Wood Species used in RMH

Does it matter which species of wood is burned if the wood is burned within an insulated firebox?  Aside from the amount of Btu's or months of seasoning, need one avoid softwoods when firing up a rocket mass heater or insulated batch-burning masonry stove?  My concern, of course, is creosote.  

Hi Alden;  Welcome to Permies!

You can burn any dry wood available to you. Hardwood or soft, pallets, construction scraps, as long as they are dry, they all burn up completely.
A properly built RMH burns so hot that particulates (like creosote) are eliminated.
There will never be anything but super fine fly ash in your burn tunnel , transition area and part way down your horizontal piping!
No chance of a chimney fire from creosote ever!

Per chance, do you have a copy of the RMH builders guide ? Readily available thru Amazon. It is invaluable in learning how to properly build your own RMH.
Of course our helpful crew of friendly rocket scientists are always available to assist in any way!

I fully agree with Thomas, As long as the RMH is running properly virtually all of the volatiles and resins will burn away. In the start-up phase there will some soot be formed but that's all.

Moreover, within a few percentages all species of fuel are equal per unit of weight. Surprisingly, coniferous species yield more (about 5%) combustion value per pound as compared to, say, oak or beech, just because of the resin content. In a slow burning woodstove that will evaporate but in the absence of high temperature and violent mixing with fresh air it won't combust and settle as tar in the chimney. Given a high enough chimney temperature it will come out as nasty smelling smoke to hinder the neighbours. Better to combust it in the combustion core itself, this will raise efficiency a surprisingly amount.

ok, so the btu rating of different woods does not reflect heating capacity in RMH?

so these charts

http://worldforestindustries.com/forest-biofuel/firewood/firewood-btu-ratings/

do not apply if you have a RMH?

bruce Fine wrote:ok, so the btu rating of different woods does not reflect heating capacity in RMH?

so these charts

http://worldforestindustries.com/forest-biofuel/firewood/firewood-btu-ratings/

do not apply if you have a RMH?

Those charts show pounds per cord, and then BTUs per cord.

It looks like the BTUs per pound is surprisingly consistent if you work those figures out, despite the variation in per-cord figures.

bruce Fine wrote:ok, so the btu rating of different woods does not reflect heating capacity in RMH?

so these charts

http://worldforestindustries.com/forest-biofuel/firewood/firewood-btu-ratings/

do not apply if you have a RMH?

Peter did not say that at all,  he simply said, that pound for pound the BTU's for wood remain about the same....  that is not say a armload of red elm has the same BTU's of a arm load of popular..  If the red elm is 100 pounds and the popular is 60 pounds, but both have about the same BTU's per POUND of wood. (not volume) then it means just that.

bruce Fine wrote:ok, so the btu rating of different woods does not reflect heating capacity in RMH?

so these charts

http://worldforestindustries.com/forest-biofuel/firewood/firewood-btu-ratings/

do not apply if you have a RMH?

They do not apply to any stove, fireplace or even a firepit out back of the house because you are confusing CORDS with Weight.

A cord of wood changes in BTU per species of tree because a cord of wood is a defined amount, 4 feet by 4 feet by 8 feet. That is a cord, but a ton of beech is going to have the same amount of btu's as a ton of White Ash.

However, the one ton of Beech is going to be a vastly smaller pile of wood then what one ton of White Ash will be. White Pine will be take up even more space to make up one ton of it. So the White Ash and White Pine will be more in terms of cords, but the exact same as Beech in weight.

Pound per pound, wood species does not matter in terms of btu's per pound.

A lot of people get this confused because in a lot of places that convert weight to cords, they AVERAGE.

The paper mill I send my pulp to does this. They say mixed hardwood has a weight of 5200 pounds per cord; green. I get $125 per cord for that, but if I cut a whole load of 100% beech, because of the extra weight that beech has...its density is higher per cubic feet, instead of having a 10 cord load, I might have a 11.5 cord load of wood. It is still hardwood, still on the same truck, but because the paper mill averages it based on mixed hardwood, I make a little more.

But do not feel bad for them. When I cut a 100% load of white ash, the weight is less, so I might only get paid for a 9 cord load, when really it is 10 cords in size...the exact same truck after all.

Where I do well is in mud. All that mud weighs up no matter what wood species it is, so I always make more money in the spring of the year during mud season, however, if you have ever logged in the mud, you will know that extra money is hardly worth it.

But cords is a VERY POOR way to measure wood. It should always be bought or sold by weight. In fact, in the State of Maine, it is against the law to sell wood by the cord. It has to be sold by weight, or by the load.

When I sell firewood, it is by the "truck load", of course the first thing people ask is, "How many cords is that?" As you can see from the example listed, it is 10 cords.

bruce Fine wrote:ok, so the btu rating of different woods does not reflect heating capacity in RMH?
so these charts
http://worldforestindustries.com/forest-biofuel/firewood/firewood-btu-ratings/
do not apply if you have a RMH?

When you scroll down the charts you mention you'll see this text, the bold marking is mine:

"The BTU in a cord of firewood is usually close to the same per pound between species. One pound of dense hardwood will have about the same amount of energy as one pound of light softwood. The difference in energy content is in the woods density. A cord of the more dense wood will have more energy than a cord of less dense softwood."

My point exactly, I'd say.
The trick is to make good use of that energy content.

Edit:
Now I see I've been too slow, four others already replied.

What is more important is how many btu's are going out the chimney!

I know for an outside wood boiler, 70% of the BTU's are escaping. A wood stove in the house is about 50%. I am not sure what a Rocket Mass heater is, but am guessing 25% or less?

What does that mean?

For an outside wood boiler, every 10 cord of wood a person buys or gathers, 7 cord is going up the chimney.

For a woodstove in the house, for every 10 cords bought or gathered, 5 cord is going up the chimney.

For a Rocket Mass heater, it has the same principal, if it is 25%, then only 2 and a half cords are going up the chimney for every 10 cord bought or gathered.

For some strange reason, it seemed the outside wood boiler people LOVE to brag about how many cords they burn, "it takes 30 cord to heat my house every year". I am thinking to myself, "yeah and 21 cords is going up the chimney." It seems like a lot of work to cut all that wood just to send it up the chimney, but that is up to them I guess.

Travis, I am confused.  If a rmh is constructed properly, wouldn't the amount of unburned wood going up the chimney be de minimus?  I know that the exhaust is pretty cool.  Do I understand correctly that even that cool exhaust is carrying away so many btu's?

Hi Alden;
The average RMH (indoors in an insulated home) ,burns 1-2 cords or less.
So if Travis's numbers are used ) 5 cords would put 1.25 up the chimney and 2.5 cords would lose .62 cords ...
So as we drop down to actual amount of wood burned, to what is sent up the chimney.
It becomes (to me) an acceptable number.

Any appliance that heats, is sending a certain amount of heat up the chimney or just out of the home.
In the case of a RMH, the amount of mass that is being heated, determines how many btu's are reaching the outdoors.

 

Thomas, thank you.  I certainly agree that the numbers are fine.  It is just hard for me to imagine 25% of the btu's going up the chimney while at the same time the exhaust at the chimney exit is so cool.  

Hey Alden; Travis's number was his guess.  He thought maybe 25% or less. I think its less.
Best way to learn about RMH's is to build one. You'll like it!