How much does it cost to heat your home? It all depends on the outside temperature of the house. The colder the outdoor temperature, the greater the heating cost. Engineers developed a method to help homeowners calculate their heating costs. This method is called the degree-days. The equation for degree-days is defined as:

DD = (65 – To) ´ N

Where

DD = degree-days

To = Average daily outside temperature

N = number of days

Note: 65 means 65º F indoor temperature

The average daily temperature in Washington D.C. for the first 5 days in February was:

 Day Average Temperature º F February 1 35 February 2 38 February 3 42 February 4 32 February 5 28

What was the total number of degree-days for the first five days in February?

(65 – 35) ´ 1 day + (65 – 38) ´ 1 day + (65 – 42) ´ 1 day + (65 – 32) ´ 1 day + (65 – 28) ´ 1 day = 30 + 27 + 23 + 33 + 37

= 150 DD

Using a similar calculation for days that the outdoor temperatures are below 65º F, we can find the total number of degree-days for the entire year. Here are the degree-day data for some U.S. cities.

 City Degree-Days Atlanta, GA 3,095 Chicago, IL 6,127 Duluth, MN 10,000 Fairbanks, AK 14,279 Honolulu, HI 0 Miami, FL 206 New York, NY 4,848

Marie lives in Atlanta, Georgia. The heating bill last year was \$900. She has a sister who lives in Fairbanks, Alaska. How much would it cost her sister to heat a comparable house?