General FAQs

A: FST Filtration ( is a fast and simple way to order air filters. Just select the size and type of filter you need, and then choose how often you want them delivered to your home. We’ll ship the filters direct to your door, exactly when they need to be replaced. Air filters from FST are a similar or better quality than what you’d find at the big box stores, often at a fraction of the price.

Just visit and click “Find Your Filter”.

From there, select your filter size, your desired filter quality, and then choose whether you want to purchase one, or sign up for a subscription.

A: A good rule of thumb is you should change your furnace filter every 60 days. If you have someone in the home with allergies or asthma, have pets, or live in a dusty environment, you may need to change your HVAC filter more often. Also factors like how much you’re using your heating or cooling system, the size of your home and your indoor air quality can determine how often your air filters should be changed.

A: HVAC filters, including furnace and AC filters, cost different amounts depending on the MERV rating and thickness of the filter itself. A thicker air filter has a higher cost, but delivers a better value since you don’t need to change it as often.

A: has a wide variety of replacement furnace air filter sizes, so the right size for you depends on your specific HVAC system.

Take a look at the existing filter inside your system to see what the dimensions are (they’re usually printed on the side of the filter). You can also determine the right size of air filter for your system by looking in your HVAC system’s owners manual.

If you need to measure your existing air filter:

  1. Measure the length (L) and the width (W).
  2. Measure the depth (D).
  3. Now combine these measurements as L x W x D.

Keep in mind that the filter’s true dimensions will be different than the manufacturer’s rounded numbers, which are called “nominal size”. For example, a filter may measure 19.5” x 19.5” x 2.5”, but be rounded by the manufacturer to 20” x 20” x 3”.