So my buddy Greg Ellis hits me up on Skype this morning and asks if I have time to “take a walk”, which is how we like to meet and discuss business. We both like exercise, and it’s a great way to get both the blood and entrepreneurial juices flowing. But today, since it’s the last day of our vacation here in Utah, I’d promised my family they could have Krispy Kreme Donuts for breakfast, so I told Greg we could talk on a donut run instead. He didn’t object, and was at my house a few minutes later. 🙂

Q: Are these for the outer door to the furnace or are they for the inside lift off compartment doors? A: depends on the furnace, there should be retainers on the door which holds the filter in place. Q: CAN THIS BE CUT TO FIT A DOOR THAT IS 19' X 26'? FilterLock® is a patented two-piece system designed for use with 1-inch air filters that eliminates air leakage at the filter slot/door to improve indoor air quality (IAQ) and reduce energy consumption. Energy Star lists air leakage at the filter slot as one of four major issues with duct work in the home.

After picking up the donuts, we were headed back to my house when I suddenly yelled out “Oh! I need sheet metal!” as I turned sharply into the Lowes Hardware parking lot. Greg laughed and said “Of COURSE you do!” as if it’s something everyone yells when returning home with a dozen Krispy Kremes.

There’s a project here at the Utah house that I keep forgetting to tackle, into which Greg was unwittingly sucked. He’s always a great sport, however, so we still talked biz as we roamed the store to grab a 6 x 18″ piece of galvanized aluminum, some tin snips, and some sheet metal screws.

Back at home, Greg was more than happy to help out as I checked this minor annoyance project off my list. Thanks again for the help, Greg!

This project centers around the filter in my furnace. The HVAC “professional” who installed the furnace in this house gave me enough room in the return duct to insert a 20 x 25 x 1 inch filter, which sits diagonally inside the duct, like this:

However, when the furnace’s fan turns on, the suction will sometimes pull the bottom of the filter towards the fan, which stands the filter straight up on the right side of the intake duct. Then, when the fan shuts off and the suction disappears, the top of the filter will fall backwards, thereby allowing unfiltered air into the furnace. It was sloppy ductwork on the part of the installer, and it’s something I’ve been meaning to fix for years.

Measure Twice, Cut Once, Cut Yourself

Because the duct is 20″ wide (I know that because a 20″ wide filter fits perfectly) I knew the width of my 18″ sheet of metal would be fine. I used my level as a straight edge to score a 3″ section on the sheet metal:

Scoring my sheet metal.

Then I used my tin snips to cut as closely as I could along the score line:

Of course, I nicked my thumb on the sharp edge of the newly cut metal, but it wouldn’t be a DIY project without a little blood.

Bend and Fit

Next, I used a an exposed 2 x 4 on the wall of the utility room a jig to help me bend the strip in half, meaning it was no longer just a strip… it was a bracket!

Strip + bending = bracket!

I placed the strip inside the duct and slid it up against the base of the filter, so I’d know where to secure it, then drew a line along the edge of the bracket with a Sharpie:

Secure and Finish

I removed the filter so I’d have a bit more room to work, lined up the bracket with the Sharpie line, then secured it to the bottom of the duct with some sheet metal screws:

Furnace Filter Slot Door Cover Replacement

New bracket secured.

The final step was to replace the filter, and check to make sure the bottom couldn’t slide forward. Success!

So what have we learned?

We’ve learned that donuts can totally help you remember DIY projects, and we now know the answer to the eternal question: “How many BYU Business School graduates does it take to fix a furnace filter duct?”

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Allergy Zone Azfl-100 Filterlock Furnace Filter Slot Seal Door Cover

Is the air filter I have too small for my unit? We hear this question from a lot of our customers. Each air conditioning system or HVAC unit has a certain size filter that allows the filter to perform correctly by protecting your heating/ac system. The filters don’t need to fit with an “air tight” seal, but you should be able to easily install and uninstall your filter without a struggle, plus the filter shouldn’t be so small that it moves freely within your unit. Your filter should be a bit smaller on each side of the filter housing slot, thus allowing you to slide the filter in with ease. Most AC and HVAC units use standard sized filters, but some do require a custom size air filter.

Some Signals that Your Air Filter is Too Small:

1. The air filter moves around too much inside the filter housing slot.
2. When your unit turns on, you hear noises such as knocking, whistling, or rattling.
3. Once installed, the air filter does not completely cover the vent or duct opening.
4. You notice that the air filter does not seem to get dirty.

Consequences of Using an Air Filter That is Too Small:

1. The filter can be sucked into the ventilation if it is much smaller than it should be.
2. Dust, allergens and pollutants will not be filtered from your indoor air, as the air is bypassing the filter and entering into the ventilation and is returned back.
2. The filter will be unable to protect your AC/HVAC unit and the unfiltered air will collect on internal components of your system, such as the coil and fan, which can lead to expensive repairs.

If you are questioning whether or not your filter is too small, here are a few suggestions on how to check:

Measure the air filter housing slot, but only the usable space where the filter can fit into. Make sure to take into consideration any overlaps or recessed edges that may obstruct installing or uninstalling the filter. For most systems you can use a standard sized filter within 5/8-in smaller than the air filter housing. If you are not able to find a standard sized filter within that parameter, you will need to order a custom sized air filter.

There are also air conditioning/HVAC units that are open-ended, meaning you don’t close a door or panel over the air filter housing. In these cases, you have more flexibility in selecting your filter size, as you can choose one that is longer than the size of the opening. This also gives you a pseudo “handle” that sticks outside the opening that allows you to grab onto for ease of removal when it’s time for the filter to be changed.

An excellent resource to help you is the US Environmental Protection Agency (EPA) Guide To Air Cleaners in The Home.

How to Choose Your Air Filter Size for Each Unit Type:

1. If your unit has wall and ceiling vents that do not have clips or brackets that secure the filter you want to find the closest fit possible (within 1/8-in. smaller than the opening) that prevents movement or noises as mentioned above.
2. If your unit has wall and ceiling vents that has clips or brackets that secure the filter you can select a filter size within a 1/2-in. smaller than the opening.
3. If your unit has a standard filter slot (typically located near the blower unit) you can select a filter size within 1/8-in – 5/8-in. smaller than the two longest sides. As mentioned above, you can also choose a longer filter as there is no door or cover that needs to be closed over the filter.
4. If your unit has a filter cabinet or drawer/large housing compartment you will need to select a specialty Whole House Air Filter (filter depth should be over 4 inches). Look for the part number or model number on the door/panel/housing or the reference number on the air filter to find the actual filter size.

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Selecting the filters that are just right for your home can be difficult and confusing at times. At US Home Filter we understand this, which is why we offer an experienced staff to help answer any questions you may have. For personal assistance with your air filter needs, please contact us now online or call us at (855) 237-1673 and we will do our very best to assist you in selecting the right filter for your individual needs. We carry humidifier filters and pads for all major manufacturers (including Air King, American Standard, Aprilaire, GeneralAire and Honeywell). We want to earn your business and we guarantee your satisfaction! Take advantage of our quality products, vast selection, low prices, and enjoy FREE SHIPPING on every air filter order within the Contiguous USA.