Wood Stove Performance Whats in the Numbers

It's mostly crap in my opinion. A non cat epa stove is going to burn pretty clean compared to a pre epa stove. You will probably average in real life 65-75 % efficiency and 3-6 grams per hour with good wood and operated properly. Trying to micro analyze the difference can be fun, but in real world use I dont see most people noticing the difference in wood usage between a Quad with a 2.0 CF firebox or a Lopi same size all other things being equal.

I do notice a difference between Cat and Non cat now that I've used a cat stove.

The rest is just eye candy IN MY OPINION!

I agree with Franks.

Also, there is no way Stove One will put out more heat than Stove Two and Three.

I think that if the epa would test real world day to day operation conditions the test results would be much different

cut btu output by a third, in my opinion

One would think that if all the testing was done the same, the numbers would be realitive, but it does not look like it.

I was told by a stove mfg rep that reason the numbers vary so greatly is due to the test procedure. Its a standard test for all sizes of wood stoves using the same wood load (essentially kiln dried 2x4s or something similar).

So I would guess from the stoves you looked at the smalled one shows higher efficiences and BTUs because the test wood load got the stove up to operating temp and it was doing a secendary burn.

As an example. Two stoves in my showroom, same brand. Stove 1 has 1.5 cu ft. fire box and is EPA rated at 43,000 btu. Stove 2 has 3.2 cu ft. box and rated at 44,000 on the hang tag. In real life stove 2 can approach 100,000 btu with proper install and wood.

As for how a stove with higher efficiency gives off more pollution. My best guess would be differences in the baffle between the stoves. Stove one might have a baffle that allow more particulate to enter the flue.

As I was told the EPA test is mostly to determine the emmisions and the btu number is not close to real world use. But I'm sure there are many folks on here that can enlighten us on this issue.

I'm sure it's a good marketing tool. Is the average consumer going to notice the difference between the amount of fuel they would put in a car rated at 24 mpg vs one rated at 27? Like a stove rated at 75% vs 85%. If that consumer drives 100,000 miles a year, or burns 25 cords of wood, then maybe.
Like a car, it also depends on how you use it. Wide open, foot to the floor, BSEG, gonna suck a lot of gas. Loaded up, air wide open, house at 80, BSEG, gonna burn a lot of wood.

jeff_t said:

I'm sure it's a good marketing tool. Is the average consumer going to notice the difference between the amount of fuel they would put in a car rated at 24 mpg vs one rated at 27? Like a stove rated at 75% vs 85%. If that consumer drives 100,000 miles a year, or burns 25 cords of wood, then maybe.
Like a car, it also depends on how you use it. Wide open, foot to the floor, BSEG, gonna suck a lot of gas. Loaded up, air wide open, house at 80, BSEG, gonna burn a lot of wood.

Click to expand...

The biggest issue I have with the numbers is square footage rating, burn time and BTU output. Those three numbers, that vary wildly from one manufacturer to another, create a huge amount of problems for new customers.

BrowningBAR said:

jeff_t said:

I'm sure it's a good marketing tool. Is the average consumer going to notice the difference between the amount of fuel they would put in a car rated at 24 mpg vs one rated at 27? Like a stove rated at 75% vs 85%. If that consumer drives 100,000 miles a year, or burns 25 cords of wood, then maybe.
Like a car, it also depends on how you use it. Wide open, foot to the floor, BSEG, gonna suck a lot of gas. Loaded up, air wide open, house at 80, BSEG, gonna burn a lot of wood.

Click to expand...

The biggest issue I have with the numbers is square footage rating, burn time and BTU output. Those three numbers, that vary wildly from one manufacturer to another, create a huge amount of problems for new customers.

Click to expand...

And the three you mention are three that the EPA is not terribly interested in. The EPA is concerned with air quality, so they don't spend a lot of taxpayer money worrying about, regulating, or measuring anything beyond emissions.

