Oil-fed furnaces tend to get dirty quickly, which significantly reduces their efficiency. The older the furnace, the more true this is. 
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<li>If you have an oil furnace, get it cleaned and tuned up once a year. This will save you 300 pounds of CO2. 
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If you have a gas furnace, be sure to clean or replace the air filter on the schedule recommended by the manufacturer.
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Whether you have an oil or gas furnace, make sure yours is running as efficiently as possible, by having your service company check it out and run a combustion efficiency test. 