Can A Dirty Air Filter Cause A High Electric Bill?


A dirty air filter not only increases your Texas electricity bill but can also damage your HVAC system and affect your family's health. Which is the right kind for what you need in your home? We'll filter it out for you.

Energy Savings From Changing An Air Filter?

You've just received your Texas light company bill and for the third straight month, it's running higher than normal. So, you're probably wondering if you've been doing different this month. Ask yourself when was the last time you changed the air filter in your home's heating, ventilation air-conditioning (HVAC) system? For some folks, this sounds crazy. After all, how can a dirty air filter run up your Texas electric bill?

The next time your home's HVAC system is running, put your hand in front of an air vent. If you can't feel very much air coming out, then that's probably the problem. Luckily, it's really easy to fix. Just replace the air filter with a new one that's the same type recommended by your system's manufacturer.

But if you don't know which filter is the right kind for your system or why it's important to use the right one or why you should even bother having one in your system, then you really should learn the dirty truths about your home's air quality. Not only will you learn how it how it affects your home's electricity usage, but also how to avoid damaging your HVAC, and why it's important to your family's health.

High Electric Bill From Air Conditioner Air Filter

With about 87 percent of U.S. households equipped with air conditioning, it's safe to say the most U.S. homes have centralized forced air HVAC systems. For many homes, the high use periods come in the winter for heating and summer months for cooling. An average HVAC system for the average sized U.S. home (2,000 sq. feet) consumes 41.5% of your annual gas/electric bill. For Texas, usage is typically higher during the summer from air conditioning. With summer heat already here, having your air conditioner ready to work efficiently is pretty important if you want to save money. So, how do you know if a dirty air filter is causing you problems?

When your HVAC system is running, the blower fan pulls air through the air filter. The filter traps dust, hair, and all kinds of other particles that float in the air. HVAC systems are set up this way to prevent dust and dirt from building up and damaging the HVAC system (blower, fan, heat exchange fins, cooling coils). Over time, the collected dust and dirt builds up, allowing less air through the filter. The more dust and dirt the filter traps, the more it clogs up until hardly any air passes through the filter and flows through the HVAC system at all.

How Bad Can It Get With a Dirty Air Filter?

When dirt chokes off the airflow, the system will run longer in order to move enough heated or cooled air throughout the home to meet the thermostat setting. The longer your HVAC system runs, the more energy it uses. The more energy it uses, the higher your electric bill.

So, the longer the problem goes unnoticed, the more money you'll pay for your home's electricity. For some folks with tiered rate energy plans in Texas, this unnecessary additional load can be painfully expensive.

Dirty Air Filters and Blower Troubles

When a blower fan is running against little or no airflow, it creates a vacuum or “pressure drop”. In the vacuum, the fan blades don't have any air to move and there's less air resistance (or friction) for the fan motor to work against. The motor spins much, much faster because the only resistance it has comes from its own bearings. You've heard this happen when something clogs a vacuum cleaner, the motor's pitch gets higher. This is same thing. And like your vacuum cleaner, your HVAC system is trying to tell you something is wrong.

Now, a motor running faster against little resistance might not seem a bad thing. Technically, it's not ??" as long as you notice the problem and change out the filter. But if you don't pay attention or just ignore the problem, then at some point those blower motor bearings will begin heating up. That happens partly because there's no airflow to cool them. If no one has oiled the bearings in a while, they are going to get hotter a lot faster every time the HVAC system runs. You'll know there's something wrong because it will screech and whine a lot. This is a warning that you need to do something soon or the motor will overheat , seize up and stop the blower dead.

At that point, you're looking at a very expensive repair bill. And, oh yes. It can get worse.

Why Change Air Filter In Your Home

Having clean air filters in your HVAC system affects your health. The air in your home is not just full of fine particles of pulverized soil, it also contains allergens, in-door pollutants, and all this nasty stuff:

  • Dead skin flakes and hair (a fraction of which are yours),
  • Pet dander (their dried skin flakes) and pet hair
  • Insect body parts
  • Lint
  • Mites (that live on insect body parts, dander, hair, and lint)
  • Mold and mildew spores (common allergens)
  • Pollens (another common allergen)
  • Bacteria (some times living in the mites)
  • Viruses, particularly on water droplets
  • Volatile Organic Compounds (VOCs)

VOCs are chemical compounds such as benzene, ethylene glycol, formaldehyde, methylene chloride, tetrachloroethylene, toluene, xylene, and acetone (nail polish remover). Commonplace things like cleaners, thinners and solvents, paint, flooring, and even some furniture release these chemicals into the air. Plus, if someone smokes in the home, their smoke contains dangerous concentrations of tobacco tar.

The good news is that most medium level HVAC air filters can remove most of the things on this list. To keep them out of your home's air, all you have to do is remember to replace the air filter.

