Buyer beware

[heaterman]

This kind of thing torques me just a little. People buying wood burning equipment need to be given information that is applicable in real world conditions. Overstating efficiency or telling only part of the facts is rampant in the wood burning industry and nearly all manufacturers massage things to represent the best possible case. Our customers deserve honest and 100% accurate information that tells the whole story.

http://forgreenheat.blogspot.com/2013/01/beware-of-ads-for-99-efficient-wood.html

 

[jebatty]

Couldn't be more true. Real world results usually are much different than test results or laboratory results. This forum is excellent as it reports how real people use their wood burning devices. And going a couple of steps further with users employing good data gathering and reporting, and then letting others critique their findings, produces very good info.

 

[BoilerMan]

In their defense, it was combustion efficiency. Misleading, but we do not know the whole story. There seem to be many happy Kumma fire furnace users on here.

TS

 

[Frozen Canuck]

Agreed HM & JB. Long past time there was a universal real world way of stating results, seems far too many are being quite "liberal" with their "scientific findings". What does 94% combustion eff. mean anyway? Does that mean that 6% of the available fuel was not burned? That's going to be quite a large pile of ash/char in a heating season in my neck of the woods. Far more interesting & relevant is an overall system eff. # that is accurate & repeatable by customers.

 

[webbie]

I've been fighting against such crap since 1979....or at least since I figured some of it out myself!

At least back then we were told the basic truth - that airtight stoves were 45% or so efficient.

Misleading efficiencies are par for the course in the USA, it seems. Really high figures are quoted for gas and pellet stuff, despite the real truth being published by a Canadian outfit. The real efficiency, for instance, of a certain gas fireplace may be 42%, while the brochures quote up to 70% (steady state).

All intentionally done to mislead the end consumer.

Sad, IMHO.

 

[DaveBP]

Caveat Emptor.

Romans had the same problem.

 

[jebatty]

I have discussed "efficiency" in many posts, generally and also specifically with regard to the 3 gasification boilers (Tarm Solo 40, Garn WHW3200 and Wood Gun E500) with which I have experience. I use a consistent, objective standard not of my own creation (wood at 20% MC and 400F stack temperature has 6,050 btu/lb) and I weigh the wood. I then have used two different primary data techniques: 1) measure the increase in water temperature of a storage tank of known capacity resulting from the burn of a known weight of wood; 2) measure the difference between supply and return temperature at a known flow rate against a burn of a known weight of wood. With regard to the Tarm, since it and storage are in my shop and the shop has heat gain from the skin of the Tarm, the stack, piping and storage heat loss through the insulation between burns, I also have calculated a higher "efficiency" rating.

While these techniques rely on assumed uniform 20% MC and constant 400F stack temperature, and while we all know that these are not scientifically or laboratory accurate, they do represent about what we all strive for: well seasoned wood. And, stack temperatures vary considerably with many boilers over the course of a burn, and 400F as an average may be close to what many experience (efficiency gain/loss from a different consistent stack temperature is about 2-3% with +/- 100 stack temperature).

I think it is pretty safe to say that at least with these three boilers, and probably most others of similar design and function, except perhaps some of the lambda boilers, btu delivery efficiency in the 80-85% range is realistic.

I won't talk about "burn" or "combustion" efficiency because I have not done any research or data gathering which would give me a basis to do so.

 

[webbie]

With boilers, at least a measurement is more possible! Although, no one is going around bragging that OWB (old style) are 25% efficient.

But with water temps in and water temps out and flow and wood you can get close.

Even then , we run into the wood thing - whether to measure lower or higher heating values, etc.

My general rule in all these things is to figure low. I think some of the super condensing oil and gas stuff used to advertise 97% - when, in fact, I think they are 90% or so. Vent free gas advertised 99% because, after all, where else would the heat go? Well, I think it turns out that there is latent moisture and other stuff that brings it down.

The basic idea here is to always figure low.

 

[ewdudley]

I think some of the super condensing oil and gas stuff used to advertise 97% - when, in fact, I think they are 90% or so.

Based on what?

Vent free gas advertised 99% because, after all, where else would the heat go? Well, I think it turns out that there is latent moisture and other stuff that brings it down.

Actually the latent heat of vaporization shows up as increased sensible heat. Don't know what to tell you about 'other stuff'.

In my experience the efficiency of vent free gas is very close to zero. I ran mine for an hour and uninstalled it immediately.

 

[BoilerMan]

My comment above still stands, we don't know the whole story, and how the info got there. Misleading, absolutly.

There should be some type of 'real world' testing that can be done to determine some actual numbers. AFUE is a best guess but is still misleading, but at least if all heating equiptment were done to the same standard we could compair between types and brands. A hot air furnace is hard to quantify outside of a lab as Craig said. When people see the work Efficiency followed by the % symbol they think somethig different than combustion only.

Case in point, I'm removing a circa 1940 coal converted to oil boiler for my FIL, it's fired at 2.75gpm and heats a large apartment building. The fuel company did a cleaning for the PO and the paperwork was near the boiler. It stated all the regular test data used to calculate 'efficiency' from the satck gas readings. It stated the antiquated boiler (which holds over 100 gallons of water) to be 86% efficient.... Well this is combustion efficiency, as it had a new carlen burner which is good at burning oil 'efficiently'. Well the overall efficiency was something much different at the 12" stack, asbestos boiler jacket, all add up to huge losses. But the "efficiency" is 86% my FIL said, why change it? He found out this fall, and that's why I'm pulling it out. I should take some pics of the monstrosity.

TS

 

[FyreBug]

I've had this discussion somewhere else, but there are various efficiency tests - combustion, heat exchange, BTU etc..

Most folks equate efficiency with 'how much of it do I get to keep in my house?'. There's 3 different tests to do this - Stack Loss, LHV & HHV. All three of them have different parameters. MFG are not legislated to state average values over a series of test so most if not all state their highest.

Frankly unless you state average values over industry monitored standards, it's almost impossible to have a fixed value. Especially with solid fuel the results fluctuate so much between BTU load, burn rate etc.. the average consumer will not understand it at all.

The alternative would be to post test results but many of these are 32 - 50 pages long and it would confuse matter further since it has to be interpreted.

In our furnaces we state HHV, LHV, Max BTU input, MAX BTU output (BTU output X % efficiency on high fire) and average BTU - which tries to baseline average heat output over the life of the fire.