Am I insulated enough or not? No one seems to know...

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j7art2

j7art2

Minister of Fire
Oct 9, 2014
545
Northern, MI
I have an external cinder block chimney, which is terracotta lined. The terracotta is in relatively good shape.

Many of the chimney sweeps in my area are wanting to charge thousands for install. I'm pricing out insulated liners with T at around $1000, and I'm getting quotes for $2000-3200 for an install. I'm about to do it myself, however none of the chimney sweeps can agree on whether or not I need a liner. Some are saying absolutely, and that they may have to break all the terracotta out (which I assume is 8x13 but may not be), others are saying that the terracotta insulates it enough that I just need a stainless liner with no added insulation.

Even reading online on some of the chimney liner web pages seems to have conflicting information. The cost to insulate isn't super significant, my concern is that it's simply not going to fit with insulation, and there's no way I'm breaking out 25 feet of terracotta. I'd just assume knock the whole chimney down and use all the triple walled stainless I've got on my barn.

I get that insulating is always better (you probably can't get enough) I just don't want to order and be stuck with a bunch of insulation that I can't use or ultimately didn't need.

I'm not 100% convinced I have a true 8x13, which is part of my concern. I did a quick measurement from front to back through the hole in my basement wall since I'm going to clean the chimney today and got a 7" measurement. I'm going to double check that once the chimney is clean, but if on the off chance I have a weird size, I don't want to wind up with a nightmare and not be able to get this done.
 
This is the current setup I have right now and I have very little draft problems with my pre EPA unit that I want to replace. Creosote build up is little to none, just fine soot, nothing significant to speak of.

[Hearth.com] Am I insulated enough or not? No one seems to know...
 
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You really need the insulation, especially with external chimney, will really help establish draft when it's not real cold out. The triple-wall isn't too good I don't think. No insulation, just air space.
 
And you need insulation to meet code with the liner, unless the block chimney has the required clearance to combustibles...1" or 2", depending.
 
Woody Stover said:
And you need insulation to meet code with the liner, unless the block chimney has the required clearance to combustibles...1" or 2", depending.
Click to expand...

It's built to code as far as I can tell, as a class A masonry chimney. The installer wasn't even convinced I needed a liner honestly, but I'm not THAT brave to run one of these new EPA units without one.
 
If the clay liner is small enough, you could get away without a liner. I think if the ID of the clay is less than 2 times that of the flue exit, it might draw good enough. Check me on that, though..
I think the term "Class A" applies only to manufactured stainless chimney.
 
You ned to get up on the roof and measure your tile liner for size. Then you will know what will fit.

The insulation on the stainless liner will help with draft and with creosote build-up.
 
j7art2 said:
It's built to code as far as I can tell, as a class A masonry chimney. The installer wasn't even convinced I needed a liner honestly, but I'm not THAT brave to run one of these new EPA units without one.
Click to expand...
To be built to code you need 1" clearance from the outside of that masonry structure to combustible materials. Trim can touch the corners but thats it. If you have that clearance then no technically you dont need insulation but especially with an exterior chimney the performance gains will be worth it.

If the stove you will be using has a 6" outlet then yes you need a liner because the clay is more than 3 times the volume of the stove outlet.

To fit an insulated liner in an 8x12 which is usually about 7x11 you have a couple options. You can break out the clay which is what i would do or go with an oval liner.

And no the terracotta offers no significant insulation value.
 
Woody Stover said:
If the clay liner is small enough, you could get away without a liner. I think if the ID of the clay is less than 2 times that of the flue exit, it might draw good enough. Check me on that, though..
I think the term "Class A" applies only to manufactured stainless chimney.
Click to expand...
Class a chimney does not just refer to prefab chimneys. Masonry chimneys can qualify as class a if they are built to code.
 
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bholler said:
To be built to code you need 1" clearance from the outside of that masonry structure to combustible materials. Trim can touch the corners but thats it. If you have that clearance then no technically you dont need insulation but especially with an exterior chimney the performance gains will be worth it.
Click to expand...

Man Bholler If you only had a nickel for every time I’ve seen you type that.
 
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Cleaned it today, 27 feet exactly according to my cleaning rods. I was close.

I stuck the tape measure in there and got 7", so yeah, it's 7x11 it looks like. Breaking terracotta out of the chimney isn't something I'm going to be able to do.

How much does the insulation "squish"?
 
Every mortar seam in the clay liner would have to be perfect..not likely. Maybe you can hire a sweep to bust out the tile liner, they have the tools and know-how to do it. Or just blow up through the house with Class A, then you have a nice, warm, no-deposit chimney.
 
j7art2 said:
Cleaned it today, 27 feet exactly according to my cleaning rods. I was close.

I stuck the tape measure in there and got 7", so yeah, it's 7x11 it looks like. Breaking terracotta out of the chimney isn't something I'm going to be able to do.

How much does the insulation "squish"?
Click to expand...
If you squish it the insulation value is compromised.
 
Just cleaned it so I measured the inside...

7x10.

What the heck. Weird size?

And yes, it's 1-2" off the house, so I'm up to code in that regard. Perfect gap for chipmunks to make a house between... Don't ask how I know.
 
j7art2 said:
Just cleaned it so I measured the inside...

7x10.

What the heck. Weird size?

And yes, it's 1-2" off the house, so I'm up to code in that regard. Perfect gap for chipmunks to make a house between... Don't ask how I know.
Click to expand...
Really that is pretty uncommon to actually have the proper clearance. If that is the case from a safety standpoint you dont need insulation. But from a performance one you really do. In this case thermix may be an option if you can really confirm proper clearances top to bottom. Because you could not get enough thermix in to get zero clearance rating but it would be enough to help allot with performance.

Be aware that it is very possible even a bare 6" liner may not fit down those liners.
 
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Maybe I'm better off paying someone else to do it after all... Not a good position to be in when it's time to upgrade from your 30 year old units. Suddenly your upgrade doubles or triples in price.
 
j7art2 said:
Cleaned it today, 27 feet exactly according to my cleaning rods. I was close.

I stuck the tape measure in there and got 7", so yeah, it's 7x11 it looks like. Breaking terracotta out of the chimney isn't something I'm going to be able to do.

How much does the insulation "squish"?
Click to expand...
You can put in a Duraliner oval pipe system. It's pre-insulated and designed to fit your sized flue.

(broken link removed to http://www.duravent.com/Product.aspx?hProduct=6)'
https://woodstovepro.com/chimney-pi...el-piping/6-inch/duravent-duraliner-6/page-2/
 
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That's an option! Maybe not the cheapest compared to a flex liner but cheaper than the professionals quoted. Thank you.

As long as that T fits down there I'm golden.
 
[Hearth.com] Am I insulated enough or not? No one seems to know...
 
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I'm running 17ft of the oval duraliner on an insert that is supposed to be a hard breather and it drafts great. was a bit of a pain to install but it seems to be very well built and looks like it will last a long time
 
Oval flex liners work fine also.
 
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