HVAC professional explaining the importance of filter on central heating system to older man
HVAC professional explaining the importance of filter on central heating system to older man

A common question among homeowners is, “Do I need a filter on my central heating system?” The answer is yes. An air filter is not an optional accessory; it is a critical furnace component with a distinct purpose. Operating your furnace without a filter damages your central heating system and poses several health and safety risks.

You should also regularly replace the air filter with a clean one. Neglecting to change the filter causes furnace issues and shortens its lifespan. Filters vary in size, quality, and type. The filters in your furnace should be appropriate for your HVAC system and air quality needs.

Why is an air filter important?

An air filter has a greater purpose than filtering your home’s air. The air filter’s primary function is to protect the HVAC system’s components from accumulations of dust, dirt, hair, and other debris in your home’s air.

HVAC systems perform better when they are free from airborne contaminants. They yield lower energy bills and have fewer breakdowns. HVAC system lifespan also increases when filters are utilized and regularly replaced.

Better indoor air quality is another perk of your furnace’s air filter. Air filters trap dust, pet hair, and allergens and prevent them from recirculating through the treated air.

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What Happens When I Run My Furnace Without a Filter?

Your furnace can operate without a filter, but it’s not recommended. You can safely run the furnace without a filter for a short time to run out and buy a replacement filter. However, running your furnace without a filter for long periods poses several risks.

A Furnace Without a Filter Creates Poor Air Quality

Operating the furnace without a filter increases allergens and dust in the home. Allergens and dust accumulate daily from dead skin cells, pet hair and dander, and mold growth. These pollutants get sucked into the return air ducts, circulated through the furnace and supply ducts, and distributed into the home’s air through the vents. Poor air quality is especially bad for people with allergies, asthma, and other health issues.

It Increases the Chances of Illness in the Home

Bacteria and viruses recirculate through the home’s air like other pollutants without a filter. According to the EPA, HVAC filters can reduce the prevalence of viruses and other contaminants by trapping them.

No Filter Can Cause System Failure

Furnaces draw in air to be heated. Contaminants enter the HVAC system without a filter and settle on the machinery. The pollutants accumulate and eventually cause malfunctions and system failures.

A Furnace Without a Filter Can Cause a Fire

The internal furnace temperature rises when dust accumulates on the electrical wiring or the motor. Furnaces have sensors to shut the system down when they overheat, but a fire can start if the sensor is defective and fails. Significant dust accumulations are highly flammable.

How often should I change the furnace filter?

A furnace filter is crucial to your HVAC system’s longevity and air quality. Maintaining a clean filter is just as important. Dirty filters cause furnaces to blow cold air, leak water, and not turn on. Clean filters effectively trap contaminants and allow good airflow through the HVAC system.

How often you should change the air filter is determined by the filter’s size and efficiency. Replace 1- to 2-inch filters every 30 to 90 days. Larger filters can be changed less often. Low-efficiency filters should be replaced more often than high-efficiency MERV air filters.

Changing the filter is simple. Each furnace has an opening or slot for the filter where the return air duct meets the furnace to filter incoming air. Most furnaces are upflow systems, and the return duct leads into the side of the furnace near the bottom. The supply duct delivers hot air to the house. If you’re unsure, judge the duct’s temperatures with your hand. The return duct will feel cooler than the supply duct if the furnace has been running.

The filter might be obscured behind a cover or door. Be sure to use the correct filter size, and pay attention to which way the furnace filter goes. Point the arrows on the filter toward the furnace.

furnace air filter time change recommendations

Additional Factors that Affect The Frequency of Changing Furnace Filters

  • Home Occupancy
    The number of people living in a home determines how quickly filters become dirty. More people put more contaminants into the home’s air, requiring frequent filter changes.
  • Number of Pets
    Pets introduce fur and dander into a home’s air and necessitate more frequent filter changes. The filter’s service life is additionally reduced with each household pet.
when to change furnace air filters based on other factors illustration
  • Indoor Air Quality
    Bad indoor air quality from outdoor pollution, dust, dirt, pollen, mold and other pollutants causes filters to fill up more quickly than homes with good indoor air quality.
  • Allergies
    Filters should be changed more often if allergy sufferers live in the home.
  • Usage
    Change the filter according to how often the HVAC system is used. Filters should be changed more often in the winter and summer when the furnace and air conditioner run constantly. Filters can be changed less often in autumn and spring when the HVAC system is used intermittently.
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Even though your furnace will operate without a filter, the filter is a crucial component. A filter’s primary purpose is to protect your HVAC system from contaminants that gum up the machinery, shorten its lifespan, and can potentially cause a fire. Filters are beneficial to your home’s air quality, too. They remove dust, allergens, bacteria, and other pollutants from the air you breathe.

Replacing the filter regularly is essential. Filters become clogged with contaminants over time, reducing efficiency and airflow. Most filters should be changed every 30 to 90 days, but filter size, efficiency, and other factors affect how quickly filters become dirty. Homes with many occupants, pets, bad air quality, and allergy sufferers should change their filters more often. Filters should also be changed more frequently when the HVAC system constantly runs in winter and summer.

Frequently Asked Questions

Which furnace filter should I buy?

Consider the filter’s size, MERV rating, and type when buying a furnace filter. Filter size is measured in length, width, and depth. Check the size printed on the current filter or measure the filter slot with a measuring tape. Round up to the following whole number for the nominal size.

The air filter MERV rating tells how effectively the filter traps small particles. The higher the rating, the more efficient the filter. Consider your current air quality and air quality needs. Please don’t pick the highest rating without verifying that it’s compatible with your HVAC system. Highly efficient filters reduce airflow and can damage your system.

Fiberglass filters are the least expensive and have the lowest MERV ratings. They allow greater airflow and energy efficiency but trap fewer contaminants and require more frequent changes. Pleated filters have moderate to high MERV ratings. They cost slightly more than fiberglass filters but trap more pollutants. HEPA filters have the highest MERV ratings, but most home HVAC systems are not designed for them because they severely restrict airflow. HEPA filters aren’t usually necessary outside healthcare facilities and laboratories where good air filtration is paramount.

Does the furnace filter affect air conditioning?

Dirty furnace filters negatively affect air conditioning systems by straining and possibly overheating the system. Air conditioners with dirty filters consume more energy, increase energy bills, yield poor air quality, cool inadequately, and cause dirty ducts and HVAC system components.

What furnace filter is best for smoke?

Tobacco smoke is a very fine particle and requires a high-quality filter to trap it. MERV 13 air filters are the best for smoke, but they are expensive and incompatible with many HVAC systems. Carbon filters can be a more affordable option.

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