What Causes Air in an Oil Furnace?

Issues

• When air gets inside an air furnace, it takes up space that should be filled with oil. This causes the oil pressure in the furnace to drop, which interferes with the furnace’s performance. At night, air inside a furnace or oil take will cool and get moist. Over time, this can lead to moisture in the interior and consequences such as scale and rusting. Rusty debris can get caught inside the furnace’s oil filter, leading to smoky odors blowing into your home every time the heat runs.

Causes

• Air can get into an oil furnace when you fail to keep the tank full. Trying to save money by letting the tank run empty before refilling it or by leaving it empty through the spring and summer opens the door to letting air move throughout the system. Air enters an oil furnace if you inadvertently create an air pocket while changing or cleaning the unit’s oil filter. This usually happens if you don’t fill the cartridge housing with oil before putting it back in place.

Solutions

• Air is easily forced out of an oil furnace by filling it with the proper amount of oil. Start by filling the oil tank to the proper level. Once the tank is full, check the oil filter cartridge and its housing. If you need to clean or change the oil filter, do that and then fill the cartridge housing with oil. Because of the rust and scaling that occur in an air-filled unit, you will probably need to change the filter again within a few weeks, so keep enough oil on hand to fill the housing again soon.

Considerations

• You might save money in the short run on the price of oil, but letting the tank get empty will cost you in maintenance problems in the long term. Keep enough oil in the tank to maintain your furnace at the proper oil pressure. If you worry about creating air pockets while working on the filter cartridge, a professional HVAC technician can handle the job for you.