How to choose the right humidifier: Demystifying the winter mist must ...

"The [optimum humidity] for healthy skin and also nasal passages is about 40 per cent to 50 per cent," says Toronto dermatologist Dr. Sonya Cook. "In the wintertime in Canada, if you don't have a humidifier, it could get really low indoors, to 20 per cent or even less." At that level of relative humidity, says Dr. Cook, the air can have a drying effect, especially for anyone with an "impaired skin barrier" (for example, individuals with eczema and older adults), that can lead to dry, itchy skin.

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"For anyone that's complaining of dry skin, or just for general health, it's good to have proper relative humidity," says Dr. Cook. "I find most people, even if they have a central humidifier, often it doesn't get up to that sort of perfect level, so it can be good to have an add-on humidifier in your bedroom." Just be sure that you keep it clean, as illness-causing mould and bacterial growth can develop over time if you're not cleaning out the mineral deposits and changing the water and filters out frequently, notes Dr. Cook.

She recommends looking for a humidifier with a built-in hygrometer, or buying a separate one at a hardware store, so that you can be sure to keep the indoor humidity level at home is in the optimal range. "In Canada, you're not supposed to have it so high that you'll get condensation on the window; we might have to keep it at a lower number just to prevent condensation," says Dr. Cook. "But hopefully you get away with 35 per cent humidity or higher."

How humidifiers work

To help you pick out the right room-humidifier for your home, we talked to George Oram, Lead Design Engineer at Dyson (he helped develop the company's humidifier) to find out the technical basics, the features to look for at all price points, and the newest innovations in the space.

According to Oram, generally speaking there are two different types of cool-mist humidifiers: "Evaporative, which takes water and evaporates it so it turns into water vapour — essentially humidifying drier air by passing it across a wet surface, such as a paper-based wick material or a plastic-covered plate — and ultrasonic, which projects water droplets out of the machine using a nebulizer (a fast-vibrating disc that atomizes the water) or centrifugal atomizer." Vaporizers that heat up water to create steam are a third option, but Oram notes that they can be dangerous for young children because of the heat and burn risk, and globally, heated humidifiers are not very popular outside of Canada and the United States.

Ultrasonic humidifiers offer a "cooling sensation when you're standing in front of them" because the water droplets "flash evaporate into vapour outside of the machine," says Oram, making them a popular choice for year-round use. Evaporative humidifiers need a lot of airflow to work well, and can be noisier, notes Oram. Plus, some models will require filter replacement over time. 

The key features to look out for

An important initial consideration, says Oram, is deciding whether you're looking for just a humidifier, or one that offers multi-functionality — pricier models can work as a fan, a heater or an air purifier, too. If you're looking to use essential oils with your machine, you'll want to find a model that's designed for that.

Beyond that, he notes that with ultrasonic humidifiers, you'll want to look for a machine with disinfection technology such as ultraviolet light (UV) or silver ion cubes built-in, because that water that's being projected into the room might otherwise contain things like bacteria or limescale, which can leave chalky white residue in your space. "That's really key because you are breathing in that room air, and so you don't really want to be projecting bacteria into a room," says Oram. And an easy-to-clean machine is also essential, because mineral or limescale build-up can be an issue with ultrasonic humidifiers. "I would also look for a water tank and machine that is easy to clean, whether you can physically remove the parts, or perhaps put your hand inside of the tank to clean it, or the machine has a specific cleaning cycle," advises Oram. For a strong machine with medium to high humidification output, Oram suggests looking for one with a 250–300 mL range, "That just ensures that it's not taking a really long time to humidify your room." Some of what Oram calls "machine intelligence" features, such an automatic mode that can monitor the room's humidity level and automatically switch on when required, can also be helpful, if they're in your budget.

With evaporative machines, which tend to have fewer bells and whistles, ease-of-cleaning should be a primary consideration. "Being able to easily either clean the water tank or the machine itself is important," says Oram. Machine intelligence and easy upkeep are other key features here as well.

The next-gen innovations to know

Combination purifier-humidifiers are becoming a big trend globally. "There's been a lot of awareness on air quality and how that affects your life," says Oram. "So it's adding that additional filter around the machine in some way, or passing the air in the room through a particulate filter to remove things like dust, pollen and smells."

