Relationship between chimney draft and height

[dafattkidd]

I generally run my unit pretty hot. 500-700 range is normal. I get spillage pretty much always. I think last year we had a couple of super cold days, and on those days the spillage seemed less. This is when I started considering extending my chimney.

I also think the offset box contributes to my problem.

 

[oldspark]

Thanks for that. Where is that from?

(broken link removed)

 

[Jags]

Temps sound good. Back to staring down the chimney.

 

[mellow]

You need more draft to compensate for that offset box, a 90 in a chimney takes off 5 feet in overall length, so I would guess an offset box takes off 8 feet.

 

[oldspark]

This is good info also.
http://woodheat.org/how-chimneys-work.html

 

[Sprinter]

I would honestly prefer the fan over the extended height. The extra pipe coming out of my chimney will look ridiculous. I am almost positive I have read Begreen express serious reservations about draft induced fans. Any feedback on the fans?

I know nothing about them but they seem to be very expensive. (broken link removed to http://www.northlineexpress.com/fireplace-hearth/fireplace-accessories/smoking-fireplace/draft-inducers/enervex-chimney-fan-rs-012-rs-012.html)

 

[brenndatomu]

Sorry, maybe this was already covered elsewhere, but I'm assuming you have a masonry chimney with SS liner? Is it insulated? That would add some draft if it was.
As to one of your original questions, how to extend your chimney height, again, assuming masonry chimney with a SS liner. They make a top plate that adapts from flex liner to class A pipe. I know I have seen a link to one here somewhere before, maybe someone else can put their finger on it more quickly than I.
I have no experience with those draft inducer fans, but to me, that looks like a real PITA on a wood burner chimney...

 

[Woody Stover]

I have insulation at the top foot and bottom foot of an interior chimney.

So you don't have a full-length stainless liner?

"The chimney must have an acceptable 6" (152 mm) stainless steel chimney liner installed."
"The 2400 Insert is not approved for use with a positive flue connector into a masonry flue."

Terminology differs, but what they are calling a 'positive connection' is what I call a 'direct connection,' where the stove connector pipe goes up through a block-off plate, then uses the masonry chimney clay liner tile the rest of the way up. They are saying this is a no-no. I call a liner all the way up, a 'positive connection.'

 

[dafattkidd]

I have a 6" liner running from an offset box which is directly connected to my stove. The liner goes up to the cap. Only the lower and upper portions of the liner are insulated.

 

[mellow]

He has a liner, he just put insulation at the top and bottom instead of the whole thing.

 

[Woody Stover]

The manual is confusing, because below that in section 1.2 it says you can use a masonry chimney....

(broken link removed to http://www.osburnwoodstoves.com/v/vspfiles/files/2400%20insert.pdf)

 

[Woody Stover]

I have a 6" flex liner running from an offset box which is directly connected to my stove. The liner goes up to the cap. Only the lower and upper portions of the liner are insulated.

OK, gotcha.

 

[oldspark]

If it is a inside chimney (I think he said it was) the insulation is less of a factor.

 

[Woody Stover]

I don't see an actual minimum flue height figure listed....

 

[oldspark]

The manual is confusing, because below that in section 1.2 it says you can use a masonry chimney....

(broken link removed to http://www.osburnwoodstoves.com/v/vspfiles/files/2400%20insert.pdf)

nothing wrong with a masonry chimney if built correctly

 

[brenndatomu]

nothing wrong with a masonry chimney if built correctly

And flue sized correctly for the stove...

Insulation at the top and bottom only? That is kind of an interesting install, no?

 

[Woody Stover]

I gotta believe that the offset box is the culprit here.

Just 6" galvanized chimney like on an oil burner?

You can get the cheap snap-together black stove pipe at a farm store.

nothing wrong with a masonry chimney if built correctly

You won't get as much draft as with a liner, but that's not the issue here.

 

[begreen]

Just 6" galvanized chimney like on an oil burner? Will that really give me a pretty accurate idea of the effects?

Yes, grab a 3 or 4' length of 6" galv. lightweight venting duct, remove the cap and temporarily put it in crimp down. Secure so that it doesn't fall down and light the fire.

 

[oldspark]

I gotta believe that the offset box is the culprit here.
You can get the cheap snap-together black stove pipe at a farm store.

You won't get as much draft as with a liner, but that's not the issue here.

A correctly built chimney has a clay liner in it.

 

[Woody Stover]

A correctly built chimney has a clay liner in it.

True, but the clay liner is going to have a larger cross-section area, slowing the draft. And according to your previous post, dropping the flue gas temp will slow draft. So an insulated liner will definitely draft better than the clay....

Most draft problems have to do with inadequate gas temperature in the chimney"

I don't know if he's got enough room in the clay liner to insulate his stainless liner, but that would have to help. I'm not sure how much it would help, though.

 

[Bluerubi]

Do you have a link to that product, sounds interesting.

I don't think what I have now is anything too special, just completely open. http://www.woodlanddirect.com/Chimney/Multi-Flue-Chimney-Caps/Stainless-Chimney-Champion-Flat-Lid

The old one was fine, just had some restriction due to the slot design around the small diameter cap. With a wide open liner I am certain my draft has gone up dramatically.

 

[oldspark]

Inside chimney so insulation may not be that big a deal.
Chimney is on the short side a little height may be the most bang for the buck.

 

[oldspark]

True, but the clay liner is going to have a larger cross-section area, slowing the draft. And according to your previous post, dropping the flue gas temp will slow draft. So an insulated liner will definitely draft better than the clay....
I don't know if he's got enough room in the clay liner to insulate his stainless liner, but that would have to help. I'm not sure how much it would help, though.

Getting side tracked here, they used to make a 7 and1/4 round clay liner and yu can go 25% larger with the liner size.

 

[oldspark]

I don't think what I have now is anything too special, just completely open. http://www.woodlanddirect.com/Chimney/Multi-Flue-Chimney-Caps/Stainless-Chimney-Champion-Flat-Lid

The old one was fine, just had some restriction due to the slot design around the small diameter cap. With a wide open liner I am certain my draft has gone up dramatically.

Those are nice, many people have reported their chimney caps are too restrictive.

 

[dafattkidd]

So what if this does work? How do I connect a 4 foot section of Class A to a liner?