Liner question for Coaly

DG1 said:

1) Which size works best ? 6", 7" Or some other size.

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Should be 8" but 7" will work.

DG1 said:

2) Does the liner need to be wrapped in insulation?

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Probably yes but it should be for performance reasons regardless. Unless you have the required clearances to combustibles from the outside of the masonry structure to any combustible material (1" for external chimneys 2" for internal ones) you need insulation.

8 inch is the outlet size (most measure 7 1/2 ID) and it is technically against code to reduce pipe or flue smaller than appliance outlet. Many reduce as small as 6 with no problems of smoke roll in with doors open. (as long as chimney is high enough) You won't get the full throttle effect that more flow creates with 7, but that isn't the setting used most of the time anyway. Some have been using 6 even with baffle installed with no issues.
The larger vent opening was due to use in larger existing fireplace flues but still didn't allow enough heat up (plus people closed damper and intakes too far) to prevent creosote in a larger flue. The firebox cubic inch area physically works fine with 6 inch if it's insulated and tall enough. bholler is a chimney pro that may know reasons for not reducing that small. I'm just going by what people have tried and told me.

I've always been ad advocate for reducing the double door stoves and when I installed the Kitchen Queen with 7 inch outlet I reduced to 6 against the advice of the instructions that state; "DO NOT REDUCE THE STOVE PIPE FROM THE TOP OF STOVE TO THE CHIMNEY Model 480 must have a 7 inch pipe and Model 380 must have a 6-inch pipe. DO NOT COMPROMISE". I have the larger 480 and not only reduced to 6, but used a 6 inch Dura-Vent chimney as well. I never had a problem with it and the oven circulation works fine. I thought maybe I wasn't getting quick heat up like it would with more flow and added a thermostat controlled intake under grate. The Kitchen Queen was just retested with 6 inch and passed! It also has an extremely similar optional thermostat. (I did speak with the stove builder years ago when designing mine) I clean at season end only now. I'd bet with 7 inch I'd be cleaning mid season as well. (or wasting more heat and overheating the house) Perhaps heating the maximum 3000 sf the stove is capable of requires the larger flue? I'm heating 1880 sf and took that into consideration when I made the 6 inch decision.

coaly said:

and it is technically against code to reduce pipe or flue smaller than appliance outlet.

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no you are allowed to reduce 1" so going down to 7" would be fine with code but not 6" and I have seen more than a couple double doors that had smoking issues on a 6" stack. Yes if you have enough chimney the increased velocity can over come the reduced volume but that does not always work.

Ah, there's your answer.

coaly said:

Ah, there's your answer.

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all of what i said there is negated though if the appliance manufacturer says you cant down size. But I don't think fisher said that so in this case it doesn't matter.