Just noticed my stove is now about 13.88% more efficient. Yours probably is too!

[jpl1nh]

We may all be able to burn even less wood this winter. My stove efficiency has increased from about 72% to about 82% since the financial crisis came about. COOL! I thought it was just the warmer weather that had decreased my wood usage so far this year, but when I started looking at various manufacturer stove ratings, then I realized my stove (and probably yours too) had recently somehow become more efficient. Too bad the Patriots are playin crappy this season cause now I won"t have to cut as much wood for 2011 and I could watch them more. I knew voting the Dems in would help! Maybe I actually have a job too and just didn't realize it.

 

[btuser]

They're fudgin' numbers to take advantage of the rebates. I noticed my Lopi Freedom insert has gone from a stated 71% eff. to a sparky 77% with nary a redesign.

 

[BrotherBart]

They're fudgin' numbers to take advantage of the rebates. I noticed my Lopi Freedom insert has gone from a stated 71% eff. to a sparky 77% with nary a redesign.

They didn't fudge anything. The government let them start using "lower heating values" like the rest of the world does to measure stove efficiency. That is what everybody but the U.S. has been using forever. Who knows, maybe we start using the metric system next? :ahhh:

Nah.

 

[carinya]

They didn't fudge anything. The government let them start using "lower heating values" like the rest of the world does to measure stove efficiency. That is what everybody but the U.S. has been using forever. Who knows, maybe we start using the metric system next? :ahhh:

closet european are you, BB ?

 

[CarbonNeutral]

They're fudgin' numbers to take advantage of the rebates. I noticed my Lopi Freedom insert has gone from a stated 71% eff. to a sparky 77% with nary a redesign.

They didn't fudge anything. The government let them start using "lower heating values" like the rest of the world does to measure stove efficiency. That is what everybody but the U.S. has been using forever. Who knows, maybe we start using the metric system next? :ahhh:

Nah.

That would be fantastic - and I'm more than a closet European..

 

[Wet1]

Woohoo, mine went from 72% to 92%, that's a 28% increase! Sadly, it doesn't seem to be any more (or less) efficient.

 

[cycloxer]

The new Jotul F 400 Castines are labeled 85% efficient at 7.2 kW. (That's 24,600 Btu's)

 

[AlexNY]

My stove efficiency has increased from about 72% to about 82% since the financial crisis came about.

The way efficiency is measured was changed.

The United States used to use overall thermodynamic efficiency as the definition:

Total heat delivered to the house
------------------------------------------
Total heat in the wood

Now, the European definition is used:

Total heat delivered to the house
-------------------------------------------------------------------
Maximum heat that can be delivered by an "ideal" stove

It makes the numbers look better, but the stove is no more efficient than before.

This is just a gimmick to get people to spend money on new stoves that they do not need, in order to get "better efficiency".

Shame.

 

[BrotherBart]

The facts.

http://mb-soft.com/juca/print/311.html

 

[AlexNY]

http://mb-soft.com/juca/print/311.html

The problem with the "low heat value" is that it is NOT the best that can be done in practical terms. Here is the key statement:

"The latent heat put into the water vapours from all three sources are removed from the calculations as being not recoverable for all practical purposes."

It is true that no commercial wood stoves currently exist that recover the heat of vaporization (this would be called a "condensing" wood stove).

However, such "condensing" wood stoves have been build in the laboratory, and the only reason they were impractical is that the condensate was too dirty to deal with (so using condensation to heat incoming combustion air was not practical). Condensing natural gas appliances are currently available across the US and Europe (in some European countries it is illegal to install any non-condensing natural gas appliance).

How can we know for certain that no inventive person will come up with a way to clean up wood heat condensate, such that exhaust gasses can be used to heat incoming combustion air to 100+ C? Certainly, it is a difficult challenge. However, commercial condensing appliances already exist for oil-heaters, something that was said to be impractical just 10 years ago.

We are all going to look like fools if, 20 years from now, a commercial wood stove is made available with an efficiency that is greater than 100%.

