secondary burn - how much more efficient?

[88bomber]

I'm trying to find some numbers on the merits of a secondary burn chamber in a wood furnace.

The 2 furnaces I am comparing is the US Stove 1557M ($1399 from tractor supply) and the Firechief 500 (about $2000 online). I read that the US Stove model has 63% efficiency, but there are no such numbers for the fire chief (I called them already...they don't have any numeric data). So I'm turning to the experts here...how much better is the secondary burn feature?

I know there are other advantages to the Fire Chief model over the US Stove model, but I would like to know more about this particular feature with real data or real experience.

Thanks!

 

[brenndatomu]

I think I remember reading somewhere that 40% of your potential BTUs are in the smoke. How exactly to translate that into how much extra efficiency that can give us in the real world, I'm not sure (doubt that it's 40% more). From my experience, when the secondary's kick in, the stove and the flue pipe temps sure jump up! There are a couple stove mfg. reps on here, maybe they can explain it all. I also remember reading not all mfg.'s figure there efficiency #s the same way, so gotta be careful that you are comparing apples to apples. For what it's worth, I think the Firechief probably has a better reputation for being a quality unit, but then again, I bet there's a lot of satisfied 1557 owners out there too. It's never simple is it?!

 

[oppermancjo]

The Napoleon that I just bought claims 85% efficiency and it has a secondary burn. I've yet to install and use it but that's what their claim is. Will be excited to fire it up!

 

[CTYank]

Of course, if you're satisfied with partial combustion of wood, consider that your neighbors downwind might not be in love with it. It's lousy PR. We have one of them nearby, but fortunately I'm almost never downwind from him.

Unburnt fuel is waste.

 

[laynes69]

I wouldn't consider either furnace a secondary combustion furnace. The 1557 is a simple firebox and baffle, nothing else. The 63% efficiency number is a default number for a non-cat woodstove from the EPA, which the furnace is exempt and that actual number would be lower.

The firecheif would be a better unit. Better built with more options. The secondary combustion chamber is more of a heat exchanger, diverting gasses to extract more heat from the unit. A larger blower and insulated cabinet are also nice. It would be the more efficient of the two, but there are others on the market much more efficient.

When wood smoke is burned, it produces quite a few btus that otherwise would go up the chimney. This results in less wood, creosote and longer cleaner burns. Those are a few benefits upgrading to a EPA certified stove or furnace.

 

[MotorSeven]

Bren is right, there does not seem to be a efficiency standard out there. My old Hearthstone H1 built in 1986 specs out at 86% efficiency and has a secondary burn tube. I can say that when it kicks in you can see the flame through the glass hovering/billowing around the top of the firebox....go outside, and you will see zero smoke.

If it were me I would go with secondary's...many new stoves have way more extensive secondary set up's then older stoves and some of the new one's so you might shop around a bit.

 

[AndrewGeib]

MotorSeven is right, my neighbor has an older stove that smokes like all hell he asked when I was lighting my wood stove, said she is lit no smoke at all:msp_thumbup:

 

[Fyrebug]

Efficiencies for EPA wood furnaces and stoves are measured with the 'stack loss' method. Basically if you can put 10 Lbs pounds in a combustion chamber at 8,000 BTU per pound you have a potential of 80,000 BTU.

If you measure the heat loss through the chimney and it amounts to 20% of your potential then your furnace efficiency is calculated at 80%. There is more to the testing than this of course but that gives you and idea.

As Layne's mentioned the 63% is a 'baseline' figure. You would have to contact the mfg for the test results or certification papers since some mfg only mention the best readings rather than the required weighted average performed during a full test.

An EPA certified furnace such as the PSG Caddy (shameless plug) will burn the smoke (energy, BTU) and by extention be more efficient since it burns all the fuel. The Max Caddy for example is rated at 85% efficiency which is impressive for such a big furnace.

If your choice is between the two models mentioned go for the for the Fire Chief. If you can afford it you can always look at our Caddy's as well.

