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What is natural gas?

Natural gas is a clean burning fuel used by homes, businesses and industry for heating, cooking, lighting and many other uses. Natural gas is a combustible mixture of hydrocarbon gases that is extracted from reservoirs underneath the earth. It is refined to remove impurities and the clean natural gas is transmitted through thousands of miles of pipelines to distributors throughout the country.

How is natural gas measured?

We measure and sell natural gas to residential customers by measuring its volume in cubic feet.  One cubic foot of natural gas would fit in a cube, 12 inches square and 12 inches high.  For more convenient billing, we measure and price gas in units of 100 cubic feet or “CCF” which is the unit of measure you will see on your natural gas bill. If a customer uses 5000 cubic feet of natural gas in a billing period, they would actually see their usage as 50 CCF on their bill. This corresponds with the rate tariff which will show the appropriate charge “per CCF” used.

How much does natural gas cost?

In order to know how much it costs to run a natural gas appliance in your home, it is helpful to know your cost per one hundred cubic feet (CCF). To calculate your average cost per CCF for a particular billing period, look at your gas bill and divide the monthly dollar amount by the number of CCF used that month. This is the easiest way to find your personal, average cost per CCF.

You can also find current rate information on this web page: Monthly gas cost changes. If you would like to review Duke Energy Kentucky's residential rate tariffs, see: Duke Energy Kentucky rate tariffs. Be aware that you must consider many small rate components found on several different pages in order to determine your cost per CCF from most natural gas rate tariffs.

What is a British thermal unit or Btu?

A British thermal unit (Btu) is simply a term used to measure heat energy. One Btu is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit. It is approximately the same amount of heat you would get from burning a wooden match. One cubic foot of natural gas has about 1,031 Btu. The amount of heat in one hundred cubic feet of natural gas (1 CCF) is about 103,000 Btu.  Some natural gas suppliers will measure and bill the customer for each 100,000 Btu that is delivered and this is referred to as one “therm” of heat energy. Rate tariffs for this kind of metering and billing will show the charge “per therm” used.

How do I read my gas meter?

The gas meter on your home is a valuable instrument. It is a very sensitive device that reads your natural gas usage much like the odometer on your car reads the total mileage since the car was new. Your meter numbers are never "reset" and represent your usage from months and even years of past consumption.

To determine the amount of gas you use in any time period you need a meter reading at the beginning of the period and at the end of the period. Subtract the first (smaller) number from the most recent reading (larger number) to determine the CCF of gas used in that period of time.

Important Note: The face of a gas meter usually has two set of dials. The dials marked "One Half Foot" and "Two Feet" are for test purposes only and are not used for meter reading purposes.

The dials on your gas meter resemble small clocks. The numbers on each dial range from zero to nine and a hand rotates around the dial. It is important to note that some hands run clockwise and others run counterclockwise. The hand follows the numbers from 0 to 1 to 2 etc. One full revolution of the hand on any dial is equal to one digit change (example 3 to 4) on the next dial to the left. The hands only advance when gas is being used.

Steps to read your dial meter:

  • Stand directly in front of the meter (this will give you the best view of where the hand is pointing).
  • Read and record the number from each dial starting from the right and moving left.
  • When the hand has just passed a number or is between two numbers, record the smaller number.(Example, if the hand has just passed the 5 or is between the 5 and 6, record the number 5).
  • When the hand appears to be directly on a number, before deciding if it is the new larger number or the smaller number before it, check the next dial to the right.  If the hand has not passed zero, record the small number instead of the number it is closest to. Here is an example

The correct reading for this example is 4 7 3 0. Notice the 3 could have been a 2 or a 3, but since the dial to the right has passed zero, the last two numbers are 3 and 0. As this home used gas in the last few hours, these two dials were changing from 28 to 29 to 30.

Some gas meters are like the odometer on your car with rolling digits instead of dials. To read this type of gas meter, simply record the numbers displayed.

Why does my energy bill vary from month to month?

In most families, energy usage will vary from month to month. Sometimes when a bill increases you may wonder if something is wrong with your meter or if your appliances are working properly. The information below will help you to understand why a gas bill can change from month to month.

