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Every homeowner must stay on top of home maintenance duties. Yes, it may be quite overwhelming, but once it is already part of the household routine, it becomes easier and it will pay off. One of the burdensome yet important home maintenance chores is furnace filter replacement. It is something that may seem difficult and even frightening at first since furnaces can be hot and it exhausts gasses, but in reality, it is something that any ordinary homeowner can manage to do.

This article gives the lowdown on how to change furnace filters, where to buy filters the benefits of routinely replacing them, what happens when a homeowner fails to replace them, and what to do in case of trouble. Alternatively here is what to check first if your heating system isn’t working and an indepth guide to it.

If after going through this guide, one is still not comfortable about changing the furnace filter, then know that we at Reliable Standard Heating Company will be more than happy to help you out with changing your filters for you. So why are furnace filters important? 

What is the proper Air Filter Direction for Air flow?

Filters will typically come with an airflow direction. You can see this on the side of the filter, typically there will be an arrow pointing the direction that the airflow needs to go. You want to air flow arrow to be point in the direction that the furnace is pushing air. For upflow configurations the is typically pointed upwards towards the furnace. A good rule of thumb is to look at where your return/supply line is (Where air is being sucked in) and follow that for the direction that the air flow is suppose to be going.

Understanding why furnace air filters must be replaced regularly

Improving indoor air quality

Clean filters help improve indoor air quality inside the home. Imagine, the furnace pulls out air through these filters and if these are too filthy with dust, allergens, and pollen then the air passing through it will have these microcontaminants as well.

Families with allergies and other sensitivities would need to be more mindful about furnace filter care. When someone has allergic rhinitis, bronchial asthma, skin allergies, or other sensitivities tend to get triggered with pollen, molds, dust, and dander. Regular replacement is key to ensuring that indoor air quality remains healthy.

The furnace becomes more energy efficient

Routine replacement of furnace filters also helps in making the furnace more energy efficient. This is regardless of the furnace’s power source. When filters are clogged, the furnace compensates for its added effort by pulling in more electricity or natural gas to keep its mechanism working. This, in turn, will increase the household’s energy consumption and drive up utility bills. Routinely changing the filters would help any household save up to 15% of its utility bills. 

Regular filter replacements extend the HVAC lifespan

Regularly replacing furnace filters extend the lifespan of a home heating system. Since the furnace does not need to exert additional effort to push and pull air through the filters, it tends to work optimally. When the furnace works in top-notch condition, its mechanical parts do not wear out needlessly, consequently extending the lifespan of the furnace.

When to change air filters

Filters need to get replaced routinely. Here is an easy-to-follow guide:

  • Every 25 to 45 Days – For homes with a family member who has allergies or who owns more than one pet.
  • Every 60 days – For homes with one pet.
  • Every 3 months – For ordinary households in suburban areas who do not have pets at home.
  • Every 6-12 months – For vacation homes that are hardly used, or for a person living alone.

What type of furnace or HVAC AC system needs regular filter replacement?

Homeowners must stay on top of home maintenance of HVAC systems that produce both hot and cold air. Below are two types of systems:

Ductless systems. Ductless systems like the mini split, have two components: the indoor unit which is usually mounted on the wall, and the outdoor unit which is installed outside the house. These two systems are connected through a refrigerant line that runs through a hole in the wall where the indoor unit is mounted.

Forced Air Systems & Central Air Conditioning. These are the air conditioning systems that utilize ducts to deliver hot or cold air through the house. From the ducts, the conditioned air is delivered through the various vents installed around the house.

Replacing HVAC Filters: An easy-to-follow guide


Below is a fuss-free guide on replacing filters for forced air duct systems. The guide is so easy to follow that it will provide information on where to buy the right filter replacement, how to locate the filter within the system, and how to remove the existing filter and swap it in with the new one.

Where to buy a furnace air filter

Physical Stores

Most big box home improvement stores like Lowe’s and Home Depot sell furnace filters. Armed with the correct filter size (more on this below), one could easily purchase one or several filters for easy routine replacement.

However, if the furnace filter size is not commonly available in stores, it may be best to get in touch with a furnace filter dealer or manufacturer, order through phone or online, and have it delivered.

Automated filter subscription

Remembering to buy and replace furnace filters can be a hassle for some homeowners. Fortunately, filter dealers and manufacturers have managed to have a workaround for this by offering a filter subscription service. With this option, air filters are delivered to one’s doorstep depending on the chosen frequency of the homeowner. This is the most convenient option given the fast-paced lifestyle of most households. 

How to buy the correct filter

The first hurdle in replacing a furnace filter is buying the correct filter size. Filters are usually available in home improvement stores like home depot. Usually, the filter’s actual size is imprinted on its edge, the boldfaced numerals are the nominal size so take a picture of this particular set of numbers as this is the reference size needed in the store. Just show it to a store clerk. The nominal size is a bit bigger than the actual size. For instance, filters that have a nominal size of 16x20x1 have an actual air filter size of 15.75×19.75×0.75.

