Wood stove pipe size VS draft

[jk96]

Most modern (i.e. EPA) stoves use 6". Double wall if it's exposed to the interior of the house, double wall insulated if it runs through a chase. Only the largest ones use 8". You need a really big space for one of those.

Like gsganzer posted, the current thinking is to keep the exhaust hot all the way through. Modern stoves expect it.

The modern EPA stoves not only burn cleaner but get more BTUs from the same load of wood. The only problem is that they don't deal with wet wood as well as older non EPA stoves.

Our stove is not EPA approved. Uses 16-in OD double wall insulated. At the time we were building I had the price of the stove factored in and never even gave it a thought to check size of flu required. Needless to say I got a bit of sticker shock once I found out a 30 ft run of flu and elbows was going to be two-thirds the price of the stove itself.

 

[CalG]

Double lining the fire box with fire brick is a WIN-WIN all the way around if the objective is to get more heat out of less fire in a too large wood burner!

For the cooments about "wet wood" and condensation. The products of rapid oxidation/ combustion are CO2 and H2O. There is no way around having water in the smoke stack! (when it's cold).

 

[CalG]

Our stove is not EPA approved. Uses 16-in OD double wall insulated. At the time we were building I had the price of the stove factored in and never even gave it a thought to check size of flu required. Needless to say I got a bit of sticker shock once I found out a 30 ft run of flu and elbows was going to be two-thirds the price of the stove itself.

16 inch! I've never seen nor heard of such for domestic applications.

 

[BnRidge]

So a new stove will be a 6" flue.

A larger pipe size slows the velocity and cools the exhaust. The condensation temperature for creosote is 250f. You can burn wet wood, all the wet wood you want, and use a larger pipe size, but the exhaust needs to stay above that temp. A larger flue dia will make it harder to do that (and not draft as well). Wet wood makes it harder to do that. I have a wood stove, with the recommended 6" flue. I had creosote dripping out the back of the stove twice, in 17yrs. Both times early on I decided to start the stove slowly. Long and slow with a cold pipe meant dripping creosote. I put in a 200-1000f thermometer to measure stack temperature. That corrected the problem right there. Get the temps up as quickly as possible, and keep them there.
If it were me, and I got a new to me stove, I would pull whatever doesn't meet installation specs and make it right, top to bottom, all of it. There is a fire in my home. I would be an absolute jerk about making it right. Just my opinion.

 

[jk96]

16 inch! I've never seen nor heard of such for domestic applications.

It's an Acucraft 44" see thru insert.

 

[kenmac]

I would say if you can change it to 6'' all the way up until it penetrates the roof and leave that section 8'' you should do just fine. The thing about oversizing the vent pipe is getting the pipe hot enough to establish a draft. But just a short section through the roof should do just fine

 

[CalG]

An aside, but.....
having just brushed my own flu yesterday, I would not like to need TWO different flue brushes, up on the roof, to do the lob.

 

[ericm979]

The stove we put in the old house needed about 32' of flue. The house is two story and has steep roof pitches. The required 6" insulated flue for inside the chase cost more than the stove did.

 

[gsganzer]

A larger pipe size slows the velocity and cools the exhaust. The condensation temperature for creosote is 250f. You can burn wet wood, all the wet wood you want, and use a larger pipe size, but the exhaust needs to stay above that temp. A larger flue dia will make it harder to do that (and not draft as well). Wet wood makes it harder to do that. I have a wood stove, with the recommended 6" flue. I had creosote dripping out the back of the stove twice, in 17yrs. Both times early on I decided to start the stove slowly. Long and slow with a cold pipe meant dripping creosote. I put in a 200-1000f thermometer to measure stack temperature. That corrected the problem right there. Get the temps up as quickly as possible, and keep them there.
If it were me, and I got a new to me stove, I would pull whatever doesn't meet installation specs and make it right, top to bottom, all of it. There is a fire in my home. I would be an absolute jerk about making it right. Just my opinion..

I think a big issue is the modern stoves have such a big turn-down ratio and your risk of condensing is greater when you do the slow overnight burn. That makes it more sensitive to oversizing.

The OP didn't mention the total vertical rise, that would impact draft. They have on-line calculators for sizing this.

 

[mikester]

People who burn wet wood should not burn wood.