Help with relining

[kurly]

Hello, I am new to the site but have been burning wood for over 30 years. I've had a couple of chimney fires, luckly with no fire into the house. I'm using a Jensen insert in a clay tile lined masonry fireplace of a 1963 home. It is a ranch home with a 15' tall exposed chimney with 11 1/2" X 11 1/4" I.D. clay tile. My Jensen has a rectangle exhaust opening of 14" X 3 3/4"(53 sq in). My tinner friend made a transition duct to 6"round(28 sq in) out of 1/8 steel. I removed my damper flap/door from the fireplace. I have search the forum for information, but still have these questions. Since I like my old Jensen (made here in Racine WI) can I neck it down to 6" and still get good results/draft? Do I need to insulate the SS liner? The 6" liner would fit through the remaining damper assembly easier than a 8" liner, or do I cut out the remaining damper assembly? I see some oval SS liners that would fit easier through the damper assembly, but how is it transitioned back to round? I would like to do this project myself. A contractor advised he would only use 8" uninsulated SS liner and remove the existing damper assembly for $1600.00. Any comments would be apprecieted as I know I've been living on the edge with my current set-up. I understand how and why the creosote build up is so great in my Slam in insert. I'm not going to use the insert until I line the chimney, and my girls are already complaining it is too cold in the family room, and too hot in the bedrooms.
Thank you, kurly

 

[jimbom]

This is only an opinion. I don't have the insert you are using. I am not a stove designer.

15' chimney is close to the minimum unless your owners manual has better information. So you are at minimum draft(negative gauge pressure).

The flow(cfm) due to the transition piece/six inch flue will be about half of the flow of an eight inch diameter liner/transition.

Insulate your eight inch liner and you may see approximately 20% additional increase in flow due to an increase in negative gauge pressure(draft) at the stove flue exit. Loose pearlite carefully sealed at the bottom block off plate would be very inexpensive, make the flue warm quickly, and stay hot. You should form less creosote due to a hotter flue liner surface.

Of course I don't know the minimum flow your Jensen needs to function and perform in a safe manner. It may be an insulated six inch liner would do the trick, but it would be about half the size of the stove exit. An insulated eight inch diameter flue would nicely match the original design exit conditions.