Humidifiers near you

Relative humidity compares the moisture in the air with the most it could hold at that temperature. Very cold outdoor air carries little water to begin with, so once it is heated indoors its relative humidity falls. Older, draftier houses exchange more air with the outdoors and tend to run drier; newer, tighter homes often keep enough moisture from cooking, showers and breathing that they never need a humidifier.

Measure before you add anything. A hygrometer in a main living area shows whether the air really sits below Health Canada's 30% to 50% range. Health Canada's page on cool-mist humidifiers is more specific for the cold months, suggesting humidity of around 30% in winter to prevent mould growth. If the house is leaky, sealing the worst gaps keeps cold, dry air out and indoor moisture in; our air sealing page explains how.

Whole-home humidifiers attach to the ductwork and add moisture to the air the furnace or air handler circulates, so every room the ducts serve benefits and nobody has to refill a tank. A humidistat on the wall or built into the thermostat switches the unit on and off. Portable units treat one room and depend on you to fill, empty and clean them.

More moisture isn't always better. When indoor air is too humid for the outdoor temperature, water condenses on the coldest surfaces first: window glass and frames, the corners of exterior walls, closets on outside walls and the attic, where warm, moist air escaping through ceiling leaks can frost on the underside of the roof. Surfaces that stay wet invite mould and can rot wood.

Natural Resources Canada's Keeping the Heat In includes a table of the highest indoor humidity windows can handle without condensation at different outdoor temperatures, and the colder it gets outside, the lower that limit. Health Canada's mould guide lists unplugging and removing humidifiers among its steps for stopping window condensation. In a deep cold snap, turn the humidistat down instead of holding one fixed setting all winter.

Health Canada warns that bacteria can collect and multiply in water left sitting in a humidifier, and that a cool-mist unit doesn't boil its water, so it doesn't kill them. Whatever grows in the tank can end up in the air you breathe, which is hardest on people who already have trouble breathing. Its advice is to clean and disinfect the water reservoir regularly, following the manufacturer's directions for your type of unit.

A whole-home humidifier brings together ductwork, a water supply, a drain and wiring to the furnace and humidistat, which is why an HVAC technician installs it. Any gas or electrical work around the furnace must be done by a licensed professional, never as a DIY project.

The technician picks the type based on the furnace and duct layout, the size and airtightness of the house, the heating system and how much moisture the home actually needs, then places the unit where a leak can't drip onto the furnace or its controls.

A furnace humidifier sits out of sight, so it's easy to forget until it stops adding moisture or starts leaking. A check at the start of each heating season, ideally during the furnace tune-up, keeps it working and catches problems early.