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Gas Hot Water Heater Questions

FredoSP Member Posts: 90
Hello All,

A buddy of mine just installed a new AO Smith gas hot water heater. It was plug and play because his old one was AO Smith of the same size. He sent me a couple of pictures because I eventually plan on changing my gas water heater out with a Bradford White. I had some questions about his setup. He lives in NJ, so I guess all things vary due to location and local codes.

1. Is that yellow flexible gas line a better solution then the usual black iron pipe? Every setup I've seen by me (NY) is always black iron pipe.

2. I made a red circle around the piece of iron pipe that goes into the gas valve. Is there a limit on the length of pipe you should stay under or it doesn't matter? For example, if I had an 8" nipple of iron pipe going into the gas valve from the "T" ?

3. Is it okay to add a small plastic shim underneath the water heater to help level it out?

4. When connecting a black iron union, how much of a gap is allowed between the two ends? I would think the smaller the gap the better, or no gap at all. What would be the absolute minimum/maximum?


Long Island, NY


    LRCCBJ Member Posts: 121
    1) The yellow flex line is for those who don't want to face the difficulty of properly piping the unit with black pipe. They don't have threader or a pipe cutter. It's legal in certain jurisdictions but it is certainly NOT preferred.

    2) While there is no limit by code, the longer this pipe gets, the more of a moment that is put on the gas valve...............thereby potentially causing the gas valve to rotate. 3-4" should really be the most you want there.

    3) Yes. Steel or aluminum is preferred for durability

    4) Ideally zero. But, of course nobody can ever get to zero due to the shape of the face on the union. Understand that the larger the gap, the more bending of the attached pipes is necessary for the connection. If you had a five foot vertical pipe coming from the ceiling and turning 90 degrees toward the gas valve, 1/4" would be nothing for "bending" that five foot pipe. Now, if you have come directly out of a cement floor for some reason and there is absolutely no movement available, you'll need to be very close to zero.
    Mad Dog_2
  • FredoSP
    FredoSP Member Posts: 90
    LRCCBJ, thank you for the input and explanation.

    Thanks Larry. My friends house is in NJ but I agree with you. Almost like flex pipe on exhaust systems, it will allow the exhaust to flex with the torque of the engine.
    Long Island, NY
    Mad Dog_2
  • Intplm.
    Intplm. Member Posts: 1,967
    All the stuff pictured is fine really.
    No gap with a union? The union nut will pull the two pieces of the union together.
    The yellow flex gas line is fine too. Especially if installed in an earth quake area as @Larry Weingarten mentions above.
    If you need to shim the water heater that's fine but it probably will not do anything to help its performance.
    Unless you feel or see something dangerous, and if its working properly you can leave the water heater alone.
    Mad Dog_2
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,963
    Shimming water heaters and boilers is all aesthetical. Mad Dog 🐕 
  • FredoSP
    FredoSP Member Posts: 90
    Thanks Intplm. I was speaking in general terms and best practice. The closer the two ends are together the better, I would think, less stress/bending on the lines. I asked the shim question because the basement floor isn't 100% level so I was planning on doing that on my install.

    Hey Matt! Hope all is going well.

    More Questions (Sorry) What type of cement should I buy when sealing around the flue pipe? Mines all cracked and should probably get a facelift. I was looking at this product.

    Long Island, NY
  • hot_rod
    hot_rod Member Posts: 22,158
    Hi, Just commenting on the flex line question. In earthquake country, which is in over thirty states, it would be bad form not to use flex connectors for gas and water. Even when tanks are strapped in, they move in a quake. San Francisco burned so badly in the 1906 quake because of gas-line breaks. Yours, Larry
    The AHJ in the area I worked had an amendment requiring flex gas lines on all appliances for seismic reasons.

    They also checked the BTU capacity on the labels.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HomerJSmith
    HomerJSmith Member Posts: 2,441
    edited March 8
    Yellow Flex Gas lines now have a self closing check valve that should be on the supply side of the flex line. If the line breaks, such as in an earthquake and the heater falling over, the gas supply is cut off.
    Also, all heaters should be firmly strapped to the studs in the wall to minimize falling over. There are kits for all this.
    Your pic show the correct connection of the sediment trap to the gas valve. The flex line in your pic doesn't have the check valve on the gas supply. Those old brass gas valves should be replaced with a modern gas valve.
    I guarantee if the water heater falls over and the gas connection is with black iron that the tank gas valve will break. I personally think that the flex line with self closing check valve is best.
  • PRR
    PRR Member Posts: 143
    edited March 23

    ....all heaters should be firmly strapped...

    I left California in 1961 and thought I'd left earthquakes behind.
    But Maine has earthquakes. Not usually big ones (different rock than Calif) but every decade a chimney spalls or a porch roof falls. The tank-straps are next to the tanks and pans so I got one. If nothing else, if kids or big dogs start romping down there, they can't easily knock the tank down.
    Earthquake probability map