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Thread: Flue Relining

  1. #1
    Join Date
    Oct 2006
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    Recently had a level 2 inspection and cleaning done on fireplace flue and furnace flue and the inspector recommends that both be relined due to deterioration of the clay tile. House was built in 1926. Oil boiler, 99,000 BTU. I had two contractors out to give a second opinion and estimate on relining the furnace flue (FP will have to wait).

    Contractor 1 will break out existing 8x8 terra cotta tiles and reline with an 8" stainless liner, insulate with light masonry fill and cap.

    Contractor 2 says breaking up the existing tiles can damage the masonry and the vibrations could crack the plaster inside the house. He says to leave the existing terra cotta tiles and go with a 6" liner that will fit in the available space, then install a reducer to tie the 8" exhaust from the boiler into the 6" liner.

    Contractor 1 says 8" is needed to maintain a proper draft and that not removing the old terra cotta means you either aren't willing or don't have the equipment to do the job right. Contractor 2 showed me a sizing chart that says 6" will handle almost 200,000 BTU for the 24' run that I need.

    So, are these both legitimate approaches to doing this job or is one or both of these guys full of it? My main concern is I don't want to wake up dead because someone screwed this up. Thanks for any input.

  2. #2
    Join Date
    May 2005
    Madison, WI
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    Does the MFG of the bioler still exist? Call thier support line and ask them about downsizing the flue. Going to 6" sounds like the easiest option if the MFG says it is allowed on your model.

  3. #3
    Join Date
    Aug 2004
    S.E. Pa
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    Talking third opinion

    At 99K BTU input with a 24ft. ht., a 5" liner should be plenty. If you are really worried about it, go with a 5.5". Breaking out 8x8 tiles for an 8" is total BS. Sounds like either he wants to charge you a fortune or he's stupid and is willing to do an awful lot of extra work for free. Just to show you contractor #1 is wrong, if you break out 8x8 tiles, you are left with an opening about 8x8 since we know most masons cannot read code books so there is not the requisite 1/2-4" airspace btw tiles and outer walls of the chimney. Therefore,unless he can prove it, he will not have the 1" space btw liner and walls for the Thermix insulation, which btw, is NOT required for heater flues the way it is for wood. You don't need a 2,100F rated liner for oil. If it is a cold exterior masonry chimney located up Nawth, insulate it with dead air- pack around the liner top and bottom with ceramic fiber to form a Dewar's flask.

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