I think it was a mistake.

 

[53flyer]

+1 Alex. I agree. If they wanted to provide a tax credit they should've just made the requirement somewhere around 63-72% (depending on weather you want to include non cats or not since all the non cats were 63 and cats 72 under the old requirements). It's a little strange that under the old system the stoves all seemed to be only 2 results (63 or 72) but now there's a wide range of results.

Why not add a gph figure (somewhere in the 3.7-4.0 range) to the requirements?

 

[cycloxer]

The biggest problem I have is not with the #'s of the stove, but of the variability of the fuel. We have no idea at what efficiency these stoves run in the real world with real wood. A laboratory simulation means nothing.

 

[53flyer]

I see what you're saying cycloxer but if the same lab simulation conditions (standardization) are used for all tests then the results can still be used for comparison purposes. It seems like regulating the moisture content should be simple in a testing environment as should using the same type of wood. Once those variables are standardized then we should be able to use the results even if, due to non-perfect conditions, we never achieve that level of efficiency &/or gph burning.

In other words, the ratio between stoves performance should stay the same. I.e. if stove A is consistently 10% more efficient and has 20% less gph emissions than stove B under ideal lab conditions, it should also have 10% more efficiency and 20% less gph under real word conditions.

 

[DAKSY]

Woohoo, mine went from 72% to 92%, that's a 28% increase!

Modern Math?

 

[cycloxer]

For comparison, yes, I agree 100%.

How do I compare the efficiency of my EPA stove to my natural gas boiler which is stamped 81%? That's the problem I have. I am fairly confident that as long as my boiler is in good working order it is running at that efficiency. My natural gas fuel doesn't vary. Home heating oil doesn't vary either. With my stove I have no idea as I burn all different types of wood cut to different sizes and at varying levels of dryness. Should I run at 400 degrees? What about 600? Which is more efficient? I think stove manufacturers could provide a little better. Either that or there are too many variables and it doesn't matter that much anyway.

 

[53flyer]

For comparison, yes, I agree 100%....
Should I run at 400 degrees? What about 600? Which is more efficient? I think stove manufacturers could provide a little better. Either that or there are too many variables and it doesn't matter that much anyway.

+1. I think those are great points that would be very helpful to stove owners. We're told not to over fire but only a few say what temp that actually is. It shouldn't be that difficult to pull out 3 data points that showed different levels of efficiency and emissions at those 3 different temp settings/burn conditions.

As far as gas and oil, I think they all have their own variables that impact how well their working such as hw clean the air filter is because that can change the ratio of air entering the burn chamber and change the efficiency to something other than optimum.

 

[cycloxer]

You know they could probably publish a graph that shows burn temp vs. efficiency. They could also do one for different wood species - ie, I am sure pine burns more efficiently at a different temp than oak. In the GB manual Jotul says: Nominal heat emission is achieved when the air vent is open approximately 40%. Of course that is with the EUR air intake plate which most people don't use.

 

[BrotherBart]

Face it folks. You heat your house with a metal box that burns any number of types of very large weeds. And unlike all other nifty heat sources you cannot meter the fuel input, just the combustion air. So any comparison to oil heat, electric or gas heat is tinkling into a head wind.

Light the stove and don't worry about it.

BTW 53flyer: You only see two numbers for cat and non-cat stoves because the EPA will either use those default numbers or an actual number provided by the manufacturer as a result of very expensive testing. The stove makers don't have squat to gain by not keeping their money in their pockets and just accepting the defaults. Especially if their stoves wouldn't test out above the default number.

The LHV numbers are actually more accurate since they are derived from the flue gas analysis from the EPA emissions testing adjusted for the moisture content of the wood.

 

[drewboy]

Brother Bart - I stole a quote from ya (with proper credit of course) because no one can state the facts quite like you...

 

[billjustbill]

So, if a Lopi Freedom Bay had a 66% rating last year, has that model now qualified for a tax credit with the newer guidelines? Is there a place that I can check?

Thanks,
Bill