Wood burning stove efficiently

[Itslay90]

Do all catalytic wood burning and secondary burn wood stoves operate most efficiently when the air control is turned down?

 

[Rob the Scott]

That is my understanding. My Vermont Casting Encore 2550 has a catalyst, and when it "fires", I turn the air down to the minimum. The stove continues to burn hot in spite of the reduced air supply. My understanding is that adding more air will either overheat the stove, increasing the losses out of the stovepipe, or flow more of the heated air out before it contributes to heating the stove.
More importantly, the mass of the stove takes a long time to heat up. Anticipating that allows me to reduce the air, reducing the losses while still heating the stove.

I suspect that my logic is flawed somehow, but my experience with my stove suggests reduced air input when the stove reaches a desired temp, slowing combustion.

Why do you ask?
PS. It will be between 91 and 98 degs at my house over the next 3-5 days, hence the irony of your question.

 

[Turbo89]

Do all catalytic wood burning and secondary burn wood stoves operate most efficiently when the air control is turned down?

Wood stoves have an efficiency curve, but strictly speaking they probably do not burn most efficient with the air control turned down. I’d guess they’re most efficient somewhere near the middle /high (where the catalyst is at optimal temperature). I don’t know of a modern stove that publishes these, but Jotul used to.

Remember, a lot of new high efficiency stoves get there by introducing more bypass air - causing the stove to run hotter and burn wood faster.

A different question (which may be what you’re asking) is do catalytic stoves run longer than secondary burn stoves on low; this answer seems to be “yes” in my experience, but I’m sure someone will come along and correct me. Haha

 

[Highbeam]

No. All stove’s are different. The pure cat BK is most efficient at low settings. The noncats don’t hit clean combustion until things are very hot. The noncats are more sensitive to stage of burn wrt to efficiency. Hybrids will have yet another efficiency curve. And then between brands there are differences with some stoves are just low efficiency.

I shoot for a clean exhaust plume but lowest flue temp from any stove for best efficiency.

Oh and don’t confuse efficiency with emissions. You can have low emissions and low efficiency. They are independent specifications.

 

[Todd]

If you read the EPA test report for your stove there will be different burn test rates at low, med and high. Every stove I’ve looked up has the highest efficiency rating at the low burn rate.

 

[MRD1985]

I just watch the chimney exhaust. I am for smokeless . If it smokes too much, I give it more air

9 times out of 10 I’m able to keep the air very low, almost all the way closed if not closed. This is on a secondary stove without a cat.

 

[stovelark]

That question has a lot of variables involved. Generally, you want the lowest air control setting while maintaining a minimum burn temp so the stove burns cleanly. For most secondary air tube stoves (the ones I'm familiar with), with a proper drafting chimney, dry seasoned wood and a stove top temp of 450-650 degrees, the air control will usually be between 1/4-1/2 setting. That can vary too, if you got exceptional dry wood, if chimney draft is higher due to it being colder out, everyone learns their stove's operation. And of course, if you need less heat, turn the air down if possible, but still keeping the STT in band (450-650ish). I'm sure the cat guys have their ways of setting it particular to their stove too. And I'm referring to full loads of wood, sometimes the air is set at minimum (you can't close the air port off completely. The important thing always is dry, seasoned wood.

 

[EbS-P]

Define efficiency…. It’s hard to measure accurately in real world conditions. I think it’s a negligible change from low to high. The operator and moisture content of the wood probably have more to do with it.

 

[NickW]

I'm considering efficiency as getting the maximum amount of heat from a load while burning cleanly.

Lots of variables to consider. I would say yes to the original question, but agree with it depends on how far by setup (and the wood type, and weather...). Low quality woods I burn with the air more open, hardwood I burn more closed. Cold and windy more closed, warmer and calmer more open.

At the old house with the NC30 and a full load of hardwood settled in I was air 1/4 open, damper 30% open. At the new place the Stratford 2 gets the air control shut all the way (eventually...). Super cold and windy the NC30 needed the damper closed a little more.

 

[bigealta]

I would say simply you want to burn the maximum amount of gasses coming off the wood load. In a secondary stove that means having them fire as long as possible without overfiring. So generally the lowest air setting you can have with strong secondaries firing. Of course that probably also means its not a set it and forget it setting. The air setting will change throughout the burn to get the absolute most out of the load. This is maybe not that realistic but you get the concept i'm sure. (Burn as much burnable gas as possible without overfiring)