By | December 25, 2023

Mastering a comfortable and healthy environment is essential for any home. A crucial aspect of achieving this is ensuring the proper functioning of your HVAC system, particularly the furnace. A traditional forced air furnace works by drawing in air through return ducts, warms it using a heat exchange then uses a blower fan to force the heated air through ducts into different rooms throughout your home. Central to the efficient operation of a furnace is the regular replacement of its filters. In this comprehensive guide, we will walk you through the step-by-step process of how to install and replace furnace filters, empowering you to optimize your home’s comfort and air quality effortlessly.

How to Install and Replace Furnace Filters

Installing furnace filters wrongly or not replacing them when they are dirty is one of the things that will slowly kill your furnace system, or worse still, it will lead to inefficiency and high utility bills.The primary purpose of the filter is to protect the blower fan from the debris in the air brought in by the return ducts while cleaning it before it is returned to the rooms.

However, some high rated filters are made for cleaning the air, these are used mainly by people with allergies and in hospitals. There many types of filters on the market which may confuse most people and end up picking the wrong choice for their homes. In this article, we will try to help you decide which type you need, explain how to install, when and how to replace it.

How to install furnace filters?

Installing furnace filters is an easy job. However, there are many ways you can go wrong. Like inserting the filter backward which will block the airflow instead of filtering it. This will overwork the furnace and shorten its lifespan. Many people will also try to fit a wrong size filter which will not be of any help. Here is a step by step guide to help you through installing for the first time.

How to install furnace filters?

1. Locate the furnace filters: This may sound very basic but there are a lot of homeowners who don’t know where the furnace is, or that it should be regularly inspected and maintained. Fortunately, this is not a heavy task. You can follow the visible ducts and pipes and they will lead you to the furnace. Mostly, the furnace is centrally located in your home. After finding the furnace you should locate the filter slot. This will be a long and thin slot with a removable cover. Although it will differ from unit to unit. If you cannot find it, you should look for any visible vents around the furnace.

2. Identify the type and the measurements of the filter: You should not leave room for mistakes when determining the size of the filter that your furnace requires, unless you have a lot of time to go back and forth to the store. Mostly, the make and model of your furnace may not be very useful in determining the size of the required filter. The size is usually indicated on the filter, if that is not the case or there is no filter to replace, you can use a tape measure. However, it is normal for the manufacturer to state a size that is less by a half inch, so you may have to round off the measurements to the nearest full inch.

3. Buy the right type: As I initially stated, there are a lot of filters on the market right now, this only makes it hard to make a decision. Apart from the dimensions, you should also make sure the filter is of the right density. There a lot of filter models you can choose from.

  • Flat disposable filters – They are made of fiberglass, they are very cheap and only protect your system from large particles only.
  • Pleated filters – these are made from cotton paper or polyester sheets. These are made to trap smaller particles.
  • HEPA (High-Efficiency Particulate Air) – They are designed to filter most of the particles in the air flowing into the furnace. They are the appropriate filters that people with severe allergies should install. These filters are thick and this may make your system to work harder.

You should also check the MERV (Minimum Efficiency Reporting Value) of the filter. This is a scale that runs from 1 (lowest quality) -16 (highest quality) with some going up to 20. However, the higher the MERV does not automatically translate to be the best for you.
The higher the rating means you will also have to dig deeper into your pockets. Make sure you pay for what you need. MERV ratings of 7 – 12 are the most appropriate for residential use as your system may not be designed to handle higher rated filters, those are mostly for hospitals and industrial use. With MERV 11 filters, which are the most recommended, have an average particle size efficiency of up to 80% and they trap up to 79% of 1.0 – 3.0 microns size particles.

4. Turn the furnace power off: This is necessary to protect you and the system. Ensure that the thermostat is turned off to prevent the system from turning on while you are changing the filter. This will ensure that debris and loose fittings are not sucked up into the ducts causing more problems. Also, some furnaces may have loose wiring near the filter that may shock you. Most systems also have a switch that may come in handy, if your furnace does not have a switch to turn it off, ensure you disconnect it from the power for maximum safety.

5. Install the filter: This is the easiest step, open up the slot, ensure that the ducts are clean. Remove the new filter from its packaging, ensure that the arrow on the filter points to the direction of the furnace. Where this is not applicable, ensure that the denser side faces the furnace. The outer side is designed to trap large particles in the air while the denser side is designed to trap small particles. If it is installed the opposite way, it will become clogged faster, and it may force the system to work extra hard due to less air flow.

6. Turn the system on and ensure it is working: If it is not working correctly or it cannot start at all, ensure you call a technician.

How to replace furnace filters?

How to Install and Replace Furnace Filters

For maximum efficiency, it is recommendable to replace filters every three months. However, there are a lot of factors that may make you change your filters more often. Furnaces used in large homes move more air and therefore they also clog much faster than smaller homes. If you have pets, you may also need to replace them more often. Here are the steps you take when replacing filter furnaces.



  1. Ensure you get the right replacement: The replacement filter should also be the right size and density. You can do this by taking note of the previous filters size and other details. If there was no previous filter you will have to measure the opening yourself. This should not be hard to do.
  2. Turn the power off: You should always do maintenance work on your furnace with the power off. This is to keep you and the system safe. Accidents may occur if the system comes back on with the filter off causing more expensive problems.
  3. Remove the old filter: Open up the filter slot and pull out the old filter. You should be careful as it most likely will be holding a lot of dust and debris. You should be careful not to shake it up as it will shed a lot of dust. A trash bag will come in handy. Note the direction that the existing filter and you can mark it on the furnaces outer surface
  4. Position the new filter: Ensure that the slot and the ducts are clean, then insert the new filter facing the proper direction. Make sure that it fits properly and there are no gaps left on the sides. If there are, remove it and put in the old one temporarily, return it to the store and buy a new one.
  5. Clean up: Close the slot and clean up any dust or debris that may have fallen off the older filter. You can now turn the system back on. It should run as it did before if not better. If there are strange smells or it does not start, turn it off and call a technician.


Furnace filters may help you reduce allergy attacks and significantly improve quality of air around your home. They can also help you further by lowering your energy usage if chosen and installed correctly. Replacing and installing filters may be an easy job to some but maybe also confusing to some, this article solves most of the problems you may encounter. If anything is not clear you should always consult your technician to avoid creating a bigger problem.

Pro tips:

  • You can always buy the filters by the case, this will save you money and the monthly trips to the store. However, you must ensure they are the right size.
  • You don’t have to stress about the size of your filter as it’s pre-printed on the unit. You should run your system with a smaller size filter as it will allow dust and debris to pass through.
  • Always switch off the power before opening the furnace.

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