I’m getting ready to install an osburn matrix insert woodstove. I have a nearly hundred year old chimney that structurally seems sound but I want to line it with a flexible liner. The liner would be about 22’ long and 6” diameter. Do I need to insulate the liner or is it a best practices type of thing?
Osburn matrix insert liner
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EbS-P
Minister of Fire
What are dimensions of the current flue?
Short answer yes insulation is always good. It is required if your chimney doesn’t meet clearance to combustibles. 1” to any combustibles. (Framing roof sheeting ect) 2” for interior chimney.
22’ is tall. I have a Drolet in 23’ insulated liner. It needed a damper.
Short answer yes insulation is always good. It is required if your chimney doesn’t meet clearance to combustibles. 1” to any combustibles. (Framing roof sheeting ect) 2” for interior chimney.
22’ is tall. I have a Drolet in 23’ insulated liner. It needed a damper.
Ctwoodtick
Minister of Fire
Insulation for sure. I bit of extra money/effort now=piece of mind later.
I have a 36' insulated liner on my Osburn. I highly recommend the insulation but you may need the damper as mentioned. In my case, I designed a plug to restrict the primary airflow instead since it all flowed through a single hole in the box.
Similar question here--planning on installing an Osburn 1900 in our small firebox. ~45ft unlined chimney at present. The chimney company says they didn't think a pipe wrap would be necessary. This is the first I've heard about an additional damper. What is that for? Thanks all!
As described, the draft may be so strong that the stove is very hard to control. A smaller diameter liner and a damper will help tame the draft somewhat but it could still be a challenge.
Code requires the liner to be insulated if an interior chimney doesn't have 2" clearance from all combustibles all the way up through the roof. If this is an exterior chimney, then it is 1" clearance. Additionally, flue gases cool down as they travel from stove to chimney top. When they cool down to below 250º, creosote starts to condense in the liner. Insulating the liner helps reduce heat loss so that the flue exit temperature is higher. With a 45' liner the heatloss over the length of the liner could be very high, likely guaranteeing buildup.
Code requires the liner to be insulated if an interior chimney doesn't have 2" clearance from all combustibles all the way up through the roof. If this is an exterior chimney, then it is 1" clearance. Additionally, flue gases cool down as they travel from stove to chimney top. When they cool down to below 250º, creosote starts to condense in the liner. Insulating the liner helps reduce heat loss so that the flue exit temperature is higher. With a 45' liner the heatloss over the length of the liner could be very high, likely guaranteeing buildup.
Unless draft is so high that the flow speed of the gases reduce the residence time in the chimney so much that the cooling is insufficient to reach condensation?
Of course that is likely to result in uncontrollable fires (and/or over fires) in the stove .
Either way, safety dictates an insulated liner here.
Of course that is likely to result in uncontrollable fires (and/or over fires) in the stove .
Either way, safety dictates an insulated liner here.
True, it could be run like a roman candle, though the longevity of the liner and stove would be compromised. That, and undershorts might need frequent changing.
Thank you. So, what would people recommend to avoid overfiring in a situation like this? Is it not possible just to close the air intake on the stove to limit the intensity of the fire?
Not if you actually have a 45' chimney. I actually wouldn't install a stove on a chimney that tall if I was asked to
EbS-P
Minister of Fire
I have 24’ of insulated liner on Drolet 1800i. I needed a damper. It may need two? But I’m ok with how it’s running. 45’ is just crazy tall. If a professional says he would not install a stove that is saying something.
Do you have other choices? If you choose to go ahead you need a a way to measure flue gas temps. (I try to keep my temps at the appliance adapter under 850. I regularly get to 900 and have had sustained burns at 1000. ) understand you will installing and immediately it following manufacturers install guidelines. This would technically invalidate the UL listing of the appliance. That may not bother you but it might bother your insurance company.
You might get by with a pellet burner. An install with the ability to have a sealed outside air kit to which you could add a control mechanism could help.
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