EPA numbers vs. Manufactuer's numbers re: efficiency and BTU

[adk4]

In looking at an EPA publication the Jotul 600 is listed with an efficiency of 63% and 4.1 g/h rating, BTU from 11,000-32,500.

The Jotul webiste lists efficiency at 71% and BTU's of up to 81,500.

The 600 owner's manual lists BTU at 13,500 to 45,900 BTU’s per hour

I figured the Jotul website is going to be the least trustworthy since they are in the business of selling these things, on the ohter hand, the EPA figures are from a government resource which isn't always the most reliable.

Which of these figures, especially BTU output is the most accurate and useful to us in making a decision? Thank you AGAIN, for your help.

 

[burntime]

63% is the epa default unless the manufacturer pays additional to certify as I understand it. Go by firebox size, I think 1 pd of wood is 8k btus, the bigger the firebox the more btus. Marketing is more about deception then fact so I would not use their numbers.

 

[Todd]

The EPA primarily tests for emissions not efficiency, so like Burntime stated the EPA just puts all the non cat stoves in a 63% rating and cat stoves in a 72% default efficiency.

There are independent cordwood tests that the manufactures pay for to get a more realistic number, but there are so many variables I don't know how realistic it could be.

Others swear that the lower the emissions or grams per hour (gph) the more efficient the stove. But that also depends on many different variables like chimney, wood moisture and type, weather and others.

 

[FrankIvy]

EPA numbers for BTUs are based on a non-cord wood fuel.

That is, they're potentially useful for relative comparisons, but not for absolute BTU production.

Despite the inclination for manufacturers to spin to sell, I'd trust Jotul's numbers. They are probably burning a full load of prime hardwood with very high BTU on full bore to get the number, but there it is.

If you want to know heat output over time, you can't size a wood stove like a boiler, because it would be almost impossible to keep a stove at maximum BTU continuously.

Figure Manufacturer's rated BTU*efficiency*60-75% and you'll have about your real life equivalent of a boiler/furnace times its efficiency.

If in doubt about size, I'd always suggest going higher. Most quality stoves can operate at low BTU output very well.

None can put out more heat than the MF BTU rating, so if you go too small, you're done.

 

[Todd]

Nice to see you back Frank.

 

[precaud]

The thing about the btu rating is that it is a rate of output (btu/hr). But it doesn't say for how long the stove can sustain that rate. Case in point; the little Jotul F602 has a max rating of 42,000 btu/hr. But it won't sustain that rate of output for more than a few minutes.The size of the firebox will show you that, more than any of the numbers.

Contrary to my convictions of a couple years ago, I DO see a direct correlation between lower emissions rating and cleaner chimney exhaust. The lower the number, the less smoke you'll see, and the cleaner your chimney will be.

 

[karl]

This is how I figured it for my Summit.


60 pounds of wood times 8000 btus a pound = 480,000 x 70% efficiency = 336,000 btus a load

If I burn all of it in four hours I get 84,000 an hour. PE says 97,000 an hour max

If I burn all of it in eight hours I get 42,000 an hour.

I got the 60 pound number from their brochure and nobody here has ever said a three cubic foot box doesn't hold 60 pounds. I've never weighed the wood.


The real point is who cares. Buy a good sized stove, stay warm, and save money.

 

[R&D Guy]

Always question a "...up to.." specification. It typically means best case possible and a test that was run in house. We can all easily get "Up To" 100 miles per gallon driving down hill in neutral. In this case it may mean if you burn a cord of greasy pizza boxes, or what's know as, "Brands" in the testing world.

EPA BTU rating is likely conservative. When certifying a unit with EPA, you put a few pieces of furniture grade (no knots) 2x4's and 4x4's in the stove at perfect measured spacing and moisture with additional 1/2" spacers between contacting pieces of wood. EPA tests a high, medium and low burn for emissions. The numbers you are seeing on Jotuls site like show their own tests with brands for high BTU and rounds for low BTU. Who knows where they got efficiency.