EPA Compliant Wood Stove + (Firebox > 3.5 cuft) = 8" Flu?

[Renovation]

Howdy,

Here: https://www.hearth.com/talk/threads/64906/P44/#745329 ,

over on a thread discussing the upcoming Woodstock "Firecat" (just a suggestion), Slow1 commented:

As I recall from discussion during my visit, they have not plans to exceed 3 cuft (there is some technical/marketing/other artificial classification reason for this).

That got me thinking, which is admittedly easy to do. Anyway, I only know of three EPA stoves with fireboxes greater than 3.5 cuft (EDIT--was 3.0)--the Hearthstone Equinox, Blaze King King, and Kuma Sequoia--and all have 8" flues.

Could it be that for some regulatory reason, all EPA stoves with a firebox > 3 cuft must have an 8" flue? Asked another way, does anyone know of an EPA stove with an over 3.5 cuft firebox (EDIT--was 3.0) that doesn't have a flue 8" or larger?

Thanks for any insights, and happy burning.

 

[davidmc]

Good morning George, My Buck 91 has a 4.4 firebox and it requires an 8". Its predecessor was a VC Dutchwest XL is why I had the 8" flue.

 

[Renovation]

Good morning George, My Buck 91 has a 4.4 firebox and it requires an 8". Its predecessor was a VC Dutchwest XL is why I had the 8" flue.

Good morning, David, and thanks! That makes four out of four... any others?

 

[branchburner]

The Country Flame BBF is 3.9 cf, also 8".
(broken link removed to http://www.americanenergysystems.com/model-bbf.cfm)

 

[webby3650]

The Enerzone Solution 3.4 has a 6" flue and 3.4 cubic foot firebox

 

[BrowningBAR]

Englander 30-NC has a 3.5 cu. ft. firebox and a 6" exhaust.

 

[BrowningBAR]

The Hearthstone Mansfield has a 3.2 cu. ft. firebox and has a 6" exhaust.

 

[BrowningBAR]

Pacific Energy Alderlea T6:
3 cu ft firebox
6" exhaust

 

[BrowningBAR]

Quadra-Fire Isle Royale
3 cu ft firebox
6" exhaust

 

[laynes69]

Our wood furnace is EPA Certified. It has a 3.5 Cu. Ft. firebox and a 6" exhaust. We run a 5.5" liner with no problems.

 

[BrowningBAR]

Jotul F600:
3.25 cu. ft. firebox
6" exhaust

 

[shawneyboy]

Hearthstone Mansfield..

EDIT:

Darn you Browning....beat me to it

 

[BrotherBart]

There is no regulation as to flue size in relation to firebox size.

 

[branchburner]

Maybe better tweak the question: "Asked another way, does anyone know of an EPA stove with an over 3.5 cuft firebox that doesn’t have a flue 8” or larger?"

 

[Todd]

Better measure those fire box dimensions yourself, they aren't always what the manufacture states. I think once you get somewhere over 3 cu ft a 6" exhaust just isn't enough if you were to burn a full load at a high burn rate, might get some back puffing?

 

[Renovation]

Maybe better tweak the question: "Asked another way, does anyone know of an EPA stove with an over 3.5 cuft firebox that doesn’t have a flue 8” or larger?"

Yes! That looks like the dividing line. So far all the EPA stoves with a firebox > 3.5 cuft have flues 8" or greater.

Any exceptions? Thanks folks!

 

[Renovation]

Better measure those fire box dimensions yourself, they aren't always what the manufacture states. I think once you get somewhere over 3 cu ft a 6" exhaust just isn't enough if you were to burn a full load at a high burn rate, might get some back puffing?

You've put your finger on the heart of my mystery--why do EPA stoves with fireboxes > 3.5 cuft specify 8" flues, even if their max BTU rating is similar to a stove with a smaller firebox?

And what might be the consequences of burning such a stove on a 6" flue?

What got me started was comparing Blaze King's King and Princess models:

Model / MaxBTUs / Firebox Size / Flue Spec / % Larger Max BTUS / % Larger Firebox :

Princess / 40K / 2.8 cuft / 6"

King / 47K / 4.27 cuft / 8" / 18% / 53%

The King's maximum output is 18% greater, and it's firebox is 53% bigger--seemingly the biggest difference.

The King's maximum output implies that it's maximum air requirement on steady state burn is 18% bigger, not a huge difference.

But it's firebox is 53% greater, a bigger difference, with a much greater potential for smoking/outgassing on a full reload in a hot firebox.

All that brings me to the heart of my question--what problems might occur when running one of these >3.5 cuft firebox stoves on a 6" flue? The ones I can think of and slightly reduced maximum output due to lower maximum flow (looking like lowered draft at high burn), or perhaps back puffing? I know someone who has done it without issue.

Does anyone else have any insights or experiences to share? I'd be very appreciative! Thanks and happy burning.

 

[Renovation]

There is no regulation as to flue size in relation to firebox size.

Are you talking about regulations on installers, or on stove manufacturers?

The current regulation on installers--that chimney cross-sectional area be at least as great as the stove outlet's--is consistent with my theory.

Does anyone know what the governments design/certification requirements are for manufacturers, or have a link to same? I'll look around and see what I can find. Have a great night!

 

[BrotherBart]

There is no regulation as to flue size in relation to firebox size.

Are you talking about regulations on installers, or on stove manufacturers?

The current regulation on installers--that chimney cross-sectional area be at least as great as the stove outlet's--is consistent with my theory.

Does anyone know what the governments design/certification requirements are for manufacturers, or have a link to same? I'll look around and see what I can find. Have a great night!

There are no government design requirements. And certification is only the EPA particulate emission testing certification. The government does not care if a stove will heat your house, burn it down or anything else just as long as it burns clean. The stove, not the house. UL, a public company, sets the safety standards.

The flue size has to be as large as the flue collar thing is in the building codes which are not formulated by any government agency but by private organizations and then adopted by localities. Easier and cheaper than doing their own.

If you want to know why you can't burn a King into your six inch flue, call BK and ask them why.

 

[ddddddden]

I think the rule is that if you build a jumb0 stove that holds 80 lbs of wood, the flue must be large enough to handle the exhaust flow generated by an 80-lb load, or you will soon be sued out of existence. Doh!

 

[ddddddden]

I think the rule is that if you build a jumb0 stove that holds 80 lbs of wood, the flue must be large enough to handle the exhaust flow generated by an 80-lb load, or you will soon be sued out of existence. Doh!

 

[ddddddden]

Sorry 'bout the double post. Cannot edit. Doh! FWIW, the Buck 80 is only 2.6 cu ft, and uses an 8" flue.

 

[ddddddden]

p.s. Fire Cat is a good name, but already used by Applied Ceramics for their combustors. Doh!

 

[branchburner]

FWIW, the Buck 80 is only 2.6 cu ft, and uses an 8" flue.

I always wondered why that was. Makes sense that all the 4 cu ft stoves have bigger flue openings, but why does this stove. The fact that it's a cat may have something to do with it - what do you suppose?

 

[Renovation]

If you want to know why you can't burn a King into your six inch flue, call BK and ask them why.

Thanks BB. I asked them the same question I asked here--why the King requires a bigger flue than the Princess, when both have similar maximum outputs. The person I asked said the information is proprietary, and related to differences in internal dimension. Hence my questions.

EDIT: If I get my courage up, I'll ask them the probable consequences.