Thinking of going to an electric water heater

Discussion in 'Water Heater Forum, Tanks' started by pete c, Jan 23, 2011.

  1. pete c

    pete c New Member

    Messages:
    52
    Location:
    CT
    With oil prices being what they are, I have been considering going to an electric water heater rather than the tankless coil.

    I realize that oil BTUs are cheaper than electric ones, but, with oil getting more expensive, I'm not so sure that the difference is that big.

    I would leave the tankless coil in place to heat the water during cold months when the boiler is working anyway. I would add the electric water heater down stream of the coil. It would handle all the heating chores when the boiler was off and serve as a tempering valve, sort of, when the tankless was providing the hot water.

    I currently have a tempering valve, but, it seems to not be doing the job currently. I suspect it needs cleaning/replacement. If it does need replacement, I would probably just go ahead and get the electric heater and do away with the tempering valve.

    Any suggestions appreciated.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    Keep the tempering valve! In-tank coils typically have a fairly low gpm flow rate, especially in the winter when incoming water temperatures can get quite cold. Depending on which costs less, you could add a recirculation system to use in the winter and turn the electricity off to the tank. Put the tempering valve on the outlet of the new tank, and the hotter water from the coil might get the new tank quite warm, then tempered to a safe level.
  3. pete c

    pete c New Member

    Messages:
    52
    Location:
    CT
    i think i get what you are saying. recirculate the water through the coil, basically turning the electric heater into an indirect, sort of.
  4. jimbo

    jimbo Plumber

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    8,997
    Location:
    San Diego
    Since many places burn oil or gas to make electricity, I don't see a reversal of the price advantage coming!
  5. hj

    hj Moderator & Master Plumber Staff Member

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    You need to rethink your idea, or get an professional's input. If the heater is "downstream" of the coil, it also has to be downstream of the tempering valve because a coil's temperature output is "unregulated", and you do not want the tank to get overheated. If it is "upstream" of the coil, (and upstream/downstream depend on which way you are thinking of the flow), then your electrically heated water is going to try to heat the boiler's water as it flows through the coil. Electric is NOT usually an "inexpensive" way to heat water and is usually the last choice if there are other fuels available.
  6. Dana

    Dana In the trades

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    Name one non-island place in the lower 48 of US with a population of over 1000 that uses oil as the primary (not peak) power generation fuel. (There might be one, but I don't know where it is.) Oil has been too expensive to use even for peak-generation ever since the price spike of the early 1980s except in the rare case.

    The price of natural gas is not in lock-step with crude oil the way heating oil is, and has a significant $/MMBTU advantage over #2 distillates (albeit behind coal by good measure, until/unless the externalities get applied to the price of coal.) Half the electricity in the US is generated by low-cost coal BTUs. Very few markets are predominantly fueled natural gas, but in acid-rain sensitve New England it comprises something like 1/3 of the total grid-source. In CT gas currently comprises ~20% of the base power generation source-BTUs, less than half the amount provided by nukes (the single largest source.) Oil-fired generatation is primarily (and very expensively) an island community artifact in that state, but there may still be some #2 peakers remaining on the mainland. Annually it's less than 20% of the total, but still far more than the national average. Nationwide oil is less than 2% of the grid-source.

    Even in a 30% efficient all-gas-grid it would still be cheaper to heat hot water with electricity during non-space heating periods than with an 85% AFUE cast iron heating boiler for a single-family home. (The economics can change in larger multifamilies with a boiler dedicated for hot water heating.) The combustion efficiency can be pretty good, but the standby losses are horrific. Except for the smallest in the lineup newer highly insulated versions, internal heating coils in cast iron boilers run 25-40% efficiency in water-heating only mode. See: Units 1 and 12a in Table 2 p.7 (p12 in .pdf pagination) http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf

    You may be able to make financial sense out of an indirect-fired tank though, if the boiler is at most 2x oversized for the space heating load, and heat-purging controls are used to cool the boiler down at the end of burns by dumping heat into the indirect (see unit #3 in the same table in that document.) A lot depends on how steep your electric rates are, ( CT electricity rates are among the highest in the lower 48) and how costly it would be to retrofit an indirect with the proper controls with a boiler. A bunch of pipe insulation (or even a drainwater heat recovery heat exchanger on the shower), can go a long way toward reducing HW heating costs with an electric tank, but less so with an oversized oil boiler with an internal coil, more than 60-75% cost using the boiler is all standby losses. (Drainwater heat recovery is subsidized by local utility rebates in some parts of Long Island, but SFAIK none in CT are doing so.)