  • Weather plays a major role in energy usage for homes heating with natural gas. Every change in the winter weather will affect your home’s heating system. These weather changes are not only temperature related but wind, sun, clouds, snow cover and many other variables will change from day to day and month to month.  Your heating will also fluctuate from conditions inside your home such as temperature settings, door traffic, use of curtains and even extra gas appliance usage when the family is inside for longer periods in the winter.
  • If you heat your home with natural gas, in addition to the affects of winter weather, you may also notice a monthly change in your average cost per CCF.  The winter months are typically the time when national market conditions can increase the wholesale price of natural gas. Duke Energy buys all its gas from wholesale suppliers and by law this cost is passed through dollar-for-dollar to our customers after review by the state public utility commissions.  Duke Energy makes no profit from an increase in the wholesale price of natural gas.
  • Your billing period can vary from 27 to 34 days, depending on when we read your meter. If your energy usage is different from the previous month, check to see if the two bills are for the same number of days.
  • Fireplace usage can affect your bill in the winter. Although you might think burning a fire on a cold winter’s day would help lower heating bills, the opposite is more likely to occur. An open fireplace flue allows your home’s heat to escape and especially a flue left open for several days will increase your home’s heat loss and raise bills.
  • Many customers expect savings when they go on vacation for several days or weeks. Unfortunately, many gas appliances like the furnace and gas water heater will continue to run on a regular cycle while you are away. You may even use more energy before or after your vacation with additional laundry.
  • Changes in the family lifestyle or living habits can result in higher energy use. For example, during the holiday and school vacations there may be more people in your house resulting in increased energy use.
  • If your current gas bill seems unusually high and the weather has been relatively normal, consider having your heating system checked by a certified heating technician. Something as simple as an air duct in the attic coming apart could cause a significant increase in your energy bill.

How much am I paying to use this gas appliance?

The cost to use a gas appliance will depend on the following variables: The amount of gas that the appliance draws when it is operating, the amount of time the appliance runs and the cost per CCF of the gas.

A gas appliance will usually have a fuel rating label or a specification in the owner’s manual that shows the rated energy input.  This number is normally listed in Btu per hour (Btu/h). For example, let’s say your gas fireplace logs have an input rating of 40,000 Btu/h when on the high heat setting.

To make your calculations easier, round the 1031 Btu/cubic foot of natural gas to 1000.  Divide the appliance input rating by 1000 to determine the number of cubic feet of gas the appliance will use in one hour. (Example; 40,000/1000 = 40 cubic feet.) Recall that your bill is based on units of one hundred cubic feet (CCF) so divide the cubic feet by 100 to determine how many CCF the appliance will use in one hour. (Example: 40/100 = .4) So the fireplace logs will use 40 cubic feet or .4CCF of gas per hour.

From the gas cost information explained above, let’s say you find your average cost per CCF is $1.20. For the fireplace logs above, .4CCF X $1.20 = $.48 to use the logs for one hour.

This procedure can be used to estimate the operating cost for other gas appliances, however it may be difficult to determine the actual run time. Many appliances like a gas water heater will cycle off and on as needed and the actual on-time is unknown.

Here is a table that shows an estimated cost to use some common gas appliances.

Important: The estimates below have been calculated
with a cost of $1.20 per CCF

Appliance Btu input
The appliance Btu input and the usage assumptions noted determine the
monthly CCF and cost estimate
Clothes dryer 22,000 7) 45 minute loads per week 5.1 $6.00
Fireplace logs 40,000 Winter month, used 2) 3 hour times per week 10.4 $12.50
Cook-top burner 9,500 Average, one hour per day 2.9 $3.50
Oven 30,000 Average, 3 hours per week 2.0 $2.50
Yard lamp 2,500 Metered usage, 2 mantels, 24 hrs/day 18.2 $22.00
Outdoor grill 30,000 2) one hour cookouts per week, medium heat 1.3 $1.50
Hot tub heater 125,000 Cost is per 10 hours of use 12.5 $15.00
Pool heater 200,000 Cost is per 10 hours of use 19.9 $24.00
Water heater 40,000 Average family of 4, general usage
with cold clothes wash
14.6 $17.50
Water heater,
additional for
hot clothes wash
40,000 Average family of 4, add this amount
for warm to hot clothes wash, cold rinse
5.8 $7.00
Pilot light
left on (ex.
gas logs)
875 This usage varies widely 6.4 $7.50

Notes to the table above:

  • The example cost per CCF used in the calculations above may not be accurate for your home.  Energy bills will normally have different average costs per CCF, depending on the amount of the bill and the current rate charges.
  • If your personal cost per CCF is significantly different from this, you can still use this table to estimate your appliance costs. Multiply the “Monthly CCF Estimate” shown for each appliance by your personal cost per kWh to determine a more accurate estimate for the appliances in your home.
  • These numbers are estimates based on many averages and are not to be used as an exact representation of what your actual costs might be.  Your exact gas usage may be different from these estimates and will also vary from month to month.  Actual gas bills are dependent on your living habits, the weather, the condition of your appliances and other hard to predict variables.

How much does it cost to heat my home?

Many of the above examples that help you estimate the energy costs for a gas appliance will not help you in estimating the cost to heat your home. Since there are many variables associated with home heating, we have dedicated two other pages on this website to help you with this question.

Check out our Personalized Energy Report (PER)™ for an estimate on your heating and cooling costs, based on your custom input for your home and heating system. This quick, interactive tool will also estimate your energy savings if you upgrade your heating system, air conditioner, home insulation or make other energy improvements.

Visit Heating Costs & Comparisons to learn how to compare the most common heating fuels, get an update on the current cost of each fuel and estimate the energy costs for your home using many heating system alternatives.

Where can I find tips on saving energy?

Return to our menu page, Save Energy & Money, for a link to all our residential energy information or go directly to Easy Ways to Lower Your Bill.