We’re going to go out on a limb and guess that you don’t change your furnace air filter very often. If you did, you probably wouldn’t be reading this blog about how to do it. If that assumption is correct, you should know that it is very important to change your furnace air filter every few months. If you don’t do this, you are actually making it easier for a fairly destructive set of problems to occur. Better to know how to change the air filter, and why you’re doing it.
Why the Air Filter Needs Changing
Every furnace has an air filter in it, which sits in the return duct. All air that flows into the furnace must pass through the air filter first. Like all air filters, this one works by snaring dust and other debris that might otherwise make it into the furnace to cause problems. Also like other air filters, this one does not have any way of disposing of the debris that it collects. If it isn’t changed every few months, it will eventually become so clogged that air can’t flow through it easily. That’s when the problems start.
Lack of air flow during operation traps heat inside the furnace. This causes the internal temperature of the system to rise. As the temperature rises above established safety standards, the limit switch activates and shuts down the system to protect it from overheating. After a set cooling off period, the furnace will reactivate and attempt to finish its heating cycle. Of course, since the root problem has not actually been fixed, the furnace will simply overheat again and shut down again. This cycle of on/of cycling every few minutes is called short cycling.
Short cycling accelerates the wear and tear on the furnace far above what it was designed to handle. Parts will wear down and break more often, and the efficiency of the furnace will drop. Prolonged short cycling will cause so much damage that it will actually shorten the lifespan of the furnace by several years. This is why you need to be very careful to replace your air filter on a regular basis. Fortunately, it’s a pretty easy thing to do.
How to Change the Filter
To save time, we’re going to assume you already have a replacement filter on hand. First, look for the air return duct. This is typically a duct segment that enters the main body of the furnace from the bottom or the side. Right before the air return duct meets the furnace, there should be a visible slot. Pull that slot out (or possibly up) to reveal the old filter. Pull the old filter out. Insert the new filter, making sure to match the arrows on the filter covering with the direction that the air is flowing. One final word of caution: turn off your thermostat before doing this. You don’t want the system turning on while you’re installing a new filter.