Many homes struggle with furnace filters that don’t fit, risking dust buildup and costly repairs. Nominal sizing and custom options can protect your HVAC system and ensure clean, efficient airflow throughout your home. Learn more: https://unitedfilter.com/pages/custom-size-furnace-filters
Many homeowners think replacing a furnace filter is simple—buy the size listed on the box, slide it in, and call it a day. But all too often, the new filter doesn’t fit tightly. Air sneaks around the edges, bypassing the filter entirely. This isn’t just a minor annoyance; it’s a common problem, and it starts with a mismatch between the filter’s labeled size and the actual opening in your HVAC system. Here’s the thing: the numbers printed on your filter frame aren’t exact. The HVAC industry uses “nominal sizing,” meaning the dimensions are rounded for convenience. A filter marked 20x25x1 inches doesn’t actually measure that size. Physically, it’s closer to 19.5x24.5x0.75 inches, small enough to slide into the housing without sticking. The trouble comes when homeowners measure their filter slot and try to order the exact measurements. A 19.5-inch opening doesn’t correspond to a standard filter size. To get the right fit, you need the nominal 20-inch version. This confusion is amplified by how homes are built. Filter openings aren’t universal. Older homes, custom builds, or properties with renovations often have openings that don’t match today’s mass-produced filters. Even newer homes sometimes use non-standard sizes to meet energy codes or architectural designs. The result? Standard filters at the hardware store just won’t fit properly. When a filter doesn’t fit, problems quickly add up. Gaps let dust and debris slip past the media, landing on sensitive components like the blower motor or evaporator coil. Over time, this can lead to costly repairs, exactly what a tight-fitting filter could prevent. Even a small gap of a quarter-inch significantly reduces effectiveness. Oversized filters are risky too. Forcing a filter into a tight slot can bend the frame or warp the edges, creating new channels for unfiltered air. Getting accurate measurements is key. Don’t rely on guesswork. Start by checking your existing filter’s printed dimensions for a reference. If no filter is available, measure the slot carefully: the length of the shorter side, the width of the longer side, and the depth. Then round each number up to the nearest inch to find the nominal size for ordering. For example, a slot measuring 19.5x24.5x0.75 inches would correspond to a 20x25x1 filter. Some homes fall completely outside the standard sizes available at local stores. Custom dimensions are often needed in older homes, unique builds, or places with modified HVAC setups. Trying to force a close-but-not-quite-right filter leads to bypass problems, while leaving a slot empty risks serious damage. Today, manufacturing allows filters in virtually any size. Accurate measurements translate into a tight seal, preserving airflow and system performance. Click on the link in the description to explore options if your home doesn’t match standard sizes. Thickness matters just as much as length and width. Most residential filters are 1, 2, or 4 inches thick. A filter that’s too thick can restrict airflow, putting stress on your HVAC system and even causing the blower motor to overheat. Choosing the right depth ensures your system operates efficiently while filtering effectively. Efficiency also depends on the MERV rating. This scale, from 1 to 20, measures a filter’s ability to trap particles. Higher numbers mean finer filtration but also greater resistance to airflow. Most homes work best with MERV 8 to MERV 13 filters, striking a balance between capturing dust and maintaining proper airflow. Using a MERV 16 filter on a system not designed for it can reduce performance and even damage your HVAC unit. Sometimes, professional guidance is the safest route. Homes with recurring fitting issues may have misaligned or damaged filter housings. A qualified HVAC technician can inspect the system, determine if the housing needs adjustment, and recommend the right filter solution. This approach avoids the frustration of repeated wrong-size purchases and prevents hidden damage. Ultimately, finding a properly fitting filter comes down to careful measurement and understanding how nominal sizing works. Keeping a record of your correct dimensions makes future replacements easier. For homes with non-standard openings, made-to-measure filters provide the secure fit your system needs, ensuring clean air, efficient airflow, and avoiding preventable repairs. Click on the link in the description to see how custom-size filters can make a difference for your home and keep your HVAC system running smoothly.
United Filter Company Ltd. City: Oakville Address: 2150 Winston Park Dr., Unit 15 Website: https://www.unitedfilter.com Phone: +1-905-403-0160 Email: sales@unitedfilter.com