Air Filter Efficiency

HVAC air filters do a great job at removing all sorts of nasty stuff from the air in your home. However, the trick for homeowners is to learn which is the best one to use for your HVAC system. Unfortunately, though manufacturers design residential HVAC systems to use a variety of air filters, home owners will need to sort through an often confusing assortment of filters to find the right one.

Air filters are rated by MERV rating (Minimum Efficiency Reporting Value). The type of filter media used in a higher MERV air filter makes a big difference. Higher rated MERV filters are designed to remove smaller particles by using smaller the pores in the filter. The MERV rating system follows “ particulate matter” (PM) sizes, starting with big particles at 10 microns ( or 0.000393701 inches) in diameter and going down to .3 microns which are used in hospitals to trap bacteria.

The Right Air Filter For Your Home

A filter's ability varies depending on what the filter is designed for. Different types of filters can be as thin as 3/4? while other higher-rated filters can be up to 5 inches thick. Consequently, HVAC systems only work effectively with only certain kinds of air filters. There are also filter systems that are electrostatic mesh or box-construction or cartridges. However, HVAC systems in most residential homes use two basic types of air filters.

First, there's the spun fiberglass filters that use layers of fiberglass fibers laid over each other to reach a desired thickness or density, usually between ¾ to 1 inch. A cardboard or paper frame holds a metal mesh or grating in the center supporting the filter material. These are the cheapest, most basic air filter and are usually disposable. They trap large dust and dirt particles, textile fibers, insect parts, dust mites, and pollen.

Spun fiberglass filters rate from 1-5 MERV. Their main job is to protect the HVAC system from dust and dirt particles that coat blower motor bearings (increasing friction that causes wear) or that smother cooling coils and reduce air conditioning efficiency. If you don't keep an air filter in your HVAC system, then it's probably not very energy efficient and it's driving your Houston energy bill higher. It's also likely that your system will need some expensive repairs sooner than later.

Pleated Air Filters Capture More Dust

The second type of filter relies on folds or pleats to increase the surface area and trap more particles. The actual filtering media can be quite thin but if there's more space for the air to come in contact with the filtering media, there's greater chances for airborne particles to become trapped with filter material.

Pleated filters come in two types.

  • Disposable pleated filters run between 1 to 2 inches thick with 10 to 16 pleats per foot. These air filters rate roughly from 5 to 8 MERV and come in a cardboard frame. These do an adequate job of filtering out basic home contaminants like dust, mold, and large spray droplets.
  • Much deeper pleated residential filters that fit into (or come with) special housings run from 4 to 5 inches thick and are able to catch even more particulates by virtue of their larger surface area. Rated 10 to 12 MERV, they also catch finer particulates as small as 1 micron. They can trap nasty things like car exhaust, VOC fumes, and larger bacteria.

At the very top end of 13 to 20 MERV are High-Efficiency Particulate Arrestance filters (HEPA). Capable of filtering out very fine particles of 0.3 micron or less, HEPA filters out all bacteria, tobacco smoke, and very fine dust. Filters at this level performance are technically difficult and expensive to incorporate into a regular home system. For that reason, it's very difficult to find a HEPA filter for standard HVAC systems at the local home center.

How Often To Change HVAC Filter

How frequently you need to change a HVAC filter depends on what your system can use and your home's environment. For filters 1 inch or less in thickness, it's best for homeowners to replace them generally every three months. However, if you have pets or someone in the home smokes or has allergies, then the filter should be replaced monthly. For pleated filters measuring 1-2 inches thick, homeowners should also be replace these every 3 months, though some can last as long as 6 months. Lastly, because the higher MERV rated 4-5 inch filters have large surface areas, a typical home-environment would only need to replace them once a year.

Do High MERV Air Filters Affect Energy Efficiency?

Not if they are used in a system designed to handle them. However, if someone installs a high MERV filter box in a system that's best suited for a 1 inch filter pad, then in time, it will reduce energy efficiency. That's because all air filters trap particulates and eventually clog up. How fast dust and dirt close off air flow is really where the impact on energy efficiency lies. For example, using 13 MERV filter in a system that's designed to use a MERV 8 might work fine but for only a short time. That's because the combination of a finer filter and clogging dirt will quickly reduce a blower motor's ability to move enough air through the system to meet demand. Additionally, there are all sorts of unintended consequences that could require extensive and expensive repairs. For example, during the summer when the air conditioner is running, a restricted air flow could cause the evaporator coil (part of the indoor half of your AC system) to freeze over. That could cause expensive damage to your HVAC system.

Always Use the Right HVAC Air Filter

This is why it's so important for homeowners to follow the manufacturer's specifications and use the kind of air filter the system is designed to use. However, if you feel your home needs better air filtration, then buy a separate air filtering unit for the room you spend the most time in. While that might sound like an additional expense, consider that this way you avoid adding unnecessary wear and tear to your home's HVAC system. And, because a separate unit can remove finer particulate matter from the air, your HVAC will be more energy efficient because the air filter will actually last longer. You'll wind up saving money on your Texas electricity usage.

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