How to Install a Whole-House Ductless Humidifier | Ask This Old House

29October 2019

Ask This Old House plumbing and HVAC expert Richard Trethewey travels to Park City, Utah to install a whole house ductless humidifier.

#ThisOldHouse #AskTOH
SUBSCRIBE to This Old House:

Time: 2 hours

Cost: $1000

Skill Level: Expert

Tools List for Installing a Whole-House Ductless Humidifier: [YT]
Drill driver []
Blow torch []
Screwdriver []

Shopping List: [YT]
Whole house steam humidifier []
Screws []
Copper pipes and fittings []
Solder []
Flux []
PVC pipes and fittings []
PVC glue []
1/4 inch copper tubing []

1. This job requires working on the water line and making electrical connections. In most cases, it’s best left to professionals.
2. Identify a good location to mount the unit that will allow for proper airflow throughout the house. It’s helpful to keep the utility side of the box near a water line, a drain, and power supply.
3. Shut off the power at the breaker and the water at the main water shutoff.
4. Mount the unit in the desired location using screws and a drill driver.
5. Cut the hole on the other side of the wall where the fan box will go and secure it into place.
6. Make the water connections, starting with the wand through the fan box and working back towards the mechanical unit using copper pipes and fittings. You’ll need to seal all the connections using the solder and flux.
7. Connect the drain lines from the mechanical unit down towards the drain. Use the PVC pipes and fittings and seal it all with the PVC glue.
8. Connect the unit to the water supply line using the copper tubing.
9. Connect the wires that come with the unit to the electrical box.
10. Mount and connect the humidistat in the desired location and set it to the desired settings.
11. Turn the water and the power back on.

Richard installed an Aprilaire 865 Whole House Steam Humidifier [] with a Wall Mount Fan for Homes without HVAC Duct System ( The unit has a higher capacity to account for the vaulted ceilings in the homeowner’s house despite the smaller square footage.

The other tools and materials required for installation, including the copper tubing, drills, and wrenches can all be found at home centers.

After the segment, Richard discussed a different kind of whole house steam humidifier, which is called an AcuSteam Steam Humidifier, which is manufactured by Thermolec (

Expert assistance with this segment was provided by Lee’s Heating and AC (

About Ask This Old House TV:
Homeowners have a virtual truckload of questions for us on smaller projects, and we’re ready to answer. Ask This Old House solves the steady stream of home improvement problems faced by our viewers—and we make house calls! Ask This Old House features some familiar faces from This Old House, including Kevin O’Connor, general contractor Tom Silva, plumbing and heating expert Richard Trethewey, and landscape contractor Roger Cook.

Follow This Old House and Ask This Old House:

How to Install a Whole-House Ductless Humidifier

Keywords: Ask This Old House, Richard Trethewey, whole-house, plumbing, ductless, humidifier

Watch the full episode:

How to Install a Whole-House Ductless Humidifier | Ask This Old House


See Your Business Here!

For more information on our listings, advertising, coupons, and mailers, please contact us today!