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  1. #1
    Join Date
    Feb 2005
    Posts
    46

    Electric Heat Pump or Gas Furnace?

    In 2006 we completely replaced our aging HVAC system with a Bryant Evolution furnace and electric heat pump. Part of the rationale for switching from a traditional gas furnace to hybrid system with an electric heat pump was that back then everyone was telling us gas costs were going to continue to climb and that electric rates would stay cheap.

    Six years later it now appears that natural gas in our area is cheap but electric costs have gone up dramatically. The good news of course is that our system has a heat pump override which lets us heat the house with the furnace only (using natural gas).

    So my question is...how can I determine if it's cheaper to heat the house with electricity or gas so I know whether to override the heat pump or not?

  2. #2
    Join Date
    Sep 2012
    Posts
    7
    This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

    Further infractions may result in loss of posting privileges.
    Last edited by beenthere; 10-02-2012 at 06:32 AM. Reason: Non Pro * Member

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,564
    Benoit, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.

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  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,455
    What's your cost per therm of gas and kwh of juice?

  5. #5
    Join Date
    Feb 2005
    Posts
    46
    Quote Originally Posted by BaldLoonie View Post
    What's your cost per therm of gas and kwh of juice?
    Average monthly electric cost is around $0.08 or $0.09 per kWh. Average gas cost looks to be $1.49 per therm (based on an average of 18.77 therms per month and an average monthly bill of $28.03, both year-to-date).

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,455
    Use the pump as cold as it can go!

    At COP of 3, which is around freezing, the heat pump costs 88 cents for 100,000 BTUs put in the house

    A 95% furnace costs $1.52 for the same heat. You have high gas prices.

  7. #7
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,434
    Quote Originally Posted by BaldLoonie View Post
    Use the pump as cold as it can go!

    At COP of 3, which is around freezing, the heat pump costs 88 cents for 100,000 BTUs put in the house

    A 95% furnace costs $1.52 for the same heat. You have high gas prices.
    It looks like he rolled the meter surcharge into the total calculation, $1.52 may not be accurate.

  8. #8
    Join Date
    Feb 2005
    Posts
    46
    Quote Originally Posted by 54regcab View Post
    It looks like he rolled the meter surcharge into the total calculation, $1.52 may not be accurate.
    $1.52 is an "all-in" number. As an example last month my bill looked like this:

    Therms used: 12.180
    Distribution & Service charges: $14.85
    Gas cost charge: $6.16
    Sales tax: $1.46
    Total charges: $22.47

    To come up with $1.52 I just divided the average therms by the average total charges. Maybe I was supposed to use the gas cost charge line item?!? If so, then the number is dramatically lower...like $0.51 per term. As a result, the gas is then much lower than the $0.88 per Kwh for electricity quoted above and would indicate I should run my system in bypass mode.

    Right?

  9. #9
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,752
    Looks like distribution and service charges may include fixed costs - billing and meter - really annoying how hard those bills are to figure out isn't it. Think they do that on purpose? (Imagine if they did that at the gas station, clerks would get shot.)

    What does your electric look like? Same thing? Did you come up with 9c kwh leaving those charges out?

    I pay roughly $1 therm/11c kwh.

    That's a great system you have. I'd run the pump at least until load is high enough that the furnace can run continuously on low, possibly take it down until register supply starts to feel cool. If the furnace cycles your efficiency drops, and as looney said heat is cheap with that pump.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  10. #10
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,434
    You will probably need to pull the rate schedule from your local gas and electric companies websites to see what you are really paying for gas/electric. Yes it's a mess, IMHO fixed charges should be separate from use charges.

  11. #11
    Join Date
    Feb 2005
    Posts
    46
    Quote Originally Posted by tedkidd View Post
    Looks like distribution and service charges may include fixed costs - billing and meter - really annoying how hard those bills are to figure out isn't it. Think they do that on purpose? (Imagine if they did that at the gas station, clerks would get shot.)

    What does your electric look like? Same thing? Did you come up with 9c kwh leaving those charges out?

    I pay roughly $1 therm/11c kwh.

    That's a great system you have. I'd run the pump at least until load is high enough that the furnace can run continuously on low, possibly take it down until register supply starts to feel cool. If the furnace cycles your efficiency drops, and as looney said heat is cheap with that pump.
    Electric is really murky. The bill shows the monthly usage in kWh and at the bottom they tell you the average cost but that's it. Multiply the two numbers together add sales tax and that's what they bill me for...absolutely no breakdown whatsoever. As an example, last month we used exactly 2,500 kWh and the average cost at the bottom is listed as $0.0869 per kWh. Multiply those two and you come up with about $217.20 add $15.20 for sales tax and the bill was $232.40.

    Where I live we have Duke Energy and as an incentive to get an electric heat pump they offered customers 15% off per kWh for each kWh over 1,000 kWh from October through March. The deal is good for the life of the unit. On average the discount saves me about $30 a year or $5 each bill for the 6 month period. Not much, but it's something...

    Anyway, thanks for the kind words. I researched the heck out of the system and have been extremely pleased with it. I guess I should be, it wasn't cheap. The heat pump is rated at 13.5 SEER. About the only thing I didn't spring for was the two stage scroll and the model with the really high SEER rating. The jump in cost was enormous and there was no return on that investment.