For meaningful measurements in other areas, we'd need to agree that consumer protection agencies should spend taxpayer money setting test standards or that the industry should spend stove buyers' money. I personally doubt that we'll see either.

IMHO, firebox volume and stove construction soap/cast/steel, cat/non-cat are what I would look at.

madison said:

IMHO, firebox volume and stove construction soap/cast/steel, cat/non-cat are what I would look at.

Click to expand...

Firebox volume is the best way to go, but even then, there are issues in how the firebox is measured. For instance, the VC Encore has the same claimed firebox size as the Hearthstone Heritage. I can tell you from first hand experience, I can fit more wood in the Encore than the Heritage.

BrowningBAR said:

madison said:

IMHO, firebox volume and stove construction soap/cast/steel, cat/non-cat are what I would look at.

Click to expand...

Firebox volume is the best way to go, but even then, there are issues in how the firebox is measured. For instance, the VC Encore has the same claimed firebox size as the Hearthstone Heritage. I can tell you from first hand experience, I can fit more wood in the Encore than the Heritage.

Click to expand...

Excellent point BBar

Huntindog1 said:

Plus i think its said that the cast stoves throw heat better so a figure for how much heat you got from that load actually into the house would be usefull information.

Click to expand...

I'm not so sure about that.

I am confused by these two stoves from the original post:

Stove Two:
Firebox size 2.1 c/f
Efficiency: 76%
EPA Emissions: 3.89 g/h
EPA BTU’s/hour: 29,421

Stove 3:

Firebox size 3.3 c/f
Efficiency: 75%
EPA Emissions: 5.7 g/h
EPA BTU’s/hour: 30,800

Forget firebox size and look at the other three numbers. efficiency is almost identical, but with very similar output (BTUs per hour) the Emissions are quite a bit different. How would two stoves burning the same wood (I assume they use the same type and moisture content wood for all of these tests) at the same rate (as indicated by BTU output) at the same efficiency produce significantly different amounts of emissions?

I recall when we started looking at stoves the last time we needed one. The very first place we went we found a stove that was 96% in the efficiency rating. Sales nut smiled wide when he stated that. But he was outdone when we found one that was 100%. Nope, those numbers really don't mean a whole lot and some so-called sales people love to throw around big numbers as they think it makes their product sound great. Somehow, it doesn't do much for the product but surely shows their true colors.

The more I learn about the test the more I find how really bogus it is. I'll bet no epa stove is anywhere close to as clean in real world use as the numbers suggest. There are tricks used to get a stove through the test and small fire boxes fair better than large ones and shallow fire boxes do better than deep ones and so on. Its a game they play. One of the tricks I heard about is to run the fan on high during the whole test. Few people probably even have the fan option on a given stove and few would run it on high all the time but doing so allows the stove to be run with more air and not over temp. Just knowing its certified is enough. How it got there doesn't matter nor do the numbers.

BTU/Hr output is the most misunderstood and misleading of the specs, and I wish they would either drop it or add more info to make it useful.

Example: Your stove #1 has a 1.4 cu ft firebox and is rated at 44,000 btu/hr.
And the Jotul F602, which has less than .5 cu ft firebox, is rated at 42,000 btu/hr

The key thing to remember is, that number is a peak RATE of heat output. It is not the average rate, but only the peak rate. It is simply the rate of heat production at the hottest point of each burn cycle. It is equivalent to saying "**IF** this rate of heat output could be sustained for one hour, this is how many btu's would be produced."

But it doesn't say for what duration of time the stove can maintain that output rate. The little Jotul would be lucky if it did it for 5 minutes. Stove #1 might do it for 1/2 hour. Maybe.

What would be really great is if they furnished a chart of output rate vs time for an average load. That would be a really useful piece of info to help pick a stove appropriate for your needs.

As others have said, firebox volume is the most useful piece of info. And even that is not spec'ed honestly by all manufacturers.