The Ukrainian Institute of Bast Crops expects hemp to yield an average of 5 ton/acre of dry stems. The cost of transporting hemp pulp, dispersed over larger territories than wood, removal of the ash content, and the lower pulp yield compared to wood pulp make non-wood pulp more expensive. However, the Ukrainian Institute compared the labor costs of growing and harvesting hemp and poplars in 1992 and found the costs were comparable. "

Heating value for woods: http://www.builditsolar.com/References/woodhvrs.htm

That was fascinating for me to read through and I think that I understand almost all of it except the 6000 degree day climate. Can you elaborate and explain the math to that figure and also "convert" that to what temperature this 2000 sqft house would be at during the day? Thanks.

Hi,
Sorry I missed your post -- better late than never

Heating Degree Days are a way of accumulating the heating load over a time period like a whole heating season.
Basically if the average outside temperature for a day is 10F lower than than the inside temperature, then that is 10 heating degree days accumulated.
To getting the total heating degree days for the whole season, you just add up each day's heating degree days.
So, when it says a 6000 Heating Degree Day (HDD) season, it means that the adding up all the daily HDDs for the whole season gives you a total of 6000 Heating Degree Days. Here in Bozeman our season is about 8100 HDD.

The seasonal HDD's are published for hundreds of locations -- some sources here:
http://www.builditsolar.com/References/Calculators/InsulUpgrd/HDDhelp.htm
There is a little more to it than explained above, but is covered at the link.

To turn HDD into how much heat a house will use, you have to know the heat loss of the house.

First start with just the hourly heat loss through an example wall:
If you have an R15 wall that is 100 sqft, and its 20F outside and 70F inside, then the heat loss per hour is:

HL = A * (Tin -Tout)/Rvalue = (100sqft)*(70F - 20F)/R15 = 333 BTU/hr

The HDD number lets you turn that hourly estimate into a whole season estimate -- the formula becomes:

HL = A * HDD * 24 / Rvalue = (100 sqft)*(6000 HDD)*(24hr/day)/R15 = 960,000 BTU

Its the same formula as the hourly loss with HDD*24 substituted for the temperature difference.
The 24 comes from 24 hours per day.

So, it says that in a 6000 HDD climate, that wall would lose 960,000 BTU over the full winter.
If it was Fairbanks with a 14000 HDD winter, it would 2.2 million BTU.

You don't have to do this all by hand, there are calculators out there that will do most of the work -- this is mine:
http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

I got the heat loss for the 2000 sf house using this calculator.

Gary

 

[GaryGary]

Is wood carbon neutral? Unless you are cutting with an Axe, bucking with a 2 handed crosscut saw, splitting with a maul, and hauling with a horse team- NO.

Its is much LOWER carbon than FF however. Assuming you plant a new tree to replace the harvested tree, eventually all that carbon in the wood will be recaptured. Same thing if the tree fell and rotted, it feeds new trees. The carbon running the chainsaw, splitter and trucks is all coming from the Jurassic however

I guess -- The whole thing could still be carbon neutral if you plant a few more trees each year than you harvest.

But, even if you don't, I think its a pretty impressive saving -- burning 10 gallons of tractor fuel to harvest your firewood is a hundred times less carbon than burning a thousand gallons of home heating oil to heat your house the usual way.



Gary

 

[barkeatr]

its hard not to "plant" as many trees as you cut. It happens automatically! As soon as you open the canopy the new available light triggers seed growth and massive growing of all the understory biomass. think about it, now the sun is hitting a much larger surface area than before the mature tree (that had optimized collecting the sun) came down.