replace gas with electric water heater

Discussion in 'Water Heater Forum, Tanks' started by young707, Aug 2, 2012.

  1. young707

    young707 New Member

    Messages:
    17
    Location:
    San Jose, California
    I have a leaking 40 gallon 40000 BTU/hr gas water heater in garage open area, at home for 2 adults in San Jose, CA.
    I am looking into to replace with 40 gallon 4500W electric water heater.
    So I need to run 220AC extension for around 5 feet, wall socket, and breaker. I also like to add shut off timer so that I only run the heater 12 hours instead of 24 hours every day. So far, I do not find this timer at Home Depot.
    What kind of work time and approximate cost for electrician to do this work?
  2. Dana

    Dana In the trades

    Messages:
    2,974
    Location:
    01609
    Replacing it with another gas HW heater would have far lower operating expense than an electric HW heater in your area (unless you went with a heat-pump hybrid type at much bigger upfront expense, in which case the operating costs might be comparable.)

    Turning off an electric HW heater for 12 hours/day with a timer has almost zero impact on the amount of power used. Electric tanks have very good insulation and very low standby loss. To get a significant reduction in standby loss and savings would require a big drop in the water temp during the "off" period, but an electric tank set to ~125F would typically lose less than 1/4 degree per hour, so you'd still be over 120F at the end of your 12 hour period. The vast majority of the power use is for raising the 55-65F incoming water up to the 120F-140F setpoint temp- the difference in standby power use between water with less than a 5F average difference is truly in the statistical noise- low single-digit percentage savings on the overall power use at best. Only if you can get a rate reduction on your electricity bill for heating water only during off-peak hours would a time-of-day approach make any economic sense.

    Whatever heater you install, you get pretty good payback on 5/8" wall closed cell pipe insulation on all the near-tank plumbing (including the first 6-10' of the cold-feed closest to the heater and the temperature & pressure overflow valve & outflow plumbing), as well as any hot water distribution plumbing that is accessible. For a primer on how to do it, see: http://www.leaningpinesoftware.com/hot_water_pipes.shtml
  3. young707

    young707 New Member

    Messages:
    17
    Location:
    San Jose, California
    Dana, Thank you. Please help me with rough estimate comparison between gas & electric water heater.
    In San Jose area, 2 adults, single family home, hot water usage is roughly around (shower + faucet + dish washing + laundry ) 32 gallons per day, is this number close, or I should use half for heated water?
    How much cost between gas & electric water heater operating cost?

    So, in this areas, you think 12 hours shut off timer will not save much in energy?
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,262
    Location:
    New England
    Shutting off an electric WH via a timer will cost more to install than you'd likely ever recover...it just doesn't cost much to leave it on. With the insulation, with no use, the tank just doesn't cool off enough to require it to turn on much (if at all) during that 12-hour period. Now, if you lived in say northern Minnesota and had the thing in a garage that got to just above freezing most of the winter, that's be another issue, but then, if you did turn it off, it would likely freeze the lines!

    1KwHr = 3400BTU
    1 Therm of NG = about 100,000BTU

    Now, the NG WH isn't as efficient as electric, but say the electrical unit ran for 1 hour/day = 40000/3400 = 11.76KwHr.

    If the NG WH had to run an hour, with the same sized burner, it would use about 1/2 a therm - giving that it isn't as efficient as electric. Some designs are better, some are worse.

    Price your electric and NG and you can get your localized numbers. Around here, that 11.76KwHr would cost around $2.11 verses a 1/2-therm of NG for about $0.75. Do you really want an electric WH? If you had to run a new gas line or even start up a new service, that initial installation cost could be quite a bit, but since it's already there, it rarely is more cost effective to go electric when NG is present.
  5. young707

