8" to 6" pipe reduction increase or decreases draft?

[THEMAN]

Hello all, I have a Buck 91 that I will be installing (my first stove) and have a question, actually I have many questions. I am going to do a direct connect with block off plate for now and do a full liner when $ is available. My question is, If I reduce from the 8" flue to 6" pipe will this radically affect draft, or perhaps improve it? I mean since its a direct connect and till only have a short length of pipe to create a draft wouldn't the reduction actually improve this? It seems to me that it would, I'm sure that there is some equation that factors in diameter x length to equal a particular draft %, but I am new to this so I leave the question to you all. Thanks.

 

[DAKSY]

DON'T reduce it. You never wanna do that.
It WILL restrict the draft.
If you're gonna direct connect, use a short
length of 8" liner that will reach into the first
flue tile...
You may hafta ovalize it depending on the size of your
damper & the size of your flue tiles...

 

[PineKnot]

It is usually best to stick with the stove pipe sizing Buck recommends: 8". But in this case, I don't think it will make any difference. If you try 6", and it doesn't work, you can post your results we everyone will know.

If the unlined chimney doesn't draw well, I would wait for the liner. Life is too short to fight with poorly drafting stoves.

Have fun with it.

 

[LLigetfa]

AFAIK it's a code requirement to stay with the size the stove is.

The theory on draft in relation to flue size is that gasses flow slower in an 8 inch flue than in a 6 inch, and therefor has more time to cool and get heavier, diminishing the draft. This of course depends on the volume of flow, flue gas temps, and the insulating quality of the flue.

 

[THEMAN]

AFAIK it's a code requirement to stay with the size the stove is.

The theory on draft in relation to flue size is that gasses flow slower in an 8 inch flue than in a 6 inch, and therefor has more time to cool and get heavier, diminishing the draft. This of course depends on the volume of flow, flue gas temps, and the insulating quality of the flue.

Ok so based on this theory since it will be a direct connect it will lessen the draft flow, so if down sizing to a 6" would increase the flow then the draft through the stove would be somewhat closer to the required draft if the chimney was fully lined with 8" liner correct? The only reason that I want to downsize is that I only have a 5" damper opening and oval 8" flex pipe is around 6" on the short diameter of the oval as opposed to ovalized 6" that is only 4 1/2". So the 6" pipe would go through the damper with out a problem. From what I understand the "flex pipe" really isn't that flexible so I'm not sure if I can squeeze and extra inch out of the ovalized 8" pipe to fit through the damper, but I have no experience with this so I again pose the question to you can I squeeze another inch out of an ovalized 8" pipe that is already been ovalized to 6" on the short diameter?