Old Stove Efficiency

[mtcates]

I have an old smoke dragon wood stove made by Englander. It has a 3 cubic feet firebox and loads from the side. I have modified it to try and make it more efficient. I have added more firebrick than it was originally designed for. I added the brick on the end and back. I left the front firebrick only one level high as to expose the front steel plate to the direct heat of the fire. I figured that I would get more heat off the front if I didn't add more brick here. Now to the good part. I added a steel plate in the top of the stove to direct the gasses to the top front of the stove and then they must pass the entire length of the top from front to back and then down 5 or so inches before they exit the rear 6 inch pipe. I insulated the top of this removable plate with a ceramic blanket to hold the heat in the firebox for a hotter more complete combustion. I also installed a 6 inch insulated stainless steel flue liner in the chimney. The liner is about 20 feet vertical from the t pipe on the rear of the stove to the exit so I can get a wonderful draft flowing. On to my Question. I can burn a moderate fire in this stove, maybe 4 or 5 splits weighing a total of 30 to 35 lbs of dry oak wood with the two draft control wheels open one full turn each. The chimney exhaust is perfectly clear and I can even go on the roof and put my nose 2 feet from the flue exit and can't see or smell the exhaust. I can turn the front and top of the stove red with a 2/3 load of wood without overheating the flue pipe. This is +/- 900 degree stovetop temps. The inside of the stove stays chalky white. Is this about as efficient a burn as I can expect to achieve even with a modern stove? Now keep in mind I don't have a secondary air supply for a secondary burn. But whatever is happening in there the fire is pretty darn efficient. My question is, considering what I have done to this stove and having absolutely no smoke at all, Would it be much of an improvement for me to buy a modern wood stove?

 

[Battenkiller]

At those temps, I doubt secondary air would add much to your efficiency. But then again... those temps! :ahhh:

 

[Jags]

The following is strictly opinion:

By running the stove hot - you are about at the peak efficiency that your gonna get from that stove. The addons that you did to the stove may help in keeping the hot fire established.

I am also guessing that you are in the "overfire" side of temps for that stove. Yes, you can run a stove too hot. It can do damage in the long run (sometimes even in the short run).

Now - will a new epa stove have benefits? Um yeah, running the old stove at max temp to obtain clean burns is gonna rip through a pile of wood in short order.

Thats what makes the new stoves such an improvement over the old dogs. Clean(er) output without going nuclear, and the side benefit is the way that it is done - will reduce wood use by a very measurable amount.

 

[mtcates]

Thanks for the replies. I really have nothing to compare this stove to as this is the only stove I have operated. I don't normally burn the stove that hot. I was just making a point that I could. It will burn clean at a more normal temperature. I can heat my house of 1800 square feet with 4 to 6 cords of oak wood per winter. 4 cords in a mild winter and 5 to 6 in a year like this one. I live in north central NC. My house is tight with few air leaks but the roof is poorly insulated. R-7 The house also has 400 square feet of glass with an R value of 2. How much wood are you guys burning in a year. I mean if a new stove only saves me a chord or 2 a year then its not very significant. I mean I do tree work for a living and I can get a winters supply of wood in a week or 2.

 

[Jags]

I would venture a guess that you would drop consumption by about 35-40%. Old stoves are not evil if run properly. They will NEVER run as clean as a properly operated EPA unit, but can be run pretty clean, depending on the user.

Heck, I would rather see a good user of a smoke dragon than a bad user of an EPA stove.

Think "reload times" and "over night" burns. I don't know what kind of burn times you are getting, but a 3.0+ cuft firebox EPA stove will yield a pretty decent over night burn.

For some, a new stove is a hard sell. Some go from old to new and HATE the new tech. (usually due to bad wood, etc.). Do what is right for you.

 

[buckdog]

3200sq ft 600+sq ft glass, alot colder climate than you. I burn 2 1/2 - 3 cords of wood and suppliment wth maybe 200-300 gal propane all year. House temp is usually around 72-78*. And yes the house has alot of glass, when temps outside are 10* the IR measures 62* on glass while temp on walls are 75-78*. Oh and I burn a insert that's "tweaked".

