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Old 03-06-2015, 01:12 PM   #1
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Tankless Water Heater Gas Piping question


Hello Pro's and thanks in advance for the help

I am thinking of installing a direct vent tankless hot water heater for my house. I have a question about the gas supply. The heater requires 3/4 inch gas piping. The pipe coming directly from the meter is 3/4 inch already. There is a dryer, boiler, oven and 80 gallon tank water heater already connected to this line, but they of course are reduced to 1/2 inch or whatever the requirement for that item is.

my question is, if i remove the 80 gallon water heater, and pipe 3/4 directly to the new tankless, do I need to upgrade the main 3/4 from the meter to 1"?


Also, a side question. I was looking at a condensing unit. How much waste water will the condensation make? I dont have a drain to point the condensation into. Would a bucket that I empty every few months be OK, or is this like a weekly activity?
Thanks!

Last edited by AdamBNYC; 03-06-2015 at 01:14 PM.
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Old 03-06-2015, 02:03 PM   #2
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We will need the BTU on your unit to answer the question. But making a wild guess I would say no. Since your line from the meter is only 3/4 your pushing the load. We will need the exact distance from meter to where your installing the unit and the BTU load of all gas fixtures in the house you plan to keep.
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Old 03-06-2015, 04:34 PM   #3
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No location in your profile.
Most areas would require a permit and a licensed plumber with a gas endorsement or the gas company to size and install this.
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Old 03-06-2015, 04:39 PM   #4
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I suggest you contact you gas company for guidance. As for the condensate, there is something called (I think) a condensate box. It's about the size of a small fishing tackle box and comes with a pump and level sensor mounted inside. My backup furnace is gas, so I have one. It pumps the condensate to a trap in my DWV system.
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Old 03-06-2015, 05:49 PM   #5
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when sizing gas pipe you should consider typical winter load and summer load of all appliances to be sure you have enough supply of demand when needed at any given time ....get the total # of btus per hr of each appliance you have and what you will be adding...
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Old 03-06-2015, 07:39 PM   #6
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Quote:
Originally Posted by AdamBNYC View Post
Hello Pro's and thanks in advance for the help

I am thinking of installing a direct vent tankless hot water heater for my house. I have a question about the gas supply. The heater requires 3/4 inch gas piping. The pipe coming directly from the meter is 3/4 inch already. There is a dryer, boiler, oven and 80 gallon tank water heater already connected to this line, but they of course are reduced to 1/2 inch or whatever the requirement for that item is.

my question is, if i remove the 80 gallon water heater, and pipe 3/4 directly to the new tankless, do I need to upgrade the main 3/4 from the meter to 1"?


Also, a side question. I was looking at a condensing unit. How much waste water will the condensation make? I dont have a drain to point the condensation into. Would a bucket that I empty every few months be OK, or is this like a weekly activity?
Thanks!
How long is the main line from the meter to where the tankless will be. How many BTUs is the boiler, dryer, and tankless, and oven.

3/4" can only handle 230,000 BTUs/230 CFH at 6" pressure for 10'.

You may need to increase your main gas line size to 1-1/4" for the first 10 or 20, depending in what order the appliances are in on the gas line.
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