First post -- tanked vs tankless

Discussion in 'Tankless Water Heater Forum' started by mar3232, Oct 31, 2011.

  1. mar3232

    mar3232 Member

    Messages:
    108
    Location:
    Indiana
    First of all, I'm SINGLE and I can guarantee that I only use hot water for one thing at a time. If I'm taking a shower, the dishwasher won't be running etc.

    My house is small, 1600 sq ft and I'm trying to decide which way to go with a water heater.

    Reducing utility costs is a high priority with this and the calculations seem to point to an electric tankless heater -- (looking at an Eemax 95 unit).

    I'll put a low flow showerhead on as well.

    Tankless --

    Needs 38.5 amps at 240v, no problem and the load box is close by in the basement.

    I take quick showers and use cold water for laundry -- rarely use my dishwasher. (I'm not a "hot water freak").

    Tanked --

    If I were to get a 40 gallon electric tanked unit, how long (based on winter Indiana well water), would it take for the water to come up to temperature?

    I know you'll tell me that a timer would be a waste of time but considering my situation, I think I would save considerably. Putting a timer on the heater is something I'm thinking about.

    A daily late afternoon shower is all I need and perhaps a few other hot water chores -- I'm sure 40 gallons would do me fine.

    Another advantage to a tanked unit is the possibility of adding a solar preheater at some point (something I will most likely do).

    So, really my question is --

    How long would it take that 40 gallon heater to get up to temperature?
    (I would think it would have the "typical" (2) 2400 w elements?)

    I think the numbers (if I use a timer) would be damn close to a tankless unit.


    THANKS


    And yes, have a water softener ahead of the water heater.
  2. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Yes. You have it. I would go tank and put r-30 or all my old clothes over it. And a timer. Most are 4500 watt elements. given your light use, and big insulation, you would always have hot water, or at least warm even with a timer.

    30 or 40 gallon at true value for about 198 bucks, cant beat that. Could turn the temp WAAY down and forget the timer too.
  3. mar3232

    mar3232 Member

    Messages:
    108
    Location:
    Indiana
    Just for the heck of it, I'd like to calculate my approx daily cost -- how long do you think it takes a 40 gallon to get up to temperature? Not scalding but say, a midway setting. The water heater is in the basement also -- which is nice, very comfy down there, even in winter.
  4. MoneyMogul

    MoneyMogul New Member

    Messages:
    3
    Location:
    New York
    I'm not sure where to post this question. I'm thinking about getting a tankless water heater. I have herd that water pressure is very low after you put one in. Does anyone know if that's true?
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    The pressure doens't change, but the volume can, depends on the design. Confusing pressure and volume is not unusual. To ensure the water lingers long enough to actually get warm, some designs include a volume limiter - sort of like you putting your hand through a candle flame. Slow it down, and it gets hot, go through fast, and you may not notice. On a water heater, you want to notice! Not all tankless systems are created equal. If your wintertime incoming water temperatures aren't frigid (now's a good time to measure them), a tankless might work out for you. Don't blindly go by the gpm ratings without reading the fine print. Also, a NG one will have much higher capacity than an electric one, but both might require upgraded supplies, either a new panel and feed, or a larger meter and regulator. They are also require more maintenance, especially if you have hard water. If you don't do this, they get caked up internally with mineral deposits like an old teapot. This adds to the cost as well, especially if you can't do it yourself. The key is to understand your maximum hot water needs - i.e., how many things do you want to be able to run at any one time, then size the thing for your local water and use. You may find it is going to cost you a lot more to install, and you may never recover or break even verses a traditional tank.
  6. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    Unless you have peak metering of your electric, there won't be any quick pay off for the timer on the water heater. Electric water heaters don't have uninsulated heat transfer surface like gas water heaters do (combustion chamber and flue). This greatly reduces their standby losses.

    Insulate the lines to from the tank (including the relief valve pipe.) That will do more than the timer to reduce losses. Uninsulated projections will bleed off an inordinate amount of heat. But if you have peak metering, you could see substantial cost reduction from a timer. This comes with the downside of the lower average temperature being ideal for legionella bacteria growth. Electric water heaters have more trouble with legionella, although in the studies I came across well water didn't seem to have the problem on the ones they sampled.
  7. Dana

    Dana In the trades

    Messages:
    3,027
    Location:
    01609
    At the insulation levels of most electric tanks I'd hazard that a timer would literally NEVER pay off (within the lifecycle of the electric hot water heater) for a 1-person household. Standby losses would be reduces by only the tiniest amount. If you only heated hot water during off-peak hours it would save dollar-wise, but that's more useful for AM showers than late-afternoon showers, since off-peak usually doesn't begin until after prime-time TV, and ends sometime in the ~7-8AM range in most locations. That would give you plenty of HW for the shower and you can probably tolerate more tepid water for other uses.

