Heat trap nipples and open water system.

Discussion in 'Water Heater Forum, Tanks' started by ourzoo, Oct 24, 2009.

  1. ourzoo

    ourzoo New Member

    Messages:
    13
    My gas tank water heater is 14 years old and I'm getting ready to replace it. The current water line installation is straightforward. We're connected to a city water supply source and we have an open water system. No expansion tank. Also we're only using our heater for domestic hot water, not house heating. One pipe in and one pipe out.

    I took a close look today at the inlet and outlet pipes on my new Rheem heater (the heater is not yet installed), and I see that they have pre-installed ball type heat trap nipples - new to me. Researching these on line it sounds like the cold water trap nipple does not completely block tank expansion flow back into the cold supply. Good to hear but is this accurate? This old 50's house does not have a basement floor drain and I'd hate to have the relief valve pop - big mess.

    Also, I've read that the ball type heat trap nipples were/are noisy, but the posts I read were from around 2004/2005. The posts stated that a flapper type nipple is available. This heater was manufactured in Sept 09 so you'd think the noise problem would be solved by now. Should I be OK with these?

    Thanks
    r/Tom
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,255
    Location:
    Cave Creek, Arizona
    traps

    Heat traps are not check valves. If the ball traps become noisy, just unfasten the pipe and remove them. In any case the heat traps are AFTER the point where you would/should install an expansion tank, so it would do NOTHING to eliminate thermal expansion if the heat traps were a problem, since it would ONLY occur in the hot side under those circumstances.
    Last edited: Oct 24, 2009
  3. ourzoo

    ourzoo New Member

    Messages:
    13
    hj - thanks for the quick reply.

    Well I'm confused. What I've read so far says that when the water in the tank is heated it expands. With my old water heater today, and its open system connection, the water expands out into city cold water supply since it is an "infinite" reservoir. The hot side side plumbing into my house is not such a big reservoir so it does not expand in that direction.

    I've read that the heat trap nipple on the cold side is set up like a check valve (but I guess not the same considering what you've said). It said that the ball is lighter than water and floats up to the ball seat, stopping warm water flow/convection into the cold inlet pipe.

    If this is right, then it seems that it would block any hot water expansion into the cold side, causing pressure to build up in the tank and in my hot water lines. Is there some sort of bypass on the cold side heat trap ball and seat?

    Thanks - Tom
  4. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    There is a hitch in your giddyup there. Your system expansion can only expand into the city pipes to the extent that the city pressure is lower than the pressure on your side. So let's say that city pressure is 120 PSI. You could have thermal expansion take place, and only when your house reached 120 PSI would it stop increasing.
  5. ourzoo

    ourzoo New Member

    Messages:
    13
    hi there Jimbo.

    Just to make sure I'm thinking right, lets start with my current set-up with the old water heater, with no expansion tank, no check valves, just a direct connection to city cold water. So lets say I start out by filling the tank with cold water. At this point the system (tank, cold water lines and hot water lines) are all at the same pressure. I turn on the burner and bring the tank up to temperature. The heated water wants to expand, and if the tank were closed-off from the in and out lines the pressure would increase, but since the city water pressure is always lower than what could be reached in the heated tank, the water will expand into the cold water pipes (right?).

    r/Tom
  6. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    I gather you are telling us you have city water pressure less than 80 PSI. In that case, you are correct. Many people have city water far in excess of that, so even if you have a bypass regulator, the pressure still increases beyond the 80 PSI MAX which the inside of your house should ever see.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,255
    Location:
    Cave Creek, Arizona
    pressure

    Unless there is something to prevent it, such as a check valve, pressure is equal in the entire system. IF the cold heat check stopped backflow, then ALL expansion tanks would be useless because the thermal expansion would be confined to the water heater and hot water piping. It is immaterial WHAT your initial pressure is, because themal expansion will start there and build up to its terminal pressure. The heat traps are just pushed into the connections so the TE will work its way through or around them.
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,319
    Location:
    New England
    The heat traps aren't perfect check valves...they will leak. So, no worries about building up pressure in the tank as a result of them being there. They do stop nearly all convection heat losses into the piping, but that's all. They do nothing for conduction heat loss, though other than that that might occur from the heat from convective sources (which is mostly stopped by the traps).
  9. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    The traps are to prevent free natural convection in the hot/cold taps. This is known as a thermosiphon. By making the path more difficult the natural convection is reduced.

    Hot water in the tank is less dense than the cooler water sitting in the inlet and outlet lines. Unrestricted it will tend to rise while cooler water sinks into the tank. This forms a thermosiphon loop.

    You can reduce this effect somewhat by insulating the inlet and outlet lines to/from your water heater. However, you don't want flammable/meltable insulation within about 6 - 12" of the flue opening on a gas water heater. This is unfortunate as this is exactly where the worst of the losses will occur. I'm going to stop by an insulation supply house this week to obtain an appropriate product for this application.

    Insulating the lines will reduce both the convection (thermosiphon) and the conduction losses.
  10. ourzoo

    ourzoo New Member

    Messages:
    13
    All,

    Thanks greatly for the advice and comments. Sounds like the cold line heat trap won't give me any problems with pressure build-up in the tank. That's good to know. Sure wish I had an overflow floor drain but this is not the case so I need to keep the chances of any spills to a minimum.

    Runs with Bison - looks like I'll be able to leave the heat traps in but will also install pipe insulation down to the inlet and outlet fittings. This is a power vent water heater so I shouldn't have any problem with the flue heat melting the insulation. Thanks for the recommendation.

    Have a good day - r/Tom.
  11. WyrTwister

    WyrTwister New Member

    Messages:
    6
    Location:
    Texas
    I am working through an install of an electric water heater . My first electric WH . Always before , I had a gas water heater .

    Did I read some one to say , insulate both the hot water and the cold water lines , going into the WH ? I have insulated all my new HW lines , that I have run . Do I need to insulate the CW line ? The CW line is really cold . I am guessing no HW is migrating back up the CW line ?

    Also , being a dummy , I did not know that the little plastic " plugs " were , in the factory installed dialectic nipples ? I used needle nose pliers and jerked them out and threw them away . :-(

    Both lines , HW & CW , leave the WH , horizontally . From there they each head down to 3/4" ball valves , mounted at about 3' Above Finished Floor , on the wall . From the valves they head down , under the house ( pier and beam construction ) .

    I am thinking I need to replace the nipples with new heat trap nipples ?

    I will also check & see if I some how managed to mess up the plastic cold water dip tube .

    Thanks ,
    Wyr
    God bless
    Last edited: Feb 13, 2014
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