chimney liner for oil to gas boiler conversion -- does size matter

One company said we needed a 6 inch liner the other said an 8 inch liner — anyone have any thoughts on why there was a discrepancy and which one we should go with to be safe/ Thanks so much in advance

lz26

in Chimney and Fireplace 10 years and 9 months ago

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rickiebrown | 10 years and 6 months ago

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Exactly, size of the liner definitely matter along with the chimney. I recently had done a chimney installation by chimney genie. They are just amazing. Great work in less time. You can also [read more here](http://www.chimneygenie.com/) about them.

brucef | 10 years and 9 months ago

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Many new gas boilers and change-overs from oil need new stainless liners. Both above posters are correct, in that the rating of potential new equipment plus any other existing gas equipment currently vented through flue enter the calculation (typically existing gas hot water heater) WE keep a few different diameter “pulling caps” to positively determine the liner size that will physically fit in your masonry flue. The new stainless liners typically come zero clearance, but that won’t help you if there is obstruction or too sharp turns in the path. Common clay liner size is 8X12″, but liners are round. So often a 6″ liner is all that will fit down. Often times we have had to eliminate additional gas appliances because the 6″ makes it for the the boiler, but the 2nd appliance ruins formula result. We have added Buderus indirect hot water storage units as additional zones to manifold. Not to reveal all our tricks, but it is possible to get a larger diameter sleeve “ovalized”, in which they draw the sleeve thru a press. This can allow a 7″ to go down a rectangular flue. This reduces the cross section of the 7″, but it remains greater than a 6″. Remember to tell the liner supplier that you need one or both ends left round to attach bottom cleanout tee or top B-vent extension flange.

steam_man | 10 years and 9 months ago

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In this case…size matters. You absolutely don’t want to choke down your chimney past the manufacturer’s recommended vent size. In general try to keep close to the original size of your chimney but you will still need to double check against your total # of appliances connected. What is the make and model of your boiler and any other appliances connected to that chimney, we will try to give you a better understanding.

ellenlourie | 10 years and 9 months ago

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Size of the liner depends on boiler input, height of the chimney and lateral lenght of the flue pipe. It is a matter of boiler sizing and calculations.