Energy cost - heat pump vs. natural gas

carol23_gwJune 13, 2010

Our subdivision in Henderson County NC is looking into having natural gas installed.

Most of us have heat pumps , and some of us have recently had new heat pumps installed.

The subdivision is trying to promote having the gas run through, and is advertising the energy bills will save us money.

When I've looked at similar square footage homes with natural gas heat, I noticed higher costs for every month.

Is the A/C part of the heat pump cheaper to operate than an A/C unit someone would have installed outdoors where they have a natural gas furnace?

How do I find out the answer for this location? Any suggestions?

Thank you.


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A heat pump IS an air conditioner. It has components which allow it to run backwards in the winter time. Result: the hot air that normally blows from an outdoor condenser (air conditioner)is now blowing through your duct system.

It has the same efficiency as an air conditioner with similar efficiency ratings.

If you are subjected to periods of cold weather, a gas furnace can be 'teamed up' with a HP to provide 'hybrid heat', which will provide enhanced comfort. If you can find out what your utility will charge per therm of gas, along with typical 'delivery' charges, you can post that information and someone will be along to help. Your nearest big city would help also.


    Bookmark   June 13, 2010 at 1:06PM
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a straight AC condenser has two efficiency ratings, SEER and EER.

a HP condenser has three efficiency ratings, SEER and EER for AC and HSPF for heating.

if you have the same mdl for an AC condenser and HP condenser (like the XL15i) and the SEER and EER ratings are identical, then the operating cost in AC mode will also be identical. of course this is a classroom exercise and in reality they won't be identical but will be very close.

Since you mentioned you have a new HP system, no need to worry or look back because of the possibility of nat gas availability down the road.

I personally don't think you made a mistake considering your location/climate.

I am attaching a fuel comparison calculator link that you can take a look at. you have to know your costs for each fuel as well as your efficiency.

I would hope you have contacted your electric utility to see if they offered any rebates and/or rate incentives for all electric heating.

let me know if you have any questions and congrats on your new Trane system.


Here is a link that might be useful: Fuel Comparison Calculator

    Bookmark   June 13, 2010 at 1:28PM
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In parts of NC served by Piedmont Natural Gas, the gas co. charges a minimum of $10.00 per month even if no gas is used. Or if customer requests disconnect to avoid the monthly charge during April-October for instance, the reconnect fee is $85.00- about the same annual cost either way. If you have no other use for the gas, these fees must be considered in cost comparisons.

    Bookmark   June 13, 2010 at 10:05PM
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I used to be in the A/C business, on the manufacturing side. The cooling condensing unit and the HP condensing unit parts list was virtually identical except for the diff parts allowing it to reverse flow. Oh, and the HP model carried a large price premium. That may not be the case as much nowadays.

    Bookmark   June 14, 2010 at 4:50AM
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I have a hybrid system in Wake cty, NC. I have gas cooking, fireplaces and heat. The $120 year fee is about 30% of my total so not insignificant. My summer bills are $11 - $10 for monthly, $1 gas usage. Winter gets up to $50. I had a $200 annual gas usage, $120 connection for a total of $320. Just to give you an idea - 4000 sq ft, new construction.

The cheapest thing would be straight heat pumps but we had to have gas cooking so hybrid makes the most sense.

    Bookmark   June 14, 2010 at 2:32PM
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Check your utility if you are interested in going hybrid because your electric utility might offer a rebate to go hybrid... yeah you read that right. The cost to buy power at peak rates is staggering and some who can't justify more generation would rather not have so much peak load.

    Bookmark   June 14, 2010 at 9:02PM
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In NC, there are no peak power issues on a cold winter's night. There are far too few homes that are all electric. We pay less for electricity in the winter because summer time is the peak problem.

In most parts of the country a heat pump helps you use more baseload, and therefore justifies a cheaper electric rate - and that is why utilities give a discount. I can't really think of an area that has peak issues at night but maybe the deep south with a large all electric housing stock but still occassional sub freezing temps. NC does not fit that as we are probably 80+% Natural gas - the only all electrics are the rural homes and townhomes/condos.

    Bookmark   June 15, 2010 at 6:33AM
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Several here have mentioned "minimum charges" for natural gas - it might be wise to consider the whole house in your figures. I.E, consider switching from electric to gas dryer, and from electric hot water to gas - it's pretty easy for an average family to spend $50 a month JUST for electric water heating. Depending on rates, you're likely to cut that bill in half just by changing your water heater to gas, and then you won't mind the minimum bill quite so much - in my old neighborhood, the cost per "therm" was less than half what electricity cost.

