I've read with interest a lot of good comments recently regarding high efficiency wood stoves. However there are some myths that I'd like to debunk from a MFG point of view.
Let me try to dispel some of these myths:
1) Wood burning appliances no matter what their brand and model do not produce BTU's. Wood has BTU. The more wood you can put in there the more BTU you will get out. If one complains his new wood stove is not heating enough, it must be because the unit was not sized appropriately or the fuel is inadequate (see below)
2) A pound of wood is worth about 8,000 BTU at 15% humidity. Wood burns best between 15% to 20% humidity. Above that it is considered ‘wet’ and its BTU output is considerably reduced. This is because the first phase of combustion is to eliminate moisture out of the wood. Therefore all the initial caloric energy (heat) has to boil off water first.
3) Smoke condenses at about 250f. Therefore, because wet wood takes longer to reach gas combustion (visible flames) you will see a lot of smoke until you can get past the 250f limit. The longer it stays below that range the more creosote formation.
4) Efficiencies are measured in EPA wood stoves with the ‘stack loss’ method. That is, whatever heat is lost in the flue is deducted from the total heat output. Ie. An 85% efficient stove means 15% of its heat is lost in the chimney. This is not bad; you need that 15% to create a draft. Old wood stoves (pre-EPA smoke dragons) were typically in the 40% to 50% efficiency range. To provide enough heat for the house they had a large combustion chamber (more BTU) and a high air to fuel ratio. That is they burned fast.
5) A wood stove is basically a carburetor. You have fuel and oxygen. You also have a third component – Heat. These three factors must be balanced carefully to provide best efficiencies and burn time. Too rich creates too much smoke and loss of efficiencies. Too lean and the fire burns out of control and burn time is reduced drastically.
6) Suggestions on raising the fire with a fire grate actually reduces heat output and affect efficiencies. A grate takes a great deal of space meaning less wood can fit in the stove (less BTU). A grate serves no purpose whatsoever in an EPA stove since the primary air intake feeds oxygen directly to the logs and the secondary air channels feed oxygen to the top re-burn tubes.
7) Trying to extract more heat from EPA wood stoves with heat reclaiming devices (flue type or water coils etc…) actually degrades the performance of the unit. The unit will take longer to reach optimum temperature and will not stay as long in the ‘sweet spot’ of secondary combustion. This will cause a cooler fire chamber, more smoke, more creosote, incomplete combustion and poor draft.
8) Your worst enemy is the ‘old guy syndrome…’ Son, you can’t tell me how to burn wood, I’ve been doing it before you were a glint in your dad’s eye… will only make matters worse. The reason your whole way of burning wood must change is the same reason we went from carburetors to fuel injectors or venting old gas appliances versus new gas appliances. The more efficient the unit, the more you have to respect their parameters. It’s a trade-off and you win at the end anyway.
9) Start your fire with small dry kindling and get a small intense fire going immediately to get your draft established. Then keep adding bigger and bigger dry pieces of wood until the biggest is no bigger than 6” to 8” max. Small splits offer more surface area for gases to escape and charcoal phase to begin. A big round log takes longer to get to temp, moisture has to follow the grain and can only evaporate at either end therefore slowing combustion and increasing creosote.
10) Wood stoves are tested and certified for safety by UL. Any attempt at removing parts, drilling holes, modifications etc… immediately voids the UL safety certification and if your house burns down you don’t have insurance.
11) Wood burning appliances no matter what their brand and model do not ‘draft’. It’s a black square box made out of metal with no moving parts. I cant repeat this often enough, a wood stove does not ‘draft’. If you have drafting problems or smoke in the house look at the following: Poor chimney design (this is a whole topic on its own), barometric pressure, temperature differential, length of chimney, house under negative pressure, wet wood and many other factors but almost never a wood stove problem.
12) If you really want to be entertained, there is nothing quite like a chimney fire. Let’s hope it’s not at your house!
In conclusion, the difference between a new EPA high efficiency wood burning appliance and the old one is the new appliance controls the combustion a lot tighter. Both will output the same BTU per pound of wood. However, the old one will burn a lot faster and waste over 50% of its energy in the chimney. The new EPA stoves on the other hand will control and optimize the combustion for a clean, efficient and long lasting burn.
If you want more heat get a bigger stove.
Your best friend is a wood moisture meter and a straight up chimney (that’s what she said!)
