Do all furnaces use the same type of "chimney" or flue? Back
All 80% furnaces use a standard double-wall vent that exhausts through a flue, normally through the roof of your home. They need to be properly lined to prevent condensation from forming and should meet your local code requirements.
90% efficient furnaces are known as "condensing" furnaces and do not require a traditional flue vent. Instead, they use a 2-3 inch PVC pipe that is easily vented either horizontally or vertically to an outside wall.
They do produce some condensate (moisture) in the combustion process that will need to be trapped and disposed of.