    young707 New Member

    Messages:
    17
    Location:
    San Jose, California
    understand.
    So you are saying, given same amount of heated water, electric will cost 3 times more compare to gas, correct?
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,262
    Location:
    New England
    That's true where I live, but we have high electric rates...your results may differ. You can easily tell by looking at your bills and comparing. Plus, typically, a NG WH will have a quicker recovery rate, and if you do need even faster recovery, you can get one with significantly larger burner. A larger burner just needs to run less time - that doesn't mean it uses more (although it may, but it's not linear). Whle you may not use a lot of hot water, a fairly typical use pattern is lots all at once...the same sized electric may not be large enough as a NG one. Having more available, though, may tempt you to use more.
  7. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    I agree with what the others have noted. I'll add this: with nat. gas prices very low for the past several years and electric rates rising, the one time I can see switching to electric making economic sense is if your only use of nat. gas is for water heating. If you can shut off the gas altogether, then getting rid of a high monthly fixed cost for being connected to the nat. gas grid could easily pay for the additional electricity cost.
  8. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,384
    Location:
    Yakima WA
    Where I live, electricity is quite reasonably priced. That said, natural gas is far more economical. I would suggest a water heater that does not use a standing pilot light.
  9. Dana

    Dana In the trades

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    Location:
    01609
    Without your actual retail-delivered electricity and gas rates it's hard to say how much more the electric tank will cost to run, but unless you have 5 cent electricity or $2/therm gas it's definitely less expensive to heat hot water with gas than electricity.

    At a buck a therm gas (typical US average- yours could be more), in a hot water heater with an EF rating of 0.60 (not the highest, not the lowest) for every buck of fuel you get (100,000BTU/therm x 0.6=) 60,000 BTUs of heat into the water (more or less- depends on how much water you use), which is 1.67 cents/1000BTUs.

    At 12 cent/kwh electricity (about the nat'l average), in a tank with a 0.90 EF rating (not the highest, by any means) every kwn delivers (0.9 x 3412=) 3071 BTUs to the water for 12 cents, which is 3.9 cents for every 1000BTU. That's 2.3x the cost of heating it with buck-a-therm gas in a standard gas HW heater.

    If you replace the gas HW heater with a ~0.90 EF condensing version like a Vertex, with $1/therm gas you'd be at 1.1 cents/1000 BTU of water heating. If the gas lines to the existing tank are big enough to handle a 76,000BTU/hr burner (probably true, unless it's a very long run from the regulator), the installed cost of installing a Vertex would likely come in at about the same as the electric tank heater that would need the extra electrical work. There may be state and utility subsidies available for going with a condensing tank heater too, which could make it even cheaper.

    32 gallons/day of hot water would be on the low end of usage for 2 adults, but not impossible if you only take short showers, and have EnergyStar clothes & dishwashers, etc. At 32 gallons /day use the EF of an atmospherically drafted gas water heater falls off by quite a bit (they're tested at roughly twice that daily volume), but not as much for an electric tank or a condensing gas-fired tank.

    IIRC you can't even BUY appliances that have continuously burning standing pilots in California (and many other states) these days, most have an electronic ignition, even though the electronic ignition only strikes a (temporarily burning) standing-pilot that lights the main burner.
  10. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Furnaces went electronic a long time ago. Just as of July 2012, no more standing pilot stoves allowed ( this is all Federal, NOT just CA). As far as I know, water heaters not affected yet, but I am sure it is coming! Even the ultra-low-nox ( burner looks like a flux capacitor) units mandated in several CA counties, they are still standing pilot.
  11. Dana

    Dana In the trades

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    jimbo: Thanks for the detailed update on the CA-state of standing-pilot ignition! I'm a bit surprised that they are still be allowed on water heaters, given the general trend.
  12. young707

    young707 New Member

    Messages:
    17
    Location:
    San Jose, California
    OK, we are in San Jose, Northern California. So what is the electric vs Gas cost comparison.

    Also, the water heater listed in Home Depot is GE "Ultra Low NOx Gas" 40 gallon, GP40T06AVR/187-918, 32 KBUT per hr, 32.3 Recovery in G.P.H. 90F Rise, 73 First hr. Del. G.P.H., Energy factor 0.59. $497.

