How to Add a Humidifier to a Forced-Air System

In this video, This Old House plumbing and heating contractor Richard Trethewey explains how to add a humidifier to a forced-air system.

Steps for Adding a Humidifier to a Forced-Air System

1. Screw the humidifier to a wall near the furnace.
2. Cut away insulation from the duct using a utility knife.
3. Position the hole-cutting template onto the side of the duct.
4. Drill a pilot hole through the duct, then cut out the hole with aviation snips.
5. Secure the humidifier’s steam wand to the duct with self-tapping sheet metal screws.
6. Attach steam hose to the wand and to wall-mounted humidifier; secure hose with cable ties.
7. Connect the flexible drain hose to the steam wand and to the humidifier.
8. Run a copper drain pipe from the underside of the humidifier to the sump pump or floor drain.
9. Cut and solder a copper tee fitting into a nearby cold-water pipe.
10. Run new cold-water copper piping to the bottom of the humidifier.
11. Have an electrician run the electrical cable to the humidifier and to the room humidistat.
12. Turn on the water to the humidifier.
13. Install the air-proving switch in the duct.
14. Set the upper limit of humidity on the high-limit switch.
15. Set room humidistat to the desired level of humidity in the house.

Materials

• Utility knife
• Propane torch

Tools