Also don't forget that many prefer gas for cooking nowdays.

    Bookmark   June 15, 2010 at 10:33PM
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I just learned of another problem with gas service. In 2010, Piedmont Natural Gas in NC did most meter readings with intervals shorter than the average of 30.4 days (365 divided by 12). One interval was just 24 days. For each interval, they billed the $10.00 "Monthly Charge". Due to the shortened billing intervals, this was collected 13 times in 2010. I do not know if this was for every customer statewide, but it did happen to at least some.

    Bookmark   February 28, 2011 at 4:41PM
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I was trying to gauge the cost(for natural gas) when my furnace has run(consumed gas) for an hour's time. I did it two ways.
First I just took the BTU input rating of the furnace and did the calculations from there. Then someone pointed out that the BTU input rating may not be an actual value.

So secondly I needed to determine the amount of gas my furnace is actually consuming per hour.

Here are the particlars:
1. I have Goodman model GMPN100-4 furnace. (natural gas, single stage, pilotless and an input rating of 100,000 BTU per Hour)


1.One cubic foot of natural gas has about 1,030 BTU.

2.Divide the furnace input rating(in my case 100,000) by 1030 to get the number of cubic feet of gas the furnace will use in one hour. So 100,000(BTU) divided by 1030(BTU per Cubic Foot) is about 97 Cub Feet.

3.My supplier's bill is based on units of one hundred cubic feet(CCF) so I divide 97 cubic feet by 100 to determine how many CCF the furnace will burn per
hour. This turns out to be 0.97 CCF

4.My supplier charges $.745 per CCF so it costs me 0.97 times $.745 = $.72 per hour for natural gas for my furnace to run.


As stated above someone pointed out that the BTU input rating may not be an actual value. So I wanted to determine how much gas the furnace was consuming per hour.

My gas meter has a 2 cubic foot dial. I set a video cam in front of the gas meter in the morning knowing the furnace would be on for at least 20 minutes to bring the house up to temperature from the night's setback. The furnace did run for about 20 minutes but I stopped my readings at 10 minutes. Here are some findings:
In 5 minutes the furnace consumed 7.6 cubic feet of gas.
In 10 minutes the furnace consumed 15.2 cubic feet of gas.

So 15.2 cubic feet of gas in 10 minutes extrapolated out to 60 minutes would be 91.2 cubic feet gas per hour or 0.912 CCF/hr.

At $.745 per CCF the cost is about $.68 per hour.
From the input rating data (100,000 BTU/hr) I calcualted .97 CCF/hr. So the actual gas consumption was a little bit less that the input rating.

Now some Notes:
1. My gas bill is broken down to a charge for gas consumption, a customer service charge of like $21 a month and of course the tax on the consumption charge.
So it's pretty straightforward how much the gas costs per hundred cubic feet. This month gas was $.745 per CCF.

2. No other gas consuming appliances(oven, stovetop or hot water heater) were firing at the time of testing.

3. I understand that outside temp, thermostat setting and how well my home is insulated are factors as to HOW OFTEN the furnace will run. That wasn't my concern. I only wanted to know how much gas was consumed when the furnace ran for an hour. How that hour was achieved was not important. It could of been 60 continuous minutes or six 10-minutes cycles. In my case I took a 10 minute run cycle and multiplied that amount of gas usage by 6.

I have since I've hooked up the following 24V hour meter to the gas valve:

The meter progresses in tenths of an hour increments anytime the gas valve is open. I can tell how long the furnace runs each day, month or season. This helps with filter changes also. I've found that about every 125 hours the filter is dirty enough to be replaced.

    Bookmark   March 3, 2011 at 9:32AM
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Generally in Alabama it is more expensive to run gas heat. The service charge is an important element to consider as it will add $60 annually to the cost. Consumption costs will have to be very cheap to compete. The TVA has a nice calculator - you will need to know the efficiency of the units and the rates. Gas rates can be very hard to get - Alagasco does not publish them on the web or fax them - just US mail....the last I have is from 2008; a little newer I have the Dec 2009 R-1 residential rate for Mobile Gas which was $9.23 customer charge; $1.61754 per therm for the first 40 and $1.53214 after that. Gas rates have been down lately and they were much higher than this a few years ago. Gas rates are generally much more volatile that electric rates. Electric rates here are on average $15 monthly plus 0.075 kWhr. With similar cost/efficiency equipment using the TVA calculator: gas is roughly 2x the cost.

Here is a link that might be useful: TVA Dare to Compare

    Bookmark   June 16, 2011 at 11:01PM
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