Average efficiency of a pellet stove - anyone know?

[sylvestermcmonkey]

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.

 

[roninnb]

The Quad manual does not give an efficiency rating. But, it estimates the maximum BTUs and provides the maximum feed rate which calculate out to 8000 BTU/lb. Somewhere on a manufacurer's site I read that 8200 BTU/lb was 80+% (don't remember the exact figure) efficiency. My limited experience is that the 8000 BTU/lb is not unrealistic.

 

[jtp10181]

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).

 

[kinsmanstoves]

Breckwell publishes 80%-81% depending on the unit. I have not seen data on this but I feel if you run your exhaust inside the room as much as possible and then out you will raise the efficiency because the exhaust will radiate more heat vs. running it directly out of the room and losing the heat to the outside. i.e. putting the 3' vertical rise in the room and then use a 90 degree elbow and out via the wall thimble.

 

[sylvestermcmonkey]

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).

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.

 

[Dougsey]

19 tons is a lot of pellets!

 

[webbie]

70% is probably an accurate (or perhaps high) figure for total efficiency. The published figures are NOT AFUE nor even seasonal and are highly suspect IMHO.

The is probably a good reason why the manufacturers are not doing independent testing.

A conservative person would use 60-70% and for efficiency and 7500 NET heating value for Pellets (when adjusted for moisture).

 

[drizler]

You know what? You will truly drive yourself nuts trying to measure this stuff up with all the mumbo jumbo and numbers juggling they throw out there. It can all become very distracting. You will never get the efficiencies with any of this stuff you will with electric, gas or oil, not even close. What you want to know is at the end of the day how much cabbage keeping from freezing is costing you. Looking at where you live I wonder why you are screwing around with a pellet stove when you can get a coal stoker that will put any of these to shame BTU or efficiency wise. Coal puts out nearly double the heat value of pellets so its hard to argue the efficiency of pellets in the face of that. Just my humble nickle's worth but like most things its not whats better but whats cheap locally that makes the most sense.

 

[sylvestermcmonkey]

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.

 

[webbie]

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

 

[sylvestermcmonkey]

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

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

 

[jtp10181]

The Mt Vernon AE has a published efficiency of over 80%

(broken link removed to http://www.quadrafire.com/Products/Pellet_Burning/Pellet_Model.asp?f=mtvernon)
(broken link removed to http://www.quadrafire.com/Products/Pellet_Burning/Pellet_Model.asp?f=MTVERNONINS)

Now if you are talking about the old Mt Vernon (I don't think you are) that would be much lower.

I think a #6 wire should be plenty. The wires that come with the battery wire kit couldn't be more than #12 if my memory serves me they were about the thickness of one of those cheap battery charges you can get.

 

[sylvestermcmonkey]

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]

You are going to burn 16tons of pellets? According to the info we are given the Mt Vernon AE will burn about 10 hours on a full hopper which is about 2 bags. In 16 ton you have 800 bags. That would be 4000 hours of use on HI. Are you going to run it for 166 days straight on the maximum output setting?

 

[webbie]

I know I'm the pundit, but who publishes the efficiency? If it is the manufacturer or even the EPA test it means nothing at all. It is, at best, a steady state efficiency at a particular setup. I agree with Driz that there are many variables, but when doing calcs for payback against appliances that have "real" (independently) verified AFUE, etc.....use 70% and 7500 BTU, or roughly 5300 BTU into the house per lb of pellets.

While I was at the HPBA show, one new pellet stove maker bragged to me that his stove was 98% efficient and that was verified by the EPA. If all these folks didn't mislead us, I would not have to correct them!

 

[sylvestermcmonkey]

You are going to burn 16tons of pellets?

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.

 

[sylvestermcmonkey]

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

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

 

[sylvestermcmonkey]

... 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.

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.