Weak/Lame secondaries?

[Swedishchef]

Hey guys

I just want to confirm something I noticed this year: when burning softwood ONLY, my secondaries are weak. They are present but not in the same amount as when I mix woods. Is it simply because softwood is less dense and therefore less off-gassing? My softwood MC is around 12-15%.

When burning hardwood I can get secondaries for a lonnnng time. Softwood secondaries will last alot less.

Andrew

 

[HVAC_Marc]

softwood generally has less btus than would any other hardwood, so there will be less of everything

 

[begreen]

Softwood has equal btus per pound. With doug fir I get huge secondaries and always thought that it outgases faster than hardwood. I also get great secondaries with good hardwood, but they come on slower and are usually bluer in color.

 

[Woody Stover]

With doug fir I get huge secondaries and always thought that it outgases faster than hardwood.

I seem to be seeing the same thing in the cat stoves; Softer woods gas faster, and I have to compensate with the level I set the air at to cruise the stove at a given temp. I just started tossing White Oak at the Buck, and I'll put a couple splits of really dry White Ash in the center to kick the load off and get the cat burning quicker at start-up.

 

[Swedishchef]

Softwood has equal btus per pound

That I agree and I know. I'm just thinking that perhaps I am not loading my wood with as many BTU's since I only put in 6-7 medium splits of softwood vs 8-9 pieces of hardwood at a time.

But it certainly does take off easier with softwood than hardwood.

Andrew

 

[stoveguy2esw]

consider this, a 1 lb block of white pine at 12% moisture will be much lager than a 1lb block of oak at the same moisture content (but they both contain the roughly 8500 BTU of "potential" (stored energy). therefore you are able to load more of it in the same space. thus more heat and a longer burn time


softwoods are less dense therefore contain less "BTU per cubic measure" than hardwoods. the same lack of density allows faster outgassing (and faster burning ) as there is less actual "potential" per cubic inch of fuel. you figure you will burn "x" lbs/hr depending on the amount of turbulence through the firebox, if fewer lbs are present the level of heat decreases more rapidly and the secondaries may not get as much fuel for as long as well as less firebox temp to generate the needed heat for the active secondaries


hope this makes it clearer as to why this happens

 

[Swedishchef]

consider this, a 1 lb block of white pine at 12% moisture will be much lager than a 1lb block of oak at the same moisture content (but they both contain the roughly 8500 BTU of "potential" (stored energy). therefore you are able to load more of it in the same space. thus more heat and a longer burn time


softwoods are less dense therefore contain less "BTU per cubic measure" than hardwoods. the same lack of density allows faster outgassing (and faster burning ) as there is less actual "potential" per cubic inch of fuel. you figure you will burn "x" lbs/hr depending on the amount of turbulence through the firebox, if fewer lbs are present the level of heat decreases more rapidly and the secondaries may not get as much fuel for as long as well as less firebox temp to generate the needed heat for the active secondaries


hope this makes it clearer as to why this happens

Very well explained for someone who doesn't know much about wood stoves

Just to note: this thread was created in 2013....not 2014. I was a newb back then .

Andrew

 

[HVAC_Marc]

Softwood has equal btus per pound. With doug fir I get huge secondaries and always thought that it outgases faster than hardwood. I also get great secondaries with good hardwood, but they come on slower and are usually bluer in color.

True, but generally people dont burn 'pounds of wood', they burn 'logs of wood'. I should have been more specific by saying 'per unit volume' (for example, 1 log 6" diameter by 20" long made of softwood would have less btu's than than the same size log of hardwood)

 

[kennyp2339]

True, but generally people dont burn 'pounds of wood', they burn 'logs of wood'. I should have been more specific by saying 'per unit volume' (for example, 1 log 6" diameter by 20" long made of softwood would have less btu's than than the same size log of hardwood)

Thus (1) 20" long x 6" wide piece of 12% oak weighs 10 pounds, the same in spruce will weigh 2 pounds, its all about density, and by the way I just made up those numbers, but its something like that lol

 

[begreen]

Generally that's true though though we still get good secondaries with softwood. The btu content depends on the hardwood vs softwood. Doug Fir has a lot more btus than alder, willow and butternut for example and about the same as big leaf (soft) maple, but about 30% less than oak.