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  1. #1

    Gas vs Electric tankless heater and Manual J

    Hello Everyone,

    two questions

    1) try as i might i can't find a calculator that shows the cost comparison of operating a 99.5% efficient electric tankless h20 heater at .14$/kwh vs a 85% eff gas tankless heater at 1.825/ therm. Does anyone know where i can find an operation cost calculator or know what is cheaper to operate?

    also, my contractor bid on installing a gas tankless unit but unilaterally decided to wire for electric. I know i can't ask install pricing questions so how can i find out how much money i should ask back for since i've read gas tankless units are more expensive to install then electric units.

    2) I had manual J done on my house (a tiny eco home) came back 23K heat gain and 27K heat loss...but the unit they sized to match this is a 46K btu furnace--that 75% larger then the heat loss--is this standard?

    Thanks!

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,171
    Electric $41.00 per million BTUs
    Gas $21.50 per million BTUs

    Furnaces only come in sizes so small. 40,000 and 45,000 are about the smallest they come in.

    I wouldn't get the electric water heater.
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  3. #3

    thanks...is there a formula

    thanks for the info. Is there a formula i can show my contractor though on the cost because he keeps telling me electric tankless heaters are cheaper using baltimore specific costs? Where do the numbers come from? Do those numbers take into consideration the 85% efficiency vs the 99% efficiency?

  4. #4
    Join Date
    Apr 2008
    Location
    Alberta Canada
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    2,246

    Tankless Water Heater

    I would strongley recommend going with gas instead of electric water heater. Electric is to slow and people are not very happy with them. Thats the feed back from the units I have seen installed. Gas on the otherhand people are happy. The best tankless out there.


    http://navienamerica.com
    Do it right the first time.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    I used 100% effifiency for electric, an 85% for gas.


    You can go here.
    http://www.hvacopcost.com/
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  6. #6
    thanks again for the input, but my contractor still says i am wrong and electric is cheaper. I told him about the website and he said that website was refering to Heating systems for a house (like a furnace heater vs electric baseboard heater) and was not a calculator for a tankless water heater. I'm still looking for something i can show him like a calculation that compared gas tankless vs electric tankless. I can't believe this doesn't exist anywhere on the WWW!!!!

    Hi--I think ifound it!!! http://www.water-professor.com/howtoselectnewheater.htm all i have t odo is multiply their cost by the % increase my fuel costs are over their assumed .06 per kwh and .6 per therm so the results are for 100% efficiency = /485 $/50 gallons/ day for ayear 80% eff gas= 266$ /50 gallons per day for a year. Alright- now i'm armed with knowledge! Electric is 84% MORE EXPENSIVE than gas--WOW!!!

  7. #7
    Join Date
    Jan 2008
    Posts
    85
    Quote Originally Posted by ecogirl22 View Post
    thanks again for the input, but my contractor still says i am wrong and electric is cheaper. I told him about the website and he said that website was refering to Heating systems for a house (like a furnace heater vs electric baseboard heater) and was not a calculator for a tankless water heater. I'm still looking for something i can show him like a calculation that compared gas tankless vs electric tankless. I can't believe this doesn't exist anywhere on the WWW!!!!
    Ask the contractor to show you his calculations. And then post them here for review.
    Is the purchase and install price of electric vs gas part of the calculation?

  8. #8
    Yes that's definately a better approach! If he still refuses i will ask him and post it here. He shouldn't be considering cost because he's already bid on it so it was supposed to be gas and that's what i paid for.

    Thanks for your help everyone. Its hard for me to argue with the "experts" when he tells me i'm wrong about something that i know nothing about! But now i feel more confident.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,171
    It sounds like he made a mistake on his estimate, and quoted it too cheap. And is trying to get you to go with a cheaper electric unit, to make up for his mistake.
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  10. #10
    Join Date
    May 2007
    Location
    Upstate SC
    Posts
    188
    For the specific formulas that Beenthere used for comparing gas and electric, use these (with apologies to Beenthere)

    Gas rate per 1 million BTU = (cost per therm) divided by (100,000 BTU in a therm) times (1 million BTU) divided by (%efficiency of gas equipment divided by 100)

    Electric rate per 1 million BTU = (cost per KWH) divided by (3415 BTU in a KWH) times (1 million BTU) divided by (%efficiency of electric equipment divided by 100)

    You put in whatever your rates are in your location. For better long-term accuracy, make sure to include the rate of inflation of gas or electric proce hikes. Also your gas bill will also have a gas factor or some other factor that they mutiply by your usuage of CCF on your meter (100 cubic ft) to account for things like varying gas quality, gas temperature affected temperature, etc.). You can neglect that factor because I think it averages out in a year to 1 (at least for my area it seems to).

    I second the motion about wanting to see the contractor's calcs.

  11. #11
    Join Date
    Mar 2008
    Location
    Central Maryland
    Posts
    246
    First she says,

    Quote Originally Posted by ecogirl22 View Post
    also, my contractor bid on installing a gas tankless unit but unilaterally decided to wire for electric. I know i can't ask install pricing questions so how can i find out how much money i should ask back for since i've read gas tankless units are more expensive to install then electric units.
    Then,

    Quote Originally Posted by ecogirl22 View Post
    thanks again for the input, but my contractor still says i am wrong and electric is cheaper.
    I've got a new flash for you, ecogirl. You don't have to PROVE anything to your contractor. You can settle this in ONE conversation.

    "We have a contract to install a gas water heater, and that is what you will install. What day will you be out to install it?"

    Your contractor may be trying to stay under the radar by a.) not hiring a licensed plumber (required in most areas to run a gas line), and b.) not getting an inspection of the gas line. A lot of areas don't require inspection of electric HVAC but do of gas lines, and plumbers won't run gas without pulling a permit, it is not worth the end of their career.

    If he still balks at giving you what the bid (contract) says, simply say, "this is your last chance, your next conversation will be with my lawyer."

    Get the Hint. YOU ARE GETTING RIPPED OFF.

    -HF

  12. #12
    Join Date
    Jul 2008
    Posts
    33
    I've heard that if you get an electric on-demand water heater you have to get a water softener or the calcium in the water will stop everything up.

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