Efficiency Riddle

[Highbeam]

Isn't it fun? Yes, bring a tape measure. Some brands are accurate and some, even good brands, are way off.

 

[BrowningBAR]

Wow! So not only do I have to question efficiency claims but firebox size as well? That's just great.......... lol

There is a difference between firebox size and useable firebox size. Some measurements include areas in which you can no fit wood or the areas at and above the burn tubes. As an example, the Hearthstone Heritage and Vermont Castings Encore are both listed as 2.3 cu ft fireboxes. I have had both stoves in my house at the same time and can tell you that the firebox in the Encore is larger.

 

[Ashful]

Isn't it fun? Yes, bring a tape measure. Some brands are accurate and some, even good brands, are way off.

I haven't looked inside nearly as many stoves as some of you, but it seems the few I've inspected are never perfect cubes inside. My F12 has a rear burn plate that protrudes from the back wall, and shortens the firebox depth approximately 2" in the center, but leaves the firebox full depth on both sides and above. Also, the firebox width is about 4" greater at the top than at the bottom of the firebox, due to internal side plates that do not extend all the way to the top of the firebox. How does one even get close on estimating firebox volume with a tape measure?

 

[Highbeam]

How does one even get close on estimating firebox volume with a tape measure?

Gotta use your noggin. The only firebox volume that matters is the firebox that you can fill with wood. If there is some area that is not accessible using regular splits the way you plan to use the stove then it is not usable firebox volume and is left out. As such, get your tape and measure the cube that actually represents what you can utilize. It will me much easier that way and actually represent a useful specification. If you have a sloping firebox roof, then measure to the center.

The most accurate and useless way to measure the volume would be to fill the firebox with water from the flue until the water sits flush with the top of stove. Then drain and measure that water volume. If the stove makers all did that then we would at least have a standard. Instead it's a crapshoot and you need to take matters into your own hands.

Firebox volume and dimensions are such a critical operational specification that you must measure for yourself.

 

[Ashful]

Gotta use your noggin. The only firebox volume that matters is the firebox that you can fill with wood.

Are you sure about that?

cu ft = the maximum interior volume which is not necessarily the normal useable volume of the stove.

https://www.hearth.com/talk/threads/jotul-firelight-model-12-repair-or-replace.86789/

 

[Todd]

Maybe a better way to figure fire box size is the amount of wood in pounds you can fit inside. There are a few manufactures that do this, I know Blaze King states this in both hardwood and softwood. I guess there can be a lot of variables in this as well but I think the industry standard is 20 lbs per cubic foot.

The stove shop guy may fine it a little weird when you walk into his shop with a big load of pre weighed splits. Lol

 

[BKVP]

When a manufacturer tests a stove for emissions, the cu. ft. size of the firebox drops into the formula. Even a slight variation can have an impact on the final EPA numbers. Suffice it to say, total wood carrying capacity hasn't ever be an issue on our line of catalytic models because they burn for extended periods of time. None the less, the size of the firebox does have an effect on the final numbers. So you ponder on that a few minutes and next time you have your head in a stove you'll get a better picture of why this or that little piece of metal is there....

 

[Highbeam]

Are you sure about that?

Absolutely. I could give a rip about unusable firebox space. For example, Attaching a 50 foot long 2" pipe to the side of my firebox makes it have a huge volume but has no bearing on how much wood I can load. As I said, the only firebox volume that matters (to the user of course) is the firebox that you can fill with wood.

 

[Ashful]

As I said, the only firebox volume that matters (to the user of course) is the firebox that you can fill with wood.

I agree, but it seems to me most are using the entire interior volume of the stove, when they quote "firebox size."

 

[Todd]

They need to change the term "fire box size" to " firewood loading capacity"

 

[BrowningBAR]

They need to change the term "fire box size" to " firewood loading capacity"

Who are we kidding, manufacturers' marketing departments would still find a way to stretch the numbers.

"Well if your wood is a perfect 2 cu ft square, it would easily fit inside our firebox..."

 

[Todd]

Who are we kidding, manufacturers' marketing departments would still find a way to stretch the numbers.

"Well if your wood is a perfect 2 cu ft square, it would easily fit inside our firebox..."

Yeah but they wouldn't be able to include space above the baffle like many do now.

 

[Highbeam]

One thing we do know is that size matters. Mostly in the amount of fuel you can load but also to a much lesser extent, the surface area of the radiating body.

We also know that manufacturers lie, mislead, misrepresent, fudge, estimate, trick, etc. in an effort to make their stoves appear to be something they are not. Not all do this, but most.

Finally, we know that the tape measure does not lie and that nothing can replace sticking your head into the stove and measuring.