Seeking install advice: oval liner vs. uninsulated?

Kilos

New Member
Sep 14, 2020
5
Connecticut
Hi everyone. Longtime lurker, first time poster. I’ve wanted a wood stove for as long as I can remember (hence the lurking) and now that we live on a heavily wooded bit of acreage I’ve finally convinced my wife that we should take advantage of the free fuel. I’ve had a few cords seasoning for over a year, and we’re getting ready to pull the trigger on a BK Princess 29 insert to plug into our basement fireplace. I’m excitedly rebuilding the hearth to exceed all clearance requirements, and I didn’t think we were going to run into any problems… but it’s only once you think you’re in the clear that the problems pop up. Ha.

Blaze King recommends an insulated chimney liner (and I know that insulating your liner is just good practice all around). It turns out that I’ve got a 6 ½” by 10 ½” rectangular flue, and it’s just not possible to blanket wrap standard 6” round and get it to fit. My alternatives are turning to something like DuraLiner’s oval liner, or even filling with poured insulation after the fact.

The company that we’ve decided to go with give us a great quote on the brand-new stove, installation, lining, and capping, but the guy insists that we don’t need insulation. I actually really trust this installer, as he runs a very large, successful business with endless recommendations and damn-near flawless reviews. Still, I’m a researcher at heart and everything I read says that you should insulate your chimney liner.

I’m torn. I suggested the 6” rigid DuraLiner, and he said that any benefits gained by insulating the chimney liner will be eliminated by the oval-shape (obviously smoke and gases vent best in a round void). He swears we don’t need the insulation (even on a high-efficiency Blaze King). In his words:

“Typically we use 316L stainless smooth wall-liners. Over the last 25 years I have found in our relatively warm climate the insulation is unnecessary and only use when requested. We have 35k customers currently heating with wood 1/2 or more are inserts and very few have insulated liners. While servicing there is no difference in creosote buildup at the top between the 2. The most important factor I have found is burning properly seasoned wood with a moisture content between 15-20 percent.”
Sorry for the long wind-up—here’s the question:

My installer says we don’t need insulation.
I want insulation.
Blanket-wrap won’t fit, and the only alternative is an ovalized liner.
The installer says that an ovalized liner will negate any benefit I get from the insulation.

What’s worse, an oval chimney liner or an uninsulated round? What should I do in this case? I’d really like to avoid poured in insulation if I can, as it sounds like a damn mess and really easy to screw up or do poorly. I’ve scoured these forums (and numerous sites and sources around the Internet) and I couldn’t find this exact situation covered—apologies if this is covered somewhere else.

IMG_20200914_105001.jpg
 

begreen

Mooderator
Staff member
Nov 18, 2005
83,687
South Puget Sound, WA
There are multiple reasons for insulating the liner. It improves draft and keeps creosote buildup down by keeping the flue gases hotter. This is why BK strongly recommends an insulated liner. But there is also safety. Ask if his installations are inspected and code compliant.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,910
central pa
If the guy says that burning 20% MC wood is ok on a modern stove than I wouldnt take his word on anything.
20% mc is ok for burning in any stove. Just about everything else he said is a call for concern but not that
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,910
central pa
Hi everyone. Longtime lurker, first time poster. I’ve wanted a wood stove for as long as I can remember (hence the lurking) and now that we live on a heavily wooded bit of acreage I’ve finally convinced my wife that we should take advantage of the free fuel. I’ve had a few cords seasoning for over a year, and we’re getting ready to pull the trigger on a BK Princess 29 insert to plug into our basement fireplace. I’m excitedly rebuilding the hearth to exceed all clearance requirements, and I didn’t think we were going to run into any problems… but it’s only once you think you’re in the clear that the problems pop up. Ha.

Blaze King recommends an insulated chimney liner (and I know that insulating your liner is just good practice all around). It turns out that I’ve got a 6 ½” by 10 ½” rectangular flue, and it’s just not possible to blanket wrap standard 6” round and get it to fit. My alternatives are turning to something like DuraLiner’s oval liner, or even filling with poured insulation after the fact.

The company that we’ve decided to go with give us a great quote on the brand-new stove, installation, lining, and capping, but the guy insists that we don’t need insulation. I actually really trust this installer, as he runs a very large, successful business with endless recommendations and damn-near flawless reviews. Still, I’m a researcher at heart and everything I read says that you should insulate your chimney liner.

