One of the first things that HVAC techs learn is how crucial a properly-functioning air filter is to a healthy HVAC system. HVAC air filters need to be sized properly, need to be the right kind of filter medium and above all, need to be kept clean. We’ll talk about the different types of filters for HVAC that you can work with, the correct way to install an air conditioner filter and why a clean filter is important to proper operation.
Problems caused by dirty HVAC filters
Obviously a dirty HVAC filter will have an impact on indoor air quality; as it becomes saturated with dust and debris, it can’t do its job of filtering contaminants out of the air. More pollen, particulates and dust are naturally going to start making their way through the ducts and into the home with a clogged filter, but that’s just the beginning of the kinds of problems that it can cause:
- Bigger utility bills: When the filter is clogged, the air handler is going to have to work a lot harder to compensate for the impaired air flow. It can actually mean utility bills that are as much as 15 to 20 percent higher than usual.
- Furnace shutdowns: In winter months, that can mean the heat exchanger overheating and shutting off too quickly so the house never reaches a comfortable temperature. If that continues happening, the system’s electronic “limit switch” safeguard can kick in and the system won’t fire up at all. Many customers have paid for a service call to remedy this, when a $10 HVAC filter would have been all it took to fix the situation.
- Short cycling: That same pattern of the system running for short times and shutting down again will happen when in AC mode as well, leading to a house that’s never all the way at a comfortable temperature.
- Frozen evaporator coil: The impeded air flow due to a clogged filter will mean not enough air is moving past the AC’s evaporator coil. The coil is relying on that airflow to evaporate the condensation that forms while the system is running, and lack of airflow can lead to the evaporator icing over.
- Uneven cooling: Poor air flow through the system will result in hotspots and cold spots through the house, with some rooms not being cooled nearly as well as others.
- Premature wear: The extra stress that is brought on by a clogged filter and poor air flow means that everything in the system is having to work harder, and things like the blower motor and start capacitor are at risk of wearing out long before the end of their normal service life.
By some estimates, 15 to 30 percent of HVAC service calls could have been avoided by keeping a clean filter in the system. Just like with a vehicle or any machine or system, an HVAC system will run better and last longer with the right maintenance. Changing the HVAC filter on schedule is the cheapest, easiest and most important part of this maintenance schedule.
Types of HVAC filters
There are several different styles and designs of HVAC filters available. The type of filter you use will depend on the type of system you have and your particular needs, and each has its advantages and drawbacks.
These are the simplest and cheapest filters on the market; their element is spun fiberglass inside a cardboard frame. While they offer little restriction for air flow, they also are not very effective at trapping particulates. Still, if things like pet dander and allergens aren’t a big concern in your household, a spun fiberglass filter can do just fine.
A pleated filter is not unlike an automotive air filter, with tight folds of woven cotton or polyester held in place by screens. A pleated filter is midway in terms of efficiency, registering 6 to 12 on the MERV scale (with 20 being the upper end of the scale), and doing a better job of trapping contaminants. While a pleated filter is more expensive, it doesn’t need to be changed as often as a fiberglass filter.
This is a more high-tech solution to AC filtration. An electrostatic filter charges airborne particles as they travel through the system, where they can be absorbed by the filter like a magnet. Their polyurethane/polypropylene fibers are formulated in such a way that they produce a static charge as air passes through, with separate layers of the filtration medium receiving opposite charges. These filters are washable and reusable, potentially saving money in the long run. The jury is still out on the effectiveness of electrostatic HVAC filters, but most studies indicate that they’re pretty effective with odors, smoke and other fine particulates.
This is an older, proven design where carbon or charcoal is incorporated into the filter medium. Molecules of contaminants actually attach themselves to carbon molecules as they travel through the filter, making them especially good at trapping smoke, odors, fumes from solvents, adhesives, paint, volatile organic compounds and other indoor air pollutants. The disadvantage of carbon filters is that they can actually start releasing the pollutants once they’ve reached their saturation point. Some carbon filters are also less effective at trapping dust, pollen and dander; it can be hard to know when it’s time to replace a carbon HVAC filter since they may not be loaded up with fuzz and debris when the carbon particles have already reached their maximum efficiency.
You might have heard of HEPA filters on vacuum cleaners; they’re a standard filtration system for cleanrooms and healthcare. HEPA stands for High Efficiency Particulate Arresting, and are designed for a MERV rating of 17 to 20, with the ability to trap particles as tiny as 3/10 of a micron in size. Not surprisingly, that level of filtration also means a real restriction in air flow, to the point of reduced efficiency, higher utility bills and premature wear on HVAC components. Your house isn’t an operating theater or cleanroom, but if you’re that concerned about indoor air quality, a standalone air purification system (separate from the HVAC) might be a better solution.
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NuComfort LLC is a wholesale distributor of both commercial and residential HVAC systems. We also stock a full line of accessories and replacement parts. We have a long history of satisfied customers, and are ready to serve you from our three Chicagoland locations in Glendale Heights, Chicago and Crestwood.