Could I please have your opinion about humidifiers for a residence? If you think they should be used, can you advise what type is preferable?
Relative humidity in homes is an important topic that has a complex scientific background for explanation, and is often misunderstood by many homeowners. Most people notice that their homes are dryer in the heating season, and more humid in the summer, but often notice moisture build-up on windows and other areas in the “dry” winter. If the air is dryer in the winter, why do we see more moisture on windows and other areas this time of year? It doesn’t seem to add up.
To properly understand this topic, we must first know a few facts. Air has a finite amount of water vapour that it can hold at any given temperature. The amount of moisture in the air relative to this saturated amount is expressed as a percentage, known as Relative Humidity. To simplify matters for our discussions, one simple scientific fact should be known. The warmer the air, the more moisture it can hold.
Warm air that is cooled will release some of its moisture in the form of condensation if the saturation point is reached, at the lower temperature. Air inside a home at 20C will be able to hold several times more moisture than cool outside air at –10C. When warm inside air, even with a moderately low Relative Humidity of 30 – 40%, hits a window that is 15 to 20 degrees cooler, the saturation point of that air may be exceeded and condensation will form on the window. This is the reason we may see more visible moisture in the home in the heating season, even though the air is dryer.
Adding moisture to the air in our homes through a humidifier, usually installed in the furnace ducting, has been done for many years. Humidifiers are not used nearly as often today, for one reason. Newer homes are built much more airtight than older ones, and the normal relative humidity levels are often higher.
With leakage of heated air to the exterior goes a large amount of the moisture in the home. Old homes with poorly sealed windows and doors, no air vapour-barrier in the walls or ceiling and little to moderate insulation, will lose a fair amount of moisture to the exterior. Newly built homes pay very close attention to these details, to minimize heat loss, essentially trapping air and moisture in the home. With newer homes the problem has changed from finding ways of adding moisture to the living space in the winter, to finding ways to minimize or eliminate it. This has to be done while still keeping the heat in the house. Dryer vents, bathroom and kitchen exhaust fans, and mechanical ventilators are often installed to help eliminate excess moisture in a home.
Why is it detrimental to have higher relative humidity in the home, which is often quite comfortable for the occupants? This is because high moisture levels in the home cause damage to components in the structure and may lead to mould and rot. A relative humidity level above 50% to 60% provides a perfect environment for this to occur. Condensation on windows and within cool wall and ceiling cavities may form, even with properly installed air-vapour barriers. Frost and mould may also appear on cold concrete foundation walls, if there is too much moisture in the home.
A low relative humidity below 30 % will provide and ideal climate for the building components of the house, but will be uncomfortably dry for the homeowner. A good quality barometer may be purchased and placed in a central location in the home to measure the relative humidity. This should be done before deciding on installation of a humidifier. If the normal levels are between approx. 30% and 50% in the heating season, then added moisture may not be required. If the levels are below 30%, then adding moisture to the air in the home will improve comfort levels for the occupant.
There are several styles of humidifiers available and the most popular types have a drum or pad that absorbs water and allows the air flowing through the heating ducts to pass through. This allows the air to pick up added moisture, which is then circulated through the home’s heating/cooling duct system.
Whichever style of humidifier is chosen, regular maintenance is critical to performance. The pad in the humidifier will become hard and stiff, due to deposits of minerals in the water, and will not absorb water, becoming ineffective. These removable components must be changed or cleaned regularly, according to manufacturer’s instructions. The water supplied to the humidifier may empty into a tray or other vessel and become dirty and contaminated, with regular use. Emptying and cleaning these trays is extremely important for preventing bacteria and mould growth and shutting off the water supply in the summer is necessary. Any heating contractor or Home Inspector can tell horror stories about mould found growing inside humidifiers that are not cleaned regularly. This is one reason that many older humidifiers have the water supply shut off and are abandoned, altogether.