I need to put a stainless steel flue liner in my old chimney. Any idea how to figure out what diameter of flue liner I will need? It’s a 300,000 Btu/hr natural gas boiler. Chimney is 30 or 35 feet tall from the thimble where the furnace feeds into the chimney to the top of the chimney.
In Northern NJ.
The boiler manufacturer (Utica) doesn’t/won’t provide any requirements.
Thanks for any help,
Bob Chapman
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"The boiler manufacturer (Utica) doesn't/won't provide any requirements."
?????
There is an exhaust collar at the back or top of the appliance, right? What size is it?
If you havve more than about 3' horizontal and two elbows, step up an inch in diameter
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There are sizing charts - I don't have carts with me.
Relevant info: btu output, efficiency, # of bends/elbows, eight of stack.
Not: the charts are NOT definitive - they are based on computer programs - the installer is always responsible for determining that the draft is within specs (not too much, not too little - typically .01 - .03 wc in)
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Using the sizing charts found in the International Fuel Gas Code and NFPA 54, we need two more items of information to answer:
1) What is the lateral distance from the appliance to the chimney?
2) Is the boiler a natural-draft appliance? (If it is, it will have a draft hood that allows room air (dilution air) to mix with the appliance exhaust.) Or, is it fan-assisted draft?
Fan-assisted draft is not to be confused with power vented appliances. Fan-assisted draft appliances are listed as Category 1 appliances (non-condensing, non-positive vent pressure), and power vented, condensing appliances are Category 4 appliances (positive vent pressure, condensing heat exchanger.)
IF it's a natural-draft appliance, with 20' or less of lateral distance, you would need a 7" liner.
IF it's fan-assisted with 20' or less of lateral distance, you could use a 6" liner.
Do you not take elbows into account in your calcs or do you assume two?
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The Table assumes two 90's--each 90 in addition to that would reduce the listed BTU capacity by 10%.
BTW--for anyone who does not want to buy the code books, the same tables are contained in the Sizing Handbooks published by the manufacturers of type B vent. Like Simpson, Metalbestos, Amerivent, etc.
I recommend the Sizing Handbooks for another reason--they are an excellent education explaining the principles of venting Category 1 appliances. If you read it, you know the reasons behind the requirements.
Thanks, rdesigns. THis site is Great!
It is a natural draft appliance, and it is just a hair less than 20' from the chimney, so it looks like 6" will do the job.
I appreciate everyone's comments. Thanks
Bob
I think you mean 7".
If it's natural-draft with near 20' of lateral, you can't use 6".
6" would only handle about 230,000 BTU's in your situation.
I hope I got this to you in time to keep you from buying 6-inch!
Yup, you did. THanks
Bob