Efficiency Ratings and effective Heat

[playernulla]

I know I am stepping into it here but here goes. I have been burning wood off and on for 30 years. Started out with old style and over past ten years I have been burning high efficienty stove with catalytics. I just went backward and installed an old Fisher and began burning. I have read on the posts here that these stove chew through wood. However the truth is I could never get the heat out of any the newer high efficiency stoves like I get out of this old monster. While I am sure under ideal circumstances the efficieny is higher for me it seems that I get more usable heat per unit of wood out of the old stoves. Like many folks we are gone all day and sleep all night. That leaves a couple of hours in the morning to get the stove built up and the evening hours when we are home. It can take hours it seems to get heat to begin radiating from the newer stoves because the boxes are so smal and the cast iron takes sol long to heat.

I threw some knuckles into the fisher the other night (which wouldnt have fit in my "large" Dutchwest) and within a matter of minutes it was radiating the heat and had the house warming in no time. Also, the big old stoves like mine seem to have a much larger radiating area so I bet the transfer is more effective. It may be a matter of my needing a much larger stove of the new style and it may be the difference between the cast iron VC and Dutchwest stoves needing much longer to come up to temp and radiate but for fast effective heat my experience is that the old well made steel stoves throw out a lot more heat and faster. And since the Fisher is so big I am now burning all the big junk knuckes and nasty pieces I could never fit in my newer stove. I understand all the EPA and insurance issues and all that but I live in rural NH where the only air quality problems we have is when the wind blows all the liberal hot air from south in Massachusetts.

I know I am going to get my ass kicked for this heresy but what the hell. My suspicion is that efficiency is a rating of btu's created per unit of wood in the box and not effective heat transfered to the room which is in the end what we are burning wood for. Can someone set me straight on this.

Thanks

 

[Jags]

Can someone set me straight on this.

Thanks

Yeah...your goofy ;-P

Joking aside, if you were really looking for a giant stove that could roast you out of a barn, you should have got a Blaze King. EPA cert., throws mega heat and would still nibble wood compared to that smoke dragon you just re-installed. Don't get me wrong, those old Fishers were built like a tank, but NOT efficient compared to todays stoves.

I understand how you are trying to compare efficiency to "how well it heats my home". Thats apples and oranges (by the way, do you know that there is no other word in the english language that rhymes with "orange")

 

[Adios Pantalones]

I don't know a huge amount about cat stoves- but my impression is that their real value is extended burns- efficiently converting wood into heat at a slower rate. You can get a non-cat EPA stove that will blast the heat as well, and use less wood in the process.

I am not sure on the measure of BTU's up the pipe vs radiated to the room, but there have been a couple of threads on the efficiency testing and what the numbers mean.

Jags- the band The Fall successfully rhymed "positively deranged" with "curious orange", but they're pretty whacked out dudes with odd accents.

 

[Jags]

Jags- the band The Fall successfully rhymed "positively deranged" with "curious orange", but they're pretty whacked out dudes with odd accents.

Heck, if I have been drinking enough, I can rhyme "peanut butter pie" with "loud exhaust pipes". :cheese:

 

[fossil]

...the band The Fall successfully rhymed "positively deranged" with "curious orange", but they're pretty whacked out dudes with odd accents.

I almost would have bought into it if they had rhymed "positively deranged" with "curiously oranged", but I think they were lazy. Rick

 

[SteveT]

My suspicion is that efficiency is a rating of btu's created per unit of wood in the box and not effective heat transfered to the room which is in the end what we are burning wood for. Can someone set me straight on this.

Thanks

I believe that the efficiency refers to the amount of particulate leaving the flue. Particulate is unburned fuel so it does correlate to how much heat is extracted from a given amount of wood.

I don't doubt that a non-EPA stove can do just what you say. I think the issue is that the EPA certified stove will always give more total heat from an amount of wood than a non-EPA stove. But, depending on the characteristics of the stove it could be spread over a longer period of time so it seems to be doing less.

I think what you are observing is more related to the size of the two stoves rather than whether one is EPA certified and the other is not.

 

[InTheRockies]

My experience is the opposite. I just got rid of an old "monster stove" that had a huge firebox and could eat about anysize wood. Because of the massive size of the firebox and the thickness of the steel, it took quite a while for the stove to begin radiating heat. I'm amazed at how quickly the new EPA-approved wood stove begins radiating heat. Granted, I bought a non-catalytic stove so maybe that's one of the reasons for the different experiences. I don't regret changing out the big, old stove.

