A Dry Subject - All About Humidifiers


Winter air in Canada can be very dry, especially for those people who live away from coastal areas.  Colder air is simply incapable of holding as much moisture as warmer air.  Depending somewhat on the way you heat your home, this low humidity can cause problems for people and items within the home.  We are going to discuss those problems, some possible solutions, pros and cons of those solutions, and the care and maintenance of the related equipment.

With people, this extra dry air can cause nasal membranes to crack and bleed, promote drier skin and its discomforts, and may cause difficulties for people with respiratory ailments such as asthma.

Some household items are also negatively impacted by dry winter air. Such as, some wooden musical instruments are sensitive to humidity and may warp or crack as they shrink from a lack of moisture in the air.  Wooden floors and furniture may also shrink when they are too dry, and house plants may need to be watered more frequently in the winter.

Pets may also suffer from dry skin conditions such as flaking and itching.

So, for people, pets and household items, this dry winter air can create health issues or expensive damage.Science and engineering have created some solutions for moisturizing interior air in homes to mitigate the results of this problem.

Portable Solutions

Room-sized portable humidifiers are primarily of two types. They are small to medium sized appliances that can plug into a typical 110-volt household circuit.

The ultrasonic type consists of a water tank with thin ceramic plates (or other thin materials) that vibrate at a very high frequency; so high that human ears cannot hear it. This vibration pushes microscopic water droplets into the air where they evaporate, adding moisture to the dry room air.

The ultrasonic humidifiers do have some potential drawbacks:

  • While most of the very small water droplets evaporate, some may not. This can lead to surface dampness near the device and consequential damage to finished materials. So, the humidifiers should be placed on a high shelf or piece of furniture to allow a better chance of evaporation before droplets settle as water.
  • The water in the reservoir may have mineral content and/or bacteria that will be pushed into the air with the water droplets. The minerals may manifest as light surface dust which can be inhaled. Accordingly, it is wise to fill the tank with distilled water. The potential bacteria in the water could lead to respiratory ailments for the home's occupants. The water reservoirs should be properly cleaned every two or three days to minimize that possibility.
  • While ultrasonic humidifiers produce a sound that is beyond the range of human hearing, it may be heard by pets such as dogs and cats and may cause these animal's distress.

The other type of portable humidifier is known as "evaporative". Instead of driving water droplets into the air, it produces a vapour using a fan to blow air over wicking material in the form of a mesh drum or filter material. This water vapour is lighter that the droplets produced by ultrasonic humidifiers, so they do not directly produce dampness on surrounding materials. Evaporative humidifiers will be noisier as they must use a fan to move air over the wicking material, unlike ultrasonic systems which do not require a fan.

Some evaporative humidifiers boil the water in the reservoir to allow for a more sanitized vapour. Those that do not boil the water can also push bacteria into the air. Please remember that evaporative humidifiers that boil the water have heating elements that may pose a burn hazard to small children. You may not want to use this type in a child's room.

Whether you use an ultrasonic or evaporative humidifier, it is very important to clean them well on a regular basis.Also, invest in a room hygrometer to monitor the humidity in the room.The desired level of humidity is generally 30% to 50 %. Beyond those levels you may be promoting condensation on items in the room.Keep the room temperature at a level that discourages condensation, say +15ºC or warmer.This reduces the likelihood of mould or mildew growth which may be harmful to occupants' health and to the contents in the room.

Whole House Solutions

The best system for providing a comfortable level of indoor humidity for the entire home throughout the Canadian winter is a whole house system. This will be associated with your central forced hot air furnace or heat pump. This is a permanent installation and is fitted as an add-on device to your warm air duct immediately where the warmed air has just blown through the heat exchanger. It is an evaporative system with similarities to the portable units already discussed.

The whole house humidifier has a reservoir which may be located inside or immediately outside the warm air plenum (the duct above the heat exchanger). The reservoir water supply is refreshed as needed by a permanently attached water line.There is a float inside the reservoir that controls a valve. When the water supply is too low, the float drops and the valve opens. When enough water has entered the reservoir to lift the float the valve closes. You do not have to manually fill the reservoir.

The inside reservoir is an older system that uses fiber type plates that wick up the water in the reservoir.  As the warm air passes over these plates, the moisture evaporates and is distributed throughout the home via the distribution ductwork.

When the reservoir is mounted outside the warm air plenum, a duct passes air from the return air plenum, through the reservoir and into the warm air plenum.Again, fiber plates may be used to wick up the moisture in the reservoir and that moisture is picked up and distributed.

Rather than using fiber plates to wick up the moisture, some systems used an electrically driven drum that is covered with a mesh material.As the drum slowly spins, it acquires water from the reservoir, and the warm air passes over that drum and picks up the moisture for distribution throughout the home.This adds a mechanical component unlike the other systems described above.Be mindful that mechanical systems may break down without proper maintenance.

The upside to the drum type system is that it is usually controlled by a humidistat.It operates like a thermostat, but measures and controls humidity instead of temperature.So, once you establish a comfortable set point, it will activate only when the humidity drops below that set point. The humidistat is frequently located adjacent to the furnace's thermostat.

Some things to note:

  • Reservoirs located inside the warm air plenum may corrode as they age and leak; thus damaging the furnace casing and possibly the heat exchanger. These older systems need to be inspected periodically to determine if they are leaking.Remember, they are connected to a permanent water supply, so the potential damage could be significant if left unchecked.
  • Like the portable systems, these whole house systems can acquire mineral and/or bacterial contaminants.They need regular cleaning during the heating season. During the warmer months, you should turn off the water supply to the reservoir and leave it dry until the new heating season.

Over many years of home inspections, it was rare to find a whole house humidifier in good working condition. Consulting with home inspectors across the country, this is a consistent trend.Hopefully you now have a better understanding of what they do and why and how to maintain them.Your burner technician can give you advice specific to your system when you have them in for their annual furnace inspection and maintenance.

The need for humidification in homes (and commercial buildings) varies depending on the season, the health of the home's occupants, and the geographic location. Coastal areas benefit from the moisture in the large bodies of water adjacent.Inland areas tend to have colder, drier winters so the need for humidification is more urgent. Your local CAHPI home inspector will note the condition of your humidifier as part of the general home inspection.  Find a CAHPI Home Inspector.

January 31, 2023
The Heat Is On
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