Your Heil furnace heats the air in your home by circulating air through the return air ductwork, through the furnace and then back into your home via the supply air duct. Since air flowing to your furnace from your home may be laden with dust or dander, an air filter must be installed to filter the air before it enters the furnace. Failure to filter the air will result in dust and debris building up on the furnace components, which can lead to failure. To replace a filter on your Heil furnace, you must find out what size your furnace uses.
Locate the filter rack on your Heil furnace. It will either be located on the side of your furnace or on the bottom of your furnace. Its location depends on where your return air duct enters your furnace.
Turn off the power to your furnace by turning the light switch off that is located on the side of your furnace. You do not want the furnace to start up when the filter is removed.
Pull out the filter end cap from the filter rack. Slide the filter out from the filter rack.
Measure the length and width of the filter to get the correct replacement size. If no filter exists, measure the length and width of the inside of the filter housing to get the filter size.
Purchase the correct filter and install it into your Heil furnace. Push the end cap back into place and turn the power back on to your furnace.