Introduction to Humidifier Filters

Introduction to Humidifier Filters

A humidifier filter, also known as a water panel, water pad, or evaporator, is an essential component of your humidifier. Without the filter, a humidifier won’t work at all. A humidifier works when hot, unfiltered air is blown across a water source – in this case, the humidifier filter, which is saturated with water. As the air passes over the filter, it picks up moisture and distributes the humid air into the room or through the HVAC system, depending on your humidifier setup.

What is a humidifier filter?

The humidifier filter captures water to deliver humid air into your home. it's also known as a water padAs I said, the purpose of a humidifier filter is solely to absorb water. Generally made of three different materials – paper, metal, or clay-coated metal – the media holds water as hot, dry air blows across it. As the water flows into the filter media, impurities and mineral deposits are removed from the water. In most cases, the filter media has an antimicrobial coating to prevent the growth of mold, bacteria, and viruses from growing on the filter.

Why do you need a humidifier filter?

If you have a humidifier, you need a humidifier filter. Without the filter media, the hot air won’t be able to pick up moisture to humidify the air. A humidifier without a humidifier filter does nothing to improve the quality of the air in your home.

Do you need to change your humidifier filter?

You should replace your humidifier filter at the beginning of each heating season. Over time, a humidifier filter can become brittle, clogged, and lose its ability to hold water, which means that your humidifier can’t deliver as much humid air to your home. Furthermore, over time, the filter media can become contaminated with impurities from the water it absorbs and the air blowing across it, meaning those impurities and contaminates are being circulated in your home.

You should change your humidifier at least once a year. Areas with hard water may require two filter changes per heating season to ensure peak performance due to extra minerals found in the water.

Types of Whole House Humidifiers

Whole house humidifiers are located within your Heating, Ventilating and Cooling system. They’re usually installed in the ductwork connected to your furnace. There are a few different options for whole house humidifiers.


Bypass whole house humidifiers use a water pad, or filter, to collect water. Your HVAC unit moves air through the pad, which is absorbed into the air. Your furnace carries this moist air through your homes air ducts and circulates it throughout your home to increase humidity. Any unused water is usually drained from the humidifier via a drain line. Always make sure to replace the water pad according to the manufacturer’s directions.


This type of whole house humidifier has a rotating drum shaped frame. The water pad is rotated by the frame and passes through a pan of water. As the pad rotates it absorbs water. Warm air from the furnace passes through the pad and picks up moisture that’s distributed throughout the home. These require a little more maintenance because you have to replace the pad regularly and clean out the water pan to avoid any health risks. These humidifiers are usually the least expensive whole house option.

Steam Humidifier

Whole house steam humidifiers use a built-in heater to boil the water inside the humidifier until steam is produced. This steam is then directed into the duct system. These types of humidifiers don’t need the furnace to be on to function. If you have children, then this type of humidifier may be somewhat dangerous since its surface can get somewhat hot.

Humidifier Operation

Be sure to turn off your humidifier at the end of the winter months. Many people forget to switch it off before summer starts, which is a problem – your air conditioner won’t run correctly if the humidifier is still on.

To turn off your humidifier:

  1. The humidistat controls the humidity level of your humidifier. Make sure to turn off the humidifier at the end of the season, when servicing, or when changing the humidifier filter. Turn the humidistat to the off position. If there is no off position, then make sure it’s at the lowest humidity level.
  2. Close the bypass duct damper if your humidifier has one.
  3. Turn off the water supply to the humidifier.
  4. Clean and replace the humidifier filter.

If you’re not comfortable with these steps, or if you have any questions, contact an HVAC professional.

Read our article on How to Use Your Humidifier for more information on humidifier operation.

Where to buy replacement parts and filters?

Whole Home Humidifier Filters

Portable Humidifier Filters and Wicks

Humidifier Parts


1 thought on “Introduction to Humidifier Filters”

  1. I am looking for a humidifier pad for a Lennox AC model # C35-36A-2F-2. Do you carry that part? If so, what is the part # and the cost?

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