Humidifier Installation

A Step By Step Guide

HVAC For Beginners

Air Quality Basics

Humidifier Basics

Portable Humidifier Reviews

With this humidifier installation guide, you can do it yourself and save a lot of money. For the typical HVAC service company to perform this job, it would cost about $500. We will help you to keep a lot of that money!


We will look at installing a typical bypass flow-through type unit on an upflow furnace with metal ductwork.

Locating the unit

The humidifier installation process begins by choosing a location for the unit. The unit should be located on the return air duct. You should ensure that there is clearance for servicing the unit.

Most units come with a template in the kit. This template is in the form of a sticker and should be applied to the selected location. Next, a hole is cut into the return duct which allows the humidified air to enter the duct system. It is a simple matter of cutting the metal with metal cutting snips along the lines on the template.

Next, the unit can be mounted to the duct. This is normally done with 1 inch sheet metal screws.


If the unit is not level after installation, then the water will not be properly distributed over the pad. This will cause the unit to waste water and possibly be unable to maintain the desired humidity.

Now, you can trace the start collar for the duct that supplies air to the unit. This should be located on the supply plenum of the furnace. The metal should be cut out with metal snips. The collar can then be inserted into the hole and secured by bending over the metal tabs. Now, the flexible duct can be connected to the start collar and the inlet of the unit. It is usually secured with metal hose clamps.

Connecting water and drains

The humidifier installation process continues by supplying water to the unit. This is usually accomplished with a saddle valve and copper or plastic tubing. The saddle valve is installed on a cold water supply pipe. The plastic or copper tubing is connected to the supply valve and the valve on the unit using compression fittings.

**HOT TIP** You should avoid over tightening these connections or a leak will result.

Next, a drain tube is connected to the unit. This is typically a plastic tube and is attached to the outlet with a hose clamp. The hose can then be ran to a floor drain, condensate pump, or the furnace or air conditioner condensate drain.

Connecting the controls

Next, the humidistat should be installed. This can either be installed on the return air duct or on the wall next to your thermostat.

To install the humidistat on the duct, it should be located above the humidifier. A template is installed on the duct and a hole is cut. Then, 18-2 thermostat wire should be ran from the humidistat to the furnace and to the humidifier. Normally, one wire from the furnace and one wire from the humidifier are attached to the humidistat. The other wires are tied together at the humidistat. The two wires at the furnace are connected to the output of the low voltage transformer.

The low voltage transformer is wired into the furnace control board on modern furnaces. The board should have a connection labeled humidifier. The black supply wire to the transformer is connected to that terminal and the white wire is connected to one of the neutral terminals on the board. In some cases, this will be done using spade connectors.

Humidifier Installation, Final checks

You should complete your humidifier installation by checking for proper operation. To do so the furnace must be running in the heat mode and the humidistat must be set above the home's humidity level. You should hear the valve open on the humidifier. Check for water leaks and then set the humidistat to the recommended level.