It is best to measure the air ducts as well to ensure that the measurement is correct. Measure the height of the air duct, the depth of the return air duct, and then the width of the area where the filter would be inserted.

Deciding on the MERV rating of the filters

The MERV or Minimum Efficiency Reporting Value rating is a measurement of the filtering efficiency of various air filters. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers came up with these ratings to guide homeowners on the specifications of filters that they will buy for their families.   

MERV ratings are between 2-20 and the higher the number, the lesser particles, and contaminants could go through it. And while having a filter with a high MERV rating may seem ideal, homeowners should keep in mind that higher ratings also come with restricted airflow that could burden the HVAC system and affect energy efficiency. A careful balance is needed when deciding on the MERV rating levels.

If the homeowner could not find the MERV rating in his existing filter then most likely it means that he has the filter with the lowest MERV rating of 2. This means that pollen, dust, and lint can get trapped in the filter, which represents 20% of airborne particles.

A MERV 8 rating on the other hand could trap 70% of airborne contaminants. Up a higher notch is the MERV 11 which can trap up to 85% of allergens and smoke – which are crucial for families with members who are sensitive to allergy triggers.

A very high MERV Rating, which is MERV 16 meanwhile filters about 95% of airborne particles that could cause illnesses, and allergy attacks, among others. Some of the contaminants that a MERV 16 filter could weed out include viruses, smoke, smog, pet dander, bacterium, dust, dust mites, lint, and pollen. 

The Location Of Where To Find The HVAC Furnace AC Filter

After purchasing the correct-sized and preferred furnace filter, the next step is to finally install the HVAC filter. Where to install it, in particular, is the most common question, especially among first-time homeowners.

The exact location of the air filter depends on the configuration of the HVAC system. Most forced air HVAC Systems have two components: the condenser and the inside unit. For this type of configuration, the filters are usually in the middle of the outdoor and indoor units which is usually within the HVAC unit itself or the air ducts, again depending on the configuration.

Upflow configuration

Air ducts with an up-flow configuration are usually used for multi-level homes, where the main unit is situated on the lowest level of the property, and the air is forced towards the upper floors.

There are three common areas where the furnace filters might be found are the following:

  • The return duct outside the air handler or furnace is installed on the lowermost level of the house.
  • The filter is installed in the return grill found in any of the walls or ceiling.
  • The filter could be inside the furnace or the HVAC unit itself. Should this be the situation, then the homeowner should dismantle the access panel to reach the air filter.

Horizontal Configuration

Conditioned air is blown from side to side, as the furnace is also installed on the side of the house. It pulls air from one side and blows processed air towards the other side.

  • Inside the furnace or the air handler itself. When this happens, just remove the panel so that the existing filter can be pulled out and replaced.
  • The filter is found on the return duct just in the outer part of the furnace system.
  • The filter is within the return grill positioned on any of the walls or ceiling.

Downflow configuration

For homes that have air ducts with a downflow configuration, the air is blown downwards and there are also three likely filter locations. The main unit is usually found on either the middle floor of the house or could even possibly be in the attic.

Here are the potential areas where the homeowner can find the filter:

  • Inside the furnace itself. Should this be the case, the homeowner should remove the access panel to reach the air filter
  • The return duct is outside the air handler or the furnace.
  • At the return grill, in any of the walls or ceiling.

How To Replace Your Furnace Air Filter

If you want to know more about how to change indoor air filters check out this other guide that we have.

  1. Use a face mask and pair of protective gloves whenever changing furnace filters.
  2. Turn off the power from both the unit and the specific circuit in the breaker panel.
  3. Get the old filter out of the furnace. For ductless units, it is usually found under the front panel of the blower unit.
  4. Throw away the disposable filter with care as it may have contaminants. Do not shake or unnecessarily move them so that the dust will not get scattered into the air and the ground. Never store used filters at home, bag them, and trash them outside the house. If the filter happens to be washable, kindly wash and dry according to the manufacturer’s instructions. Usually, it only needs plain water and detergent, and the sink nozzle to clean. Air dry thoroughly.
  5. Insert the washed or the new filter. Insert the filter towards the direction of the arrow. Usually, the direction is towards the blower.
  6. Use silver tape or a magnetic cover to properly seal the opening and prevent air leaks surrounding the filter. Never use duct tape for this purpose. For ductless units, just cover the blower unit correctly.

Find out if an HVAC Service contract is worth it for your home.

Pros and Cons of using washable air filters

Washable filters are usually utilized in ductless heating and air conditioning systems. The advantages of having washable filters are that they would save time as it does not require going to the store or buying online to purchase, and it is eco-friendly. The disadvantage is that washing takes a bit of effort, and more often than not they require pressure washing to fully clean. Also, unlike disposable filters that only need to get replaced every three months, washable filters need to be washed monthly. We only recommend disposable filters. We do not recommend washable filters.

If replacing the furnace filters is still challenging

If it still seems difficult to change the furnace filters, please do know that you can always call us up at Reliable Standard Heating, Air, & Solar to help you. We will be more than happy to keep your furnace or HVAC system well-maintained, not just through filter replacement but thorough inspection and tune-ups. Call us today! 

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