Hope this helps
Let me try to dispel some of these myths:
1) Wood burning appliances no matter what their brand and model do not produce BTU's. Wood has BTU. The more wood you can put in there the more BTU you will get out. If one complains his new wood stove is not heating enough, it must be because the unit was not sized appropriately or the fuel is inadequate (see below)
2) A pound of wood is worth about 8,000 BTU at 15% humidity. Wood burns best between 15% to 20% humidity. Above that it is considered ‘wet’ and its BTU output is considerably reduced. This is because the first phase of combustion is to eliminate moisture out of the wood. Therefore all the initial caloric energy (heat) has to boil off water first.
3) Smoke condenses at about 250f. Therefore, because wet wood takes longer to reach gas combustion (visible flames) you will see a lot of smoke until you can get past the 250f limit. The longer it stays below that range the more creosote formation.
4) Efficiencies are measured in EPA wood stoves with the ‘stack loss’ method. That is, whatever heat is lost in the flue is deducted from the total heat output. Ie. An 85% efficient stove means 15% of its heat is lost in the chimney. This is not bad; you need that 15% to create a draft. Old wood stoves (pre-EPA smoke dragons) were typically in the 40% to 50% efficiency range. To provide enough heat for the house they had a large combustion chamber (more BTU) and a high air to fuel ratio. That is they burned fast.
5) A wood stove is basically a carburetor. You have fuel and oxygen. You also have a third component – Heat. These three factors must be balanced carefully to provide best efficiencies and burn time. Too rich creates too much smoke and loss of efficiencies. Too lean and the fire burns out of control and burn time is reduced drastically.
6) Suggestions on raising the fire with a fire grate actually reduces heat output and affect efficiencies. A grate takes a great deal of space meaning less wood can fit in the stove (less BTU). A grate serves no purpose whatsoever in an EPA stove since the primary air intake feeds oxygen directly to the logs and the secondary air channels feed oxygen to the top re-burn tubes.
7) Trying to extract more heat from EPA wood stoves with heat reclaiming devices (flue type or water coils etc…) actually degrades the performance of the unit. The unit will take longer to reach optimum temperature and will not stay as long in the ‘sweet spot’ of secondary combustion. This will cause a cooler fire chamber, more smoke, more creosote, incomplete combustion and poor draft.
8) Your worst enemy is the ‘old guy syndrome…’ Son, you can’t tell me how to burn wood, I’ve been doing it before you were a glint in your dad’s eye… will only make matters worse. The reason your whole way of burning wood must change is the same reason we went from carburetors to fuel injectors or venting old gas appliances versus new gas appliances. The more efficient the unit, the more you have to respect their parameters. It’s a trade-off and you win at the end anyway.
9) Start your fire with small dry kindling and get a small intense fire going immediately to get your draft established. Then keep adding bigger and bigger dry pieces of wood until the biggest is no bigger than 6” to 8” max. Small splits offer more surface area for gases to escape and charcoal phase to begin. A big round log takes longer to get to temp, moisture has to follow the grain and can only evaporate at either end therefore slowing combustion and increasing creosote.
10) Wood stoves are tested and certified for safety by UL. Any attempt at removing parts, drilling holes, modifications etc… immediately voids the UL safety certification and if your house burns down you don’t have insurance.
11) Wood burning appliances no matter what their brand and model do not ‘draft’. It’s a black square box made out of metal with no moving parts. I cant repeat this often enough, a wood stove does not ‘draft’. If you have drafting problems or smoke in the house look at the following: Poor chimney design (this is a whole topic on its own), barometric pressure, temperature differential, length of chimney, house under negative pressure, wet wood and many other factors but almost never a wood stove problem.
12) If you really want to be entertained, there is nothing quite like a chimney fire. Let’s hope it’s not at your house!
In conclusion, the difference between a new EPA high efficiency wood burning appliance and the old one is the new appliance controls the combustion a lot tighter. Both will output the same BTU per pound of wood. However, the old one will burn a lot faster and waste over 50% of its energy in the chimney. The new EPA stoves on the other hand will control and optimize the combustion for a clean, efficient and long lasting burn.
If you want more heat get a bigger stove.
Your best friend is a wood moisture meter and a straight up chimney (that’s what she said!)
Hope this helps
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Ya’ know? Sometimes I have way too much fun for my own good. 
