Wood Stove BTU Rating

[ColdNorCal]

Moved to separate thread

He is referring to another thread where @BKVP said there is no standard for determining the BTU output so numbers are basically bogus.

I see, thanks. I agree, the manufacturers numbers are bogus. Hence, I looked at EPA numbers, users comments, spoke with a couple reputable manufacturers, vendors, members on this site... and two very nice and helpful stove reps that support several American stove companies.

 

[Happy Stacker]

I am no BTU expert...but I play one on TV and can tell you this. It's currently 82F in my living room.

 

[Highbeam]

I see, thanks. I agree, the manufacturers numbers are bogus. Hence, I looked at EPA numbers, users comments, spoke with a couple reputable manufacturers, vendors, members on this site... and two very nice and helpful stove reps that support several American stove companies.

No, the epa numbers are bogus too. They are not tested as I would have thought. There is no way to know how many btu a stove makes.

 

[BKVP]

To be clear, they are not comparable, as I don’t recall saying or writing bogus. So how does one get an actual btu production from a stove, let alone at a specific burn rate? This is how I look at the calculations.

Pounds capacity (not from a brochure) but real world, with hot coals in the firebox. Let’s say it’s 50lbs. Then using your m.m., everybody has one, correct?, subtract for m.c. So let’s say 20%, 50lbs-10lbs of water leaves 40lbs.

Btus per pound is fixed so multiply the two. 8,600 btus x 40 = 344,000.

Take the result and multiply it by the HHV efficiency of a particular burn rate. So let us pick the low burn rate and assume 70%. You can expect 240,800 deliverable btus for that burn rate. So if it burns 10 hours....24,800 deliverable btus per hour.

You can do the same for each burn rate, just change the HHV efficiency value and corresponding burn time.

If this aligns to sales numbers from brochures, excellent!

 

[Happy Stacker]

Btus per pound is fixed so multiply the two. 8,600 btus x 40 = 344,000.

OK I am confused. Isn't BTU/lb variable and not fixed, based on wood species?

 

[BKVP]

OK I am confused. Isn't BTU/lb variable and not fixed, based on wood species?

Nope. The weight is variable based on specific gravity. So a full load of oak might be 50lbs in a stove, but a full load of cottonwood in the same unit may be 25lbs. You have more input energy in the oak load.

 

[Highbeam]

To be clear, they are not comparable, as I don’t recall saying or writing bogus. So how does one get an actual btu production from a stove, let alone at a specific burn rate? This is how I look at the calculations.

Pounds capacity (not from a brochure) but real world, with hot coals in the firebox. Let’s say it’s 50lbs. Then using your m.m., everybody has one, correct?, subtract for m.c. So let’s say 20%, 50lbs-10lbs of water leaves 40lbs.

Btus per pound is fixed so multiply the two. 8,600 btus x 40 = 344,000.

Take the result and multiply it by the HHV efficiency of a particular burn rate. So let us pick the low burn rate and assume 70%. You can expect 240,800 deliverable btus for that burn rate. So if it burns 10 hours....24,800 deliverable btus per hour.

You can do the same for each burn rate, just change the HHV efficiency value and corresponding burn time.

If this aligns to sales numbers from brochures, excellent!

It was me that concluded the EPA BTU ratings are bogus. Based on statements you made that there is no regulation, testing, or procedure applied by the EPA for checking, verifying, or regulating the random number that manufacturers provide the EPA for their BTU publication. I own a stove with a maximum EPA output rating that is almost half of what the maximum EPA output rating is for a stove from another brand that is the same size. Weird. That is why this number is bogus and end users apparently have to calculate it yourself based on firebox size as you detailed above. It's really disgraceful. You don't see this on other HVAC equipment do you? Imagine buying a furnace this way.

Some manufacturers will do that math and be honest. Some are ignorant. And some will flat out lie to make a sale. The end user is the victim here.

 

[Highbeam]

OK I am confused. Isn't BTU/lb variable and not fixed, based on wood species?

BTU per unit volume is variable based on wood species. There is a slight btu/lb advantage to particularly pitchy woods like evergreens where some energy is available from the tar but this variable is not the wild card.

Also beware of published weight capacity of fireboxes. The manufacturers like to be creative on this one too. They will assume you have access to some ridiculously high density species like ironwood and certainly not give back any firebox volume for coals or airspace. I have weighed a load of firewood into my stove, on an actual scale, using a medium density local hardwood and was way way below what the manufacturer said I should be able to put into the stove. Since the OP is from Nor Cal he may be also be burning low/moderate btu woods.

You can't even trust the published firebox volume from manufacturers. Some flat out lie. Some will include space above the firebox roof that is impossible to load wood into. You have to measure this with a tape measure.

 

[BKVP]

Actually, fb volume is calculated by the test lab. So if you look at test reports on mfg websites, you'll find fb volume. This should then translate over to brochures and point of purchase materials.

 

[begreen]

So if you look at test reports on mfg websites, you'll find fb volume.

I don't recall seeing actual test reports located on stove websites. Are they on BK's?

 

[Highbeam]

Actually, fb volume is calculated by the test lab. So if you look at test reports on mfg websites, you'll find fb volume. This should then translate over to brochures and point of purchase materials.

Okay but is it correct or does this official volume include volume above the baflle or inside the cat dome that is obviously unavailable for fuel? In my experience with a tape measure on a previous stove, the published volume is completely false and useless for fuel capacity considerations.