 

[88bomber]

Thanks everyone.

Layne,
"The secondary combustion chamber is more of a heat exchanger, diverting gasses to extract more heat from the unit. A larger blower and insulated cabinet are also nice. It would be the more efficient of the two, but there are others on the market much more efficient. "

Does that mean that the FC500 doesn't really burn the gasses at all? Is it false marketing?...I'm honestly asking, not being a smarty.

Also, how would I compare the FC500 to the others on the market in terms of efficiency? I wish I had the numbers to simply compare them, but it doesn't seem they exist.

Thanks again for the advice.

 

[ft. churchill]

Iv'e have three wood stoves in my life time and I'm glad I coughed up the coin for a new one instead of installing an older Lopi that I already own. We bought the Kuma, made in America, but strongly considered the Lennox as well. Both have very similar secondary burn systems. You can see the smoke burst into flames at the top of the chamber thru the glass window. As soon as the super heated air hits the smoke, it combusts into rolling flames. Our neighbors commented, " Aren't you going to use that new wood stove?" We'd been using it for two weeks. Almost no smoke comes out of the flue pipe, and then only when the fire is "new" and the box has not heated up yet. Also look at the Quadrafire and the pacific energy stoves, quite nice. Saw some junk out there also, heatalator and drolet. Poor quality ones have low weight, (think sheetmetal) and non replacable burn tubes. Good stoves will weight in at 500+ lbs, and have replaceable stainless steel burn tubes made of pipe, not sheetmetal.

 

[PA Plumber]

My Jotul has secondary burn and it's still warm from the wood I put in in April!

Wow, impressive.

We are currenltly being warmed by wood from 2010 and 2011.

 

[laynes69]

The firecheif will burn the smoke, you just need to push it harder to keep things clean, or burn small hot fires. I'm skeptical about efficiency numbers that some use, based on design. Just about every furnace that has a higher efficiency has a fully lined firebox, insulated baffle and preheated secondary air directed into the burn zone to promote clean combustion.

 

[sdt7618]

we installed this aarrow stove last october,

Aarrow Ecoburn 11 Multi-Fuel / Wood-Burning Stove

so the 80%+ eff is def worth the extra few bucks now and save over the years, 20% diffrence is 1 cord in 5? how much is that worth to you?

To say our wood use fell is an understatement, we had an aarow before this one, but was about 25 year old, 7 kw and had to burn wide open all the time to even get a decent heat in the house, this one just load her up, let her get hot, damp the air back and stay warm. we live in a 125 year old house and our oil boiler is feeling unloved!!:hmm3grin2orange:

 

[haveawoody]

My woodstove has a secondary and it is a bunch of plusses and a couple minuses.

Up side.
More heat from the same wood, less nasty smoke outdoors, nicer fires as gas rolls into flame in the main window, cleaner chimney pipes.

Down side.
Harder to start fires, just a bit.
Dirtier glass.

Worth the extra glass cleaner maybe 1 extra time per month IMO to have a much cleaner warmer stove.

 

[Whitespider]

Late winter/early spring, I switched from an old “smoke dragon” (manually operated) furnace to an EPA certified stove I converted into a (manually operated) furnace. The old “smoke dragon” used a flue damper, the EPA firebox isn’t supposed to have one (I did install one just in case). I used it a bit last year, and I’ve used it a bit this year… there are positives and negatives to both.

When the secondary burn kicks in it produces a ton of heat… a ton, but it’s relatively short lived. Over-all I’d say I’m gonna’ use less wood, but I’ll be loading it more often. The old “smoke dragon” burned on top of grates, and the draft air was directed under them. This kept the firebox producing plenty of heat well after the fire had been reduced to a bed of coals. The new EPA fire box burns directly on firebrick, and once the fire burns down to a bed of coals the air is directed over the top of them, and the heat output becomes greatly reduced. I can actually place my hand on the bare front steel of the fire box… yet not on the stack. That tells me once the fire reduces to coals most of the heat is lost through the stack and not being transfer to the space around the firebox. Yeah, I still have coals 20 or 24 hours after starting the fire, burn times are longer… but “heating time” is shorter, a lot shorter. I’m not willing to say the EPA version is a better way to go… at least not yet.

