unusual chimney setup, need help

[stoveguy2esw]

hey guys, i got an chimney question for you, fella called my shop today with a 30-nc unit he bought and installed , he is having a draw related issue with the unit, stove dies when he shuts the door. his flue system is what has me wondering , he describes it as such" 6" single wall pipe off the top of the unit up 10 feet to a 90 degree elbow, through the wall (vaulted ceiling) at this point with 2 ft run mating with triple wall duravent 6" pipe at the wall to a clean out tee and up an additional 6 ft. and capped, the house has a parapet wall that the flue extends a couple ft above , has a 4/12 (he thinks) pitch , coming up from the base of the parapet wall. he has a tile roof and also has flashing issues so a through the roof installation did not seem attractive to him. my question is could the fact that the flue goes up that high then passes through to a short 6 ft run outside be restricting his draw to where the flue is not pulling the stove enough? stove burns heartily until the door is shut then it just dies when he shuts the door, the draft control on the primary is opened all the way up. any ideas how i can solve this guys dilemma? note also that he is at 5000 ft above sea level near sierra vista az.

 

[begreen]

The fact that it drafts well with the door open makes me less suspicious of the stack than the intake air supply or perhaps negative room pressure. Does the stove have an OAK? If a nearby window is opened does the stove draft better? A less likely concern would be something blocking the air intake or a faulty air intake control mechanism.

 

[stoveguy2esw]

checked the air intake , he is getting airflow just doesnt seem to be enough , nothing from secondary either, dunno about outside air yet, just havent heard of this chimney installation before with long inside vert with a jog through the wall followed by short stack outside, there is some draw there , im just wondering if the short stack outside is not sufficient enough to generate enough pull after the horizontal.

 

[BrotherBart]

If I read that right Mike the guy has an 18' chimney with an effective length of 8' after the five foot reductions for the two 90's are considered. Not even worrying about the horizontal he is screwed with a 30-NC bro. I just have that 45* into a twenty one foot liner straight up unsulated at top and bottom and when the weather is above 40 degrees it has a hard time pulling through that stove. A heifer's knee caps above sea level. Door open the fires of hell, close it and it can keep the fire going but it is sluggish. It could be when you factor in altitude, those nineties and the horizontal that guy isn't going to have any draft at all, much less what the 30 needs to suck wind through it.

On the preburns outside twice I didn't have enough draw through that stove to close the door with the 12' stack stuck in the top of it because it was too warm out.

People with more experience that me will be along soon, but I don't think that chimney would have much of a chance with a small firebox stove, with the 30 I think he is screwed.

Edit: That air has to be pulled a long way from the back of that dude to the front.

 

[stoveguy2esw]

ok , kool BB was thinking along those lines, biggets thing with me was where the 2 90's are , so high up does that have a more adverse effect than if the were lower? i just havent run into a setup quite like this before with the pass through being so close to the top of the flue. thanks for the reply though bro, appreciate it

 

[BrotherBart]

It is one of the dymanics of big firebox EPA stoves that doesn't get much press. On this stove or the ones like it like the Quads that air has to be pulled in through a 3 inch opening low on the back and then make its way around two 90* corners in the bottom manifold and then 26 inches forward to two more 90* corners. For the top airwash air it has to go up fifteen inches or so and then make the same trip. Lots of resistence along the way.

That is why my replacement stove burns so differently than the first one. Daylight and dark between them. The first one was letting air in around the door in addition to the regular path so it would take off from the get go. The new one has to have more draft and a more orderly start-up. When the guy opens that door it doesn't take much draft at all. Boom, the air is right there available with no resistence.

I think MSG runs into this a lot up on the mountainsides in CO.

 

[stoveguy2esw]

yeah, i know where he is and he is one of the main guys i am hoping that will pop in and take a look at this, figured altitude probably plays into this as well, so i will definately pay attention to what he says on this. as well as anyone else that can give me somthing that i can give to this guy that will help him.

 

[elkimmeg]

First suggestion would be to double wall that connector pipe. Prevent heat loss and weakening draft. Changing the smoke path with 2 90's in less than 2' creates a lot of friction loss.
At that point there is not enough verticle run above the transition area to regain the lost momuntun. This is setup has nothing to do with the stove model, all modern stoves would have a tough time pulling draft in that chimney setup.

Second suggestion is to forget that jog and go threw the tile roof and have it flashed correctly . It can be done and done correctly