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Question DetailsAsked on 10/28/2017

I am converting oil to gas,i already have a chimmy liner,do i need a new one when i change over?

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1 Answer


Depends on the rating of the furnace (including any water heater, etc feeding into same flue), the flue size, and (at least in most areas) the fire rating of the flue.

Generally, you cannot have oil and gas appliances on the same flue - so hopefully if water heater and furnace are on same flue you are converting both at the same time.

Generally, oil fired requires a bit larger flue for a given appliance BTU rating and in stud construction (as opposed to if run inside an old fireplace chimney) has to be triple-wall, and in many areas, stainless liner. Gas generally can use a slightly smaller flue and double-wall flue - so you are probably good for fire rating but if the diameter is too large by code it may have to be sleeved with the next smaller size flue - which depending on circumstances and local code may be galvanized double-wall or stainless - which can typically run about $500-1000 depending on length, it is sleeve in nicely from the roof or has bends, and if stainless or not.

Your Heating and A/C contractor (your Search the List category) can work out the requirements and whether your existing flue meets it or not for you - in many cases the appliances themselves (or the conversion kti if converting) will also have the flue dimensions required in the manual/instructions.

One other factor - if your "converting" means new appliances rather than burner conversion kits, then yuou may end up with high-efficiency condensing units which discharge directly through the outside wall through plastic pipe (condensing units), so in that case the existing gravity flue to the roof would be removed or capped and sealed.

FYI - here are some previous questions with answers about oil to gas conversion which might be of interest too;

Answered 2 years ago by LCD

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