Converting From Oil To Gas Not Always Wise

HOME CLINIC: With the unsettled political climate in the Middle East and the constant upward spiral of oil prices, I'm considering an offer by the local gas utility to convert my oil furnace to a natural gas furnace. This would be by installing a conversion burner. What can you tell me about fuel conversions, and are they a good idea?

- F.A., Seattle

DEAR F.A.: Yours is a concern expressed by many of our readers. Oil prices have risen the last few years, while natural gas prices have actually fallen. Whether this trend will continue in the future is anyone's guess, but both oil and gas are limited resources and the prices of these fuels are likely to continue to increase as supplies begin to dwindle.

Converting an existing oil-heating system to natural gas is usually done by adding a conversion burner to the furnace. It may save you money in fuel costs in the short term, but the conversion itself may not be as inexpensive as it sounds. It also may reduce the overall efficiency of your heating system.

An oil furnace burns hotter than a natural-gas furnace. The heat exchanger of an oil furnace - that portion of the furnace that transfers heat from the combustion chamber to the air that comes out of your heating ducts - is made of a much heavier material in order to withstand the higher temperatures of oil combustion.

When the furnace is converted to natural gas, it takes longer for the cooler-burning gas to bring the heat exchanger up to a temperature where the blower comes on. This results in a delay in getting heat to the house, and a decrease in furnace efficiency. While the heat exchanger is being heated up, much of the heat you're paying for is going up the chimney, not into your house.

Another problem with oil to natural-gas conversion is the temperature of the furnace exhaust. Because gas burns cooler than oil, its exhaust temperature is cooler too. When oil burns, it leaves a fine residue of soot on the flue walls. The cooler exhaust from natural gas contains moisture that may condense on the walls of the flue during cold winter months.

This moisture, when combined with the soot left over from oil combustion, becomes somewhat acidic and can actually attack the mortar holding the flue together. If this happens, the flue may become blocked by fallen mortar and create a dangerous health hazard.

We suggest before converting fuel sources, you consider doing some basic weatherization. Install weatherstripping and caulking around windows and doors, insulate ceilings and floors, and install storm windows or double-pane windows that will reduce your home's heating load, regardless of the heating fuel used. Making the building "shell" more energy efficient is often wiser economically in the long term than changing fuel sources.

If you do elect to convert to natural gas, be sure to have your flue inspected and swept by a professional. To further reduce your risk of future flue blockages, you may want to have a flue liner installed. This will add about $450 to the cost of your conversion, but will virtually eliminate any problem with flue blockage caused by fallen mortar.

Before converting fuels, you may want to investigate a flame retention burner for your oil furnace. These burners may increase the efficiency of your furnace by as much as 35 percent, and can be installed for just a little more than a flue liner.

For additional information on way to increase the efficiency of your oil furnace, contact the Oil Heat Institute at 548-1500, or call the Energy Hotline at 1-800-962-9731 for a free information packed titled "Furnace Tune-Up Tips."

Home Clinic answers questions about home maintenance, repair and energy conservation. It is prepared by the Energy Extension Service, a division of the Washington State Energy Office. It appears Sundays in the Home/Real Estate section of The Times.