Tankless water heater or tank? How about for this particular use?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by dereks, Jun 22, 2011.

  1. dereks

    dereks New Member

    Jul 4, 2007
    Seattle WA
    I know people keep asking this but how about in my specific planned use?

    I am planning a mother-in-law type cottage which will be connected to the main house. Think of it like an addition which is what a future buyer could use it for. The planned use is to have a bathroom and a kitchen sink but no cooking. The person living there could eat in the main house.

    I am thinking of a tankless water heater because the hot water usage will be low. Why heat 50 gallons of water that might not be used much?

    I thought that tankless water heaters are good for little hot water usage and a lot of usage (where the tank wouldn't have time to heat up). If intermediate usage, then a tank water heater is better. Is my logic flawed?

    Last edited by a moderator: Jun 22, 2011
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    How cold does your water get in the winter? The things have a couple of deficiencies, in my view (they can be overcome, but it usually costs more): they can only raise the temp of the incoming water a certain amount at any volume (typically about 70-degrees), and, they don't generally turn on until the flow rate is over say 1/2-gallon/min or so. If you like to have warm water at the sink for something, you might need to run both the hot and cold fairly high to get the flow to cause it to turn on. Too low, no hot, turn it a little more, and it may jump in temp radically once the thing actually now senses it needs to be on.

    Installation costs are generally a lot higher than a tank. Depending on your water, a tankless may need to be de-limed annually. So, running costs may be lower (but standby losses aren't huge), but maintenance costs are likely to be higher. You may or may not ever break even verses a tank.

    How were you planning to power this: gas, propane, electric? I would not consider an electrical tankless except maybe for hand washing only. One large enough to provide decent flow would likely require upgrading the electrical service. Some places base their minimum charge on the capability - bigger possible service, bigger base costs (even if you don't use it). This is in addition to the per KWH use. Unless you have really ecconomical electrical rates, I'd not consider that type. Gas, maybe, electrical, no.
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  4. SacCity

    SacCity In the Trades

    Mar 14, 2011
    Sacramento, CA
    You are in Seattle so temp should not be a significant issue.
    I would question the idea of not having a cooking area,
    Tankless is fine considering the temperate climent. Lack of kitchen makes it a non servicable rentable unit.
    Offering independence but not.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona
    Your initial costs will be greater than the cost of maintaining the temperature in a tank type heater for a LONG time. If it is attached to the main house why not just connect it to the existing hot and cold lines in the house?
  6. ballvalve

    ballvalve General Engineering Contractor

    Dec 28, 2009
    "retired" and still building and troubleshooting
    northfork, california
    Get Granma a nice 30 or 40 gallon electric tank rig for 200 bucks at true value and save a bunch of headaches and future issues. Insulate it, and your losses drop to near zero
  7. Ramon Leigh

    Ramon Leigh New Member

    Jul 25, 2011
    Same idea I had - if cottage is close, tap into house's hot water.
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