Pipe decision, 3" versus 4"

[geek]

My friend is finally getting ready for his stove in the in-ground basement, he would need to go up about 6 or 7 feet up and then out through the sill.

When he got quotes from different dealers 3 out of 4 quoted/recommended using 4" pipe stating it was overall better for exhaust and they do only 4" pipes for pellet stoves.

One dealer, from which he might be getting the stove, said they use 3" pipe stating the manufacturer only recommends using 4" if the run is more than normal (say the total pipe might be around more than 15 feet or so). He also said most dealers only carry/install the 4" pipes because is more $ and they get more $ selling the 4" versus the 3". Going 4" would cost my friend about over $100 more for the parts compared to using 3".

So, what's the real consensus here?

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[imacman]

Basically, if the EVL (equivalent vent length) adds up to more than about 15 ft, most manufacturers recommend going to 4" right after the stove exhaust outlet. The only thing that changes this is if the altitude where the stove is located is more than 3000 ft......then the distance is 7ft.

90 degree elbow = 5.0 EVL
45 degree elbow = 3.0 EVL
1 foot vertical = 0.5 EVL
1 foot horizontal = 1.0 EVL

If he uses a cleanout T out of the stove, and then just goes straight up 7' to a 90 degree elbow, and then straight out a few feet to a cap, it sounds like he could go with 3". (5 + 3.5 + 5 + 2 = 15.5). Anything more than that, I'd go with 4".

 

[geek]

but, say his install is fine with 3" pipe based on your math, is there any benefit of going with 4" pipe anyways?
Someone mentioned that 4" pipes are better because they provide a better flow and tend to clog less (obviously is a bit bigger).

I really wonder if it's true that most dealers install 4" pipes because they get a better margin profit selling those......hmm

 

[hearthtools]

I installed 3" pipe for short runs
4" pipe for long runs or more that one bend in the run.
4" pipe will give you less problems for less clogs and better draft.

 

[imacman]

......Someone mentioned that 4" pipes are better because they provide a better flow and tend to clog less (obviously is a bit bigger).

I really wonder if it's true that most dealers install 4" pipes because they get a better margin profit selling those......hmm

Actually, the smaller pipe should keep the exhaust velocity higher. I would tend to think that would be better as far as not clogging, IMO.

As for the pipe dealer having a bigger profit margin with the larger pipe, I can't believe ANY dealer would EVER do THAT!! :roll: ( did my sarcasm come through loud enough??)

 

[Xena]

I really wonder if it's true that most dealers install 4" pipes because they get a better margin profit selling those......hmm

When I was shopping for my stove I visited four stove dealers
and three of them said they usually use 3" unless the install requires 4".
The fourth told me he only uses 3". I asked him what if the installation
requires 4" and he parroted what he said previously. I just shook
my head and left.

 

[geek]

Basically, if the EVL (equivalent vent length) adds up to more than about 15 ft, most manufacturers recommend going to 4" right after the stove exhaust outlet. The only thing that changes this is if the altitude where the stove is located is more than 3000 ft......then the distance is 7ft.

90 degree elbow = 5.0 EVL
45 degree elbow = 3.0 EVL
1 foot vertical = 0.5 EVL
1 foot horizontal = 1.0 EVL

If he uses a cleanout T out of the stove, and then just goes straight up 7' to a 90 degree elbow, and then straight out a few feet to a cap, it sounds like he could go with 3". (5 + 3.5 + 5 + 2 = 15.5). Anything more than that, I'd go with 4".

I looked at the manual and your math sounds right; he wants a corner installation as shown in the image; I just don't understand why these 2 dealers quoted him a 90 degree elbow, I think it should be a 45 elbow, right?

Also, is it cheaper buying pipes/elbows online?

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[geek]

this chart is interesting....

from the manual:
"If you fall below the diagonal line, 3 or 4 inch (76 to 102mm) pipe may be used. If it is anywhere above the diagonal line, a 4 inch (102mm) diameter pipe is required. The chart reveals that a 90° elbow is 5 times as restrictive to the flow of exhaust gases under
positive pressure as 1 foot of horizontal pipe, and a foot of horizontal pipe is twice as restrictive as a foot of vertical pipe."

 

[geek]

based on the chart, looks like 3" or 4" is fine, but they don't ellaborate more stating why you'd want to install 4" even if the 3" pipe qualifies.

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[imacman]

based on the chart, looks like 3" or 4" is fine, but they don't ellaborate more stating why you'd want to install 4" even if the 3" pipe qualifies.

..
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Well, again, based on what you said about his install, it seems that if the EVL is close to or under 15, I'd go w/ the 3"....I don't see the need to spend the extra $$ on larger pipe if it's not needed. I still stand by what I said above, that I think the 3" pipe will keep the exhaust velocity up, and should result in a cleaner pipe (given a clean stove and clean combustion blower), but again, that's my opinion.

 

[geek]

one more question, since this install will need a clean out T out of the stove, and then straight up 6 or 7 feet, I guess the 90 degree elbow is the only option in the basement ceiling, not a 45 degree elbow, I don't understand why these dealers have the discrepancy, one of them quoted only the 90 degree elbow and the other quoted for both a 45 degree and a 90 degree elbow.

The stove is going in a corner as shown in image, I understand that a straight-out install (for example on a first floor) must use a 45 degree elbow but in this case the stove is getting installed in the basement and he needs to go up and then out, I think he only needs and the only option is the 90 degree elbow, is this correct ?

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[imacman]

From what I understand of his install, he will need a cleanout T out of the back of the stove, the vert. pipe up to a 90 to go out through the sill, and whatever length of straight pipe there, plus a cap. Might need an appliance adapter on the back of the stove too.

 

[Breckwell Tech]

Just remember you can never go wrong with 4"

 

[BJN644]

I have a set up with no combustable clearance issues to worry about and vent directly into a masonry chimney. I use 6" single wall with no problems at all. A local stove dealer has several in store demo units piped up the same way in his store and he said no problem.


I just noticed that you said your friend is going through a sill, single wall pipe is NOT what you want to do. Stick with pellet pipe in that situation.