Opinions wanted: Necessary to insulate exterior masonry chimney around new SS flue?

[cj-8_jim]

UPDATE: I decided to install 1/2" insulation on the new SS liner. See post #12. Thanks all for your replies!

Hi,
I'm new... what a friendly and informative website!
Being new to fireplaces and wood inserts, I have a question about chimney lining...

1) Does the stainless steel chimney lining need to be insulated?
2) If so, by what product(s)?
3) For what length of the chimney?

BACKGROUND:
- 40 year old masonry exterior chimney with three flues (3 fireplaces)
- Only the one flue (with the liner) of the three flues will really ever be used.
- Location/use: Chicago with only occasional use for supplemental heating and ambience.
Will probably get used more regulary on the 30 days or so when temps < 15* F (i.e., < -9* C).
- I'm installing a VC Century (CW2500X00) insert.

Thanks in advance for your ideas,
Jim

 

[edthedawg]

Jim,

Is the center flue the one you're planning to use here? Or one of the side flues?

I'd roll the dice and not insulate the center flue. But I'd cap both the others, for sure. If you can squeeze an insulated liner in there, it is worth the extra cost for performance and peace of mind.

 

[cj-8_jim]

Ed - I think it's the center flue. Of the two other flues... one will definitely not be used... the other flue for the basement fireplace may be use 1-3x per season.


All -
If I do insulate, what insulation name(s) should I google?

Just regular unfaced fiberglass batt insulation?

I also see that the local big box retailer (Menards) has some type of oiled insulation... not sure if either of these are appropriate for a chimney.
Jim

 

[branchburner]

Not fiberglass, you need mineral fiber. Best and easiest (but not cheapest) to get the liner kit with insulation blanket made for the liner. Is the ss liner already in, or do you still need that too?

 

[CarbonNeutral]

Flue size?

 

[Wet1]

You're going to want to insulate it since it's an exterior chimney in a cold climate, the other flues will only cool it even more since they aren't used regularly. Depending on the construction or the condition of the existing flue, you might be required to insulate it. As noted above, you'll need to know what the internal dimensions are of your flue before you do anything. The most common way to insulate the liner is to wrap it. This type of insulation is available from the liner retailers. Generally speaking, an adhesive is placed on the liner and then the insulation mat is wrapped around it. Finally, a wire mesh is wrapped around the insulation to keep in in place. This is a little bulky, so you'll need to know how much room you have inside your flue. If things are tight, you can also pour in insulation. Many guys pour vermiculite or perlite around the liner. Thermix is another option.

 

[Northeaster1]

I am certainly no expert, but read here about the need to insulate last year, when having a liner installed. When the liner installer said I didn't need one, and that they (or other local companies) rarely put in liner insulation, I decided to try without. We have an external cinderblock chimney, with a 12" x 12" clay liner. We are in eastern Canada, so it gets pretty cold. I cleaned the chimney twice last winterm and had very little creosote. And, since I would not want the house any warmer than it is, when burning a full load, to get good overnight burns, I don't know how it would be better off with the liner insulated.

Not saying you should not insulate, but just saying that ours works juts fine without it.

 

[dave11]

I'll second that. I put a SS liner down an unused masonry flue, but no room for insulation. No problem with draft so far.

I think it's probably worthwhile if it can be done without too much trouble. Better though probably is to get really good at building hot fires quickly. Slow or cold fires probably cause far more creosote than uninsulated liners, as do prolonged end-burns with the air supply closed off.

 

[budman]

I burned mine two years with out and two years with and i see a big difference
with the cleaning of the stack.

 

[kbrown]

I'm not gonna say one way or another, but we didn't insulate on our ss liner. Exterior chimney, north side facing, cold Michigan climate. Chimney is 15'. My belief is the same as others in that I certainly don't need it any hotter in the house! If we loose a bit of heat to the chimney, that's ok with me. What matter's most is keeping the chimney clean which I have yet to see anyone say that they never have to clean an insulated chimney. Build the fire well and get a good draft going, well seasoned wood and proper use of the damper all contribute to how well the chimney will work. If you have a taller chimney, then insulation would be well recommended as the goal, as I understand it, is to keep the exhaust gases as warm as possible until the leave the chimney thereby reducing the ability to cool and condense causing the creosote. At 15', we are right at the minimum height to run our insert and don't have the need to insulate.

Just another set of facts from another wood burner! Ultimately, each person has their own reasoning for their particular setup.

 

[cj-8_jim]

Thanks for all the replies... keep them coming!

This chimney I'm going to reline with a SS liner is a 25' flue.

Is the ss liner already in, or do you still need that too?

No liner is installed yet. I haven't found yet a place that sells SS liner with insulation attached. I did find a place on line that sells insulation wrap, some Elmer's spray adhesive, aluminum tape, etc for as much or more than the cost of the liner.

I'm wondering if it's possible to buy something from Home Depot, glue it, wrap it, tape and put some chickenwire-like wire around the outside.

Flue size?

From the ground, the exterior measurements of the square clay chimney liner look to be 11"x11" or so (or inside dimension probably of about 10"x10").

Jim

 

[bluefrier]

I did not insulate my exterior chimney and just like the other posters I don't think I compromise a whole lot. The liner stays relatively clean, no draft problems and no creosote only powdery soot. Every situation is different though...YMMV.

 

[cj-8_jim]

Thanks everyone for all the replies.

I decided to put 1/2" insulation on the liner... I was able to find a $240 shipped insulation kit (i.e., insulation, clamps, adhesive and mesh).

I figured it was a small price to pay as I'm installing the new liner and considering:
- 40 y.o. exterior brick chimney in a wood-framed and wood-sided home in Northern Illinois
- The insulation will give us some piece of mind that reduced levels of creosote are forming when we run the insert on a low setting (we only need to heat about 750 sq ft. with the 1.3 cu ft insert).

Thanks again,
Jim

 

[Wet1]

Good call Jim.

 

[weatherguy]

Im not insulating but I have an interior chimney with three flues, Im using the middle flue for the woodstove. Im going to put in a block off plate but I cant see any reason to insulate. If it was an exterior or single flue I probably would insulate.

 

[kbrown]

With a 25' chimney, that's a good call to insulate Jim. At $240 that's a small price for peace of mind. With a chimney that tall, what's it like to get access to the top? What's the pitch on your roof?

 

[ansehnlich1]

I got an external brick chimney, stainless liner, poured insulation around it, hotter than HADES in the house

I say insulate if you can, for sure.

 

[cj-8_jim]

With a chimney that tall, what's it like to get access to the top? What's the pitch on your roof?

I think I'm lucky... the exterior chimney stands 3' or so above the peak at the roofs peak.
That means I get to put one foot on each side of the peak and drop the liner down the chimney at a little more than countertop height.