Filters

Let’s be honest, nobody really likes to talk about their furnace filters. Heck, many of us even forget our indoor units even have them. But the reality is, they play an extremely important part of our HVAC system. So here we are, talking about them.

Just taking a walk down the filter isle at our local hardware store, we see that there are dozens of options when it comes to filters. Different sizes, different thicknesses, different material and so on. So why so many options, and why doesn’t a furnace come with one already?

The easy answer as to why we have so many choices is simple, because people will buy them. If they didn’t sell, they wouldn’t make them. But the real answer is, each piece of equipment has a different filter need. But let’s start with a very important fact about filters from the equipment’s point of view. The filter is only there to keep dirt and dust out of the blowers, coils, heat exchangers and other components. Period, end of story. That’s right, the filters #1 priority is to keep the inside of your unit clean, not filter out allergens and odors and whatever else they like to advertise now. And keeping the inside of your unit clean can save you a lot of money and energy over the life of your equipment (we’ll get to that later).

So let’s take a look at what the most common choices are as we walk down the isle of the big box store.

Fiberglass

If you get down on your hands and knees and look real hard, you will probably find a three pack fiberglass filters, and they probably only cost a few dollars for all three. Standing there holding them in your hand you’re thinking to yourself, “Do these really even catch any dirt”? I can assure you, they do in fact catch and stop the dirt and grime before it makes its way inside your system. But as you look at it, you realize it won’t catch the small particles; but remember, job one is protect the equipment, and that filter will do just that. So why would we want to use these if they only catch the big stuff (relatively speaking)? Well for starters, their inexpensive, and they work, and second, they don’t restrict airflow to the equipment (we’ll get to that later as well). If we have a piece of equipment that is on undersized ductwork (that a whole different article of its self), we really need to be careful with our filter choice as the wrong filter can put our airflow in danger. On systems like this, we like to keep the filter simple, and free flowing as possible, so we like the fiberglass filter. When using these, we like to make sure they are changed every 30 days.

Pleated

One row up from the fiberglass were going to find the pleated filters. Pleated filters are the ones that zig zag back and forth all the way across the filter. The zigging and zagging are to increase the area of the filter material. Pleated filters branch off in many different directions starting with you basic pleat all the way up to you “HEPA” filters. We rank pleated filters with a MERV rating that tells us how efficient the filter is at catching the small stuff. Basically, the higher the MERV rating, the smaller the particle it will catch. But keep in mind, in order to catch smaller particles, the air has to move through smaller holes. And it’s a whole lot harder to fit through a small hole of a pleated filter vs the large hole of the fiberglass filter. These filters do a great job of keeping our equipment clean, but these are the filters we need to keep an eye on regarding our system performance. Depending on the MERV rating, we like to see these filters changed between 1 and 3 months.

Media Filters

An expansion on pleated filters is media air cleaners. These are big bulky filters that cost a lot more than the rest, but there is a reason for that. There are several variations of these filters, from pleated to bags but the idea is the same behind all of them, increase the surface area of the filter. Media air cleaners are our favorite and come standard with our installs. They typically have the lowest pressure drop, last longer between changing, and are a little more forgiving if you are 30 days past due for a filter change. Media cleaners come in a wide variety of merv ratings and sizes. As a general rule of thumb, we like to stick to merv 11 or 13 filter filters, as we feel those provide the best filtration for the system, while allowing adequate airflow. These filters can last anywhere from 3-12 months depending on use. 

Earlier we mentioned keeping the inside of your unit clean make a unit last longer, so let’s briefly expand on that. If we allow dirt and dust to accumulate on the inside surfaces of our units, it start to lower efficiency and the life of the unit. First dust starts to build up on the blower wheel, which means were moving less are. That can mean were not moving enough heat from the heat exchanger or enough cooling from the a/c coil. Less air in either case, is bad for the equipment, causing overheating and iced up coils. Once the blower can no longer hold the excess dirt, it then makes it way to the heat exchanger, and a/c coil. Now were compounding the issues mentioned before. Excessive overheating and coil freeze up can potentially lead to failed heat exchangers and damaged a/c compressors. What we’re trying to say is, changing you filter is a pretty big deal.

We also brought up filters and restricting air to equipment. This is where we’re going to talk about the ever popular HEPA or Allergan filters. These filters are your systems worst nightmare. Remember how we just talked about dust and dirt build up and its effects. These style filters have the exact same effect on your system as dirt build up on you a/c coil. Because they are designed to catch just about everything that flows through them, they even catch and stop the air from flowing through them. Many in the industry call these filters “furnace killers”.  Airflow is one of the main factors in your systems performance, and that is why we must pick filters that don’t hinder the performance of our airflow.

To wrap up this longer than should be discussion on filters, let’s do a quick recap.

• Fiberglass allows the most airflow, does a good enough job at keeping your equipment clean, but need changed the most.

• Pleated come in a wide variety of efficiency’s, offer better air cleaning, cost a little more, and last a little longer.

• Media cleaners (standard with all JBH installs) last the longest, allow better airflow than basic 1” pleated, but cost the most (are also out favorite).

• Allergan filters are the devil and should never be used.

And remember to change your filter, unless of course you miss me and want you equipment to break so I have to come fix it. If that is the case, no need to change the filter, better yet, put an allergen filter in. Bottom line, change you filter to keep breakdowns to a minimum, and efficiency to a maximum.