HVAC Maintenance: When Should You Replace Your HVAC Filter?

Like any other appliance, your HVAC system has parts and components that need to be maintained or replaced to extend its shelf life. One recurring job for HVAC owners is to replace the filters after a particular period. A standard one-inch fibreglass filter usually requires owners to replace it once every 30 days. However, you shouldn’t always follow the 30-day guide attached to your HVAC system’s manuals, depending on a few factors.

“Why shouldn’t I follow the instructions?”

Many people and organizations usually follow the 30-day replacement guideline. In reality, you won’t necessarily have any issues if you follow this guideline. However, you may end up wasting too much money and resources if you choose to follow this rule strictly.

Like other appliances, such as refrigerators, your HVAC system will only overwork itself in specific seasons. In fall and spring, your filter won’t gather as much dirt and grime if you’re not using your system frequently. Also, if your house is kept clean regularly with low duct leakage and the presence of dust, then you can stay with the same filter for longer than the prescribed 30-day limit.

“What product l should I buy to replace my HVAC filter?”

Replacing your HVAC filters is far from being a cheap obligation. Your expenses will start to increase, especially if you’re buying high-MERV filters for optimum performance and ventilation. MERV filters are expensive and can burn a hole through your wallet, but it’s the price you pay for the level of indoor air quality that it provides.

Nonetheless, high-MERV filters are costly because they have a larger surface area with pleated filters, which allows them to capture the same level of dirt that a one-inch screen would have without putting a drop in your air pressure performance. To know when to replace your filter, you should be familiar with checking your HVAC’s pressure readings.

“So, when should I change my HVAC filter?”

An excellent way to give you an accurate signal to change filters is by checking the quality of your total system pressure. However, if you wait for your HVAC system’s pressure to drop for the filter to double, you need to ensure that your duct systems don’t have excessive resistance to natural airflow.

If you install a brand new MERV-13 filter and the pressure reading is at 0.25 i.w.c., you should only let it load until the pressure is below 0.5 i.w.c. It will signify that its pressure drop is equal to what’s allowed for its total external static pressure. That gives you a sign that the filter has used up all the pressure it can handle through the drops from the whole duct system.

You need to assess if your duct system and filter design are functioning correctly for this to work. If they’re not fit for your current setup, you should allow it to handle a doubling of the filter pressure drop so that you can have a better idea of when it’s time to change your HVAC filter.


There’s nothing wrong with being too cautious by following the instructions recommended by the manufacturer. However, if you want to be savvy about how you use your HVAC maintenance budget, you should pay attention to how your components work and when the peak seasons are when you’ll need your HVAC for. Doing so will prepare you for when you should be more attentive to its needs.

You must give your HVAC unit a check-up at least once a year. Doing so allows you to see if it needs repairs or cleaning from professionals. If you need dependable furnace experts, get in touch with Legacy Heating and Cooling’s HVAC technicians in Edmonton and Calgary.

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