Remodelled returns often shrink by three to four millimetres.

Variable-speed blowers depend on a deep media filter; swapping in a thin pad can raise static pressure and shorten motor life.

Brands like Honeywell or Lennox shave or add fractions to lock you into their cartridges.

15 ⅜ × 25 ½ × 5 ¼ (Carrier)

15 ⅞ × 24 ¾ × 4 ⅜ (often called a Honeywell five-inch)

15 ¾ × 24 ¼ × 4 ⅞ (Air Bear)

Start by turning off the system.

Next, locate the old filter and pull it out gently.

Measure the opening: check its height, width, and depth.

Write down the exact numbers, like 15 ⅞ × 24 ¾ × 4 ⅜ in.

Order custom size filters today.

MERV 5-8: These are basic pleated filters that work well for most homes. These filters can capture dust and mould spores.

MERV 9-11: MERV 11 furnace filters are a step up from MERV 8, and they are great for trapping pet dander and fine dust. So, if you live with pets or in an area more prone to pollution, these custom furnace filters could be an excellent option for you.

MERV 12-13: These are high-efficiency home filters that can capture smoke and bacteria-size particles. If you're looking for the most effective choice, these are the best air filters for furnace.

Nominal versus actual size matters: Again, this is key when choosing the right custom size filters. As you're aware now, the bold 16x25x5 on a box is rounded marketing. The real frame can be 15 ¾ × 24 ¾ × 4 ⅜ or something else entirely.

Buy the right depth: Keep in mind that Honeywell cabinets can take a 4 ⅜-in deep cartridge, Carrier needs 5 ¼ in, and Air Bear sits smack in the middle at 4 ⅞ inches. If you buy the wrong depth, the door won't latch.

Always check blower capacity before jumping to MERV 13: Higher MERV ratings can capture finer particles and provide higher resistance. Make sure your blower is capable of a higher rating, and only then get appropriate custom size furnace air filters.

Measure the sheet-metal ledge inside the rack: A common mistake when choosing the best custom size furnace filters is measuring the old filter instead of the cabinet opening. Remember that pleated frames can compress over time.

Don't ignore the airflow arrow and gasket seal: EPA installation guidance stresses that the arrow on the frame must point toward the blower and the frame must sit tight against all four rails. Otherwise, dust can bypass the media entirely.

Order in bulk: Another common error we see is ordering too few filters and paying repeat shipping. The truth is that five-inch pleats can weigh up to 1kg each.

Enter your nominal label (like 16x25x4).

Type the exact size from your ruler, and make sure it's correct.

Choose between MERV 8, 11, or 13.

Select a pack; The price usually drops per unit, so order in bulk for the most cost-effective option.

Checkout with flat-rate shipping across the US and Canada.

Gaps on the side: Always make sure you're ordering the correct custom size furnace filter online. The wrong depth can also make the filter rattle or prevent the door from properly closing.

Sudden whistle: This usually happens due to a collapsed pleat from high static pressure. We recommend moving down one MERV tier or installing a deeper frame.

Static shocks at vents: When the filter is overdue or the humidity is low, you might notice static shocks. It's best to run a humidifier and swap pads.

Remodelled returns often shrink by three to four millimetres.

Variable-speed blowers depend on a deep media filter; swapping in a thin pad can raise static pressure and shorten motor life.

Brands like Honeywell or Lennox shave or add fractions to lock you into their cartridges.

15 ⅜ × 25 ½ × 5 ¼ (Carrier)

15 ⅞ × 24 ¾ × 4 ⅜ (often called a Honeywell five-inch)

15 ¾ × 24 ¼ × 4 ⅞ (Air Bear)

Start by turning off the system.

Next, locate the old filter and pull it out gently.

Measure the opening: check its height, width, and depth.

Write down the exact numbers, like 15 ⅞ × 24 ¾ × 4 ⅜ in.

Order custom size filters today.

MERV 5-8: These are basic pleated filters that work well for most homes. These filters can capture dust and mould spores.

MERV 9-11: MERV 11 furnace filters are a step up from MERV 8, and they are great for trapping pet dander and fine dust. So, if you live with pets or in an area more prone to pollution, these custom furnace filters could be an excellent option for you.

MERV 12-13: These are high-efficiency home filters that can capture smoke and bacteria-size particles. If you're looking for the most effective choice, these are the best air filters for furnace.

Nominal versus actual size matters: Again, this is key when choosing the right custom size filters. As you're aware now, the bold 16x25x5 on a box is rounded marketing. The real frame can be 15 ¾ × 24 ¾ × 4 ⅜ or something else entirely.

Buy the right depth: Keep in mind that Honeywell cabinets can take a 4 ⅜-in deep cartridge, Carrier needs 5 ¼ in, and Air Bear sits smack in the middle at 4 ⅞ inches. If you buy the wrong depth, the door won't latch.

Always check blower capacity before jumping to MERV 13: Higher MERV ratings can capture finer particles and provide higher resistance. Make sure your blower is capable of a higher rating, and only then get appropriate custom size furnace air filters.

Measure the sheet-metal ledge inside the rack: A common mistake when choosing the best custom size furnace filters is measuring the old filter instead of the cabinet opening. Remember that pleated frames can compress over time.

Don't ignore the airflow arrow and gasket seal: EPA installation guidance stresses that the arrow on the frame must point toward the blower and the frame must sit tight against all four rails. Otherwise, dust can bypass the media entirely.

Order in bulk: Another common error we see is ordering too few filters and paying repeat shipping. The truth is that five-inch pleats can weigh up to 1kg each.

Enter your nominal label (like 16x25x4).

Type the exact size from your ruler, and make sure it's correct.

Choose between MERV 8, 11, or 13.

Select a pack; The price usually drops per unit, so order in bulk for the most cost-effective option.

Checkout with flat-rate shipping across the US and Canada.

Gaps on the side: Always make sure you're ordering the correct custom size furnace filter online. The wrong depth can also make the filter rattle or prevent the door from properly closing.

Sudden whistle: This usually happens due to a collapsed pleat from high static pressure. We recommend moving down one MERV tier or installing a deeper frame.

Static shocks at vents: When the filter is overdue or the humidity is low, you might notice static shocks. It's best to run a humidifier and swap pads.