How to Keep Furnace Filter in Place? [3 Possible Fixes]

Once you’re done setting a furnace filter into its place, you don’t check it out every now and then. Unless it’s time for a change, you might even forget about it anyway.

Meanwhile, what if the air filter won’t stay in place? Or bends towards the motor in a very inappropriate way?

If so, it’ll pass dirty and impure air through the furnace. In the worst case, it might blow up the whole system. 

We are glad that you’ve noticed a misplaced filter and landed on this page. We’ll take you through 3 possible fixes(with reasons) on how to keep furnace filter in place.

Let’s get on the board- 

Let’s Understand the Situation First

When one says that his “furnace filter won’t stay in place”, that comes up with two clear indications- 

1. The filter itself has moved away from its ideal position in the slot. 
2. No matter if it’s in a correct/incorrect position, the center pleats bend towards the motor.

As a matter of fact, both of these issues can take place individually or all together. So, we’ll not split them into our discussion and enlist the fixes in one place.  

7 Reasons(w/ Remedies) of The Furnace Filter Not Staying in Place

If your furnace filter is not in place, there can be a number of reasons behind. Go through the list below and see which one ticks the box for your case- 

Furnace Filter Fits Loose in the Slot

Filters have their own slot, where it should fit accurately without any loose fitting. But often, the slot with left with some more space than the filter actually requires. 

The same issue can also happen if- 

• You decide to go for a wrong size filter in furnace. Example- 1” filter in a 4 inch furnace filter housing(1st image).
• If there’s a channel to house the filter at the bottom, but not at the top(2nd image).  

Here’s how both of them look like-

We’ve seen many users to wonder- “Can I use a 1 inch filter instead of 4 or 5 inches? Well you might, but as a consequence of such misplacement, the filter center often moves towards the motor and calls up further problems. 

Anyways, we need to ensure that the filter can’t get to move anywhere out of it’s place that we’ll define. To make it happen, there are two ways- 

Remedy 1: Use A Furnace Filter Metal Frame/Bracket

Many brands provide furnace filters with metal backing to prevent furnace filter bending issues. In case yours one doesn’t, it’s imperative that you get one right away. 

These metal brackets contains a metal/cardboard frame around the edges and a wire mesh onto the pleats. The frame holds the filter itself on a static position, where the mesh prevents the pleats to bend towards the motor. 

Before you buy one, don’t forget to match the size anyway. FYI, they are often called as metal furnace filter slot cover as well. 

Here’s some of our favorites- 

1. Best for 12”x12” filters- Filtration Group 38363
2. Best for 20”x20” filters-  Air Handler Pad Holding Frame 20x20x1″
3. Best for 22”x22” filters- Air Handler Pad Holding Frame 22x22x1″

If your filter comes with its own mesh, you might face a frame misplacement issue only. In that case, you might try out a furnace filter rack without mesh. 

Here’s our pick of a furnace filter rack– 

1. Famco Furnace Filter Rack 16×25.
2. Protech RXHF-17
3. Rheem #RXHF-21

Once you get the right fit of size, you’ll learn how to hold a furnace filter in place with no hardship. 

Sometimes, furnaces have their own racks provided. But mostly, there is no filter rack in a furnace. In some cases, even using a furnace filter retainer clip can solve the issue anyway.

Remedy 2: DIY Furnace Filter Channel

If the metal bracket is still unable to cover up the ‘space’ between the filter and the slot, you’ve to build a metal channel as a proper way to place furnace filter. 

Don’t worry if you haven’t done it before. We’ll take you through the steps below-  

Before you start, these are the tools you’ll require- 

1. A sheet metal.
2. Tin snips. 
3. Sheet metal bending jig. (DIY tutorial). 
4. Sheet metal screws. 

Got ‘em all? Here go the steps- 

Step 1: Measure the Length and Width

Measure the length of the filter bottom(as it’s put in the slot). Taking it as a length of the sheet metal strip, take 3-4” of width from it. Mark the length and width with a pencil.  

Step 2: Cut it with A Tin Snip

Now, cut the strip across the score lines with a metal snip. Beware of nicking your fingers.  

Step 3: Bend It

Use a jig to bend the metal halfway across the length. The metal should take an ‘L’ shape with an angle of 90 degrees. Based on your furnace type, it can be 45 degrees as well. 

Here’re the sequences of bending a metal sheet with a jig-

Step 4: Place Securely

At first, put the filter on its place and mark a line where the channel should be. Take it away and put the channel on the line. Tighten up it at its places with sheet metal screws. 

Once done, make sure that the bottom of the filter isn’t sliding forward once you turn the furnace on. Also, check for any furnace filter gap and make sure that you hold the furnace filter in place.  

Note: A slight variation of what we’ve created is called furnace filter u channel. Making sure that it serves your purpose, you can look up one in the local store. 

The Static Pressure on Ductwork

Sometimes, the filter might be clean enough to let enough air to pass through it. But just because a static negative pressure takes place on the ducting, it forces the filter to bend inwards. 

The unit of static pressure is “ W.C.(inches water column). If you know how to measure static pressure in your furnace system, you might check the difference between the ideal pressure and the pressure you’re having in your system. 

If the ideal stat hovers around 0.5” W.C. and yours one at 0.7-0.9” W.C., the furnace static pressure is too high in your furnace. 

 So, what causes such static pressures on the filter? Here are the reasons- 

1. A narrow ducting comparing to the motor speed.
2. A higher blower motor speed comparing to the ducting size.

As you can sense, both of these issues can not take place together. But both of them indicates that your ducting and the motor is having a mismatch anyway. 

The fix? 

Remedy 1: Use A Variable ECM Blower Motor

With basic furnace setups, you get to use regular PSC(Permanent Split Capacitor) motor. And these can not work with static pressure above 0.5” W.C. 

On the other hand, using an ECM(Electronically Commutated Motor) can expand this range of workable static pressure up to 0.8” W.C. 

Our Favorite ECM Motor: ZHONGSHAN BROAD OCEAN M0081903R 

Remedy 2: Fix Your Ducting

A problem with the earlier fix was, it might fix the issue if the furnace filter keeps bending, but it puts a whole lot of pressure on the system if the static pressure hovers around 0.7-0.8” W.C.

However, if you can make up your mind to use wider ducting, this might deduce the static pressure on the furnace system. The reason, the wider the path is, the less the air pressure is. 

However, a whole new furnace ducting installation might cost you quite a fortune. 

Clogged Up Filter

Based on how much of a ‘dirty’ environment you have, the furnace filter changing interval varies a lot. As an example, if you have double storied home with central conditioning, a 1” pleated filter might not serve you well for more than one month. When it’s time is up, it gets clogged up with dirt. 

Now, a clogged up filter is quite poisonous for the entire furnace system. As most of its pores are saturated with specks of dirt, even a mild airflow can make its central part towards the blower motor. In the worst case, it might get into the motor. 

Remedy: Change the Filter More Often

The one and only solution to this problem is to be aware of when the filter gets saturated and change it right away. 

In case you are not certain about when exactly to change your filter, get an air filter monitor. It will identify the clogged furnace filter symptoms itself and alert you immediately. 

Here are two of our favorites-

• Dwyer Series Mark II 25 (Shows filter health through dial).
• General Aire G99 (Shows filter health through dial but cheaper). 
• FILTERSCAN WiFi AC & Furnace Filter Monitor (Shows filter health through Wi-Fi, text, and email).

Bottom Line

Alright, this is the end of today’s post about filter placement in the furnace. Let us know if we’ve missed anything, and we’ll be happy to update it by all means. 

Happy living!

Tim David

HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.