 

[buck master]

I agree with playernulla, allthough i've never used one of the newer stoves im allways reading about how to get over night burns,the amount of cords a year, and other issues. i will tell you as a 24/7 burner I load twice a day, use 2.5-3 cords a year and often have to open doors and windows to cool the house down. I use a "92" buck model 80. can't imagine one of the newer stoves doing any better. and would'nt settle for less than a 10 hr. burn.

 

[Todd]

I've burned every type of stove from an old Montgomery Wards barrel stove to the steel aitight beasts to the cats and noncats. I think what you are feeling is the immediate searing heat from the Fisher. You can load a lot of BTU's into those old huge fireboxes, but they also eat it like candy and cool down just as fast. New stoves produce a clean burn and even out the BTU's over a longer time.

 

[snowtime]

I have 2 fishers in my greenhouses. Used to have one in the house. I think your comparing apples and oranges. I mean besides cat your comparing small cast to large steel. Try comparing large new steel to old steel. I also bet you are just use to the searing radiant heat of steel. Easier to get away with wet wood on the old burners could be you never got your new stove dialed in? Our new T6 is great but its a change as no searing heat out sides most all the heat is out the top and door. It means someone can sit near the stove so you can take back part of the living room. I would never go back.

 

[buck master]

al-though the buck 80 is an old air tight, it has a cat with a probe thermometer inserted that reads like this 100-500 inactive, 500-1700 normal range, 1700-2000 too hot.

 

[shady]

I've been burning wood for the better part of the last 30 years.
I've had two stoves: a Fisher papa bear and now a Fisher Grandpa.

They can and do heat a whole house and are easy to use and easily burn
for the whole cold season, never going out.

The grandpa stove is so big you can stack wet wood inside it beside
the fire to dry it out before putting it on the fire. Not the greatest way to get
heat though.

I just put in an order for a Jotul F600. should be here next week.

I love the Fisher but I'm looking for a nicer looking stove, a cleaner burn,
more efficiency and easier to clean ashes.

I've read with interest all I can about burning in the newer stoves

I'm hoping I get the heat I'm used to getting from the Fisher.

 

[woodburn]

Good Post. I do believe the comparison is a bit of apples and oranges, however, I remember growing up my friend's dad a big old stove. He used to load that sucker up and not touch it all day. I am loading my Arbor with 12-18 hour burntime (bull sh*t) every 4-5 hours. I'm sure firebox size is the main factor here but still, not too sure about all the burntime hype put out by these EPA stoves. I believe they put less particulate into the air and increase burntimes some, but not that big a deal. Lots of other things come into play like appearance, clearances, blah blah blah, but strictly talking heat, I think knowing what I know now, if I had a big old stove that didn't have anything wrong with it, I would never change it out.

 

[playernulla]

I am thinking that everyone is right. I think the newer stoves are like BMW's and the old stoves are like Mercedes 240D's. If the newer stoves are run very right and loaded regularly and the wood is dry they will outperform the older stoves. My wood is not always dry. I am not available to either feed the stove regularly and often come home to an empty house with the stove almost out and the temperature in the house in the fifities and the outside temperature near zero. There is a chance that I have not had time to bring inmore wood and so what I bring is going to be cold and maybe a little damp. Under these real world circumstances I believe I need a big mother old steel stove that I can load to the gills and crank the hell out of to get some heat or I have to run oil. The 30% efficiency I give up I think I can make up by burning knuckles, crap wood and all kinds of stuff I get for free that I couldnt fit in my "large" consolidated dutch west. Had a fire tonight and burnt big slabs of old pine my neighbor gave me and it burned great. Wouldnt have fit in my old stove. I will try the old stove this season and see. The suggestion of the Blaze King was a good one. Maybe a big mother newer steel stove with the ability to bypass the catalytic will give me the best of both worlds. If so I will buy one for next season. What I do know is that given my "lifestyle" I need a big mother steel stove so, like Donald Sutherland said in Ryans Gold, I like to be able to get out of trouble as fast as I can get into it". I think that was the name of the movie where he had a tank with five reverse gears. Great movie, I think Clint Eastwood and Telly Sevalis were in it too.

 

[fossil]

Is that the one where Sutherland had great big loudspeakers on his tank and was blasting "I've Been Workin' On The Railroad" as he was demolishing a station/switching yard/tunnel complex-looking place? I loved him in that movie. Rick

 

[playernulla]

Plus there is always old furniture around, like the piano the kids never played that would fit nicely in the Fisher. Almost whole. I remember in the 70's Yankee magazine published the btu value of the different furniture in the house. Kind of wish I had hung onto. Those winter nights when the wood is running low and there's a northeaster blowing off the ocean with wet snow and I'm looking at that maple chair my wife bought at the yard sale that I never liked.....

