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Thread: HELP - Std electric tank versus indirect

  1. #1

    Question HELP - Std electric tank versus indirect

    Can we please revisit this? With low hot water usage, the thought was to get a standard electric tank because stand-by loss is best. But I'm hearing the following.

    I'm getting a new gas boiler. It will be cold start. I have low water usage. In summer, I read the boiler only fires up 1 or 2 times a day to heat an indirect tank. If you are gone all day (use no hot water) it might not fire at all. If firing, that is maybe 20 minutes of firing. This gives the efficiency of gas as a fuel, but also that indirects are very well insulated and are as good as electric tanks for stand-by loss. Indirects also have quick recovery.

    I'm beginning to think the indirect may be better (a bit more expensive at install) but less maintenance as no anode rod and all that standard tank parts and maintenance like heating elements, needing flushing, etc.
    Last edited by netmouse; 10-10-2013 at 12:43 PM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    An indirect might still have an anode...depends. Some with say a SS tank shouldn't need one. The specs I've read on some indirects are 1/4-degree per hour. SOme of that depends on how hot you heat it, and how cold the place it is sitting, but standby losses are minimal on a good tank. It probably still doesn't hurt to flush them a bit (more of an issue maybe with a well that might have silt or sand pumped up occasionally). It doesn't get the minerals deposited like a directly heated tank because the incoming hot water used to heat it is not hot enough to cause them to precipitate out.

    So, yes, on a boiler designed for a cold start, an indirect is a very good choice! You typically don't need as big of a one as you might with a directly heated one, because it is likely your boiler has more output than a typical WH, and can reheat things faster. There are commercial WH that could outstrip it, but those are not typically installed in homes.

    FWIW, in a non-heating season, it is not uncommon to walk by my boiler and notice that the system temperature is ambient (i.e., room temp), meaning it had not fired in quite a long time.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    In the trades Dana's Avatar
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    Jim- his is a ~400lb ~105MBH cast iron steam boiler, not some tiny 2-gallon 3-plate low volume hydronic boiler, and definitely not a mod-con. As such it has a large fraction of thermal mass of a 40 gallon indirect. Even though the standby loss of a cold start boiler is low, the abandoned heat on every water-heating-only burn is substantial-enough to kill the efficiency argument for a low volume hot water user. At 50+ gallons/day, sure, indirect would still be the way to go. But "low volume" would be sub-30 gallons, maybe even sub-25. (A couple of 6-7 minute low-flow showers/day, a load of laundry & dishes every other day just doesn't add up to much.)

    netmouse: 20 minutes of firing at 82% efficiency of say, the Burnham IN4 is on the order of 29,000 BTU, enough heat to raise 50 gallons of water by 70F. A 50 gallon/day isn't exactly low-volume use.

    At about the same installed cost of a stainless indirect, a stainless heat pump water heater like the Air-Tap would cost less to run, last as long as an indirect, and does double-duty in summer lowering the latent-cooling load of the house, reducing the mold issues in the basement.

  4. #4

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    I think we are back to electric. Thanks for the review. I am a shower a day, laundry and dishwasher once a week. Brush my teeth, wash my hands a few times a day. Getting a 38-gallon electric tank. Others also said stick to electric as Dana initially evaluated. Thanks again.

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