 

[geoxman]

You could add some secondary air combustion tubes pretty easily. I did it to an old Daka I inherited and it works just fine. They could be installed directly under the upper baffle. I got my idea from this guy on youtube, his name is Steve and will help you out if you give him a buzz.

http://www.youtube.com/watch?v=3YxrP_YHwJk&feature=channel

http://www.youtube.com/watch?v=IKsCprppqs0&feature=channel

http://www.youtube.com/watch?v=EYgk65hgw0g&feature=channel

there are many more videos on his channel. good luck

 

[mtcates]

3200sq ft 600+sq ft glass, alot colder climate than you. I burn 2 1/2 - 3 cords of wood and suppliment wth maybe 200-300 gal propane all year. House temp is usually around 72-78*. And yes the house has alot of glass, when temps outside are 10* the IR measures 62* on glass while temp on walls are 75-78*. Oh and I burn a insert that's "tweaked".

I forgot to say that I have no heat at all except wood. No supplement heat at all, and the roof with the r value of 7 means that I loose over 5 times more heat through the roof as I would if it was up to current code. I guess I cant complain at all. I found a program that calculates the heat I need for the average winter at my climate. I punched in all the correct information and I need around 85 million btu during the average winter. If I got 100% of the heat off the wood, which we all know is impossible, thats still 3 and 1/2 chords an average winter, and I use about 4 and 1/2. At that rate I'm getting about 75% efficiency with my old stove. Isn't that as good as a new one? Thats about as efficient as the newer ones and it does not smoke at all with a proper burn. I am still thinking about adding secondary air to this old stove. I have already bought the parts I need. I just need it to be summer so I can take it out to the shop. I still might buy a new one just for the sake of seeing the flame through the glass. With the 1500 dollar tax credit thats a free stove. If I do I'll put this old stove in my shop.

 

[buckdog]

I have 2' of insulation in 2/3rd's of my roof the other is what builder stuffed in 12" space in a "true cathedral" ceiling. No attic in 1/3rd of house. If you blow insulation in the attic (cheap to do yourself) that will be a big heat saver.

 

[mtcates]

I have 2' of insulation in 2/3rd's of my roof the other is what builder stuffed in 12" space in a "true cathedral" ceiling. No attic in 1/3rd of house. If you blow insulation in the attic (cheap to do yourself) that will be a big heat saver.

I wish it was that easy. My house has a timber framed ceiling / roof. Its a 10 pitch framed with 4 x 8 beams 48 inches on center with 2 x 6 tung and grove over the beams. There is a couple of layers of tar paper and a 1 inch layer of foam under the shingles. Total r value is about 7. It would cost me 10 grand + to install SIPS and reroof. I did the math on it and now I loose 24 million BTU's per winter through the roof. If it was up to code I would loose 5 million BTU's through the roof. Thats a difference of one Chord of Oak burned in my stove. I do tree work for a living. I'll save the 10 grand and cut one more Chord. I do sometimes think I'd like to do this but I just can't justify it. The cheap way would be to insulate the underside and put up sheetrock but I would rather drop the 10 grand than cover up my wood beam, tung and grove ceiling. I'll just burn another cord a year. What the heck, I like the wood stove.

 

[Battenkiller]

Thanks for the replies. I really have nothing to compare this stove to as this is the only stove I have operated. I don't normally burn the stove that hot. I was just making a point that I could. It will burn clean at a more normal temperature. I can heat my house of 1800 square feet with 4 to 6 cords of oak wood per winter. 4 cords in a mild winter and 5 to 6 in a year like this one. I live in north central NC. My house is tight with few air leaks but the roof is poorly insulated. R-7 The house also has 400 square feet of glass with an R value of 2. How much wood are you guys burning in a year. I mean if a new stove only saves me a chord or 2 a year then its not very significant. I mean I do tree work for a living and I can get a winters supply of wood in a week or 2.

If I was in your situation, I'd continue with what you are comfortable doing. Wood supply is not a problem, and you are obviously burning clean based on the description of your burn. Just recognize the fact that not seeing smoke doesn't automatically mean you are consuming all of the combustible gases in the burn.

Firewood is primarily hemi-celluloses, lignin and water, but that's never what is actually burning. A whole cornucopia of combustible gases are being formed and re-formed and eventually (hopefully) combining with oxygen to produce CO2 and water as products. Many of these intermediate gases (CO, methane, hydrogen, etc) have high ignition temps and they are totally transparent . They also have to be at those temps in the same place and at the same time as the oxygen molecules that they need to combine with in order to burn. That means at lower firebox temps and/or conditions of oxygen deprivation (as in no secondary air supply), these gases are not being burned and are sneaking up the flue undetectable to the eye.

