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Hot Water Heater Acessories with City Water

cubicacres Member Posts: 360
We have pumped city water that's supposedly pretty good quality per the plumbers I talked to, and we're wondering about some of the following items we saw in the installation instructions:

1. Expansion tank need if city-pumped supply water should be consistent around 60psi?
2. Mixing valves need if we keep the 2 parallel hot water heaters at the reccomended settings for the 5 units?
3. Drip pan need if each water heater is near a floor drain?
4. Anode rod replacement need every few years (the store that sold our water heater thought we'd likely replace the heater in about 10 years before the high-quality city water corrodes the rod enough to replace it)

Any thoughts on how important each of these items are for the longevity of our water heater?


  • hot_rod
    hot_rod Member Posts: 22,498
    Has the water been tested? The water supplier will have some test data available, mostly for the safety of the users.
    For tank and fixture life it is good to check hardness, and TDS, possibly chlorides with stainless tanks. Water heater scaling and performance decline is directly related to the scaling minerals in the water, and the temperature of the tanks. The hotter you run the tanks the more mineral precipitation you can expect, also shorter tank life..

    Good chance you have a back flow device on the meter or in the piping on a city water supply, so yes an expansion tank should be sized and installed on the system.

    120- 122F is the typical required water temperature. if you plan on running the tanks warmer than that add a mixing valve. With thermostatic type mix valves the tank hot supply needs to be 20- 25° hotter than the mixed output, for accurate mixing.
    Also size the mix valve to the expected GPM load when all HW taps are flowing. Undersizing the valve can cause considerable pressure drop at high flow conditions.

    On a concrete floor near a drain?

    Anode rod life depends on water quality, the amount of water through the tank, and I think temperature. Hotter water is more agressive. Some tanks have dual anodes now.

    It's a bit of a catch 22 with WHs these days. You want to run them hot to prevent potential bacteria growth, above 140F. But then by code you need to temper the temperature supplied to the users. And as mentioned above, hotter tanks use more energy and seem to fail sooner.

    With hard water plan on servicing a thermostatic valve yearly, or more depending on hardness.

    Is there a DHW recirculation system on the building?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • cubicacres
    cubicacres Member Posts: 360
    Just the water supply pipes with 2 40 gallon parallel atmospheric gas water heaters supplying to each fixture and our single-pipe steam radiators, no recirculation sytem that we know of.

    We didn't combine the boiler/water heaters-just replaced the 24 yr old residential water heater with a new one with similar 1st hr capacity. The old one didn't have any of the accessories & lasted 24 years with no complaints, so I was curious about how important those reccomended accessories in the installation manual were. It seems the 6 yr warranty drops to 1 yr if used in a commercial building (5 units), so we may just have to see how good the operating/environmental conditions are.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,390
    Hello, At a minimum, I'd check the anode in three or four years to see how it's holding up. The rule of thumb is that when six inches of the core wire of the anode is visible, it's time for a new anode. Use only magnesium! The other thing I'd check is the relief valve. Check it yearly and be prepared to replace it, as many valves fail testing.

    Yours, Larry
  • cubicacres
    cubicacres Member Posts: 360
  • Henry
    Henry Member Posts: 998
    Insurance companies are now forcing condo owners to replace HWT after 10 years. The normal life of a gas hot water heater here is over 15 years. Our plumbing code requires a pan under each tank unless in the basement and "near" a floor drain. You must keep the water in the tanks at least at 140F to prevent legionella! Therefore by code you need to provide hot water no higher than 120F at any faucet. So a tempering valve is necessary. Most if not all hot water tank manufacturers require an expansion tank if there is a backflow device before the cold water inlet of a tank.