Tankless Gas Line Sizing


  #1  
Old 06-23-07, 05:01 PM
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Question Tankless Gas Line Sizing

We are prepping to install a new TANKLESS WATER HEATER (in place of our standard 40 gallon water heater that died on Monday)... The old WH is gas, and so is the new TANKLESS WH. The new one should arrive in 2-3 days and we are installing it ourselves.

The mfr insructions for TANKLESS WH say "the branch gas supply line to the WH should be a minimum of 3/4" black steel pipe".

Question: The current gas supply line is 1/2". Can we put an adapter on the 1/2" pipe to bring it up to 3/4"? Or, do we have to run a new supply line that is 3/4" from the gas source?

Hope that is enough info. Thanks for any help :-)
 
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Old 06-23-07, 07:00 PM
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Depending on the BTU's of the tankless, they probably specify that if you are more than 10 feet or so from the gas meter, then 1/2" is too small. You MUST comply with their specs. If you have insufficient gas supply, it simply will not develop rated BTU and you will be back here asking why you can only get warm ( not hot ) water from your new unit!
 
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Old 06-24-07, 10:26 PM
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You need a 3/4" supply line the full length of the run (from just past the regulator, or possible before, if the heater has a regulator). The longer the run, the higher in pipe size you will need to go. As mentioned, too small a pipe and you will be starving the heater for fuel. You may also need a new house regulator, if it cannot flow the amount of fuel needed for the higher intake of the tankless plus any other gas fired appliances.

Hope you bought the vent kit, every tankless I've seen requires stainless steel venting and it's a safe bet that your old water heaters venting is inadequate.
 
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Old 06-26-07, 02:59 AM
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I'm with the others. You will need to upgrade the whole gas line to compensate for the extra amount of gas required for the new water heater to operate.
 
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Old 06-26-07, 09:17 AM
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Yes, we are aware it needs a stainless steel vent.

We have a plumber coming today to make sure the gas line is upgraded properly.

Cross your fingers that all goes smoothly!

Thanks
 
 

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