Selecting the Correct Air Filter

As a business owner, you understand the need for routine maintenance to protect the equipment you use every day. One of those valuable investments is your HVAC system. When you match your system with a filter that is the right size according to specs, and it seems to fit just fine, you are all set for another year, right? That’s what a lot of people would assume.

But there are four ways to know you are using the wrong air filter on your HVAC system – and the wrong filter wastes energy, and in turn increases utility bills.

1. You hear a “popping” sound while installing the new filter.

If it takes any real effort for you to remove the old filter – especially if you hear a “popping” sound when you do so – that is a sign the filter was too dense (e.g. too thick). This makes the HVAC system less efficient, which means it costs more money to operate and may lead to expensive repairs.

In addition, a filter that is too small will be sucked into the filter holder – and again you may hear a “popping” sound. In a case like this, you should either install a larger filter holder or add a second holder. Or if you have a pleated cotton filter that appears bowed when you are removing it, that lets you know that it was the wrong size.

Depending on the type of HVAC system, you may not be able to add a filter holder. In some cases, all you can do is slide in the new filter. In such cases, you can monitor the volume of air coming out of his ductwork by removing a grille. If you feel a rush of air after removing the grille, then you have the wrong filter. The air flow should be constant – a rush of air means the filter is too dense.

However, regardless of the exact HVAC system, it cannot be overemphasized that an incorrect air filter size will decrease air flow and increase strain on the air handler. This leads to the following:

  • Higher utility bills
  • Shorter equipment life span
  • More frequent repairs

2. How to “read” your filter and see if it is worth your “salt”.

If you can read the newspaper through your filter, then you know it is not dense enough to capture most dust and dirt. Another good test is to shake some salt on the filter. If the salt goes right through the filter, then is not keeping out dirt and other particles the way it should.

This sometimes occurs when using a cheaply made, woven filter (often these are blue in color). While inexpensive, as the saying goes, you get what you pay for. Pleated filters made of cotton – usually 1 inch thick – are recommended for most standard grilles, as they keep out more contaminants.

Remember that a filter that isn’t dense enough is just as bad as one that is TOO dense (thick)!

  • The coil and ducts get dirty due to the dust and dirt passing through the filter.
  • A dirty coil and fan lead to more energy consumption (and higher power bills).
  • The increased number of particulates and pollen getting through the filter and stirred up by the HVAC system leads to poor IAQ. And poor IAQ can lead to health issues for Rich, his employees, AND his customers!

3. Your air registers are dusty or dirty.

The supply and return vents for your HVAC system are more commonly known as “registers”. Supply registers are the covers for the openings in walls through which conditioned air is blown out into your workspace.

The return vents also have register covers, except they are connected to the return ducts. When your system is running, it sucks the air from the return vents through the ductwork and back to the HVAC system. Return vents are typically larger than supply vents and typically you won’t feel air being blown out of them.

If any of the registers are not clean – supply or return – this leads to poor Indoor Air Quality (IAQ). The most common reason for this problem is a dirty air filter. With clean registers and a clean filter, you can improve IAQ quickly and easily. This also lets your system work more efficiently, using less energy and saving you money.

4. Your workplace is dusty but it takes more than a month for the air filter to look dirty.

Like the previous point, this is an indication that:

  • Your air filter is, in fact, dirty.
  • Your filter is either too small or not dense enough.


In conclusion, indoor air often is dirtier than outdoor air. It’s imperative that business owners like you have the correctly sized air filter. Further, keeping registers clean and replacing your system’s filter at least every three months is recommended for most HVAC systems. Considering how much you spent on your system and the cost of running it, a few filters a year are far less expensive than an inefficient and unhealthy system. Well worth it, don’t you think?