It is totally possible to get a non-polluting, non-creosote forming burn and still have fairly low efficiency because these clear gases are going up the flue unburned. This can even happen in an EPA stove if a large coal bed forms and internal temps drop lower than the ignition temperature of CO gas (1100ºF) since CO is constantly being formed from burning charcoal. At low temps, much of this unburned gas is rising up and out the stack ... totally invisible.

BTW, you are burning a large amount of fuel for such a small area in your location, at least compared to me using the same amount of wood, burning full-tilt most of the winter. How many heating degree days do you have in a full season down there?

 

[mtcates]

Thanks for the replies. I really have nothing to compare this stove to as this is the only stove I have operated. I don't normally burn the stove that hot. I was just making a point that I could. It will burn clean at a more normal temperature. I can heat my house of 1800 square feet with 4 to 6 cords of oak wood per winter. 4 cords in a mild winter and 5 to 6 in a year like this one. I live in north central NC. My house is tight with few air leaks but the roof is poorly insulated. R-7 The house also has 400 square feet of glass with an R value of 2. How much wood are you guys burning in a year. I mean if a new stove only saves me a chord or 2 a year then its not very significant. I mean I do tree work for a living and I can get a winters supply of wood in a week or 2.

If I was in your situation, I'd continue with what you are comfortable doing. Wood supply is not a problem, and you are obviously burning clean based on the description of your burn. Just recognize the fact that not seeing smoke doesn't automatically mean you are consuming all of the combustible gases in the burn.

Firewood is primarily hemi-celluloses, lignin and water, but that's never what is actually burning. A whole cornucopia of combustible gases are being formed and re-formed and eventually (hopefully) combining with oxygen to produce CO2 and water as products. Many of these intermediate gases (CO, methane, hydrogen, etc) have high ignition temps and they are totally transparent . They also have to be at those temps in the same place and at the same time as the oxygen molecules that they need to combine with in order to burn. That means at lower firebox temps and/or conditions of oxygen deprivation (as in no secondary air supply), these gases are not being burned and are sneaking up the flue undetectable to the eye.

It is totally possible to get a non-polluting, non-creosote forming burn and still have fairly low efficiency because these clear gases are going up the flue unburned. This can even happen in an EPA stove if a large coal bed forms and internal temps drop lower than the ignition temperature of CO gas (1100ºF) since CO is constantly being formed from burning charcoal. At low temps, much of this unburned gas is rising up and out the stack ... totally invisible.

BTW, you are burning a large amount of fuel for such a small area in your location, at least compared to me using the same amount of wood, burning full-tilt most of the winter. How many heating degree days do you have in a full season down there?

There are 3880 Heating Degree Days where I live. Yes I burn on the average 4 and 1/2 cord of oak in a year heating 1800 square feet. The wood stove is my only heat source. I cherry pick my firewood because I do tree work for a living and supply is not a problem. I did the math on my house to see what it it would take to heat it in terms of BTU content.
If you will read a few posts up you can see why that is so. At my climate, 3880 HDD, I loose 42 million BTU's through my roof and windows alone. Never mind the floor, walls, and air infiltration. Total BTU's for my 1800 Square feet is 85 million per year. You did enlighten me to the fact that a clean burn does not mean an efficient burn. I can see no smoke at all from my chimney and wondered just what you described. I do plan on adding a secondary air supply at the top of the fire box just under my insulated baffle. I cant wait to see what the improvements may be in the heat output. Right now I'm getting 85 million usable btu's from a little over 4 cords of oak. Thats pretty good. At 100% the wood only makes 120 million at max.

 

[Pagey]

Mtcates,

I think what Battenkiller is getting at is that "efficiency" in terms of an EPA certified stove is a rating of how much heat is extracted from the wood and sent into the room rather than up the chimney. When you say you get "75% efficiency," what are you basing those numbers on? Just as Batten has suggested, you can get a clean burn while NOT being very "efficient". If you burn clean but send a ton of heat up the flue, then you're clean but not efficient. So, when you ask about the efficiency of an old stove, you're not asking about what percentage of your heating you achieve with wood alone - rather, you are asking how much heat is your non EPA stove extracting from the combustion process. By design, I would venture to say it is less than 75% efficient given the definition above.

