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  1. #1
    Join Date
    Nov 2008
    Posts
    36

    Duel Fuel Hybrid Heat Pump versus Electric Heat Pump

    My current heating and cooling systems is the original 25 year old system. It consists of a Rheem heatpump and Rheem Air Handler unit with electric resistance heating coils for backup. My average monthly energy bill is $275 and my home is completely electric. The home is two levels at about 1825 square feet. I live in the Baltimore, Md area and the utility rates are about
    $.147 per kWh and $1.30 per therm.

    I am considering upgrading to a energy effecient system. The heating and cooling salesman suggested going with a duel fuel heatpump system. That is a heatpump and gas furnace system. I am leaning towards a 16 SEER, 9 HSPF Heatpump and 93.7 AFUE gas furnace (or even higher at 96.7 AFUE).

    I have a few questions.

    1.Based on the rough numbers I've presented is this a wise choice or should I go with a total electic efficient heatpump and new airhandler with electric backup. If I go with gas I'll have to have the gas line run and plumbing installed and I've factored that in.

    2. Does anyone have any figures or know where I can calculate what kind of savings I can expect?

    The energystar website for the government allows you to calculate some rough numbers if you go with a straight airconditioner and gas furnace setup. They also have a calculator for a straight electric heatpump. I don't see anything that allows you to calculate a combination electric heatpump with gas furnace.

    I've used a rough number with just the straight airconditioning and gas furnace, but I suspect this is not correct. I'm guessing that the combination heatpump and gas furnace should be less expensive. Any ideas or sites with calculators that would allow me to plug in some numbers and figures.

  2. #2
    Do you already have gas service to your home? If not, you will need to factor in the base charges for natural gas, which in some states can be significant. With a total electric bill of only $275, I would question if the small savings you would get from the dual fuel would pay off quickly enough. A new technology heat pump will do much better than your 25 yr old system. Based on the rates you have given, the heat pump should cost less to operate at all temperatures above the balance point of the heat pump..(usually 25-30 degrees). A 9.6 hspf hp should exceed a COP of 3.0 above 30 degrees. For your rates, a COP of 3.0 means the hp will cost about $1.40 per 100,000 btu. A 93% furnace at your rates will also be about same operating cost. So, the benefit only comes in at really cold temperatures. The base charges for the gas and additional installation costs as well as your climate will dictate the time for payoff. Good luck with your new system!

  3. #3
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,579
    I would spend the money and go to 18 seer and can the idea of gas in your area. I am in Ct and have a 16 seer heat pump and have not used my back up heat yet and do not intend on using it unless the temps drop below 10 degrees.

    I see no way for you to save by using gas. A 80% variable speed furnace would cost less unless venting will be hard.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,931
    You have a high electric rate.

    Get the dual fuel system if you feel both your electric and gas rate are going to continue to maintain the same ratio between them.

    With your electric and gas rate, even if the HP's COP is 3, your gas is cheaper(even with only a 92 AFUE furnace).

    By getting dual fuel, if your gas goes up, you can switch to the HP, if it becomes cheaper to use.

    EG: Home that has a 60,000,000 BTU's load for for the year.
    HP with electric aux, with the HP providing 80% of the heat, and aux 20% = $1,205.98
    93.7 AFUE nat gas furnace providing 100% of the heat = $832.44
    HP at COP of 3 providing 60% of the heat, and nat gas furnace at 93.7AFUE providing 20% of the heat = $849.98
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  5. #5
    Join Date
    Nov 2008
    Posts
    36

    The information is great so far for the comparison

    I'm using the rates from the local providers website. I guess it's as close as you can come to an actual rate assuming the other fees included. If I use the Energy Star Website here are the figures I come up with:

    1. Straight Gas Furnace 93.7 AFUE - $1.30/Therm rate, Programmable Thermostat = $740 per year (495 Therms plus 15 percent for 73 degree temp)

    2. Straight Airconditioner, 16 SEER, 3 Ton, Programmable Thermostat, $.147/kWh = $292 per year

    3. Heatpump, 16 SEER, 9 HSPF, 3 Ton, Programmable Thermostat, $.147/kWh= $1558 per year ( plus 15% 73 degree temp 9216 kWh)


    I guess the combination Heatpump and Gas Furnace might be a good combination.

  6. #6
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,579
    Quote Originally Posted by Freezeking2000 View Post
    I would spend the money and go to 18 seer and can the idea of gas in your area. I am in Ct and have a 16 seer heat pump and have not used my back up heat yet and do not intend on using it unless the temps drop below 10 degrees.

