Average efficiency of a pellet stove - anyone know?

Pellet stoves aren't AFUE rated, which makes the manufacturer's published BTU output data suspect. Has anyone conducted any measurements on their pellet stove to determine an overall efficiency rating? Or, would anyone at least care to take a SWAG at what a new stove's efficiency might be?

For what it's worth Quadra-Fire's web fuel calculation cost web page implies an efficiency of 70%.

What with the price of all sorts of fuel spinning wildly out of control, I'd like to compare a pellet stove efficiency to my (new, recently installed) oil hot air furnace.

jtp10181 said:

Most Quad units are going to be 60-70%. The Mt Vernon AE has an actual published efficiency which should be close to accurate (probably with ideal conditions).

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jtp, I can't find where that's published but I'll take your word for it. At an efficiency of 70%, the Mt Vernon will start paying for itself in about 3 years assuming that oil and pellet prices don't change. Of course that's unlikely, but I'm assuming the difference between the two will be the same.

By the way on the question of battery backup (if you recall what I want to do) - I downloaded the Mt Vernon installation instructions and read that it will function down to 10 V. I can tolerate a 10% voltage drop with no problem at all. If the peak demand is 20 A - a wild assumption on my part - #6 AWG will be more than adequate in my installation. I'd just like to be sure about the 20 A.

Why Wood Heat couldn't provide me this information is beyond me. All I did was read the instructions.

Oh, I agree. First of all I don't intend pellets to completely replace my oil usage (and 2000 gal oil is a lot too). I also have an oil fired water heater so it's difficult to determine how much oil is dedicated to warm air alone. The point of the spreadsheet is that given some reasonable assumptions, the pellet stove will eventually pay for itself. Propane, which I had been considering, won't. Gas would be great but it's not installed here.

There are other intangibles in the purchase decision including the desire to put something in the gaping hole where my coal stoker used to be, and the fact I can have heat when the power fails, which it's done in the past for as much as three days.

Coal is readily available and cheap yet I took the coal stoker out and sold it. Coal is fine if you can put up with the dust - I can't. I also cut and split wood in the past and I'm done with that too.

Webmaster said:

Syl, pellets create dust also.........but it is tan instead of black!

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There is nothing on Earth more evil than coal dust. I'll welcome almost anything else.

Thanks! I've seen that spec sheet many times but never noticed the efficiency. Yes I'm installing the AE. Damn, that's good. At 80% my ROI begins in two years!

I also added coal to the comparison. Interesting that its heat content isn't that much more than pellets. Of course its cost is much lower.

Oh the wire sizing is for voltage drop. 12 AWG would result in about 10% drop with the length I require but I'm trying to keep it to around 2%. I desperately need the current requirements of the AE to be sure.

jtp10181 said:

You are going to burn 16tons of pellets?

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Eventually

Per year? Not bloody likely. That's not the point of the comparison. Although the AE should be able to heat my whole house, I don't intend to do that unless the power goes out. And as I pointed out, I don't use 2000 gal oil just for heat. A lot of it is for hot water. How much is difficult to determine. I'm not even certain if I've been using 2000 gal a year anyway. I'll get more accurate data, plug it in and refine the result.

The point is not to determine just how long the ROI would be, but to determine if there will be one at all. Clearly propane won't, ever. My actual fuel usage and ROI can't be determined without knowing the future cost of oil, pellets, repairs, outside temperature, and a lot of other stuff, and my crystal ball is in the shop right now

The effect of 70% vs. 80% efficiency merely changes the ROI, and it's not a significant difference as far as I'm concerned. To their credit Quadra-Fire's cost comparison web page uses an efficiency of 70% despite their published claim of 81.4% - 83.6% for the AE insert.

Webmaster said:

While I was at the HPBA show, one new pellet stove maker bragged to me that his stove was 98% efficient

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Uh huh. How does it push the exhaust gases out?

sylvestermcmonkey said:

... voltage drop... 12 AWG would result in about 10% drop with the length I require but I'm trying to keep it to around 2%. I desperately need the current requirements of the AE to be sure.

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And today I got it! QF engineering says 12 A. Not bad! To be conservative I'll assume 15 A, so #6 will be within my 2% margin. Smaller would be OK but #6 allows a greater supply tolerance - the battery voltage can drop below 11 and the QF will still run.