A Guide to Changing Your HVAC System Air Filter
- Post By: Greg Crumpton
- Date:
- Category: Blog
Air Filters for Dummies
Have you ever wondered when, why, and if to change your air filter(s) at home or in the office? Sometimes your thermostat tells you… how does it know when? Sometimes you happen to think about it when you see those ugly blue filters in the grocery store. And then, you really think about it when the air conditioning stops working, the technician shows up and the culprit is… you guessed it, dirty air filters.
Back to basics:
Air filters are designed to catch fairly large, relatively speaking, particulates out of the air stream. Most filters are great at catching dust, pet hair, etc. The “ugly blue” air filters are really great for catching pigeons, children and other items of that size, and not so good at removing the proper sized particulate from the air stream.
To really help with dust control, pet dander, and pollen we suggest using pleated air filters. They have more surface area, due to the folded pleats designed into them, and they do a much better job than old blue.
Why are air filters really designed into an HVAC system?
Air filters are designed into the total HVAC system for only one reason, and it isn’t to control the dust on the end-table. The main purpose of these filters is to prevent the dust and debris from collecting on the face of the coil (heat exchanger) of the air conditioning portion of the system. The refrigerant (trade name Freon) in the system requires that heat be transferred from the air stream into the refrigerant circuit, it can only do this efficiently when the entire coil surface is clean and available for this exchange. The natural by-product of air conditioning (cooling) is dehumidification, hence when dehumidifying, the evaporator (indoor coil) is wet with condensation. This would really gum-up with dust and grime if the filter was not there to PROTECT the coil surface. That is the entire purpose for the filter, all of the other benefits we enjoy are just icing on the cake.
The BIG question… how often to replace the filter(s):
As I said above, sometimes your thermostat will tell you to do it, but it’s simply guessing. It uses a hypothesis to say to do it based upon hours of operation, not “dirtiness” or pressure drop or anything scientific. This is really a convenience feature that is there to simply serve as a reminder to do it. We suggest changing the air filters in your home and office environment quarterly, four times per year. Most residential systems typically only have one or two filters, many office buildings have a much larger count and therefore will need to be considered in the budgeting process. Your HVAC service contractor can help with the value to add in for that replacement program.
The other thing to consider:
In a commercial office building, there are systems that allow you to induce outside air into the space as the primary cooling source. This is called an air-side economizer, there are water-side economizers as well, but that is for a different day. These will require a little more monitoring of the air filter condition due to the high percentage of ambient air that is being pulled through the filters. The economizers are a great money saving tool, and even though the filter replacement cost will increase with use, your overall power consumption will be reduced so far that there will be a “No Brainer” conversation to be had. Read more on economizer use in our April, 2012 newsletter.