There are also lots of new water disinfection and purification technologies starting to be used with humidifiers today. For example, "There are a couple of products now that have UV-C LEDs, so they have a smaller space package, use less energy, and can treat higher amounts of water," says Oram.

Ultrasonic Humidifiers

A shapely, no-frills option, Crane's drop humidifiers are available in a variety of colours and can humidify a space up to 250 square-feet. (The company's distinctive, animal-shaped humidifiers are a popular choice for children's rooms.) 

Crane Ultrasonic Cool Mist Humidifier Blue Drop, $84.99, Hudson's Bay

The priciest humidifier on the market, Dyson's sleek AM10 comes with features such as a sleep timer, UV-C anti-bacterial cleaning technology, automatic temperature and humidity reading, and a remote control. And, it can be used as a high-powered fan.

Humidifier AM10, $599, Dyson

Noma's modern looking, top-fill humidifiers are available in a variety of sizes (there's even an evaporative option, which costs a bit more). This one is recommended for spaces up to 400 square-feet and offers multiple fan settings, a pre-set timer, and built-in nightlight.

Noma Cool Mist Ultrasonic Humidifier 3.5-L, $119.99, Canadian Tire

Evaporative Humidifiers

This very reliable machine, recommended by review-site Wirecutter, is easy to clean and fill, and doesn't make too much noise — look for the model with ultraviolet sanitizing built in, which will cost a bit more than the one without. One drawback is that you'll have to buy replacement wicks a few times a year, and they're not cheap.

Honeywell Germ Free HCM-350 Humidifier, $122.04, Overstock.ca

Made in Germany, this boxy humidifier and air purifier combo doesn't require a replacement filter and comes with a 10-year warranty. It has an auto shut-off feature and is recommended for rooms up to 200 square feet.

Venta Airwasher LW15 2-In-1 Humidifier And Air Purifier, $279.99, Bed Bath & Beyond

Humidifiers are a big part of HVAC systems in dry locations, especially in the winter. I have no experience with them personally because they aren't prevalent at all in Florida.

I asked some of the HVAC School contributors to weigh in with some of their top humidifier tips. Thanks to Nathan Perney, Steve Domansky, and Allen Pavolko for weighing in.

First, Nathan Perney gives us a detailed look at humidifier selection and sizing:

We do a LOT of humidifiers here in dry old Denver.

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My take on selection, like most things I do, is a little different than most.

If we look at section 27 in the eighth edition of Manual J, there is a great methodology for determining winter humidification load.

It's pretty straightforward.

First and foremost, get a good estimation of wintertime infiltration and exfiltration. That’s right! Set up the blower door. This step rarely happens.

Next, determine your target indoor humidity. That part is a little tricky. Manual J shows some calculations for determining winter humidity that will keep the building safe. Safe means dry. Dry means no hidden condensation. Page 139 in the Builder Guide to Cold Climate Construction shows the same calculation. I like Lstiburek’s approach over Rutkowski with regard to the humidity target. It’s the same math; I’ve just been a disciple of Lstiburek for longer. Haha.

Once you get the target humidity, convert your CFM of air leakage to a mass airflow of air leakage. Let's say we have a house leaking 100 CFM at my air density of . lb per cu/ft; that would be 6.13 lbs of air per minute.

At this point, get out your psychrometric chart. (Here is the one I use often.)

Now, convert your mass air leakage to grains of air leakage. 6.13 lb/min of air leakage at 50% RH at 70°F = 66.6 grains per minute x 60 minutes x 24 hours = 95,904 grains per day. WOW! We know there are 7,000 grains per pound. That gives us 13.7 pounds of water a day, or about 1.7 gallons per day, or .07 gallons per hour.

All right! Now we can take the gallons per hour and look at the humidifier specifications:

Based on the Aprilaire data, we might want the 400, 600, or 700 series.

The manufacturer alludes to this calculation in the performance information:

The really interesting thing is the air leakage component. Older leaky houses need WAY more humidity than new tight houses. Just as the warmth from our heating systems leak out before we can feel it. In old, leaky buildings, the humidity leaks out before you can sense it. However, in newer, tighter houses, we can have problems. In fact, I have seen several new, tight houses over-humidifying and having serious condensation issues. Water is amazing; it moves mountains. It also destroys buildings better than pretty much anything—aside from explosives. The good thing is cold air is dry air, so drying buildings in the winter is much more realistic than during the summer.

