How to Install a Whole-House Humidifier to Defeat Dry Air

Stop settling for dry air. Instead, install a whole-house humidifier. It's easier than you may think.

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Project Overview
  • Working Time: 2 hours
  • Total Time: 2 hours
  • Skill Level: Intermediate

Protect your family from dry air by doing a DIY whole-house humidifier installation. These systems are relatively simple to add. They typically attach to the main stack of a forced-air furnace where the unit draws its water from a nearby hot or cold water pipe. Some humidifiers are installed in the return-air duct and add moisture to the air before it's heated. Others employ a bypass duct to move heated air through the humidifier and reintroduce it to the air going to the house.

Installing either system involves cutting a hole in the venting using templates provided by the manufacturer. You'll need about two hours to mark the template, cut holes, and install the humidifier. Before you begin, make sure to shut off the furnace.

What You'll Need


  • Felt-tip marker
  • Humidifier unit
  • Vent pipe
  • Sheet metal screws
  • Wire nuts


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    Mark the Hole

    Using the manufacturer's template and instructions, mark the hole for the humidifier with a felt-tip marker. Drill a starter hole in a corner of the outline, then cut out the hole with aviation snips. Position the mounting plate, drill screw holes, and attach the mounting plate with sheet metal screws.

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    Mark Outline of Humidistat

    Refer to the manufacturer's instructions for the location of the humidistat (most are attached to the cold air plenum). Mark the outline for this unit and cut out the hole.

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    Install Humidistat

    Install the humidistat mounting plate and attach the unit. Next, connect the humidistat to the furnace controls following the instructions. If the unit requires a step-down transformer and you haven't yet run the wiring, shut the power off, install the transformer, and wire the humidistat.

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    Connect Humidifier

    Use the correct-size wire nuts to connect the leads from the humidistat to the solenoid valve on the humidifier. Insert the wire ends into the nuts (do not twist the ends of the wires) and turn the nuts until they're tight.

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    Run Line to Humidifer

    If local codes allow tapping water lines directly, install a saddle valve on a water line—preferably a hot water line—and run a line to the humidifier, fastening it with the compression fitting. If saddle valves aren't allowed, turn the water off, cut the water line, and install a T-fitting.

  6. Install a Bypass Vent (Optional)

    If your humidifier requires a bypass vent, use the template to mark the hole for a 6-inch bypass pipe. Drill a starter hole and cut the vent hole with aviation snips. Install a round collar in the hole, securing it with sheet metal screws. Measure the distance between the humidifier air inlet and the collar and cut the vent pipe to length. Install elbows on both ends of the vent pipe and fasten the assembly to the collar and humidifier air intake.

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