Cost to run new heat pump in 30 degree weather

garygDecember 7, 2007

I have a new 3-ton Goodman heat pump that was installed in June. Maryland electric rates went up 65% thanks to de-regulation and no competition. I countered the 65% rate increase by replacing a 21 year-old 7 SEER heat pump with a new 14 SEER, 12 EER, 9 HSPF system.

Goodman is great at providing technical data to homeowners. In reviewing the heating data for the system, I found that the unit draws 2.64 kilowatts at 30 degrees outside temperature.

(2.64 kw) x (12.74 cents/kw-hr) = 33.63 cents/hour to run the heat pump. That's cheap heat.

I measured the heated air just after the coil and got 90.1 degrees after the system had run for an hour straight. The auxillary heat didn't come on last night when it was 28 outside, so my balance point is below 28 degrees (with a 68 degree setpoint temperature).

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Tinmantu

We are setting up more and more heat pumps here... fossil fuel setup. With electric rates of .05 per kilowatt (usual rate of .11) with a separate meter, it's very attractive to customers. We set most to switch over at 30 degrees. Adequate ductwork is VERY critical with a heat pump and some houses where changes can't be made because of a finished basement, they just can't be recommended.

    Bookmark   December 7, 2007 at 12:56PM
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speedymonk

Gary, how have the past two months bills compared dollars and cents compared to the same time period a year ago? If I remember, all you have is electric, correct?

    Bookmark   December 7, 2007 at 7:00PM
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garyg

Speedymonk.

Yes, all-electric.

I haven't compared any heating bills yet, as the heating season is just underway. I did compare kilowatt usage in the prime cooling month of August to August '06, and the kw's were reduced 40% which I was very pleased with.

For heating, I assist the heat pump with a fireplace in my below grade family room. It takes the chill off the room and can raise the temp to a nice 74 for several hours. I have 2 cords of wood ready to go for this winter.

Last 2 electric bills were $90 and $96 which is excellent for a 1600 square foot split-foyer. My wife can't believe our utility bill compared to some of our neighbors who do have larger homes with more people (we have no kids).

So far so good with the Goodman.

Take care.

    Bookmark   December 7, 2007 at 8:58PM
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speedymonk

Those are very nice bills to pay-- and you have the rates from h*** too! I had a wood stove in Idaho that I used and I sure miss it. Can't really burn wood around here anymore. When you want to --like when it's cold-- it's not allowed because of pollution standards. However, if it's your only source of heat, then it's ok.

I noticed when working in Aberdeen earlier this week when the flooding killed the power to most of Gray Harbor County, that many folk were using wood burning stoves/fireplaces to stay warm.

I should get my power bill tomorrow to see if adjusting the balance points on the HP helped. Only got about a shy three weeks on the settings but it was cold for here. Probably will need to track everything for a year to get a good idea.

I figured out my KW useage for the new house is .38 kw per square foot vs. .70kw per square foot in the 20-year-old rambler I sold. I'm using between 80 and 100KW less power each month in the new place vs. the old place...and I've got 1,200 more square feet. Insulating is the same, windows, too. HP is better so we'll see how the winter fares.

Have a great holiday, Gary.

    Bookmark   December 7, 2007 at 10:04PM
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mike13

Gary,

So why do the Goodman charts show it takes 2.64KW with an outdoor ambient temp of 30 degrees but it takes 2.91KW with an outdoor ambient temp of 65 degrees? Both calculations are done w/ a 70 degree indoor dry bulb.

    Bookmark   December 8, 2007 at 4:25PM
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brickeyee

"how have the past two months bills compared dollars and cents compared to the same time period a year ago?"

Without an adjustment for degree days (heating or cooling) the comparison does not really tell you very much.

    Bookmark   December 8, 2007 at 4:51PM
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speedymonk

Brickeyee, I realize the comparrison isn't accurate without knowing the temps, but I figured Gary might have that info for comparrison purposes. I've been charting my figures and temps since I moved into the new place and got the power company to give me figures for the old place for 2.5 years until we sold and moved. It was then 10 months of renting and moving twice before getting into the new joint.

    Bookmark   December 8, 2007 at 7:07PM
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garyg

"So why do the Goodman charts show it takes 2.64KW with an outdoor ambient temp of 30 degrees but it takes 2.91KW with an outdoor ambient temp of 65 degrees?"

- I noticed this too Mike when I was looking at the heating data. I always knew the btu output dropped like a rock with outside temps, but I didn't know the amp draw dropped too. I don't know why this is (effect of cold temps on motor cooling?). At 15 F, the amp draw is 2.47 which is 18% less than the draw at 65. Interesting to compare these numbers to the amps in cooling mode at 95 degrees outside and 75 indoor - 2.82 amps.

"Without an adjustment for degree days (heating or cooling) the comparison does not really tell you very much."

I don't have a degree-day comparison. The average monthly temp was within 1 degree from Aug '07 and Aug '06.

"I figured out my KW useage for the new house is .38 kw per square foot"

- Fantastic. That's impressive. I'm jealous - that kicks my butt.

"Have a great holiday, Gary."

- Thank you and same to all.

    Bookmark   December 8, 2007 at 11:02PM
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pilchard

My heatpump provides for us down into the teens. I keep reading of people who cross over at 30F. To me that seems a bit high. 14 SEER Ruud.

    Bookmark   December 9, 2007 at 11:21PM
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