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Sizing Natural Gas Piping For New Boiler

D107D107 Posts: 1,564Member
edited March 9 in Gas Heating
Installing new atmospheric 70mbh boiler and Turbomax; 3/4 line runs from meter 32 ft into boiler, 9 Els @ 2ft per EL, so figuring 50 ft total run to boiler. After boiler, the line goes on to 22mbh drier and then 65mbh stove (that's max stove cap if all stove and oven burners on.) So 157mbh max capacity. Meter capacity 275cfh. I didn't count piping after boiler, a mix of 3/4 and 1/2inch, probably another 25 feet with all the ELs. Table I'm using shows 3/4" black pipe can handle 151mbh at 50 ft. So do I need to add the after-boiler piping into the mix? Contractor says good to go.

Also you can see from photos that within the meter the piping seems to be half inch, hard to tell. I started counting the pipe right after the meter, not at the regulator or from where it comes into the house. (Comes in at 3/4, then through regulator at 1 inch, then down again to 3/4.) There will be no more stand-alone hwh. Note that for years the total load was 210mbh boiler--since downfired to 170, hwh 30-40mbh, drier 22, stove max 65 = 337mbh with no issues. However that boiler is quite old and I'm figuring the new Peerless MI-03 or Buderus GC 144 would be more sensitive and less forgiving of undersized piping or perhaps warranty wouldn't cover it.


  • kevink1955kevink1955 Posts: 65Member
    I do not know about the sizing but that street el is a problem as it is much more restrictive than a nipple and regular 90, also is that copper on the way to the HWH. Some areas will violate you for that
  • D107D107 Posts: 1,564Member
    @kevink1955 Yes, copper is likely grandfathered for 40 years but that will be going with the new indirect.
  • ZmanZman Posts: 5,215Member
    From what you are describing, the pressure of the gas in the pipe when it gets to the boiler will be right about at code (0.5" WC less than at the meter). The problem is, that does not leave any room for the required pressure drop to the downstream appliances. The downstream appliances might see more like 1" WC pressure drop.

    Does this setup meet code? No.
    Will everything work just fine? Probably.

    It looks like the access is pretty good to just run a new 3/4" line from the meter to the boiler. That would be the right way to do it.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • D107D107 Posts: 1,564Member
    edited January 15
    @Zman You mean Y it at the meter? got to chop some ceiling sheetrock. If I went through that trouble maybe better to put in a 1" line.(?)
  • ZmanZman Posts: 5,215Member
    You would TEE off near the meter and run a new 3/4" line parallel to the old. Once you take the boiler off the old line should be big enough to handle everything else. The new 3/4" is plenty big to handle just the boiler.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
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