 

[MotorSeven]

88 you also need to look at Cat stoves(catalytic converter). There are pro's and con's to cat's...must burn well seasoned wood/ cat must be replaced every few years/building and maintaining a fire in them requires a learning curve, but they do burn clean efficient. The cat is a grid of either SS or ceramic that is at the top of the firebox. Once it gets super hot and the smoke passes through it the cat burns almost all particles.

I've never owned one, but there are those that swear by 'em.

 

[Fyrebug]

Saw some junk out there also, heatalator and drolet. Poor quality ones have low weight, (think sheetmetal) and non replacable burn tubes. Good stoves will weight in at 500+ lbs, and have replaceable stainless steel burn tubes made of pipe, not sheetmetal.

I beg to differ... very few stoves including the good quality ones weigh over 500 lbs. Small stoves will be in the 200 Lbs range and only the very largest of any brands (unless they are cast iron or soapstone) will tip the scale past 500 Lbs.

We make Drolet, it's made in North America with a lifetime warranty. The HT2000 tip the scale at 550 Lbs and some of our other stoves are over 400 Lbs. I wouldnt call them 'junk' since we offer a limited lifetime warranty and back it up 100%. If you're not sure check out the customer reviews on Northern Tools or Solutions de chauffage : Poêle à bois, Foyers, Encastrable | Drolet

All the best

 

[Fyrebug]

My woodstove has a secondary and it is a bunch of plusses and a couple minuses.

Up side.
More heat from the same wood, less nasty smoke outdoors, nicer fires as gas rolls into flame in the main window, cleaner chimney pipes.

Down side.
Harder to start fires, just a bit.
Dirtier glass.

Worth the extra glass cleaner maybe 1 extra time per month IMO to have a much cleaner warmer stove.

One of the pluses of an EPA certified solid fuel burning appliances is you will reduce your wood consumption by at least 1/3rd since you are burning all of the fuel (smoke is fuel). That is 1/3rd less cutting, splitting stacking etc...

Starting a fire with an EPA appliance is not necessarily harder. Just need a lot of dry kindling to get the fire box up to temp then gradually add bigger and bigger sticks of wood until the largest in no bigger than 8" circumference. Since they are more efficient they are a little bit more fussy on the fuel.

If your glass is smoking up it may be due your wood is too damp (should be below 20% humidity) and there's some issue with your draft.

The glass on the Caddy furnace stays clean for a long time.

 

[Fyrebug]

When the secondary burn kicks in it produces a ton of heat… a ton, but it’s relatively short lived. Over-all I’d say I’m gonna’ use less wood, but I’ll be loading it more often.

It depends on the size of the unit too. Which model do you have? If you are undersize for your BTU load requirement you will need to add more wood frequently.

Many of the largest units on the market can give you overnight useable heat.

With either wood stoves of furnaces it is important to size properly. Remember the BTU rating on the label and marketing material only refers to the 'high burn' that is when the firebox is fully loaded and the fire is roaring. That only last a short time. The average BTU over the life of the fire has to be considered.

 

[88bomber]

My bottom line is value. I live in east TN, so the winters are mild compared to most of you guys up north. I originally wanted to know the payoff of spending $600 for the Firechief...of course, I don't buy my wood, so the payoff would be in sweat due to burning less wood. But it sounds like the answer to that is pretty much unknown.

I don't think its worth it to drop $2500++ on a furnace for me. My heat pump takes care of me in Fall and Spring...I'm just looking to supplement during winter.

The wood furnace/stove would go in my unfinished basement, so I don't think a stove is going to do much for heating my 2700sq ft upstairs...which is why I was looking at a furnace.

In any case, thanks for the feedback.