How to Install a 16x20x1 Air Filter: Step-by-Step Guide

Install a 16x20x1 air filter by turning off your HVAC system, removing the old filter, and sliding the new one in with the airflow arrow pointing toward the blower or furnace.

For the full breakdown, see our best 16X20X1 Air Filter guide.

Swapping a 16x20x1 air filter doesn’t need a technician or so much as a screwdriver. It’s a five-minute job you can handle with zero tools, and doing it right keeps your furnace or AC running efficiently and your indoor air cleaner. But there’s one detail that trips up most first-timers: the airflow arrow. Get that wrong and you’re circulating dust straight into your equipment.

What You Need Before You Start

The only thing you need is a correctly sized replacement filter. That 16x20x1 label is a “nominal” size, not the exact measurement. Most actual filters measure around 15.5 x 19.5 x 0.75 inches or 15.75 x 19.75 x 0.75 inches, so there’s a little wiggle room. The slot is what matters, so check the opening before you buy if you can.

Filters in this size come with three common MERV ratings: 8, 11, and 13. The right one depends on your system and how much filtration you want. A higher MERV catches more particles, but a very high rating can restrict airflow in some systems. When in doubt, stick with what your old filter’s label showed.

The Step-by-Step Install for a 16x20x1 Filter

Whether your filter lives in a central furnace, air handler, or a return grille, the procedure is the same. The only difference is where you look for the slot.

1. Turn off the HVAC system. Flip the thermostat to off, or kill the breaker on the furnace or air handler. This keeps the blower from pulling air through while you work.
2. Open the access panel and remove the old filter. Take a mental note of which direction it sits in the slot. If the old filter looks dirty, good — that means it was doing its job.
3. Check the arrow on the new filter. The airflow direction is printed on the cardboard frame. Filtrete’s instructions say to point these arrows toward the blower motor or furnace.
4. Slide the filter in with the arrow pointing toward the blower. Keep the cardboard frame intact and push it in so it sits flush. It should fit snugly, but never force it — if it doesn’t slide in easily, the size is wrong.
5. Close the panel and restore power. Turn the thermostat back to its normal setting. You’re done.

A properly sealed cover ensures air actually passes through the filter instead of sneaking around it.

Common Mistakes and How to Avoid Them

Three errors lead to most filter install issues. All are easy to dodge once you know they exist.

• Installing it backward. The arrow always points toward the blower or furnace, never toward the return duct. A backward filter lets debris hit your equipment first.
• Forcing a filter that doesn’t fit. A snug fit is right. A filter that bends or bulges means it’s the wrong size, and gaps let unfiltered air bypass the media.
• Leaving gaps around the frame. The access panel must seal completely. If your panel doesn’t have a gasket, that’s worth fixing — an unsealed cover is a silent leak.

One more thing: filters also hide in wall or ceiling return grilles. If your equipment is hard to reach, a filter at a return grille does the same job.

How Often Should You Replace It?

Standard guidance says check your filter monthly and replace it every one to three months. Homes with shedding pets, high dust, or allergy sufferers should lean toward the monthly end of that range. That’s the single best habit for keeping a 16x20x1 filter working as intended.

It’s worth a glance before you order, since brand quality varies.