Draft: How far is too far for connector pipe to be inserted?

[redhorse]

I've read that if you insert the stove pipe too far into the chimney, it can negatively affect draft. We have a 6" pipe feeding into an 8" stainless steel oval liner. How far is "too far"? Half way across the liner? A quarter? A couple inches?

We're having issues with our new wood stove and the dealer thinks it could be a draft problem. We had a wood/coal stove there before this new stove and never had any problems. But the installers said that when they went to install the new stove pipe they found the old one was simply butted up against the liner, so they crimped the ends and pushed it inside. I'm wondering if it's possible that they pushed it in too far and affected the draft.

I checked the gasket on our top load door this morning and on a two week old stove, the gasket is not sealing (was able to pull out paper all the way along the front). I think that is most likely our "draft issue", but I wanted them to check the installation of that crimped stove pipe while they are here to make sure they didn't push it in too far.

Thanks.

 

[fire_man]

If the new stove has a 6" exit pipe, maybe the problem is that it's going into a bigger 8" oval pipe. That will affect draft, it should be into a 6" liner unless the stovemaker says 8" is ok.

If the connector pipe is in too far, I can see how that would be a problem, too. Can you tell how far inserted it is?

 

[redhorse]

I tried to look up the chimney with a mirror this morning and can't get the right angle to see anything. It's either get a better mirror or take things apart. I suppose I could call the guys who installed it and see if they remember (since it was only a couple weeks ago).

They told us 6" to 8" should be ok.

 

[fire_man]

I would first check with the manufacturer of the stove to see what they recommend for flue size. What make/model stove do you have?

I doubt the installer will remember the exact installation depth. Best thing is to take it apart or get the better mirror - or get installer back.

 

[DanCorcoran]

According to his other post, OP has a Harman TL-300. On page 5 of the TL-300 installation manual, it says it takes a 6" flue. On page 11 of the same manual, it says it takes a 6", 7", or 8" round flue.

My understanding is that if there's poor draft, smaller flue is better. Also, OP, does your chimney meet the 3-foot, 10-foot, 2-foot rule described in that manual?

 

[redhorse]

According to his other post, OP has a Harman TL-300. On page 5 of the TL-300 installation manual, it says it takes a 6" flue. On page 11 of the same manual, it says it takes a 6", 7", or 8" round flue.

My understanding is that if there's poor draft, smaller flue is better. Also, OP, does your chimney meet the 3-foot, 10-foot, 2-foot rule described in that manual?

The 8" oval should not be an issue since a TL 300 will also work with an 8"x8" or 8" x 12" square or rectangular masonry chimney (I would think stainless in the same size or smaller would actually be better).

Yep, it meets the 3/10/2 rule: 3 feet above the roof exit point (it's actually closer to 6'), and 2' higher than anything within 10' of the chimney (there is nothing within 10' of the top of the chimney). The stove is on the first floor of a two story home and to clean the chimney from the top, we need a 4' step ladder to effectively reach the cap.

 

[begreen]

How are these two pipes joined? Is there a tight, sealed connection between the 6" round and 8" oval pipe?

 

[redhorse]

How are these two pipes joined? Is there a tight, sealed connection between the 6" round and 8" oval pipe?

No, they crimped the one pipe and fit it into the liner. I believe they stuffed it full of insulation, but I'm not sure.

 

[begreen]

That connection needs to be tight. Normally a manufactured transition piece is required to join them. If air is leaking in around this connection it will spoil draft and cool the flue gases.

 

[fire_man]

I think BeGreen is on to something. A leak at the joint is trouble. I found a leak at the cover to my cleanout T - fixed it with high temp 3M tape.The temps at your joint are probably higher than my T cover.

 

[redhorse]

Not a draft problem. Checked the stove with bypass open and got 0.08; with bypass closed, got 0.06; minimum for this downdraft stove is 0.03.

 

[begreen]

And yet still, the stove seriously underperforms. Something is amuk here. This connection sounds like one place that can be improved.

 

[redhorse]

And yet still, the stove seriously underperforms. Something is amuk here. This connection sounds like one place that can be improved.

We're going to have someone out to check that next. I was told when they crimped it, they stuffed insulation everywhere, but no one mentioned using any tape.

Thanks.

 

[fire_man]

Not a draft problem. Checked the stove with bypass open and got 0.08; with bypass closed, got 0.06; minimum for this downdraft stove is 0.03.

Redhorse: How does one test the draft? It's not something I have ever measured or seen measured. You have some kind of draft measuring instrument?

 

[DanCorcoran]

I put "measure draft" in the search box at the top of this page. I got lots of results, among which, from Battenkiller, was this:

"A simple manometer can be had for less than $40. I was told by an engineer at PE that one of the few things that wood stoves all have in common is the amount of draft they need - between 0.04†and 0.08†of water for most stoves at operating temperature (roughly 300-350ºF flue pipe temp, or 600-700ºF internal flue gas temp). He said most stoves will perform poorly below 0.02†and will tend toward difficult to control or even overfire above 0.12†of water. "

Google manometer for more information...

 

[fire_man]

Thanks, Dan. That's good info. Makes sense draft is dependent on flue temp as well. If the joint in redhorse's liner were leaking, I would have expected his draft to be much worse. Redhorse never actually defined what the problem with his stove was, just said "issues".

Redhorse: can you give us more details of the actual stove performance problems?

 

[begreen]

And yet still, the stove seriously underperforms. Something is amuk here. This connection sounds like one place that can be improved.

We're going to have someone out to check that next. I was told when they crimped it, they stuffed insulation everywhere, but no one mentioned using any tape.

Thanks.

Tape is not the best thing to use on the hot pipe. A solid, tight, mechanical connection is preferred.

 

[redhorse]

Redhorse: can you give us more details of the actual stove performance problems?

The stove draws really well with the ash pan door open (or the front load door or top load door). When all doors are shut, the fire acts as if it is starved for air.

We have had problems keeping it in secondary combustion. Last night, we couldn't get a fire at all unless we left the ash pan door open. Clearly there are air flow problems, but since the draft measured 0.06 with the bypass closed, we're wondering if something could be blocking the airflow in the stove itself. Not sure what that could be actually.

 

[redhorse]

Tape is not the best thing to use on the hot pipe. A solid, tight, mechanical connection is preferred.

Not knowing much about this, I'm wondering how they would even get to it to put in such a connection? We had an 8" stove pipe running through a crock thimble to an 8" steel liner. This was installed about 10 years ago and the installers simply butted the 8" pipe up to the liner (which had a hole in it).

This new stove has a 6" pipe. When they pulled the 8" pipe, they found a cracked thimble (which we will have replaced this summer). So they took the existing 8" pipe, used it for an extra liner (and to make sure the thimble didn't crack more they thought it best to have the 8" in there as the 6" would have allowed the thimble to drop). They crimped the ends of the 8" to extend it into the liner. But I'm not sure at all how the 6" is "attached". It may just be lying inside the 8" pipe, with no airtight connector. They may have used a 6-8" connector (they were supposed to but I'll have to call the installer to make sure).

I guess I'm wondering how to get a solid connection. The crock and hole in the liner are roughly the same size, so I'm not sure how one would even attach anything to the liner to make a solid connection. I'm thinking to make a connection like this a plate with a collar would have to be placed at the liner, but if the hole is almost the same size as the thimble, I'm not really sure how they would even get it in there...

To fix it, I'm wondering if we're going to have to pull the liner.

 

[begreen]

You may not have to pull the liner. But I would fix the thimble now, then connect with 6" from stove to the cap with good tight connections. The other think to check is to be sure the liner didn't get flattened or crushed.