 

[playernulla]

Yes and welded big pipes around the tanks gun so it looked bigger and scarier to the germans.

 

[playernulla]

No wait. It was Kelly's heroes I think and clint eastwood was Kelly

 

[fossil]

I think you may have been right the first time...wasn't it all about collecting up the gold bullion the Germans had stashed? I dunno, been a long time. Guess I should have the wife put all the old classics in the Netflix queue. %-P Rick

EDIT: Had to look it up on IMDB. You're absolutely right...Kelly's Heroes (1970). Great movie. Time to see it again.

 

[Martin Strand III]

Playernulla:

I resurrected the following from an older post of mine about efficiency and heat transfer. It's not specific for cat/non-cat stove, just general but maybe more to the point than other responses here.

The amount of the heat that is actually transferred into the room depends on a number of factors:

1. Combustion efficiency. In all new technology stoves this percentage is in the high nineties.

2. Heat transfer efficiency (thermal efficiency). How much of the heat generated in the firebox escapes through the chimney into the atmosphere (stack loss) depends on the
firing strategy and the thermal mass of the heater. Newer metal stoves and fireplace inserts with firebrick lining are designed to be clean burning but still have poor thermal efficiency because they lack a thermal mass that functions as a heat exchanger. The combustion efficiency multiplied by the heat transfer efficiency, is the overall efficiency, but this term still does not fully characterize the true efficiency of a heater.

3. Linearity of output. For clean combustion, wood requires a brisk, hot fire which results in short burn times. If the heater has no storage capacity the fire must be
damped, otherwise all the heat is transferred into the room during the burn time. As a result, the room becomes overheated while the fire is burning and under heated after the
fire has died down. An overheated room loses more heat to the environment because of the higher temperature differential between the room air and the outdoor air.

4. Partial charge efficiency. Many stoves do not handle small fuel charges efficiently because high temperatures are needed to obtain non-smoldering combustion. Some
soapstone heaters handle all reasonable fuel charges with equal efficiency, which is important during milder days of the heating season when only a partial charge is required.

MORE ABOUT “EFFICIENCY”

“Heating efficiency shows how rapidly the heat produced by the fire is transferred to the room. It does not, however, measure how comfortable the room will be, only how quickly the heat is delivered. A combination of high combustion efficiency and moderate heat transfer efficiency is the ideal in any wood burner.

Metal stoves and wood furnaces typically have relatively lower combustion efficiencies and relatively higher heat transfer efficiencies ... Metal transmits heat very well, in fact within minutes of the fire being lit. Similarly, the wood furnace heats the air instantly and immediately distributes this hot air to the home. This makes for a very responsive heater, which is able to throw heat into a space very quickly. However, this fast response comes with two critical drawbacks.

Firstly, it becomes very difficult to regulate the heat output so that it is comfortable. If the heat output (heat transfer) is controlled by restricting the air supply, combustion efficiency drops off drastically, causing a smoky fire, huge amounts of air pollution and probably creosote deposits. If the air supply is not restricted, combustion efficiency improves but the room becomes too hot and dry, which also has an adverse effect on the health of the occupants. This clearly demonstrates that high heat transfer efficiency is not a desirable quality in a wood heater.

Secondly, combustion efficiencies of metal stoves and furnaces are comparatively low, because the heat is given off too quickly and the temperature of the fire cannot build to the point where the gases are fully burned. Most metal stoves and furnaces cannot be burned safely over 900 degrees F. (482 deg. C) because the metal becomes too hot and the unit is severely "over-fired". They are usually not comfortable to be around when burned at over 400 degrees F. (204 deg. C), due to their high heat transfer efficiency.”

www.tempcast.com/planningguide/plan01.html
_______________________________________

ABOUT EFFICIENCY AND THERMAL MASS

“Heat transfer efficiency (thermal efficiency). How much of the heat generated in the firebox escapes through the chimney into the atmosphere (stack loss) depends on the firing strategy and the thermal mass of the heater. Newer metal stoves and fireplace inserts with firebrick lining are designed to be clean burning but still have poor thermal efficiency because they lack a thermal mass that functions as a heat exchanger. “

www.hotrockmasonry.com/PDFs/Planning_Guide.pdf

and

“Heating efficiency of any wood heater depends on 2 factors:
(1) Combustion Efficiency - how completely it burns the wood and
(2) Transfer Efficiency - how much of the fire’s heat gets into the room rather than going up the flue.

