Over draft caused by bad fit at stove neck and chimney pipe !?!

[Dennis 2]

I read this article about over draft ( or overdraft situation )
Look for leaks in the stack pipes, make sure all joints are tight and well sealed.

Particularly check the junction between the stove exit and the chimney pipe. You should NOT see any corrugations, the pipe should fit in far enough so that the ridge above the corrugations is touching the flange on the stove exit or close to it, and the joint should be sealed with stove cement. On many stoves the collar is not as deep as the corrugations on the standard pipe, so the pipe will bottom out before it is properly seated UNLESS you either use a special “stove connector” pipe that has short corrugations, or trim a normal pipe so that it is about 1/8” shorter from the end of the pipe to the ridge than the depth of the flue collar on the stove. Air entering via a leak at this junction can cause short, hot burns that look like an overdraft situation.

I thought that a leak of this type would cause less draft. What do you think ?
Dennis

 

[Mandoo]

I'm guessing from experience that it causes a venturi effect causing the wrong burn atmosphere in the stove.

After I sealed my terrible collar adapter connection (huge gap) the stove performed better than advertised.

BTW my stack temps climbed 100* and burn times were extended after the repair or should I say band aid on my very expensive new stove!
The manufacture is still looking into this problem and I will post my results.

 

[Dennis 2]

Anyone else have any insight on this

 

[seaken]

It appears that this has become an issue due to the new designs in many stoves. In the old days we used to insist that a small air gap at the junction of the pipe and collar would not be a problem and that the natural draft would be sufficient to overcome any potential negative effects. Now, with the new stove designs, where the air movement inside the stove is more tightly controlled, we see the wisdom of sealing that joint. It is possible in some circumstances for that gap to allow air to enter the combustion gas stream and feed the fire. This can lead to loss of control of the combustion rate through the normal means (the air controls on the stove). This is a recent phenomenon. The best way to approach this is to seal the gap. We are still adjusting to this in our shop. We have for so long said "don't worry about it" (and it was in fact a small issue previously) that we have a hard time remembering that things have changed.

(I say"we" because I have no problem remembering the need to be more up-to-date and pay attention to what is happening in the field. But we have some old-timers in our shop who are still a little slow on the uptake. It's hard to change long held views.)

 

[Dennis 2]

Everyone, Thank You . I guess it could make a diffreance .
Dennis

 

[EddyKilowatt]

Only way I can see a leak at the flue collar causing an overdraft would be if it was somehow contributing to secondary combustion up inside the flue. Of course with a modern stove, the secondary is supposed to happen IN the stove... so the possibility seems remote to me.

Note that it does say looks like an overdraft... maybe not necessarily an actual overdraft.

Maybe an air leak at the collar does in fact cut down on the draft seen by the stove (as measured in inches WC), causing the operator to open the draft control to compensate, and thereby screwing up the primary-secondary balance in stoves with "automatic" secondary draft?

Just thinking out loud...

Eddy

 

[moondoggy]

i was worried about seeing the corragated lines on the black pipe at the collar on my interpid. the collar is not all that deep.
i cut the pipe so the corrigated lines were not showing, and then wrapped in that silver foil tape i had left from the flue insulation, didtn want to cement it though.
suprisingly enought, the tape is still on.