Increasing height of masonry chimney with oval liner

[Gnanneb86]

We had a VC defiant flex burn installed last winter and now have issues with it puffing. This usually happens once the stove has been burning a while and we start reducing the air a little at a time. The old stove, 80s blaze King king model never had the issue, my guess because it dumped so much heat up the chimney and kept better draft. I get no puffing at all if I leave the the air open all the way but the stove climbs above 700 quickly if I do that and no matter how little I try to cut it back it starts to puff.

I'm thinking it wouldn't hurt to increase the height of the chimney 3 to 5 feet to add some draft but not sure the best way to go about this. How do you go about attaching to an oval liner with something that doesn't look terrible and still functions well?

Currently the chimney is an 8 x 12 rectangular with a appx 7 x 11 oval insert.

 

[begreen]

I wouldn't raise the chimney before addressing easier to fix issues. There are 3 90º turns plus a level horizontal run in the flue path. That is definitely a problem for draft. I'd eliminate those 90s and the horizontal section for better draft. If it would be possible to come off of the stove's oval to round pipe with a 45º elbow pointed at the thimble with a diagonal pipe tying into another 45 elbow at the thimble there would be a dramatic improvement. That may be all that is needed to make the Defiant happy.

If the current oval liner is not insulated, then the next step would be to pull that and replace it with a preinsulated liner like DuraLiner oval. These changes would greatly reduce resistance to the free flow of flue gases and help keep them hotter throughout the flue system. That will result in better draft, a cleaner flue system and a happier stove.

 

[Gnanneb86]

I wouldn't raise the chimney before addressing easier to fix issues. There are 3 90º turns plus a level horizontal run in the flue path. That is definitely a problem for draft. I'd eliminate those 90s and the horizontal section for better draft. If it would be possible to come off of the stove's oval to round pipe with a 45º elbow pointed at the thimble with a diagonal pipe tying into another 45 elbow at the thimble there would be a dramatic improvement. That may be all that is needed to make the Defiant happy.

If the current oval liner is not insulated, then the next step would be to pull that and replace it with a preinsulated liner like DuraLiner oval. These changes would greatly reduce resistance to the free flow of flue gases and help keep them hotter throughout the flue system. That will result in better draft, a cleaner flue system and a happier stove.

Thanks for the suggestions.

The blaze King had been installed with two 45s as you have suggested and I had asked the installer to do it that way again however he could not figure out a way to do it due to the oval connector. I may need to just go buy some pieces and see if I can get something to work. When the stove was installed the quote came with an estimate to put in a new liner but during installation they determined the oval liner was in great shape and they thought for sure it would come apart in the chimney if they attempted to pull it out. Anybody have experience pulling a liner? I'll start with playing around with two 45s and see what I can get to work, I agree I need to get rid of all the 90s and horizontal sections if it's possible.

What is the outer diameter of an insulated liner? Would it fit inside the 7x11 liner or is that a no no? The defiant requires 6 inch flue minimum. We wanted to keep it 8 inch to burn doors open but willing to give that up for a good running stove!

 

[begreen]

8" equivalent DuraLiner oval is 10.5" x 4.75" It would not fit in the current oval liner. Also, there would need to be a DuraLiner snout going to the thimble.

I'd address the interior portion first and then try that setup for a few weeks. It may be sufficient. Those 90º elbows may be adjustable. If so, that is a good way to experiment with configurations.

 

[Gnanneb86]

So here is what the blaze King setup looked like before we had the VC put in. I have the installer coming over to try to fix it however I feel like the setup on the blaze King looked terrible and on the VC with the oval adapter coming up first it will look even worse, is there some wonderful solution to this that I'm missing or am I just going to have to live with it looking terrible if we can get the two adjustable elbows to work like the old setup.

 

[begreen]

Yes, it's going to look something like that, but with a gentler slope due to the height of the oval to round adapter. The stove wants 16' of vertical flue to draft properly. It looks like there might just be that amount outside, but each 90º turn in the flue path slows the flue gases down. In effect it's like removing 2 ft of height for each 90º turn. The horizontal section further reduces draft. So even if there is a total of 18' vertical, the flue system is acting like a 11-12' system.