I’m torn. I suggested the 6” rigid DuraLiner, and he said that any benefits gained by insulating the chimney liner will be eliminated by the oval-shape (obviously smoke and gases vent best in a round void). He swears we don’t need the insulation (even on a high-efficiency Blaze King). In his words:



Sorry for the long wind-up—here’s the question:

My installer says we don’t need insulation.
I want insulation.
Blanket-wrap won’t fit, and the only alternative is an ovalized liner.
The installer says that an ovalized liner will negate any benefit I get from the insulation.

What’s worse, an oval chimney liner or an uninsulated round? What should I do in this case? I’d really like to avoid poured in insulation if I can, as it sounds like a damn mess and really easy to screw up or do poorly. I’ve scoured these forums (and numerous sites and sources around the Internet) and I couldn’t find this exact situation covered—apologies if this is covered somewhere else.

View attachment 263177
Did they inspect your chimney before telling you you don't need insulation?
 
  • Like
Reactions: begreen

Supersurvey

Burning Hunk
Jan 25, 2015
191
New Jersey
Will the insulated oval liner fit?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,910
central pa
You can also use a flexible oval liner
 
  • Like
Reactions: Kilos

Kilos

New Member
Sep 14, 2020
5
Connecticut
Update: called BK and one of their techs confirmed what we all already knew (that the oval liner wouldn't cause that much of a draft reduction and that they very much recommend an insulated liner). I emailed this installer back and asked if we could use an insulated oval liner, and he said
yes but it will increase the price a bit and we would need to use single wall rather than the double smooth wall we would normally use
I don't want him to downgrade the kind of liner he uses in order to get this to work. I think I might just pause until I have a better understanding of my options.

Did they inspect your chimney before telling you you don't need insulation?
I paid for a chimney inspection when I bought the home, and they said it was in great shape aside from needing a bit of mortar repair on the exterior. They didn't mention anything about whether or not a liner would need insulation at the time. This guy hasn't seen the chimney aside from a bunch of pictures I sent him. It's impossible to get somebody to come and consult or provide an estimate around here. They all charge somewhere between $120-250 just to come out. One guy wanted a $575 deposit to come out and look.

You can also use a flexible oval liner
Do you have a specific example you can link? Any recommended brand/product?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,910
central pa
Update: called BK and one of their techs confirmed what we all already knew (that the oval liner wouldn't cause that much of a draft reduction and that they very much recommend an insulated liner). I emailed this installer back and asked if we could use an insulated oval liner, and he said


I don't want him to downgrade the kind of liner he uses in order to get this to work. I think I might just pause until I have a better understanding of my options.


I paid for a chimney inspection when I bought the home, and they said it was in great shape aside from needing a bit of mortar repair on the exterior. They didn't mention anything about whether or not a liner would need insulation at the time. This guy hasn't seen the chimney aside from a bunch of pictures I sent him. It's impossible to get somebody to come and consult or provide an estimate around here. They all charge somewhere between $120-250 just to come out. One guy wanted a $575 deposit to come out and look.


Do you have a specific example you can link? Any recommended brand/product?
An oval liner would cause a bit of a draft reduction if it was not upsized to account for the volume lost when ovalizing. As long the correct volume is maintained there will be no problem.

Moving away from the 2ply smooth wall crap is a good thing and in no way a downgrade. That stuff is complete crap

The fact is this guy has absolutely no idea if your chimney needs insulation without doing an on-site inspection.
 

Kilos

New Member
Sep 14, 2020
5
Connecticut
The fact is this guy has absolutely no idea if your chimney needs insulation without doing an on-site inspection.
Yeah, starting to realize his low estimate was just bait.

Moving away from the 2ply smooth wall crap is a good thing and in no way a downgrade. That stuff is complete crap
Good to know. He keeps talking about it like it's preferred (and it probably is, for his bottom line)

An oval liner would cause a bit of a draft reduction if it was not upsized to account for the volume lost when ovalizing. As long the correct volume is maintained there will be no problem.
This is where I need to keep doing research. I think the chimney is a straight shot down. The top flue tile opening is 6.5" x 10.5". I just need to figure out what OD insulated liner I need (and then account for the wrap insulation thickness, or find insulated oval liner)

Appreciate the insight.
 

begreen

Mooderator
Staff member
Nov 18, 2005
83,687
South Puget Sound, WA
Duraliner rigid oval is 4.75" x 7.75". It's made for this size chimney and works well.
 

brenndatomu

Minister of Fire
Aug 21, 2013
5,258
NE Ohio
Moving away from the 2ply smooth wall crap is a good thing and in no way a downgrade. That stuff is complete crap
This! ^ ^ ^
This installer is starting to sound less and less like a true professional...
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,910
central pa
This! ^ ^ ^
This installer is starting to sound less and less like a true professional...
He sounds exactly like most guys running big operations. Maximize profit and minimize time on the job. That means dismiss insulation because it adds time on-site and makes things more complicated. It also adds cost to the job without allot of increased profit. Which means more potential to loose a bid. They will many times upsell people on something that increases profits without benefit like those crappy liners.
 
