Changing an Aprilaire humidifier filter takes about 10 minutes and requires no tools

An Aprilaire humidifier filter should be changed once a year, usually before the heating season starts in fall. The exact timing depends on your water hardness and how often you run the unit — if you live in a hard-water area, you may need to change it twice yearly. The filter catches mineral buildup that would otherwise clog the humidifier's water panel, so a clogged filter is the most common reason an Aprilaire stops working properly.

The process is straightforward: turn off the humidifier, locate the filter cartridge inside the unit, slide it out, and slide a new one in. You do not need a technician, and the filter itself costs between $25 and $40 depending on your model.

Key Takeaways

  • Turn off the humidifier and let it cool for a few minutes before opening the access panel.
  • The filter cartridge slides straight out horizontally — do not force it or twist it.
  • Write the installation date on the new filter with a marker so you know when to replace it next year.
  • If water is leaking from the unit after you reinstall the filter, the cartridge may not be seated all the way in.
  • Order your replacement filter by your humidifier model number, which is printed on the unit's nameplate or in your manual.

Locate your humidifier model number and order the correct filter

Aprilaire makes several humidifier models, and each one uses a different filter cartridge. Using the wrong filter will not fit properly and the humidifier will not work. Find your model number on the nameplate attached to the humidifier itself — it is usually on the side or back of the unit and looks like "Model 600" or "Model 700M". Write this number down.

Once you have the model number, search for "Aprilaire [your model number] filter" online or call your HVAC contractor. The filter is sold under the name Water Panel or Filter Cartridge. Common part numbers include 45 (for Model 600), 50 (for Model 700), and 60 (for Model 800), but do not assume — verify against your model number. You can also check your humidifier's manual if you have it; the filter part number is listed there.

Turn off the humidifier and open the access panel

Switch the humidifier to Off on the control dial or switch. If your unit has been running, wait two to three minutes for any water inside to settle and for the unit to cool slightly. This prevents water from spilling when you open the panel.

Locate the access panel on the front or side of the humidifier. On most Aprilaire models, this panel is held in place by two or four clips or latches — no screws. Press or pull these clips outward or downward (the direction varies by model) until the panel swings open or slides out. If the panel is stuck, do not force it; check whether you are releasing the correct clips.

Remove the old filter cartridge

Inside the humidifier, you will see a rectangular cartridge made of a tan or white material. This is the water panel. It sits horizontally in a slot and slides straight out toward you — it does not twist or lift. Grip it gently on both sides and pull it straight out. If it resists, wiggle it slightly side to side as you pull; do not yank hard enough to tear it.

Once the old cartridge is out, set it aside. You may notice mineral deposits (white or tan crusty buildup) on the cartridge or inside the slot where it sat. If the buildup is heavy, wipe the slot clean with a damp cloth before inserting the new cartridge. Do not soak or rinse the old cartridge — it is not reusable.

Insert the new filter cartridge and close the panel

Take the new water panel out of its packaging. Align it with the slot where the old one came out — the cartridge should slide in horizontally, with the same orientation as the old one. Push it in slowly and steadily until it stops. You should feel it seat fully; it will not slide all the way to the back of the unit, but it should be snug and not wobble.

Before you close the access panel, write the current month and year on the new cartridge with a permanent marker. This makes it straightforward to remember when you installed it and when to replace it next. Then swing or slide the access panel back into place and find the clips or latches. Make sure the panel is fully closed and seated — a loose panel can cause water to leak.

Turn the humidifier back on and check for leaks

Switch the humidifier back to On or set it to your desired humidity level. Let it run for five to ten minutes, then check for water leaking from the access panel, the bottom of the unit, or the ductwork connections. A small amount of condensation is normal, but steady dripping means something is not seated correctly.

If you see a leak, turn the humidifier off, open the access panel again, and check that the water panel is pushed all the way in. Sometimes it shifts slightly during installation. Reseat it firmly and close the panel again. If the leak continues, the cartridge may be damaged or the wrong size — contact your HVAC contractor or Aprilaire customer service.

When to call a professional

You can handle filter changes on your own, but call your HVAC contractor if the humidifier is not producing moisture even after you have installed a new filter, if water is leaking and reseating the cartridge does not stop it, or if you cannot locate or remove the access panel without forcing it. A technician can also check whether your water hardness is high enough to warrant more frequent filter changes or whether a water softener would extend the life of your humidifier.

If your humidifier is still under warranty, check the manual to see whether changing the filter yourself affects coverage. Most manufacturers allow homeowner filter changes, but it is worth confirming.

Frequently Asked Questions

How often should I change the Aprilaire filter?

Once a year is standard, usually before heating season starts in fall. If you have hard water or run the humidifier constantly, change it twice yearly. A clogged filter reduces moisture output and can cause the unit to stop working, so if you notice less humidity in your home, check the filter first.

Can I clean and reuse the old filter instead of replacing it?

No. Aprilaire water panels are designed to be replaced, not cleaned. Rinsing or soaking does not restore the material's ability to absorb and distribute water evenly. A new cartridge costs $25 to $40 and lasts a full year, making replacement the most cost-effective option.

What if water is leaking after I install the new filter?

The cartridge is probably not pushed in far enough. Turn off the humidifier, open the panel, and push the water panel all the way in until it stops. Make sure the access panel itself is fully closed and latched. If the leak continues after reseating, the cartridge may be the wrong size or damaged — contact your HVAC contractor.

Do I need to turn off the whole HVAC system to change the humidifier filter?

No. You only need to turn off the humidifier itself using its control dial or switch. The furnace and air handler can stay on. Turning off just the humidifier prevents water from flowing while you work and keeps you safe.

Where do I buy an Aprilaire replacement filter?

HVAC supply stores, online retailers like Amazon, and your local HVAC contractor all stock Aprilaire filters. Verify your model number first, then search for the correct part number. Buying from your contractor may cost slightly more but ensures you get the right cartridge and can ask questions if you run into trouble.