    By the way, the whole question of whether I should be over-riding the electric heat pump and using the gas furnace was spurred by an article in the local paper this week about a $1.1B coal gasification plant that's being built. The article made mention of the fact that when this plant was planned 5-7 years ago (right when I bought my HVAC system) the cost of natural gas was significantly higher (which made an electric heat pump sound really good) but with the glut of shale gas in the market today, the cost of natural gas is less than half of what it was back then.

    So really my thought process was very simple. If natural gas is really cheap right now use the furnace all the time. Eventually, when natural gas supply and demand work themselves out and there isn't a glut anymore and prices rise, switch back to the hybrid heat.

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,374
    Quote Originally Posted by michael73 View Post
    Electric is really murky.
    The bill shows the monthly usage in kWh and at the bottom they tell you the average cost but that's it.

    Multiply the two numbers together add sales tax and that's what they bill me for...absolutely no breakdown whatsoever.
    As an example, last month we used exactly 2,500 kWh and the average cost at the bottom is listed as $0.0869 per kWh.
    Multiply those two and you come up with about $217.20 add $15.20 for sales tax and the bill was $232.40.

    Where I live we have Duke Energy and as an incentive to
    get an electric heat pump they offered customers 15% off per kWh for each kWh over 1,000 kWh from October through March. The deal is good for the life of the unit.
    On average the discount saves me about $30 a year or $5 each bill for the 6 month period. Not much, but it's something...

    I guess I should be, it wasn't cheap. The heat pump is rated at 13.5 SEER.
    About the only thing I didn't spring for was the two stage scroll and the model with the really high SEER rating.
    The jump in cost was enormous and there was no return on that investment.

    If natural gas is really cheap right now use the furnace all the time.
    Eventually, when natural gas supply and demand work themselves out
    and there isn't a glut anymore and prices rise,
    switch back to the hybrid heat.
    What's ( or Who per mitt) is the Gas company in your area?
    Your city ? ___ > 37'F most of the time (or at least many 100's or 1,000's of hours)
    may make heat pump somewhat less costly than you realize.

    Utility Rate structures are provided in detail on-line, if one knows the company - residential rates can be reviewed.

    At > ~ 37'F, C.O.P. (HSPF) might be > 3.0 (10.2).
    The economic balance point could be in the 37'F to 43'F range if natural gas distribution charge is what I think it might be.

    I don't see exact numbers here for $/ Nat Gas therm including distribution.

    > 40'F, $0.09 * 100,000/ 3,412 * 0.85 / 3.0 = $ 0.75 per therm [equivalent] using heat pump
    ______________________ ( __ 3.0 to be confirmed based on heat pump model #, if provided).
    __ I currently work for Duke Energy in S.C.

    I believe that Natural Gas could be anywhere in the $0.55 to $0.90/ therm range
    depending on how the distribution charge is actually applied.

    _____ $0.09+/ kw Total for > 1,000 kw-Hr / Winter month
    100,000 BTU/ therm
    3,412 BTU/ kW __ 29.3083 kw/ Therm
    Discount 0.85 ( 15%)
    COP ___ 3.0 ( depending on temperature and heat pump model)
    Effective $0.0255 $/ kW > 40'F
    ______ $0.74736 / therm using heat pump > 40'F
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  13. #13
    Join Date
    Feb 2005
    Posts
    46
    Quote Originally Posted by dan sw fl View Post
    What's ( or Who per mitt) is the Gas company in your area?
    Your city ? ___ > 37'F most of the time (or at least many 100's or 1,000's of hours)
    may make heat pump somewhat less costly than you realize.

    Utility Rate structures are provided in detail on-line, if one knows the company - residential rates can be reviewed.

    At > ~ 37'F, C.O.P. (HSPF) might be > 3.0 (10.2).
    The economic balance point could be in the 37'F to 43'F range if natural gas distribution charge is what I think it might be.

    I don't see exact numbers here for $/ Nat Gas therm including distribution.

    > 40'F, $0.09 * 100,000/ 3,412 * 0.85 / 3.0 = $ 0.75 per therm [equivalent] using heat pump
    ______________________ ( __ 3.0 to be confirmed based on heat pump model #, if provided).
    __ I currently work for Duke Energy in S.C.

    I believe that Natural Gas could be anywhere in the $0.55 to $0.90/ therm range
    depending on how the distribution charge is actually applied.

    _____ $0.09+/ kw Total for > 1,000 kw-Hr / Winter month
    100,000 BTU/ therm
    3,412 BTU/ kW __ 29.3083 kw/ Therm
    Discount 0.85 ( 15%)
    COP ___ 3.0 ( depending on temperature and heat pump model)
    Effective $0.0255 $/ kW > 40'F
    ______ $0.74736 / therm using heat pump > 40'F
    Gas company = Vectren
    City = Carmel, Indiana
    Heat pump model = Bryant 264ANA (13.5 or 14 SEER and 9 HSPF)
    Furnace model = Bryant 355AAV (80,000 BTU)

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