    Lowes is Whirlpoot, 40 gallon, 6 yrs, $418, #333578, 125lb, 62"x18" dia,
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,262
    Location:
    New England
    YOU have your utility bills, and thus know what your local utility rates are! We can only tell you what OUR rates are. Most places, NG WH is cheaper to run than an electric one...run the numbers using YOUR rates, and you'll know!
  14. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    One thing to remember is that PROPANE is a rip off and then the electric looks great.

    I hate to see gas in any house from a safety standpoint. Every year many end up looking like the twin towers.

    I do not believe there are ANY pilots in California. Hot surface igniters, mainly.
  15. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,032
    Location:
    Cave Creek, Arizona
    You do NOT connect an electric water heater with a "5 foot extension cord receptacle, and breaker", not do you use a "plug in timer" to control the heater. The only time a timer saves electricity is if you use ALL the water in the tank, and can wait until the timer turns it back on to reheat the water. In the meantime, you will only have "cold" water. A 40 gallon elecltric heater is almost a dinosaur these days because 50 gallon heaters either cost about the same, or in some cases less, than a 40 gallon one.
  16. young707

    young707 New Member

    Messages:
    17
    Location:
    San Jose, California
    according my PG&E bill:
    Gas 12.13333 Therms @ $1.06335 = $12.90
    Electric
    Baseline Usage 286 Kwh @ $0.12845
    101 - 130% Baseline 63.2667 Kwh @ $0.14602
    total $45.98
    How do I compare the electric and gas between Therms and Kwh?
  17. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,262
    Location:
    New England
    for 100,000BTU in electric, it would cost you around $4.27; for 100,000BTU in gas (one therm) $1.06. Now, with an electric WH, you get almost all (not quite) of the energy applied as heat, but with NG, some of it goes out the flue and doesn't heat. A low-end WH is about 60% efficient, some are over 90%. It would have to be about 25% efficient to cost the same as electric, and none are that bad.

    Plus, a NG WH will recover quicker than an electric one, at least most of them.
  18. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,384
    Location:
    Yakima WA
    My gas water heater is a power vent and uses pipe. What this means is, there is very little heat loss through the vent. Anyway you slice this pie, natural gas is far cheaper than electricity.
  19. Dana

    Dana In the trades

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    Location:
    01609
    Using source-fuel BTUs isn't a very good way to estimate when efficiency factors of the equipment differ so widely. You can't just use the source-fuel BTUs to come up with a good cost comparison.

    The EF of an electric tank is ~0.90, the EF of a typical atmospheric-drafted tank is about 0.55.

    So for that $1.06 therm of gas you're actually only getting (0.55 EF x 100,000 BTU=) 55,000 BTUs in hot water...

    ...at a cost of ($1.06/55=) 1.9 cents/1000BTU

    With the 0.90EF electric tank that 14.6 cent kwh of electricity you get only (0.90 EF x 3412 BTU/kwh =) 3071 BTU in hot water...

    ... at a cost of (14.6/3.071=) 4.75 cents/1000BTU

    So heating hot water with electricity would be about (4.75/1.9=) 2.6x as expensive as using gas.

    While still dramatically more expensive, it's much less egregious than the $4.27/$1.06= ~ 4x cost multiplier estimate based on source-fuel BTU only, ignoring efficiency factors.

    Very rare is the local US market where heating hot water is cheaper with electricity is cheaper than heating with natural gas. If you have 5-cent/kwh electricity it's still possible though, and those markets DO exist (but not in CA.)
  20. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    Locally the cost of service for gas runs in the ~$30/month range, tax included. The gas itself is dirt cheap, running less than $0.60/ccF with tax at present. However, if I didn't have gas heating I would consider electric water heating, even though it is far less thermodynamically efficient overall (when the power generation loss is figured in.) Electric water heating has greater health concerns, slow recovery, etc., but eliminating a fixed monthly charge has an appeal when you spend less than $10/month for fuel for actual water heating for a family of four (our winter time usage, summer is 1/3 less.)
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