How efficient your wood heater operates depends on 2 more factors:
(1) Installation - location on outside v inside wall. Heater too big for house? Flue draw?
(2) Operation - Is wood green? Firebox load? Adequate air?

Your operating technique accounts for the largest variations in your woodstove’s heating efficiency. And, unless you burn consistently above 1000* F] most of your [$$] investment in wood goes up in smoke.

www.baaqmd.gov “Woodburning Handbook”
____________________________________________

Aye,
Marty

 

[FireWalker]

It is amazing as I read more and more threads here how many times you read about people having bad feelings/experiences about modern EPA rated stoves and more often than not I've noticed that the EPA stove that generates the bad rating is the Duchwest line.

I ran the same stove as you for 12 years and I agree completely regarding long heat up times and the limitations of the fire box and also the absolute need for perfectly seasoned wood.

Just how many of these old duchwest stoves are out there?

If people only base their opions on their experience with Duchwest, that IMHO is not enough. Unfortunately we connot road test wood stoves.

 

[playernulla]

The info is great and makes perfect sense and here's how I relate it to my big metal stove theory. There is a way, I think, to operate the stove to yield the best compromise of efficiency and comfort. I come home from work and the house is cold and I need a lot of heat fast. I get a fire roaring in the big metal stove and use it's high heat transfer rating to both burn efficiently because I am burning hot and transferring heat into the room for use. When the house is warm i load the stove with an amount of wood that burns hot but due to the smaller amount of wood in the stove it only throws off as much heat as I want. If the house gets cold I add a bigger load, if it gets warm I wait longer to reload or reload a smaller load. Clearly this is more of a hassle than just burning a fixed even load in a smaller cast iron stove and for those who are home to add the right load at the right time its not an issue. But if you have a cast iron stove with a small box you have zero flexibility. You can only get it so hot because the box only fits so much wood and because the cast iron takes so long to heat you arent going to impact the temperature of the room for a much longer time so you are kind of doubly screwed. Its what I experienced with all the smaller cast iron stoves I've owned. If I fell behind the curve it was very, very hard to catch back up and I ended up having to burn oil.

The more interesting point is that I would venture a guess that not many people know of, or consider the efficiency factors you noted which are very important. So the truth is that the efficiency rating published is in many ways irrelevant because a stove could have excellent burn efficiency and horrible transfer efficiency and partial charge efficiency and be less efficient in practical terms than a lesser rated stove. In fact a designer would be incented to design to optimize burn efficiency at the expense of the other efficiencies because that is the only published in the brochures. I started my career many years ago as a quality assurance technician and then manager and a big part of the job was understanding what to measure and why you were measuring it. It would be interesting if the stove companies published a graph that showed a line for each of the metrics: burn efficiency, transfer efficiency, linearity, and partial charge efficiency so buyers could determine which stove would meet their specific needs.

Interesting.

 

[sapratt]

Honey wheres the chair I just bought?
I don't know maybe someone....Man if feel good in here doesn't it?

 

[Bill]

I believe there is some truth to the old smoke dragons burning hot. I remember a few I had that made the house into a sauna. But with an airtight stove, you can manage the fire, for even, long burn. By checking the stack temperature and stove top temperature you can get an efficient burn, for a longer period.

I also remember how much wood I use to use years ago, my old stove ate it. I also don't see why a smaller stove cannot run at high temperatures just like a large stove. The only difference I see is the length of time it produces productive heat.

 

[playernulla]

Well the smaller stove can run at the same high temperature but it cant put out the same amount of heat in the same period as the big stove. I have a big steel stove capable of radiating a lot of heat and I bring it up to a certain temperature and keep it there it is going to pump out a lot more heat than a smaller stove with less radiant area at the same temperature so I can heat a bigger space or heat the same space hotter. Thats why i am thinking that for my world, where I have to "catch up" and throw out a lot of heat in a short time I am better off with a bigger steel stove even though I dont always use the extra capacity. If I get one of the newer high efficiency ones like a Burn King I will have the best of both worlds. What happens if you are away and your stove goes completely out? Is it hard for you to get the stove to warm the house? For me on really cold winter days in NH I can't get enough heat out to catch up. Now my wood wasnt super dry so that might have been a part of the problem but I never seemed to have the extra capacity I needed.