Wait. What did I just say drying a building during the winter? You better believe it. Depending on what you do in your home, how tight your home is, and what the building assemblies are comprised of, you may well need to dry the building during the winter. Just ask the Canadians. As building codes are pushing building tightness tighter and tighter (this is a good thing), we will see more over-humidification issues. Over-humidification of new buildings in cold climates is a very serious issue we will begin seeing more and more.

The biggest install failure is not getting the drainage correct. Test the drains, or you're asking for problems. Test the operation, or you're asking for problems. Make sure they turn on and off when you ask them to. I had a job recently where a steam humidifier was wired to create steam any time the unit had power. The installer wired the relay incorrectly, and we had 75°F 70% humidity in the house. The windows were raining. It was awesome. Like anything, read the dang manual. Steam humidifiers are very temperamental, so if you don't follow the manual, you will have problems. Steam humidifiers have very specific tolerances for where and how they can and cannot be installed. One thing to be wary of is that you are setting up a steam humidifier to operate with a constant fan. Check the velocity of the air during the fan-only mode. If the air is not moving fast enough, you will get condensation in the ductwork (this is bad). Another common install error is the HUM terminal on the control board may r 24 VAC. All residential humidifiers that I  know of require 24VAC to control the unit. If you don’t install an isolation relay, you will fry the solenoid valve.

—Nathan Perney

Allen Pavolko shared his perspective from the Eastern US:

Proper Selection

Choosing the right humidifier for your home depends on multiple things. These include but are not limited to the size of the home, heating system, ductwork availability, and geographic location. Where I live (Southwestern NY, near Buffalo), most homes that have a forced-air furnace have a bypass humidifier installed to help keep the relative humidity in the living space during those dry winter days. Due to cold air not being able to hold as much moisture, we tend to lose humidity in the wintertime. That can lead to higher counts of airborne viruses staying alive in the air, static electricity buildup, drier skin, improperly sealed/treated wood cracking, etc. Keeping the humidity between 30% and 50% in the living space year-round can help battle all of those things.

The biggest element of choosing a humidifier, in my opinion, is what ductwork you have available to attach a system to. If you have enough room to install a bypass humidifier, you can treat up to a 4,000 sq ft house with one, but you need ample room to mount the humidifier and pipe it to the other airstream. If you don’t have the room to do that or have a bigger house, you can do a power humidifier. These have a fan built into them to push the air through the media and can treat up to 4,200 sq ft. The last option for ducted systems is a steam humidifier, which can be remotely installed and piped into the airstream. These systems can treat up to 6,200 sq ft of living space, take significantly less space to install, and can be remote, as I stated prior.

Note: Obviously, coverage size is specific to the humidity needs and design of the home, as Nathan pointed out.

If there is no ducted system in the space, then you can get a non-ducted system that just adds water vapor to air and lets natural convection currents take over to distribute. Or you can use a steam humidifier paired with a fan pack to distribute the water vapor to a central location.

How to Install 

The best scenario is to install the humidifier unit on the supply air plenum with it piped over to the return air drop. Our local rep for a well-known humidifier manufacturer advised using hot water for the feed tube as often as possible, as it helps the water evaporate faster. Always utilize a flow restrictor on the water supply, as not to add way too much water to the evaporation pad. Together, these things make for the best, in my opinion, way to get humidified air into the living space. The hottest air passes over already warm water on the pad and evaporates as quickly as allowed. This goes into the airstream and passes back through to the house. If possible, install an outdoor air temperature sensor to control humidity levels in the home automatically.

Common Mistakes

The most common mistake I have seen in the field is failing to make sure the humidifier is level and plumb. This can cause the unit to leak!

Another common mistake is removing the fabric out of the distribution tray because it looks and feels gritty. This is there for a reason, and that is to allow the water to flow through each distribution channel evenly.

Common Service Failures 

I have often seen a solenoid valve misdiagnosed as being bad due to water not flowing through it. I live in an area with high mineral content in the water; this, coupled with the small diameter water piping and small orifice, often leads to a plugged-up orifice/flow restrictor.

—Allen Pavolko

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