Advice 6" easy flex in an 8" prefab flue

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Apr 6, 2016
Southwest VA
So I need a bit of advice. I have a 1989 Majestic MBUC36 prefab with an 8" flue and I am looking at getting a Hearthstone II with 6" outlet. Spoke to the local Heating and Air folks and they said I would need to add a 6" liner and fill the gap with some concrete/vermiculite like substance costing $2700. Spoke to the local city code enforcement and they said drop a 6" liner like easy flex, cap off the gap at the top so no embers or anything get back inside and you are good to go. Is the business trying to up-sale or is the code guy the one full of something other than concrete/vermiculite?
You should insulate it for sure but I would wrap it not pour it. And I don't know how tall your chimney is but $2700 sounds a bit high unless your chimney is very tall.
Typical 2 story. I figured 30 ft but probably more like 25 realistically. Have not measured yet. The store said it would not fit in the 8" flue if you wrap the 6" insert.
1/4 inch wrap or preinsulated? At least in a 8 inch flue you should not have to worry about tile offsets eating up your clearance, right?
A 6" liner is 6.25" on the OD, adding a 1/4" blanket will make the OD about 7".
Using 1/2" insulation will make it about 7.75".
6" Pre-insulated liner OD 7.25"
Duraliner (preinsulated) is 6 5/8" OD. or maybe go with a 5.5" liner.
Go with 1/2" wrap or preinsulated. 1/4" is not enough insulation to meet the ul listing of the liner for use with wood. There is plenty of room for it in an 8" flue.
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