 

[mtcates]

Mtcates,

I think what Battenkiller is getting at is that "efficiency" in terms of an EPA certified stove is a rating of how much heat is extracted from the wood and sent into the room rather than up the chimney. When you say you get "75% efficiency," what are you basing those numbers on? Just as Batten has suggested, you can get a clean burn while NOT being very "efficient". If you burn clean but send a ton of heat up the flue, then you're clean but not efficient. So, when you ask about the efficiency of an old stove, you're not asking about what percentage of your heating you achieve with wood alone - rather, you are asking how much heat is your non EPA stove extracting from the combustion process. By design, I would venture to say it is less than 75% efficient given the definition above.

I found a program that calculates the heat I need for the average winter at my climate. I punched in all the correct information and I need around 85 million btu during the average winter. If I got 100% of the heat off the wood, which we all know is impossible, thats still 3 and 1/2 chords an average winter, and I use about 4 and 1/2. At that rate I’m getting about 75% efficiency with my old stove.

My house has a timber framed ceiling / roof. Its a 10 pitch framed with 4 x 8 beams 48 inches on center with 2 x 6 tung and grove over the beams. There is a couple of layers of tar paper and a 1 inch layer of foam under the shingles. Total r value is about 7. It would cost me 10 grand + to install SIPS and reroof. I did the math on it and now I loose 24 million BTU’s per winter through the roof. If it was up to code I would loose 5 million BTU’s through the roof. Thats a difference of one Chord of Oak burned in my stove. I do tree work for a living. I’ll save the 10 grand and cut one more Cord.

There are 3880 Heating Degree Days where I live. Yes I burn on the average 4 and 1/2 cord of oak in a year heating 1800 square feet. The wood stove is my only heat source. I cherry pick my firewood because I do tree work for a living and supply is not a problem. I did the math on my house to see what it it would take to heat it in terms of BTU content.
I At my climate, 3880 HDD, I loose 42 million BTU’s through my roof and windows alone. Never mind the floor, walls, and air infiltration. Total BTU’s for my 1800 Square feet is 85 million per year. At 100% the amount of wood I use only makes 120 million at max.

 

[Battenkiller]

I think what Battenkiller is getting at is that "efficiency" in terms of an EPA certified stove is a rating of how much heat is extracted from the wood and sent into the room rather than up the chimney. When you say you get "75% efficiency," what are you basing those numbers on?

I don't think there are any stove manufacturers that measure the actual heat output into the room. Besides, I can keep almost all of the heat produced by the stove in the room just by shutting it way down, using a key damper, having a long horizontal run, maybe even a heat exchanger. But then I'd have a very inefficient, sluggish, dirty, and dangerous burn going on.

No, I am strictly talking about unburned fuel going up the flue. The new stoves achieve their efficiency the same way they reduce emissions - by adding heated secondary air at a critical point and time in the burn, or by using a catalytic combustor. My flue temps are usually about the same as an EPA non-catalytic stove, so I waste no more heat up the flue than they do. However, if I shut my primary air way down for a long burn, I waste a lot more fuel than a stove with real secondary combustion, even though I burn very, very clean.

 

[Pagey]

I think what Battenkiller is getting at is that "efficiency" in terms of an EPA certified stove is a rating of how much heat is extracted from the wood and sent into the room rather than up the chimney. When you say you get "75% efficiency," what are you basing those numbers on?

I don't think there are any stove manufacturers that measure the actual heat output into the room. Besides, I can keep almost all of the heat produced by the stove in the room just by shutting it way down, using a key damper, having a long horizontal run, maybe even a heat exchanger. But then I'd have a very inefficient, sluggish, dirty, and dangerous burn going on.

No, I am strictly talking about unburned fuel going up the flue. The new stoves achieve their efficiency the same way they reduce emissions - by adding heated secondary air at a critical point and time in the burn, or by using a catalytic combustor. My flue temps are usually about the same as an EPA non-catalytic stove, so I waste no more heat up the flue than they do. However, if I shut my primary air way down for a long burn, I waste a lot more fuel than a stove with real secondary combustion, even though I burn very, very clean.

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My bad.