3" or 4" stove pipe for new install?

Right from the manual

Pellet vent type
A UL listed 3-inch or 4-inch type “PL” pellet vent exhaust system must be used for installation and attached to the pipe
connector provided on the back of the stove (use a 3-inch to 4-inch adapter for 4-inch pipe). Connection at back of
stove must be sealed using Hi-Temp RTV. Use 4-inch vent if the vent height is over 12-feet or if the installation is over
2,500 feet above sea level.

mralias is correct....you can use 3' for those installs. Now it is not recommended that you go from the 3" to the 6" or 8". you'll need to run the 3" all the way to the end. You will have to check with the chimney Manufacturer to see if they are ok with running the pellet pipe through their chimney.

Why would it be necessary to run it all the way up the pipe when the installation manuals for every stove I've seen shows, as an option, running the exhaust into an existing large masonry chimney and stopping a couple feet above the block-off plate? Draft isn't a problem because they are all draft-induced with a blower. None rely on chimney draft to operate. Only in the event of a power outage would that become an issue and you'd have plenty of draft with those chimneys.

BrotherBart said:

Yeah, pellet into a six or eight inch is fine. My stove in the basement is pellet pipe to the thimble and then 5.5" liner 33 feet to the sky and works fine.

I asked a whole bunch of pros before doing it and none said it was an issue. I have to remove the pellet pipe to clean the liner though.

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My basement dwelling P38 has a 3" pipe running about 9' to an existing 27' / 8" air-cooled fireplace vent. No issues at all. Great draw during a power outage a couple of years ago.

Can it work...YES. It is recommended to run it to the end. Some people do run into issues venting that way. It does make it easier to clean and at that connection you can get ash and soot build up. The issue that may occur is a flow problem you are going from a 3" diameter (7 sq. in.area) to a 8" diameter (50 sq. in area) it could stall the draft. It could not as well, but if you do have a problem when you call tech support they will tell you to reline to the top and not doing so could void warranty. It is stated on page 9 of the manual:
" Do not terminate the venting into an existing steel or masonry chimney."


EDIT: how many people do it that way and it works is unclear to me, but I do know we get around a dozen calls a year from people who it doesn't work with.

Consider will it work vs: potential issues down the road. You have to assess the risk and decide. Consider if your local town inspectors would pass a set up that does not terminate at the top? Consider the warranty and cleaning issues as stated above. Consider home owners insurance issues in the unlikely event of a fire if it was not properly installed (insurer's are always looking for a reason to deny a claim) Consider the cost of running the extra pipe. Consider posting some pics when your done so we can all see how you made out.

Another way to look at it is in a HVAC system would you run a 6" by 10" trunk for the first 15 feet then expand to a 20" by 20" trunk for the last 15 feet?(7 times larger same as 3" into an 8") The AC/heat will still get to the last room but at what force?
My 1st concern is having that stove work 100% correct for you so you don't have to call our tech support line

Owen1508 said:

Another way to look at it is in a HVAC system would you run a 6" by 10" trunk for the first 15 feet then expand to a 20" by 20" trunk for the last 15 feet?(7 times larger same as 3" into an 8") The AC/heat will still get to the last room but at what force?
My 1st concern is having that stove work 100% correct for you so you don't have to call our tech support line

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Apples and oranges Comparing the situation to horizontal runs of HVAC piping has no bearing. It's already been said that draft is not a problem with those who have terminated into a larger diameter. Reading the info on amfmenergy about their stoves, it sure sounds like legalease to protect their butts.

I just re read the OP 18 feet I mis read inches. There is no real safety concern with it. You can always try it and see if it works. 18 feet less pipe times 2 is a good chunk of money. Worse case it doesn't work. Like I said I don't know how many people do that and it works , on that stove, but I do know it doesn't work for about 12 people a year. Some units do better then others. For 36 feet of flex pipe I might try that first as well. That being said I do have to say it is not recommended, but there is a chance it will work. If you find you are have some issues in the beginning I would suggest running the draft fan at 1 or 2 over the heat range setting. That will give the combustion fan a boost. Good make up air will also help it (ie OAK) if possible. Just my suggestion.

I'm using 3" stainless flexpipe up 20' in a chimney, should of went 4", i was unemplolyed at the time and just bought my house, works fine anyway, once it got a clog running on low for too long and used the leaf blower from inside my living room and pushed out the creosote outside

Gunner1 said:

I recently bought 2 us stove company king 5502m pellet stoves. One is for our old house that we rent out. I'm taking out a hearthstone wood stove and putting in one of the pellet stoves. Can I use the 3" pipe? It will be coming out of the stove and up about 6' into an existing 8" metalbestest pipe. The other stove will be in our basement and coming out of the stove up 5' 90 elbow into an existing 6" stainless chimney. The 8" chimney is 18' tall and the 6" is about the same. This is our first time with pellet stoves so trying to install right to not have problems thanks for the help

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If you run it 24/7 you shouldn't have a problem. I've been running a 3 inch into 8 inch brick with clay liner chimney for 9 years and the only issue I had was when I first start the stove the smoke is going up a cold chimney and it doesn't want to go up good. But after a few minutes the chimney gets warm and you won't have any trouble.