    How much oil do you burn over the summer when heaing loads are nonexistent? (It's ofetn hard to tell unless you top it off in mid-late May, and again in early-mid September.) If it's under 50 gallons swapping over might not be worth it, but I've seen a situtation in central MA where it was over 200gallons/summer for a family of 4 using the tankless coil. That family got religion or something and sprung for evacuated tube solar w/ electric backup, taking advantage of hefty state subsidies. But there are more cost-effective solutions than that, unless you're literally on one of those oil-fire island utilities with 40-50cent/kwh electric rates.
  7. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Here, electric beats propane on $ per btu in a big way, with simpler equipment. And electric doesnt send houses into the sky when it leaks.
  8. pete c

    pete c New Member

    Messages:
    52
    Location:
    CT
    thanks for all the replies. sounds like going electric might make sense. would still like to hear opinions on issues with a boiler sitting cold for extended periods.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    Turning it off for the season should be okay...but, if things like the circulator were getting close to failing, that may be frozen when it is time to restart it in the fall.
  10. Dana

    Dana In the trades

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    What Jim said- leaving the boiler cool & idle for the summer does it no harm. Pumps that would lock up from 3-5 months of idle weren't long for this world anyway (and it's better to have it fail in October than January, eh?)
  11. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    You figure out what you are paying...

    CL&P Rates

    UI Rates

    All said and done You'll be around $0.27/kWh on the actual bill with all the taxes and charges...
    Not the perceived Generation Rate which they tout as 9.482¢ per kWh or 10.615¢ per kWh
    Good luck at saving money with that!
    Last edited: Jan 26, 2011
  12. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    finished cost on an old rate schedule the utility-mafia-crooks were made to grandfather in, is about .11 cents here.
  13. Dana

    Dana In the trades

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    2,922
    Location:
    01609
    The sample bill from your CL & P for 700kwh came to $123.74 with all charges included, which is just shy of 18cents/kwh. Where do you get the extra 9cents/kwh to come up with 27?

    With all is said and done I've never seen power sold by non-island utilites in southern New England going for more than 22-23 cents at their 2007-2008 peak, but in NYC & Long Island I've seen 25cents+.

    But even 20 cent cent electricity can still be competitive than heating hot water with a beastie-boiler with an internal coil with $3 oil, depending on the boiler, it's size, and insulation levels. Taking a middle-of-the road estimate of 30% efficiency in hot-water heating mode, 30% of the ~139,000 BTUs or ~ 41700 ends up in the water for that $3. Converting that to kwh: 41700/3412= 12 kwh, so you're looking at 25cents/kwh for heat deliver to the water. A 0.90EF electric tank at 20 cents/kw is giving you the same heat for 20/0.90= 22 cents. At a more realistic $3.40/gallon oil and 18 cent electricity you're looking at paying 28 cents to heat the same amount of water with oil that you'd be paying 20 cents to heat with electricity.

    Mind you the savings would be a May-September scenario in CT- the rest of the year you're splitting the standby losses on the boiler with the space heating load and the average efficiency much higher. Whether putting the electric tank in series with the boiler coil makes financial sense depends a on what the price of oil & electricity do over the next decade. The nukes that run half of the grid CT are mostly paid for, and the natural gas that makes up another significant slice of the grid while volatile, is likely to track a lower price curve (very flat through 2035 according to EIA projections) than oil as the world economy recovers, so it's not a BAD option- electricity prices are much more stable (and local) than world oil pricing. In large developing Asian economies the masses are itching to start driving, and are developing the financial means, which puts a strong upward pressure on oil pricing in the intermediate & long term.

    But whether the probably-reduced utility costs would cover installation costs within the life-cycle of an electric tank is not at all a sure thing. There are many variables with big unknowns looking out a decade or two- you might give it a year or so and see how it breaks down, or you can punt now, and see how right you are in predicting the markets.
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