  • Like
Reactions: Kilos

Kilos

New Member
Sep 14, 2020
5
Connecticut
Duraliner rigid oval is 4.75" x 7.75". It's made for this size chimney and works well.
Yes! This is the stuff I linked to the installer and asked for by name (because I saw so many people on here recommending it) and he said it wouldn't work if there are any bends. I'm going to go snoop up the chimney and see if I can find daylight.

This! ^ ^ ^
This installer is starting to sound less and less like a true professional...
Just to be clear, you're saying that you'd prefer the single wall corrugated vs the double wall smooth? Why is the double-ply stuff so garbage? I'm legitimately curious--I know nothing here.

This is more or less what he's been telling me:
 

brenndatomu

Minister of Fire
Aug 21, 2013
5,258
NE Ohio
You can also use a flexible oval liner
You talking about factory ovalized, or site ovalized? Kinda sounds like this guy might do a hack job on site ovalized...
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,910
central pa
You talking about factory ovalized, or site ovalized? Kinda sounds like this guy might do a hack job on site ovalized...
We have an ovalizer so we can ovalizer our own. But doing it without one turns into a hack job.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,910
central pa
Yes! This is the stuff I linked to the installer and asked for by name (because I saw so many people on here recommending it) and he said it wouldn't work if there are any bends. I'm going to go snoop up the chimney and see if I can find daylight.


Just to be clear, you're saying that you'd prefer the single wall corrugated vs the double wall smooth? Why is the double-ply stuff so garbage? I'm legitimately curious--I know nothing here.

This is more or less what he's been telling me:
I really prefer heavy wall or midweight liners. They are still smoothwall but way more durable. But I would choose regular correlated light wall over the 2ply stuff any day.
 

brenndatomu

Minister of Fire
Aug 21, 2013
5,258
NE Ohio
Update: called BK and one of their techs confirmed what we all already knew (that the oval liner wouldn't cause that much of a draft reduction and that they very much recommend an insulated liner). I emailed this installer back and asked if we could use an insulated oval liner, and he said
My math shows that ovalizing a standard 6" flex liner only reduces the area by .78 sq inches...any loss of draft easily made up by insulating the liner and/or adding a foot or two on height to the chimney (if its less than, say 18' tall total...anything over 18' tall you will probably have plenty of draft anyways IMO)
Height can be added by mounting a transition plate on top of the masory chimney to attach the new liner to, then height is added by going on up with class A insulated chimney pipe from there.
 
Last edited:

Kilos

New Member
Sep 14, 2020
5
Connecticut
I really prefer heavy wall or midweight liners. They are still smoothwall but way more durable. But I would choose regular correlated light wall over the 2ply stuff any day.
Good to know, thanks. The installer I've been talking to just got back to me today. He says he can do the job insulated with ceramic wrap, but he'd be using a standard 6" liner ovalized on-site down to 5" x 7" ish. He told me this is the brand they'd use:

I wonder if it's decent product?

I'm not sure if I can just ask him to upgrade to midweight or heavy liner (I don't know how these companies do ordering or what).
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,910
central pa
Good to know, thanks. The installer I've been talking to just got back to me today. He says he can do the job insulated with ceramic wrap, but he'd be using a standard 6" liner ovalized on-site down to 5" x 7" ish. He told me this is the brand they'd use:

I wonder if it's decent product?

I'm not sure if I can just ask him to upgrade to midweight or heavy liner (I don't know how these companies do ordering or what).
I have never heard of that company but it is a listed liner system so it is probably fine. Ask them if they have an ovalizer they will be using. Or if they will just be smashing it with a board and hammer. If it is the second one find someone else to do it. And yes you should be able to request a heavier liner. They may say no but it can't hurt to ask. We get requests for light wall to save money and we always say no for wood or coal.


Aldo ask him how he is going to maintain proper volume in that ovalized 6" liner.