gas water heater timers - are they worthwhile?

Discussion in 'Water Heater Forum, Tanks' started by rap, Oct 6, 2013.

  1. rap

    rap New Member

    Messages:
    63
    Location:
    california
    Are gas water heater timers worthwhile?

    I've never seen one in operation, and the reports by consumers and plumbers are mixed.

    The energy lost in make-up time seems to be the main criticism of gas w/h timers. However, this seems like a replay of the arguments of some time ago that a constantly burning pilot light was necessary to keep the water heated to a minimum, "ticking over" temperature.

    Anyone out there with an installed gas w/h timer who has done any before and after calculations?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    The main reason a gas WH isn't as efficient as electric is two-fold - it has an uninsulated flue going up the middle and not all of the energy gets into the water you're trying to heat - some goes out the flue. But, in most places in the US, NG is MUCH less expensive per BTU than getting the equivalent in kWHrs.

    There are potential health risks if you let the water in the tank cool off too much...the stuff can start to grow things when the temperature drops. Keeping it above the typical minimum, keeps that stash of water safe for when you turn the thing back on. Keeping it above 140 may end up being safer, but the higher the storage temp, the bigger the standby losses, and if it had been off for awhile, I'd want to get it at or above 140 for awhile before I used it. All residential tanks should be regulated to no more than 120, and that's done with a tempering valve - required where I live, regardless of whatever temp you choose to set the WH.

    I haven't looked at timers for a long time, but the ones I saw when I was uses a motor clamped onto the gas valve to turn it back and forth. The gas valve really wasn't designed to be moved back and forth on a regular basis. As electronics have been applied to some of them, there may be other ways, and some may be offered by the manufacturer as an option.
  3. Dana

    Dana In the trades

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    At current US gas pricing the thing would not pay off even a little bit, unless you allowed the tank to cool off QUITE a bit (more than an 8-hour overnighter kind of deal.)

    It's not the energy lost in make up time, it's the fact that the rate of heat loss out of the tank doesn't change much unless the temperature of the tank drops very dramatically. If you took a shower bringing the average temp in the tank to 100F or so when the timer is in "off" mode you'd get some savings, but if you parked the tank at 140F at 10PM, it would still be above 130F at 7AM, and still losing at a good clip.

    What does pay off is insulating all of the near-tank plumbing (including the temperature & pressure overflow and the nearest 10' of cold-water feed plumbing) as well as all of the accessible hot water distribution plumbing with at least 5/8" wall closed cell foam (R4+), and NOT the crummy 3/8" wall goods sold at box stores. About half the standby loss of an atmospheric gas-fired tank is through the center-flue heat exchanger convecting 24/7. The tank walls are insulated- heat conducting out the near-tank plumbing is more BTUs than are getting through the tank walls. But heat abandoned in the distribution plumbing between draws is also a double-digit fraction of the total energy use, and by insulating the distribution plumbing you end up dumping a lot less tepid water, since water that was drawn 20-30 minutes ago is still hot enough to be usable.

    [​IMG]
  4. rap

    rap New Member

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    63
    Location:
    california
    Thank you both very much for your informative replies.
  5. hj

    hj Moderator & Master Plumber Staff Member

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    Cave Creek, Arizona
    Unless you use enough water while the timer is off so that the tank goes cold and you can get by with cold water, then the timer will save some money, otherwise, when it does come on, you will use about the same amount of energy to heat the water you did use, and bring it back up to the normal temperature. And this applies to both gas and electric heaters. Standing piiots has nothing to do with "keeping the tank hot". They were a simple method to light the burner when it was needed. ANYTHING else would have required an electric source and a more sophisticated thermostat.
  6. rap

    rap New Member

    Messages:
    63
    Location:
    california
    HJ,

    Thanks for that. So, the demon in the mix appears to be the pilot light - around the world there might be as many as say, one billion (i've no real idea) pilot lights burning up one big PG&E bill when its all totalised. We owe our grandkids better.
  7. Dana

    Dana In the trades

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    Standing pilots are no longer allowed on new equipment in the US. Electronic ignitions on newer water heaters usually light off and "prove" a pilot before turning on the main gas flow, but at the end of the burn all gas flow is halted.

    A standing pilot on it's own puts out about the same heat as the standby loss of an insulated gas hot water heater, in which case a timer saves almost exactly nothing.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,309
    Location:
    Cave Creek, Arizona
    Well, I wouldn't shut off your standing pilot in order to give your kids an inheritance with the money you would save
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