    I see no way for you to save by using gas. A 80% variable speed furnace would cost less unless venting will be hard.
    I quess I was wrong, with gas rates like yours it does not compute. Our electric is close (.165 KWH) and gas is 30% higher in Ct.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  7. #7
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by rjack90 View Post
    My current heating and cooling systems is the original 25 year old system. It consists of a Rheem heatpump and Rheem Air Handler unit with electric resistance heating coils for backup. My average monthly energy bill is $275 and my home is completely electric. The home is two levels at about 1825 square feet. I live in the Baltimore, Md area and the utility rates are about
    $.147 per kWh and $1.30 per therm.
    Wow. I think I met my twin.

    I am in Abingdon, Harford County. I also have an 1800 square foot split-foyer, all electric home. Built in 1986.

    In 2007, I replaced a fully functional 21 year-old Trane heat pump (estimated at 7 SEER) with a new 14 SEER, 12 EER, 9 HSPF Goodman system to combat the 72% rise in electric rates thanks to de-regulation without competition. I have reduced my summer power consumption by about 40% with the new sytem.

    Our electric costs are 16 cents per kw-hour when I divide the total bill by my kw-hr consumed. BGE doesn't always update their web page with the latest prices. Non-summer rates are a tad cheaper.

    Compare the costs of 1 million btu's of heat for gas furnace and heat pump.

    Gas at $1.30 per therm, 94% efficient furnace:
    (1,000,000 / 100,000 btu per therm) x 1.3 / .94
    = $13.83

    Heat pump w/electricity at 16 cents per kw-hr delivered, C.O.P. = 3.25 at 35F ambient (for my 3 ton Goodman):
    (1,000,000 / 3414 btu per kw-hr) x .16 / 3.25
    = $14.42

    Close. Very close. Gas is 5% cheaper for the same 1 million btus. The above does not include the cost of a defrost cycle.

    C.O.P. increases with increasing temp.

    You will need auxillary heat when the outdoor temp falls below the balance point. My balance point is mid 20's.

    Electric strips for auxillary heat are expensive to run. The same 1 million btus costs $46.86 for resistance strips.

    I also have a masonry fireplace w/insert in the below-grade family room. This helps to even out the temps between the 2 floors. The family room is typically 4 degrees cooler than the upper floor.

    Good luck.

  8. #8
    Join Date
    Jun 2007
    Location
    The Twilight Zone
    Posts
    2,964
    Quote Originally Posted by rjack90 View Post
    I'm using the rates from the local providers website. I guess it's as close as you can come to an actual rate assuming the other fees included. If I use the Energy Star Website here are the figures I come up with:

    1. Straight Gas Furnace 93.7 AFUE - $1.30/Therm rate, Programmable Thermostat = $740 per year (495 Therms plus 15 percent for 73 degree temp)

    2. Straight Airconditioner, 16 SEER, 3 Ton, Programmable Thermostat, $.147/kWh = $292 per year

    3. Heatpump, 16 SEER, 9 HSPF, 3 Ton, Programmable Thermostat, $.147/kWh= $1558 per year ( plus 15% 73 degree temp 9216 kWh)


    I guess the combination Heatpump and Gas Furnace might be a good combination.

    There's no way that the heat pump costs twice as much to run as the gas furnace ($740 vs $1558) with your rates. Something is wrong.

    Take care.

  9. #9
    Join Date
    May 2006
    Location
    Tampa, FL
    Posts
    82
    I would imagine the heat pump costs include heating and cooling.

  10. #10
    Join Date
    Nov 2008
    Posts
    36

    Heatpump figure does include heating and cooling

    You are correct. The Heatpump figure of $1558 does include heating and cooling. The gas furnace figure of $740 plus $292 for cooling/ac would be a total of $1032. The calculator I'm using is the energystar.gov website.

    I believe the energystar website might be neglecting the electricity that would be used for the gas furnace to run the air handler. Another website energydepot.com gives the electricity usage of the electric furnace at about 750 kWH. At a rate of about $.147/kWh this can add an extra $110 or so to the gas furnace electric combo for a total of $1142.

    So now a straight electric heatpump is around $1558 per year
    Gas Furnace and AC combination is about $1142 a year

    I have no idea what the electric heatpump/gas furnace combination would be. I'd guess somewhere less than the Gas furnace and AC combination. Would this be correct?

  11. #11
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,579
    Quote Originally Posted by gary_g View Post
    Wow. I think I met my twin.

    I am in Abingdon, Harford County. I also have an 1800 square foot split-foyer, all electric home. Built in 1986.

