Humidity control for Scarborough, Durham and GTA homes
Humidity is the half of comfort that thermostats do not measure. A house at 21 °C can feel cold and static-prone in February and clammy in July, and in both cases the temperature is fine — it is the moisture that is wrong. Metropolitan Heating and Air Conditioning fits and services whole-home humidifiers and dehumidifiers on forced-air systems across Scarborough, Durham Region and the GTA, and has been doing it since 1979.
Call (416) 283-5698, Monday to Friday 8:00 AM to 4:00 PM.
What relative humidity is measuring
Relative humidity is the share of the moisture the air could hold at its current temperature that it is actually holding. The "relative" part is what catches people out: warm air holds far more water than cold air, so the same quantity of moisture gives a very different reading at different temperatures.
That is the whole reason Ontario houses get dry in winter. Outdoor air at −15 °C holds almost no moisture even at 100% relative humidity outside. Bring it indoors through normal air leakage and heat it to 21 °C, and its relative humidity collapses into the single digits. The house did not lose moisture — the air's capacity went up while the water content stayed the same.
The winter number moves with the outdoor temperature
Roughly 30 to 40% relative humidity is a reasonable indoor target in winter, but the top of that range is not fixed. It is limited by the coldest surface in the house, which is almost always your windows.
Air in contact with a cold pane cools until it reaches its dew point, and then it gives up water as condensation on the glass. A double-glazed window on a −20 °C night has an interior surface far colder than the room, so the humidity level that was comfortable at 0 °C outside will start streaming down the glass in a cold snap.
The practical rule is to turn the humidifier down as it gets colder outside and up as it warms. Persistent condensation is not a cosmetic problem: water runs off the glass into the sill and the wall cavity, and sustained wetting there causes damage you do not see until it is significant. A humidistat with an outdoor sensor makes that adjustment automatically, which is the main reason to fit one.
The three humidifier types, and how they differ
Bypass humidifiers mount on the supply or return plenum with a duct linking the two. Furnace airflow passes over a wetted evaporator pad and picks up moisture. They have no fan of their own, cost the least to fit, and only add moisture while the furnace blower is running.
Fan-powered humidifiers add their own blower, so they pull air across the pad themselves and deliver noticeably more moisture per hour than a bypass unit of the same size. They need no bypass duct, which helps where plenum space is tight.
Steam humidifiers boil water in their own canister and inject vapour into the duct. They are independent of furnace heat, which means they can humidify on blower-only operation, and they deliver the highest capacity — the answer for a large or leaky house where a pad unit cannot keep up. They need a larger electrical supply and consume more energy.
All three need a water supply, a drain, and wiring into the furnace control so they run with the blower. Sizing comes from the volume of the house and how leaky it is, not from floor area alone.
Summer is the opposite problem
An air conditioner dehumidifies as a by-product: the coil runs below the dew point, water condenses on it and drains away. That works well while the system runs long cycles. It works badly on mild, humid days when the house barely calls for cooling, and it works badly with an oversized unit that satisfies the thermostat in short bursts — the coil never stays cold long enough to strip much water out.
The result is a house at the right temperature that still feels clammy, often in the basement. A whole-home dehumidifier ducted into the system handles moisture independently of whether cooling is called for, and it can be set to a humidity target rather than a temperature one. Around 50% is a sensible summer ceiling. Getting the air conditioning sizing right in the first place is the other half of the answer.
Book an assessment
Call (416) 283-5698 weekdays 8:00 AM to 4:00 PM, or tell us what the house is doing. See also air filtration and purification, all indoor air quality services and heating. Licensed and insured, in Scarborough since 1979.