Pellet stoves are 75-85% efficient? See this.

[MCPO]

I got a real kick out of this one. Regarding average stove efficiencies thought to be 75-85% efficient and EPA even better. Something just don`t add up according to this ad. Below is a paragraph taken from the adverstising of a well known stove brand.

"What's so good about E.P.A. certificationand being "green"?
Most other pellet stoves burn at a higher air-to-fuel ratio, typically resulting in lower efficiency. Our E.P.A. certified stoves have a 78% efficiency rating, and burn less fuel for the same amount of heat when compared to lower-efficiency stoves. Choose a certified stove to get more heat for your "green" dollar!"

 

[jtakeman]

As far as I know almost ever brand of stoves has models that are certified to meet the EPA's guide lines. What makes this Co. so special?

 

[MCPO]

As far as I know almost ever brand of stoves has models that are certified to meet the EPA's guide lines. What makes this Co. so special?

Jay, Aren`t all pellet stoves in general EPA exempt but individual stoves can be tested and if it meets a certain standard it can be classified as EPA certified?
Actually it doesn`t appear that this stove maker is claiming anything special since it is touting the stove as being only 78% efficient. It`s kinda baffling to me.

 

[jtakeman]

As far as I know almost ever brand of stoves has models that are certified to meet the EPA's guide lines. What makes this Co. so special?

Jay, Aren`t all pellet stoves in general EPA exempt but individual stoves can be tested and if it meets a certain standard it can be classified as EPA certified?

Gio as far as I know the stoves were sent out for independent testing to meet the cert standard. Please correct me if I am wrong. But I email Enviro for my cert and they said they were waiting for results from the independent lab. This was last January. I though I could claim on last years taxes. But I had to wait until this year to claim my stove.

 

[MCPO]

As far as I know almost ever brand of stoves has models that are certified to meet the EPA's guide lines. What makes this Co. so special?

Jay, Aren`t all pellet stoves in general EPA exempt but individual stoves can be tested and if it meets a certain standard it can be classified as EPA certified?

Gio as far as I know the stoves were sent out for independent testing to meet the cert standard. Please correct me if I am wrong. But I email Enviro for my cert and they said they were waiting for results from the independent lab. This was last January. I though I could claim on last years taxes. But I had to wait until this year to claim my stove.

Sounds plausible , on my tax credit form it lists the particular models of my stove brand that qualify for the credit and the form wasn`t issued until June 3, 2009.

 

[smirnov3]

This sounds like typical advertizing hogwash

you know, like the bottles of olive oil that say in big letters "cholesterol free", implying that those _other_ olive oils DO have cholesterol.

(FYI, no cooking oils have cholesterol, unless you buy one made out of meat (Mmm, shmaltz...))

 

[cncpro]

Neither the pellet stove efficiency claim nor the olive oil label sound anywhere near as misleading as the Amish-built Miracle Heater. I can't imagine anybody buying those things...

I guess the moral of the story is Buyer Beware.

 

[BDPVT]

There are many misconceptions about efficiency ratings that the marketing gurus love to throw around to confuse the consumer.The pellet stove efficiency rating published by their manufacturers is a combined rating which includes combustion efficiency, electrical efficiency and heat transfer efficiency. Pellet stoves mostly burn at over 98% combustion efficiency, and the electrical efficiency is about 99%. Assume, for the sake of argument, that the heat transfer efficiency of a pellet stove is 60%. If you add up 98%, 99% and say 60%, you get 257. Divide that figure by three to get the overall efficiency and it comes out at 85.7%.
78% is the EPA's assumed default efficiency for a pellet stove's overall performance. Its clear then, that the heat transfer efficiency of pellet stoves is often less than 60%. The published Btu rating of a pellet stove relates to its combustion efficiency. This is a measure of the heat produced from burning fuel. It does not directly relate to heat available to the home as some of it disappears up the flue.
One pound of hardwood pellets will produce around 8,200 BTU’s. Softwood pellets slightly more. As combustion efficiency is so good in pellet stoves, this figure is very close to the actual heat 'input' of the stove. So take a stove with a published rating of 40,000 BTU/hr. Divide 40,000 by 8,200 and you see that at that output, the stove is burning 4.8 lbs. of pellets an hour. This 'heat input rating' is the main figure we have for assessing the capability of a pellet stove.
As well as assuming an efficiency of 78% for pellet stoves, the EPA also stipulates that they produce particulate emissions of less than 2.5 grams per hour to be approved. Tests for this must be carried out at an independent testing laboratory such as Omni. To be exempt, a pellet stove must have an air to fuel combustion ratio of more than 35:1.
From the above heat transfer efficiency figures, it's clear that there must be a wide range of heat exchanger efficiencies in pellet stoves. To be effective a heat exchanger must have a large surface area, and the stove must direct hot air evenly over that area. Bottom line? Pellet stove efficiency is only as good as the efficiency of its heat exchange system

 

[jtakeman]

Pellet stove efficiency is only as good as the efficiency of its heat exchange system

Amen!

 

[MCPO]

There are many misconceptions about efficiency ratings that the marketing gurus love to throw around to confuse the consumer.The pellet stove efficiency rating published by their manufacturers is a combined rating which includes combustion efficiency, electrical efficiency and heat transfer efficiency. Pellet stoves mostly burn at over 98% combustion efficiency, and the electrical efficiency is about 99%. Assume, for the sake of argument, that the heat transfer efficiency of a pellet stove is 60%. If you add up 98%, 99% and say 60%, you get 257. Divide that figure by three to get the overall efficiency and it comes out at 85.7%.
78% is the EPA's assumed default efficiency for a pellet stove's overall performance. Its clear then, that the heat transfer efficiency of pellet stoves is often less than 60%. The published Btu rating of a pellet stove relates to its combustion efficiency. This is a measure of the heat produced from burning fuel. It does not directly relate to heat available to the home as some of it disappears up the flue.
One pound of hardwood pellets will produce around 8,200 BTU’s. Softwood pellets slightly more. As combustion efficiency is so good in pellet stoves, this figure is very close to the actual heat 'input' of the stove. So take a stove with a published rating of 40,000 BTU/hr. Divide 40,000 by 8,200 and you see that at that output, the stove is burning 4.8 lbs. of pellets an hour. This 'heat input rating' is the main figure we have for assessing the capability of a pellet stove.
As well as assuming an efficiency of 78% for pellet stoves, the EPA also stipulates that they produce particulate emissions of less than 2.5 grams per hour to be approved. Tests for this must be carried out at an independent testing laboratory such as Omni. To be exempt, a pellet stove must have an air to fuel combustion ratio of more than 35:1.
From the above heat transfer efficiency figures, it's clear that there must be a wide range of heat exchanger efficiencies in pellet stoves. To be effective a heat exchanger must have a large surface area, and the stove must direct hot air evenly over that area. Bottom line? Pellet stove efficiency is only as good as the efficiency of its heat exchange system

Sounds like a very good explanation of how they arrived at that 75-85% efficiency rating. Thanks.
I`ve always maintained that the greatest improvement to a pellet stove can be made with the heat exchanger itself.

 

[MCPO]

So in summary and in real world use a non EPA certified pellet stove can actually have a higher net efficiency rating than one that is EPA certified if the heat transfer/heat exchanger itself is more efficient , (all other things being equal).