Service technician Kevin O’Rourke cleans a furnace in a North Providence home so it will operate more efficiently.

The Providence Journal / Mary Murphy

If federal forecasts are correct, it will cost Rhode Islanders about as much to heat their homes this winter as it did last winter.

Federal data predicts it will cost Rhode Islanders who use oil heat $1,547 this winter, $1,222 for those who use natural gas and $1,088 for those who use electric heat. Those figures are based on a 2,000-square-foot house with a thermostat constantly set at 68 degrees.

The government forecasts a slightly warmer heating season for 2009-2010 than for last year, but slightly higher heating prices.

Two federal agencies forecast conditions that will affect how much heat costs.

The Department of Energy’s Energy Information Administration predicts the retail residential cost of various heating methods, including oil, natural gas and electricity, the three methods primarily used in Rhode Island. The agency predicts prices about 3 percent higher this winter in New England.

The National Oceanic and Atmospheric Administration’s Climate Prediction Center forecasts heating degree-days for the winter. A degree-day measures the cumulative effect of cold temperatures, by measuring how much and how long temperatures are below 65 degrees, the baseline. If a three-day period has an average temperature 10 degrees lower than 65, 30 degree-days accumulate from multiplying 10 degrees by three days. The center predicts about 3 percent fewer degree-days this winter in Rhode Island.

As Rhode Islanders pay about 3 percent more for heat, but use about 3 percent less, their bills should not be much different.

But, as with any forecast, a number of unknown factors could change what ultimately happens. Some of those include: world events that affect the global price of crude oil and weather not behaving as forecast over a six-month period. Even seemingly small factors, such as how sunny or windy it is, can affect how much heat is needed to keep a house warm, even though the outside temperatures might not change.

Rhode Islanders can also affect how much heat they need by taking energy-saving steps, such as increasing insulation, using energy-efficient windows to stop heat loss and turning down thermostats.

A Providence Journal calculation based on NOAA and Energy Department data shows that Rhode Islanders with oil heat can save about $50 total from November through April for every degree they turn their thermostats down. Gas-heat customers can save about $40 for every degree, and electric-heat customers about $35.

Those figures are based on a 2,000-square-foot house with average energy efficiency. Different houses and different habits by the people who live in them can result in different savings.

The Journal calculation used the Rhode Island degree-day forecast from NOAA, a Department of Energy study on how much heating fuel or electricity New Englanders use per degree-day and the department’s forecast of energy prices.

On Monday, the state Office of Energy Resources released its weekly survey of heating oil prices. It found a low price of $2.37 a gallon, a high of $3.09 and an average of $2.74. That average is 8 cents higher than a week ago and about 7 cents lower than the average at the same time last year, $2.809.

The federal Energy Department forecast calls for prices in October and November to be lower than a year ago, but to rise above the year-ago price from December through March.

National Grid customers in Rhode Island currently pay about 15 cents per kilowatt hour for electricity, though the company has asked state regulators to raise that rate by about a penny. The federal forecast uses a New England number of about 17 cents per kilowatt hour.

National Grid’s natural gas rates are not directly translatable to the federal forecast, because it uses a different measurement of how much gas a customer burns.

pparker@projo.com