1980s Fisher Insert adapt to chimney pipe

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.


New Member
Sep 9, 2023
Carlotta, CA
I have an old 1980s fisher fireplace insert

currently I have a clay liner. I’ve attached some pics of the insert and flu. I think the flu is around 8” and the hole inside the insert is around 7”

Maybe 20 ft from top of insert to top of chimney.

I want to put a new stove pipe inside the flu so it's safe and attach it to the insert. I'm thinking about putting a 6" pipe in and adapting it to the top of the fisher insert. so if in the future I want to swap the insert out for a new more efficient insert, I don't need to replace the chimney pipe. I'm not too worried about it not drafting well, I'm more concerned about it being safe.

Does that sound like a good plan?

also can anyone suggest what pipe to use and how to adapt it to the top of the fisher insert? I've heard suggestions of using a cast iron boot.

I think I have a smoke shelf too, so I'll probably need to go at an angle to get around the smoke shelf to the straight chimney pipe.

Is anyone familiar with this process, have any pics/videos, suggest what pipe, boot/collar, and adapter to get from the top of the stove to the pipe?

all advice is very much appreciated.

1980s Fisher Insert adapt to chimney pipe1980s Fisher Insert adapt to chimney pipe1980s Fisher Insert adapt to chimney pipe1980s Fisher Insert adapt to chimney pipe1980s Fisher Insert adapt to chimney pipe1980s Fisher Insert adapt to chimney pipe
A stainless steel chimney liner is required, not black stove pipe. That environment will pinhole black steel pipe quickly.

If the existing chimney does not have the following minimum clearances to combustible material, an insulated liner is required. 2 inches from outside of masonry chimney to combustible for an interior chimney, 1 inch to combustible material for exterior chimney.

The reason is due to open fireplaces being built for a free breathing fire that allowed much more heat up flue preventing creosote formation. The fireplace chimney was not normally built with clearance to withstand a chimney fire fueled by creosote from a oxygen controlled appliance.

When changing the USE, the chimney must be brought up to current code.

Older Inserts were designed to use the larger original fireplace flue which proved to allow the hot flue gases to cool as they expand into the larger area forming excessive creosote, hence the reason for a liner the same size as Insert outlet.

The cast iron boot idea is fine for connection, and I would also use a 6 inch liner to allow an upgrade to newer Insert with 6 inch outlet. It is technically against code to reduce, but many physically work fine. You won’t get full BTU reduced, but most never run wide open anyway. Worst case scenario is smoke roll in when opening doors you learn to work around.
@coaly thank you for the reply, this is all very helpful.

I'm very much a novice in working with these inserts/fireplaces so appreciate the advice and patience.

is a double walled chimney pipe the same as an insulated liner?

could you please send links to examples of the types of liner/pipes you're mentioning, or related threads?

also links to a cast iron boot or adapter would be really helpful.

how do you suggest getting from the top of the insert around the smoke shelf to the the chimney pipe? I think I heard that flex pipe isn't ok since the fisher inserts get too hot.
Chimney pipe is not the same as a liner. It is not used for lining an existing chimney. A flexible liner is fine for the Fisher or other stoves. It is possible over time to stress a stainless liner by running it wide open for hours so that the flue gas temperature is too hot but that is not good for the stove or liner and a waste of fuel.

A stainless steel liner can be flexible or rigid. Typically it takes a flexible connection for the last few feet to connect the stove even if the liner is rigid. Liner insulation can be external or a liner can be purchased pre-insulated.