6" stove to an 8" flue SPECIFICS

[Blue Vomit]

I know this subject has come up before several times but other than draft issues, I can't find any other specific negative to venting a 6" stove into an 8" flue.
Like many others, I had an existing 8" insulated ss liner, about 25 ft. When researching stoves we really liked the Oslo. We researched the question, "can you vent a 6" stove into an 8" flue." general consensus seemed to be: many people do it and are fine, some people experience draft issues.
Fast forward, purchased the Oslo, had it installed, been burning about 2 months now. The Oslo can be a little sluggish in my setup, especially in shoulder season but still performs well.
My question is: Other than the minor draft issue, would transitioning to a 6" flue help me with anything else? I know the stove was designed to run with a 6" flue. Would this give me a longer burn time? Would less heat be going up the flue? Are there any other benefits, other than improving draft, or would improving the draft translate into longer burn times or more sustained heat?
I think I can drop a 6" liner in there relatively easily, just wondering if it would be worth it? Would my stove performance be that much better, and how would it be better?
Thanks in advance.

 

[oldspark]

I bet it will cure the sluggish problem, not sure about the other things you mentioned.

 

[Blue Vomit]

Just a little more info. The only minor complaint I have about the Oslo is that it seems to take a little time to get up to temp. When it finally does get up to temp, 400 to 500, and I can start to back down the primary air in increments, it seems like a lot of the fuel has been used up(to get it up to temp) and I'm losing that fuel on the back end(longer burns). Does this have anything to do with the 8" flue?
I can get a 7-8 hour burn if I pack it to the gills, just trying to see if I can do better.

 

[fossil]

My guess would be that the only noticeable improvements would involve the stove's draft and the flue's creosote accumulation. I can't imagine that wood consumption or burn times would be affected one way or the other. Rick

 

[oldspark]

The reason I said it would cure the sluggish problem is from my chimney change out, 7 1/4 round flue to the 6 inch and my stove is a rocket compared to last year, it did change a few other things, gained a little on the top end and it lowered my flue temps some but the most impressive was how fast the fire gets going now.

 

[oldspark]

My bad, I forgot I removed 2 90's when I put the new chimney in. :red:

 

[Blue Vomit]

Mine is rear vented, 6 to 8 expanded/reducer, then to a 8" tee, then straight up about 25' , all 8".

 

[cberst26]

I've got a GREAT idea. How about I get you the 6" pipe that you need and we trade? I am in need of 8" and don't want to pay for new stuff. I can find used 6" all day long, but no 8". I'm being totally serious, and since you're in PA, OH isn't that far. We could easily meet in Harrisburg or something. PM me if you want. It's killing me to have my burner in the basement, unhooked and doing nothing.

 

[Blue Vomit]

If I'm going to do anything I would just drop an uninsulated 6" down inside my insulated 8". But it sounds like that wouldn't really help me all that much anyway. Sorry smoldering.

 

[Shari]

I can't find any other specific negative to venting a 6" stove into an 8" flue.

An 8" diameter liner has around 50" cu. in. vs a 6" diameter has around 28" cu. in. which means your 8" diameter liner is around 56% larger than manufacturers specs. Does this mean you will see a 56% improvement? No - but you will see an improvement.:

Other than the minor draft issue, would transitioning to a 6" flue help me with anything else?

Yes

Would this give me a longer burn time?

Yes

Would less heat be going up the flue?

Yes

would improving the draft translate into longer burn times or more sustained heat?

Yes to both.

 

[Shari]

Now, if your next question (reading your mind here) is "Should I insulate my liner or not?"

Let's stop and think here a sec: What does 'insulating a liner' do?

1. Does it keep my chimney warmer?

Answer: Yes. A warmer chimney = an easier starting / better drafting stove, especially in the shoulder season (above 50 degrees) and insulating your liner is especially beneficial if your chimney is an external chimney.

2. Is an easier starting /better drafting stove the ONLY reason to insulate a liner?

Answer: No - a really, really big NO. The main reason to insulate a liner (in my opinion) is the liner acts as an additional fire barrier. I want to heat with wood in the safest manner possible. My chimney is an interior chimney - it's a short chimney. Did I HAVE to insulate it? No - but I did, for safety sake I did. Your mileage /opinion may vary.

 

[cberst26]

I hope that your opinion is taken, Shari. I'd love to get my hands on his used 8" pipe. As it stands, I'm thinking about not installing my stove, but selling it. Then come Spring, buy an NC-30 and vent with 6". This is so depressing to me. :-(

 

[Blue Vomit]

Thanks Shari,
I have an insulated 8" liner now. I was thinking I could drop an uninsulated 6" liner down inside the 8". Is it that easy, and wouldn't the existing 8" liner act as insulation for the 6"?
If I can get more heat, longer burn times, and use less wood, I think I would bite the bullet and spend the money.

 

[Shari]

Thanks Shari,
I have an insulated 8" liner now. I was thinking I could drop an uninsulated 6" liner down inside the 8". Is it that easy, and wouldn't the existing 8" liner act as insulation for the 6"?
If I can get more heat, longer burn times, and use less wood, I think I would bite the bullet and spend the money.

Kinda like putting on two pairs of socks when the weather is cold. (sorry - my attempt at humor on a cold winter's night!)

My initial reaction would be this: Right now your 8" chimney is supported 'somewhere / somehow'. If you ran a 6" down inside the 8" you will have to then also support the 6". My gut tells me you shouldn't do this as it's just going to get too complicated to support both liners.

But, hey, what do I know. After all, I do sometimes wear two pairs of socks on a cold winter's day.

 

[Blue Vomit]

Thanks Shari,
I have an insulated 8" liner now. I was thinking I could drop an uninsulated 6" liner down inside the 8". Is it that easy, and wouldn't the existing 8" liner act as insulation for the 6"?
If I can get more heat, longer burn times, and use less wood, I think I would bite the bullet and spend the money.

Kinda like putting on two pairs of socks when the weather is cold. (sorry - my attempt at humor on a cold winter's night!)

My initial reaction would be this: Right now your 8" chimney is supported 'somewhere / somehow'. If you ran a 6" down inside the 8" you will have to then also support the 6". My gut tells me you shouldn't do this as it's just going to get too complicated to support both liners.

But, hey, what do I know. After all, I do sometimes wear two pairs of socks on a cold winter's day.

Yup, I had the install done by the pros. I'd post a pic now but it's too dark to climb on the roof. It almost looks like the liner is cemented in at the top. I'm assuming there is some sort of plate or tray at the top, liner exits through the middle, then it is sealed in by what looks like cement? Top of the chimney has my liner sticking up surrounded by what looks like cement, then of course the chimney cap on top. I don't know how much that makes sense but that is why I'm reluctant to remove it and was thinking, just drop an uninsulated one inside it.

 

[Hardrockmaple]

I installed a 6" SS liner in a 30 ft. interior masonry chimney 2 years ago as the old clay liner had deteriorated badly. This to exhaust my DW 2400 (small) stove w/ rear vent. I've experienced no noticeable changes to date, well there was one major disadvantage, the chimney is no longer is the heat sink it once was. Same stove, same set up over 11 years 'til now.