Venting a Tankless Water Heater

Old 01-05-04, 04:28 PM
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Smile Venting a Tankless Water Heater

I am going to install a Aqua Star tankless water heater. I have a question about venting this heater. I have a 5" metal chimney that will be used exclusively for this heater. The instructions call for a 12" minimum clearance from the top of the heater to a combustible surface. I have plenty of clearance. I can use a 45 degree type B tube directly from the heater to the chimney. The run of the vent is approximately 3'. Here is my question: can I come right out of the heater into the 45 degree elbow to the chimney or should I use a 12" riser out of the heater before I hit the 45 degree elbow? The BTU rating of the burner is 117,000. Thanks
Old 01-05-04, 11:10 PM
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You should be able to do it either way. Provided what you are planning to do does not exceed the max length of the vent you should be fine. Normally you are supposed to add 5' for every 90 degree elbow that you use. On that basis I add 2.5' for a 45 degree elbow. So add this to the remaining run of vent pipe and if this meets the max allowed length you should be fine.

btw I also have an Aquastar (but the 240FX model which is 165,000 BTU max) and I installed a 45 degree elbow on the vent pipe immidiately after the heater.
Old 01-07-04, 07:53 AM
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Smile Tankless Water Heater

Hey, thanks for the replys. I installed my tankless water heater yesterday. I came right out of the heater with a 45 and into the stack. No problems, it works great and really happy with the results. Jimraz
Old 01-07-04, 09:22 AM
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I'd follow the venting instructions that came with the heater. It may be different for tankless, but for a conventional WH, I believe that there must be a minimum 6" vertical rise before any bends in the exhaust piping.

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