How to Replace a Humidifier Evaporator Pad

Replacing a Humidifier Evaporator Pad

Humidifier pads

A humidifier is an essential piece of furnace equipment in your home. It works to maintain correct humidity levels of air moisture. Proper humidity levels are important for comfort as well as protecting wood furniture and flooring. It also helps to reduce skin problems and breathing-related problems.

There are few different kinds of humidifiers, which in order of good, better, best, include:

  • Reservoir humidifiers
  • Flow-through drip-style humidifiers
  • Steam humidifiers

Of these, the flow-through humidifier is most common. A flow-through or drip style humidifier uses a media element to transfer water vapor into the supply air of the furnace.

This media element goes by a few names such as evaporator pad, evaporator panel, drip pad or water wick. The evaporator pad is a specially coated screen, usually made of metal, that has water constantly dripping across it in small amounts while the furnace operates.

Evaporator pads should be replaced annually and inspected monthly. In this tutorial, we will walk you through the steps involved in replacing an evaporator pad in a flow-through humidifier. The steps may vary a little depending on your manufacturer and model but will generally follow these steps based on a GeneralAire Model 1099.

With the humidistat set to 0 percent humidity (this turns the humidifier "off"), proceed as follows.

Remove Top Retaining Side Clips

Removing the top fasteners

The first step is to remove the top cover which conceals the evaporator pad:

  • OPTIONAL: Remove nuts holding the water distributor trough cover to the top cabinet cover (Note: you do not have to remove these nuts if you are not going to separate the trough cover from the top cover);
  • Remove the side retaining clips holding the top cover of cabinet assembly to the bottom cabinet housing;
  • Be careful not to lose these small parts and put them in a safe place.

Loosen Water Distributor Tube

Water distributor

Loosen the nut securing the water distributor tube (water inlet feed tube) to the solenoid/water inlet valve assembly and swing the tube out of the way of the cover.

Remove Top Cover of Humidifier

Top of humidifier

With the retaining clips removed and the water distributor tube out of the way, proceed as follows:

  • Lift and separate the top cover from the bottom cabinet housing;
  • Lift the used evaporator pad out of the bottom cabinet housing.

Prepare New Evaporator Pad

New evaporator pad

Check the condition of the used evaporator pad. In the photo above you can see how a used pad on the right is clogged and calcified as compared to the new pad on the left.

Remove the new evaporator pad from its wrapping and set it aside. Once you clean the interior of the cabinet it will be inserted.

Note: If the used pad is being checked as part of a quarterly inspection and is not in too bad shape, you can attempt to clean the calcified scale with a 1:3 solution of vinegar to water. You can also try using commercial calcium-removing cleaner (like Lime Away®). Soak the pad until the deposits dissolve. Rinse the pad with clean water and repeat if necessary.

Clean Interior of Humidifier Cabinet Housing

interior of cabinet housing

Clean the humidifier housing as follows:

  • Clean the interior of the cabinet housing with a commercial mold and mildew spray;
  • Clean the sides and bottom and the underside of the top cover.

Insert New Evaporator Pad

inserting evaporator pad

Insert the new humidifier evaporator pad into the lower cabinet assembly. It will slide down guide tracks on the side of the housing to ensure a proper position.

Replace Humidifier Cover

replacing humidifier cover

Replace the humidifier cover as follows:

  • Carefully place the top cover in place over the evaporator pad. Just as the side cabinet had guide rails, the top cover will have its own guides to properly locate the top of the pad. The top will be properly fitted when the sides of the top are flush with the cabinet and the top is setting squarely.
  • Insert the retaining clips to hold the top and bottom cabinet assembly together;
  • Reconnect the water distributor tube to the top cover

Tighten and Check Water / Drain Connections

checking water

Make your final connections as follows:

  • With the water distributor tube in place, tighten to snug the nut holding the tube to the solenoid.
  • Turn the humidistat to 35 percent (to turn it back on) or whatever your desired humidity level is;
  • Check for proper drainage in the condensate drain.

Periodic Cleaning of the Evaporator Pad

cleaning evaporator pad

As described in Step 5 of this tutorial, during a monthly maintenance check you may find the pad only needs some light cleaning. In that case, you can use a commercial cleaner like Lime-Away® or CLR®. Follow the manufacturer's instructions for dilution strength when cleaning the pad.