 

[Highbeam]

I hope the OP doesn't mind. This is a really fascinating conversation about the published "information" available for these stoves. So often we have forum members asking about what stove to buy or looking in to a new model stove that nobody has experience with so we look at the specs.

 

[begreen]

Good info, but it will be lost. This needs a separate thread so that it is more discoverable in the future. Will move posts to this new thread .

 

[Marshy]

EPA has no interest in the efficiency of wood stoves or how many BTU's they produce they are strictly interested in the emissions. That is the only certification/standards they meet (besides UL). The HHV LHV is a standard to help determine the efficiency of the stove but is not a mandated test which all manufactures have to comply with to determine the stoves efficiency. They can use other methods and make claims about stove efficiency and output thst would be difficult to achieve in the real world. The HHV method is probably the best standardized method to regard when comparing stoves but it's not a required method. Does thst make sense? Thst is my "in a nut shell" explination and understanding of the difference between EPA emissions and stove efficiency or btu output. Don't confuse EPA with output or efficiency. Two separate things.

 

[BKVP]

I don't recall seeing actual test reports located on stove websites. Are they on BK's?

Yes! Required under Federal Law.

Look at bottom of ours for "Test Reports"

 

[BKVP]

Okay but is it correct or does this official volume include volume above the baflle or inside the cat dome that is obviously unavailable for fuel? In my experience with a tape measure on a previous stove, the published volume is completely false and useless for fuel capacity considerations.

Some space may be not usable space.

 

[begreen]

Yes! Required under Federal Law.

Look at bottom of ours for "Test Reports"

I did find the info on Quadrafire's and Lopi's site, but not finding this on BK's. Probably there, I just haven't been able to locate it.

 

[BKVP]

EPA has no interest in the efficiency of wood stoves or how many BTU's they produce they are strictly interested in the emissions. That is the only certification/standards they meet (besides UL). The HHV LHV is a standard to help determine the efficiency of the stove but is not a mandated test which all manufactures have to comply with to determine the stoves efficiency. They can use other methods and make claims about stove efficiency and output thst would be difficult to achieve in the real world. The HHV method is probably the best standardized method to regard when comparing stoves but it's not a required method. Does thst make sense? Thst is my "in a nut shell" explination and understanding of the difference between EPA emissions and stove efficiency or btu output. Don't confuse EPA with output or efficiency. Two separate things.

Actually, the 2015 NSPS does require efficiency testing. So it is HHV and is required. Keep in mind, 99% of stoves are tested with dimensional lumber .

 

[BKVP]

Not finding this
View attachment 225048

BeGreen...my glasses are yours for the asking. Look under information. See Test Reports?

 

[Marshy]

Actually, the 2015 NSPS does require efficiency testing. So it is HHV and is required. Keep in mind, 99% of stoves are tested with dimensional lumber .

Thanks for clarification. All the research I performed on this subject was the winter of 2014. Good to know it's been changed.

 

[ColdNorCal]

EPA has no interest in the efficiency of wood stoves or how many BTU's they produce they are strictly interested in the emissions. That is the only certification/standards they meet (besides UL). The HHV LHV is a standard to help determine the efficiency of the stove but is not a mandated test which all manufactures have to comply with to determine the stoves efficiency. They can use other methods and make claims about stove efficiency and output thst would be difficult to achieve in the real world. The HHV method is probably the best standardized method to regard when comparing stoves but it's not a required method. Does thst make sense? Thst is my "in a nut shell" explination and understanding of the difference between EPA emissions and stove efficiency or btu output. Don't confuse EPA with output or efficiency. Two separate things.

After researching wood stoves for a few weeks that is what I realized. For example, the large Englander 30-NC is EPA rated at 1.63 grams/hr. with BTU of 12000-28300. Yet it has a LARGE fire box of 3.5 cu ft. I wonder what the emissions and efficiencies are when the BTU's are in the range of how customers actually use the stove and more importantly, how the stove was designed to perform.

Two different companies both told me the same thing when I asked about what will happen to their current line of stoves when the 2020 EPA standards are required. They both said, the EPA tests numbers are not difficult to achieve and require only a few tweeks/adjustments to pass.

This is very confusing for us novices and to be honest, all this seems very dishonest, or misleading at best.

As mentioned in an earlier post, I do live in Nor Cal and on 5 1/2 acres. The trees on my property are oak and some med-hard wood fruit trees that were planted many years ago and have far outlived their fruitfulness

 

[begreen]

BeGreen...my glasses are yours for the asking. Look under information. See Test Reports?

There is no listing of Test Reports in the Information column. Magnified for your glasses, mine are prescription.

 

[BKVP]

http://www.blazeking.com/TestReports

Refresh you browser or remove history. I logged on found it instantly.

Link above...

 

[Marshy]

Actually, the 2015 NSPS does require efficiency testing. So it is HHV and is required. Keep in mind, 99% of stoves are tested with dimensional lumber .

NSPS - New Source Performance Standard
Says it all here if anyone wants the link.
https://www.epa.gov/residential-woo...mary-requirements-wood-fired-hydronic-heaters

It doesn't call out HHV test specifically, just an approved one. I can't imagine there are several to choose from which one would offer better results over another.

 

[BKVP]

NSPS - New Source Performance Standard
Says it all here if anyone wants the link.
https://www.epa.gov/residential-woo...mary-requirements-wood-fired-hydronic-heaters

It doesn't call out HHV test specifically, just an approved one. I can't imagine there are several to choose from which one would offer better results over another.

Yes, look at method 28R. We are required to capture and report HHV.