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Michael Thompson

Home Energy Efficiency Specialist

Published on June 22, 2026 • 7 min read

How to Install a Humidifier in a Furnace (A Canadian Guide)

A correctly installed whole-house humidifier can aid in keeping your indoor air quality optimal during the winter months to ensure a healthier living environment, protect your hardwood flooring and furniture, and reduce static electricity throughout your living space. Our guide below explains where you can mount your equipment, how to supply your unit with water and drain it safely, how to wire a humidistat, and how to program humidity levels for your next Canadian heating season.

WHY ADD A WHOLE-HOME HUMIDIFIER

Comfort, health, and home protection

Installing a whole home humidifier can offer homeowners several benefits that make investing in this type of HVAC system worthwhile:

Better winter comfort

Maintaining optimal humidity levels within your home can help reduce dry skin, static electricity shocks, scratchy throats, and dry nasal passageways during the colder months of the year to improve your overall well-being.

Protects your home

Low humidity levels can cause your hardwood flooring, paint, baseboards, and furniture to shrink and crack. By maintaining correct moisture levels in your indoor air, you can protect your personal belongings.

Works through your existing ducts

A furnace humidifier is designed for even moisture distribution throughout your interior using your ductwork, whenever your HVAC equipment is operating, reducing the need for portable humidifier appliances in very room.

Automatic control

A humidistat is a humidity controller that allows you to adjust your moisture levels based on the conditions of your indoor living environment, accounting for weather and temperature changes in real-time.

Maintenance is simple

Maintaining a whole-home humidifier is very straightforward. It only requires a seasonal pad replacement, standard cleaning, and a drain line check, making it a manageable investment for most Canadian homeowners.

QUICK ANSWER

Where the humidifier goes and what you need

Most whole-house humidifier installations use a mounting plate to attach the equipment to a supply plenum, which is the supply duct used to transfer warm air from your furnace. Other installations include:

Bypass humidifier: Bypass models connect between the supply and return duct with a small bypass duct.
Fan powered models: These are mounted on the supply duct and feature their own internal fan.
Steam humidifier units: A steam humidifier is mounted on the supply plenum or a nearby wall with a steam dispersion tube.

What you'll need when installing a whole-house humidifier includes:

A cold water supply with a shutoff valve.
A drain line to a condensate pump or floor drain.
24-voltage control wiring to the humidistat and furnace.
Access to a 120V or 240V plug in for a fan-powered or steam unit.
Installation tools.

Health Canada recommends maintaining a relative humidify level (RH) between 30% and 50% during the winter months to prevent mold and condensation indoors.

CHOOSING THE RIGHT TYPE

Bypass vs fan powered vs steam

Here's a quick overview of the different types of whole-house humidifiers below:

Type of whole-house humidifier	Optimal location	Power requirements	Pros	Cons	Best for
Bypass humidifier	Supply plenum with a bypass duct to return air duct.	24V control only.	Lower cost, standard equipment design.	Depends on furnace runtime; needs bypass duct	Homes with average winter temperatures and moderate humidity need.
Fan powered	Supply plenum only	120V for the fan and 24V for the control electrical wiring.	Stronger moisture output than bypass models, has no bypass ductwork.	Higher cost, requires an electrical outlet.	Homes needing more moisture output, but don't want a steam unit.
Steam	Supply plenum or wall-mounted with steam tube on a nearby wall.	120V or 240V depending on the model circuit, and 24V for the control wiring.	Highest output; works without heat cycle	Highest cost to install, requires more maintenance throughout the year, more complex installation process, water hardness can impact long-term performance levels.	Large homes in very dry climates where optimal humidity levels are required.

TOOLS, PARTS, AND SAFETY

What you need before you start

Before beginning your whole-house humidifier installation process, here's a closer look at the tools, materials, and safety knowledge you need to ensure a proper install:

Common tools

Tubing cutters, adjustable wrench, screwdrivers, level, drill, tin snips, hole saw, nut drivers, and multimeter.

Materials

Humidifier equipment, mounting plate, sheet metal screws, shutoff valve, water supply line, drain line, humidistat, thermostat wire, and an an electrical transformer.

Safety and code

Shut off the main power to your home's HVAC system before starting your whole-house humidifier installation to ensure you can complete the job safely. Follow all manufacturer instructions, and local electrical and plumbing codes. If you are not comfortable performing the installation yourself, contact a local technician for professional installation assistance.

HOW TO INSTALL A FURNACE HUMIDIFIER

Step-by-step overview

Here's a step-by-step guide on how you can install a whole house humidifier in your home:

Plan the layout

To ensure a proper installation, choose a flat section on the furnace supply plenum. Ensure there is enough space around the unit to ensure you can conduct maintenance on the equipment. Confirm there is a direct route for your drain line and water line.

Cut and mount the cabinet

Refer to the installation template in the installation manual. Cut an opening and place the humidifier into the cutout before fastening it to the sheet metal. Seal any edges around the cutout with foil HVAC tape to prevent warm water leaks.

Run the bypass or confirm supply only

For bypass models, cut an opening on the return air duct and connect the bypass line with a damper. You can skip this step if you have a fan-powered or steam system.

Connect the water supply

Install a shutoff valve on your cold water line. Route the tubing to the solenoid valve or float valve.

Add a drain

Run a drain line to a nearby floor drain or condensate pump. To prevent standing water, ensure the drain line is installed in a downward slope and secured.

Wire the humidistat

Connect the electrical wiring from the humidifier to a HUM terminal or accessory on the furnace. This will send power to the humidifier only when your HVAC system is heating.

Test operation

Restore power to your HVAC system and set your thermostat to its heating mode. Look for any air leaks, water flow, and how the drain operates to ensure the unit's been properly installed.

Set humidity

Set your humidistat between 30% and 50%.

MAINTENANCE AND TROUBLESHOOTING

Settings, water quality, and winter tips

For most Canadian homeowners, maintaining humidity levels between 30% and 50% is ideal and recommended by Health Canada. As hard water is common across provinces, consistently check for mineral buildup to prevent performance issues over time.

Frequently Asked Questions

Where do you install a humidifier on a furnace?

On the supply plenum, sometimes with a bypass connection to the return duct.

Do you need a drain for a furnace humidifier?

Yes, you need a drain line or condensate pump to remove excess water.

How do you wire the humidistat to the furnace?

Typically 24V electrical wiring from the humidifier to the HUM or accessory terminals.

Which is better, bypass, fan-powered, or steam?

Bypass humidifiers are more affordable, while fan-powered units offer a stronger moisture output. Steam units are great for larger homes in dry air environments.

What humidity level should I set in winter?

Levels between 30% and 50% are ideal.

Will a humidifier cause mould in the ducts?

Not if you maintain levels within the recommended range.

Can I install a furnace humidifier myself?

Some homeowners can, but a professional installation is recommended if you have no prior electrical or plumbing experience.

How often do I replace the humidifier pad?

Aim to replace the humidifier pad at least once a year.