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Chimney liner sizing problem

Yois Member Posts: 8
Hi, I manage a 12,000 square foot commercial building in Providence.  We currently have an oil fired steam boiler, as well as an oil fired water heater.  We are looking into converting the systems to natural gas.

The problem we're running into is that the interior dimensions of the brick unlined chimney is 10x10 square, with a 7 foot lateral run on both appliances, and 52' from the tee to the top.  8 inch from boiler, and 6 inch from the water heater.  The raw input BTU ratings of the boiler and water heater are 931,000 and 173,000 respectively. (Smith 19A-6 and Bock 71E).  That makes a total of 1.1 million BTU.  A 9 inch round liner won't do the trick for this.

First question:  How are exhaust BTU's calculated?

Second question: Was this oil setup also against code?

Third question:  If I'm using conversion burners, do I need a liner?

Fourth question:  Do conversion burners have a power venting option, or do they only vent atmospherically?  What are the downsides of power venting?



  • Bob Harper
    Bob Harper Member Posts: 969
    chimney venting

    All chimneys must be suitable for the class of service. All chimneys must be lined. Therefore, your original setup was non-code compliant. According to the sizing tables in the gas codes, the 10x10 was undersized for this load.

    Since you cannot common vent both appliances into this chimney, you have two options:

    Power vent or get rid of the water heater and replace it with an indirect tank. I would opt for the second with a single properly sized listed liner. To power vent, you have two methods: push it out or suck it out. Sucking it out with the fan on the building's exterior allows you to use conventional vent connector and a listed liner. Yes, you would still need the liner. If the fan was at the appliance, the venting must be listed for positive vent pressure, meaning listed to UL 1738. This is the AL29-4c stainless steel with gaskets. You have to verify your termination meets all the code requirements and is not below snow level. Either type of fan will require a pressure proving switch of some sort. I recommend you have a pro perform a level II inspection of the chimney to ascertain its suitability even if relined before going farther. HTH,
    DIY_HOME Member Posts: 1
    Chimney Liner

    Hello Yois-

    I know your problem was posted back in February, but have you resolved the issue yet?
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