Exhaust question..6" stove venting to a 8" chimney

[fuchef]

I have a 8" pipe in my mason fireplace that extends to an Metalbestos 8" SS all-fuel double insulated pipe. It runs 25' to the top of my house and is very solid. I have talked to my local installers in my area and they seem to think I need 6" pipe (flex) or total change out of my pipe. One salesman called a tech at Napoleon and said 8" was too big to vent a stove into. I called US stoves and he told me the same thing. I'm going to call Englander tomorrow and ask the same question. The crazy thing is I called Sellkirk techs(maker of the pipe) he said it should be fine. that I might have more creosote build when burning low, but with the tall chimney it will create enough draft on its own. He also said under normal conditions I should be fine, just maintain it at have it inspected and cleaned before each season. Am I wrong for thinking the installers are trying to up sell or is there a safety issue here that must be followed. I understand makers of wood stoves tests the stoves under 6" pipe conditions and wont speculate and guarantee performance under different conditions? I'm just confused.. My thinking is that there is a fair amount of people who have wood stoves with 6" exhaust going into 8" chimneys, and all is well. Am i wrong?

 

[Seasoned Oak]

Iv been venting various 6" flued wood stoves into a 12" terra cotta flued chimney for years. All have worked fine so far ,and now im about to try venting the first EPA stove, an englander 30-NCH into it. If it dont provide enough draft i will have to drop a 6" liner down there. Ill let you know how it works out.

 

[pen]

Here is information from Englander's 30 manual. Link to the manual http://www.englanderstoves.com/manuals/30-NC.pdf

Page 3

5. A 6†diameter flue is required for proper performance.

Page 4

WHY THE CORRECT FLUE SIZE IS IMPORTANT: 6â€
“Draft†is the force that moves air from the appliance up through the chimney. The amount of draft in
your chimney depends on the length of the chimney, local geography, nearby obstructions, and other
factors. Too much draft may cause excessive temperatures in the appliance. An uncontrolled burn or
a glowing red part or chimney connector can indicate excessive draft. Inadequate draft may cause
back puffing into the room and “plugging†of the chimney and/or cause the appliance to leak smoke
into the room through appliance and chimney connector joints.
Today’s solid fuel appliances are much more efficient than in the past. The units are designed to give
you controlled combustion, as well as maximum heat transfer, using less fuel to do so.
The design of your new appliance is such that the exhaust “smoke†is now at lower temperatures than
in the past, therefore requiring proper chimney size to give adequate draft. If your chimney is too
large, the heater will have a difficult time raising the temperature of the flue enough to provide
adequate draft, which can cause a "smoke back," poor burn, or both.

Page 5:

The area of the chimney liner must also be equal to or greater than the area of the flue collar on the stove. If the area
of the flue is greater than the collar, it should never be more than two and 1/2 (2.5) times greater

The area of a 6 in flue is 28.27 inches. 2.5 times larger than that would work out to be a little less than a 9.5 in round flue.

I ran my englander for a year connected to a 7.25x7.25 clay liner. It ran OK. I really needed temps to be in the 30's or less for decent performance. After installing a 6 inch liner, I can run the stove easily at 50 degrees.

Is this stove going straight up and into this 8 inch chimney then 25 foot up? Or does it need to make a couple of 90 degree bends? I ask because bends do reduce your draft.

Regardless, if it were me and the current 8 inch chimney were safe I'd give it a try and see what happens. With well seasoned wood, I'll give you a good shot at success and you won't be taking any real risks. If it doesn't work out well, and you trust your fuel, then consider the 6 inch.

pen

 

[jeromehdmc]

I'm running a 6" stove into 8" pipe. So far it works, I am thinking about adding another 2' to the top and see if it does pull better draft. I would be willing to bet that with 25' of chimney you will be just fine.

 

[fuchef]

Thanks for all your responses..I spoke to the Englander tech this morning and he said I shouldn't have a problem with my set-up. He was very nice and went over everything I asked him and also brought up some points I need to go over. I was very pleased with his honesty and knowledge. I'm having my chimney cleaned and inspected next week and then hopefully by sunday i'lll purchase the Englander 30-NCH at Homedepot..I'll be using the "change store" trick to get it at a better price. hopefully there wont be any issues with the chimney..

 

[fuchef]

Here is information from Englander's 30 manual. Link to the manual http://www.englanderstoves.com/manuals/30-NC.pdf

Page 3

5. A 6†diameter flue is required for proper performance.

Page 4

WHY THE CORRECT FLUE SIZE IS IMPORTANT: 6â€
“Draft†is the force that moves air from the appliance up through the chimney. The amount of draft in
your chimney depends on the length of the chimney, local geography, nearby obstructions, and other
factors. Too much draft may cause excessive temperatures in the appliance. An uncontrolled burn or
a glowing red part or chimney connector can indicate excessive draft. Inadequate draft may cause
back puffing into the room and “plugging†of the chimney and/or cause the appliance to leak smoke
into the room through appliance and chimney connector joints.
Today’s solid fuel appliances are much more efficient than in the past. The units are designed to give
you controlled combustion, as well as maximum heat transfer, using less fuel to do so.
The design of your new appliance is such that the exhaust “smoke†is now at lower temperatures than
in the past, therefore requiring proper chimney size to give adequate draft. If your chimney is too
large, the heater will have a difficult time raising the temperature of the flue enough to provide
adequate draft, which can cause a "smoke back," poor burn, or both.

From the opening in the hearth it makes a 45 deg turn out and then once out of the house its another 45 deg turn up following the side of the house 25' up.

Page 5:

The area of the chimney liner must also be equal to or greater than the area of the flue collar on the stove. If the area
of the flue is greater than the collar, it should never be more than two and 1/2 (2.5) times greater

The area of a 6 in flue is 28.27 inches. 2.5 times larger than that would work out to be a little less than a 9.5 in round flue.

I ran my englander for a year connected to a 7.25x7.25 clay liner. It ran OK. I really needed temps to be in the 30's or less for decent performance. After installing a 6 inch liner, I can run the stove easily at 50 degrees.

Is this stove going straight up and into this 8 inch chimney then 25 foot up? Or does it need to make a couple of 90 degree bends? I ask because bends do reduce your draft.

Regardless, if it were me and the current 8 inch chimney were safe I'd give it a try and see what happens. With well seasoned wood, I'll give you a good shot at success and you won't be taking any real risks. If it doesn't work out well, and you trust your fuel, then consider the 6 inch.

pen

From the opening in the hearth it makes a 45 deg turn out and then once out of the house its another 45 deg turn up following the side of the house 25' up. as far as I can tell there is not a 90deg turn in the line..thanks for the info..

 

[oldspark]

No reason to change any thing until you try it, should work fine IMHO.

 

[Blue Vomit]

Before I had the Oslo installed I researched the same question. I have an existing 8" liner. After researching, most said it should be fine and at least give it a try. Only a few fires so far this year but no problems as of yet. I have a 25' flue as well.
good luck

 

[leeave96]

No reason to change any thing until you try it, should work fine IMHO.

+1

I'd wait and give the 8 to 6 reducer a try.

Good luck,
Bill