    In 2007, I replaced a fully functional 21 year-old Trane heat pump (estimated at 7 SEER) with a new 14 SEER, 12 EER, 9 HSPF Goodman system to combat the 72% rise in electric rates thanks to de-regulation without competition. I have reduced my summer power consumption by about 40% with the new sytem.

    Our electric costs are 16 cents per kw-hour when I divide the total bill by my kw-hr consumed. BGE doesn't always update their web page with the latest prices. Non-summer rates are a tad cheaper.

    Compare the costs of 1 million btu's of heat for gas furnace and heat pump.

    Gas at $1.30 per therm, 94% efficient furnace:
    (1,000,000 / 100,000 btu per therm) x 1.3 / .94
    = $13.83

    Heat pump w/electricity at 16 cents per kw-hr delivered, C.O.P. = 3.25 at 35F ambient (for my 3 ton Goodman):
    (1,000,000 / 3414 btu per kw-hr) x .16 / 3.25
    = $14.42

    Close. Very close. Gas is 5% cheaper for the same 1 million btus. The above does not include the cost of a defrost cycle.

    C.O.P. increases with increasing temp.

    You will need auxillary heat when the outdoor temp falls below the balance point. My balance point is mid 20's.

    Electric strips for auxillary heat are expensive to run. The same 1 million btus costs $46.86 for resistance strips.

    I also have a masonry fireplace w/insert in the below-grade family room. This helps to even out the temps between the 2 floors. The family room is typically 4 degrees cooler than the upper floor.

    Good luck.
    Here in Ct the gas price was as high as $2.30 and a low of 1.67 this year and I do not believe that included delivery charge? I am not sure on the current rates.
    Bump the gas cost up by including the 10 amps to run the blower to distribute the heat to the home, bang we are even.

    Now add 16-20 seer (14eer) with the higher (10+)HSPF and I know what would win.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  12. #12
    Join Date
    Nov 2008
    Posts
    36

    Electricity and Gas Rates One Step Further

    Hey Gary,
    Thanks for the information. You must be in the industry and I am obviously not, lol. Your calculations look great. I would have never been able to come up with most of the numbers. I took a closer look at the BGE rates.

    Yes the summer and winter rates are different. The base rate in summer and winter this year are almost equal. They call it 11.8 cents per kWh. What I can do is add up all the fees they charge and come up with 14.95 cents per kWh. There is a fixed fee of $7.50 for electricity service.

    I guess the gas is a little trickier. I see the rates have gone from $.93 per Therm to $1.58 per Therm this year. BGE suggested I use the base rate $1.10 per Therm. After adding all the fees that BGE adds to gas the rate would be $1.37 per Therm and there is a fixed fee of $13.00 per month for gas service.

    Looking at your calculations again:
    Gas at $1.37 per therm, 94% efficient furnace:
    (1,000,000 / 100,000 btu per therm) x 1.37 / .94
    = $14.57 (plus a fixed fee of $13 per month for gas)

    Recalculating the electric:
    Heat pump w/electricity at 14.95 cents per kw-hr delivered, C.O.P. = 3.25 at 35F ambient (for my 3 ton Goodman):
    (1,000,000 / 3414 btu per kw-hr) x .1495 / 3.25
    = $13.47 (plus a fixed fee of $7.50 per month for electric)

    You mentioned a 14 SEER 9 HSPF Heatpump. I'm looking at an American Standard 17 SEER 9.2 HSPF Heatpump. I think that would slightly lower the numbers for the all electric heatpump setup. So the balance might tilt back to the Heatpump. I'm not sure what kind of average calculations to use for the defrost cycle. Also, I haven't had gas since I've been in this house. I looked at the spread sheet for the 7 year BGE gas rates. The rates are different each month. The best I can guess is that the rates are highest in the non-heating months and lower in the heating months.

    I guess I still need a strong compelling argument to go with a gas set up of any kind. The combination might be gas/ac or gas/heatpump.

    There is an additional fee of up to $3650 to have gas put in my house.

    BGE fee for laying gas pipe and meter: $850
    Plumber to install gas piping in home: low $800 high $1500
    Extra cost associated with having gas furnace (94% AFUE) installed versus ( 17 SEER 9.2 HSPF)electric heatpump $1300

    If I use the lower number of $800 for plumbing I'm looking at nearly $3000 over a straight electric heatpump that is similarly outfitted. I was thinking of a 6 year payback on a new electric heatpump set up.

    With the additional $3000 dollars to keep the same 6 year payback the gas furnace/ac or gas furnace/heatpump needs to save about an additional $500 per year over the electric heatpump set up.

    Does anyone know if the gas furnace/ac or gas furnace/heatpump will gain that additional $500 per year over the straight electric heatpump?

    Thanks for all of your help

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