    Costs are largely linked to volume use- standby is low for electric tanks and can be made much lower by doing as Runs with Bison suggests: Insulating all near-tank plumbing within 6-10' of the tank with 5/8" wall closed cell foam pipe insulation (not available at box stores, but at Grainger, plumbing supply houses, online, etc). Insulating all accessible hot water distribution plumbing with the same further reduces the volume of hot water used for short-draws by increasing the length of time the hot water drawn-but-abandoned from the tank in prior draws stays hot enough to be useful.

    Placing the hot water tank so that it has the shortest possible runs to taps where low-volume draws happen most often and/or doing "home-run" plumbing also reduces the volume of hot water abandoned in the distribution plumbing. (About 17% of the total HW heating energy is abandoned & lost to distribution plumbing, according to one careful study done in CA a handful of years ago. But that was the average- yours could be better or worse- it's a matter of plumbing layout.)

    Drainwater heat recovery might have payback if you're a volume-showerer, cutting showering energy use in half, but it's not clear that it will EVER pay off for a 1-person household. It would beat the ROI of any solar pre-heat options though. In fact in your case photovoltaic solar would probably have a better return than solar hot water of any type.

    Heating & cooling costs far outweigh hot water for any home in Indiana, but even more so in your case. Before throwing a ton of cash at exotic and expensive HW solutions, first fix all the air leaks you can (concentrate on the attic and basement first, since stack effect drives infiltration) then pay a pro the $500 or whatever to do a blower door test with infra-red imaging to find and document all of the non-obvious air leaks in the house, then fix (or pay somebody to fix) those. Air sealing is by far the most cost-effective way to spend the money on reducing utility cost for most homes, including brand-new homes. The hot water heating costs for an energy-conscious 1-person household are truly miniscule, far outshadowed by the heating and cooling costs. In most homes infiltration accounts for more than a third of those costs, and in many older 2 story + basement farmhouses & Victorians it could be approaching half. The first $1-2K spent on targeted air sealing with blower door & thermal imaging verification usually pays back in under 5 years in reduced heating & cooling costs.

    As jadnashua correctly stated pressure drop across a tankless is a function of the instantaneous flow, and can be problematic with some anti-scald valves & shower mixers, but for most installations it's not a problem. The reasons for selecting a tankless are many, but from a utility savings or green-factor there are almost always far better ways to spend the money. If you have big tubs or spas to fill and don't have space for a monster-sized tank big enough to handle it they can make sense. Most will not pay sufficient dividends on utility savings to make it work in a present-value financial analysis at anything other than a whole lifecycle cost, and if there are higher than average maintenance costs (as would be the case if you have hard water), it's a liability.
  8. ditttohead

    ditttohead Water systems designer, R&D

    Messages:
    1,942
    Location:
    Ontario California
    I agree that a tanked water heater is almost always preferable to a tankless heater. I am currently writing a follow up article that takes traditional water softener efficiency in a residential application to the highest level by using tankless designs. Even with a 60% increase in efficiency of a whole house softening design, the energy savings of the tankless, etc, the ROI is still barely less than the life expectancy of the tankless heater. http://www.wcponline.com/pdf/June_Horner.pdf
    I am a huge fan of tankless water heaters and have installed one in my house, but I have just replaced my moms, and my grandmas water heaters with tank types. The tank design is too simple, reliable, efficient, etc.
  9. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    That was my thinking exactly, though I hedged a bit since the peak kwh rate is the determining factor.

    Pretty much my take as well. A 1-person low volume user is not going to be able to payoff the drainwater heat recovery installed cost. For my home the system would serve 3 of the 4 occupants and is a wash on payout over any ordinary timeframe because we use 1.5-1.6 gpm shower heads for 7-10 mins each. I'm still tempted to do it because I have an ideal retrofit location for the installation, and it appeals to my inner geek. With nat. gas now running only 60 cents/CCF in mid-winter, the econ. is decidedly sour. (With electric running 15 cents/kwh now I'm glad I decided to forego a heat pump.)
  10. Dana

    Dana In the trades

    Messages:
    3,027
    Location:
    01609
    The price of natural gas varies widely with region- my gas rates are about 2x yours. But even then DWHR would fail in any net-present value analysis for a hot-water sipping 1-person household.

    Higher efficiency heat pumps are competitive on operating cost here though. Electricity has backed off to the 15-17 cent range from it's 18-22 cent peaks of a few years back when the economy was humming, but even at 20cent electricity a top of the line ductless mini-split will beat an 80% gas burner if the heat pump is oversized ~1.5-2x and almost always operating in the lower third of it's compressor speed range.
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