You should replace or clean your furnace filter about once a month. A clean filter not only maximizes your furnaces efficiency, but it also minimizes your electric bill.
How to replace, or clean the filter:
First you should check the area in front of the furnace. A lot of times this is a breeding area for dust. If it is dusty, clean the area before you remove the filter.
Locate the service panel on the furnace. Usually this is located on the front of the furnace.
Turn off the furnace, and remove the panel. No tools are needed for this
Locate the filter
Gently remove the filter
Check for buildup on the filter. If you are unable to see through it, then it needs to be cleaned or replaced
Many furnaces have reuseable plastic framed filters. If you have one, then simply take the filter outside, and clean it with a water hose. Let it dry outside, and replace it.
* Many furnaces have disposable cardboard framed filters. If you have one of these, write down the size of the filter. Make a trip to your local hardware store, (Lowe’s, Home Depot, or even WalMart) and buy a filter that is the same size as the one you removed. When you are done, replace the filter.