In our previous blog posts, we discussed the impact of indoor humidity on Covid-19 transmission, and the importance of humidifiers at home. Now you may be considering investing in a humidifier to help make your home healthier and more comfortable. With so many different types of humidifiers currently on the market, selecting the right one may seem like a daunting task. In this article we discuss how to select a humidifier that is best suited for your home, as well as how to use and maintain it.
Common Types of Humidifiers
Standalone humidifiers allow for flexible installation, which makes them a good choice for most homes. However, the HVAC systems in some residential buildings can also accommodate in-duct humidification systems. The mechanism of in-duct humidification systems is similar to that of standalone humidifiers. The only significant difference is in the installation and operation. Below we dive into three main types of humidifiers — ultrasonic, evaporative, and vaporizers.
Ultrasonic humidifiers use high-frequency oscillation to transform water into vapor at low pressure. Oscillation drives the water particles up from the surface so they can be quickly absorbed into the airstream and generated into the air as a cool mist. The droplets in that cool mist are relatively large and unlikely to be carried far through air movement. However, some droplets may deposit on surfaces near the humidifier (such as furniture, floors, or walls), potentially leading to uneven humidification of the room. Water droplets in the mist released from the humidifier will contain any impurities (such as mineral contents) that are present in the water tank, including minerals and germs. If your home water has lots of impurities, the droplets that deposit on surfaces or furniture may form sticky-white dust. In addition, if the water in the humidifier contains mold, bacteria, or other pathogens, the mist may spread these contaminants throughout the room. Thus, water treatment should be considered when using ultrasonic humidifiers; distilled or nano-filtered water are some of the best options.
Finally, it is essential to clean the water tank regularly to avoid mold growth inside the humidifier. This also helps reduce the chance of spreading mold or other pathogens throughout the space.
Evaporative humidifiers circulate water over a porous media and generate airflow to aid in water evaporation. The droplets in evaporated water are very small and can be delivered further throughout the space via air movement, compared to the large droplets released from ultrasonic humidifiers, thus humidifying a space more uniformly.
In addition, the rate of evaporation varies with air temperature, humidity, and airflow velocity. For example, a room with low temperature and low humidity will have a higher evaporation rate compared to a room with high humidity. That’s why evaporative humidifiers can be considered partially “self-regulating”: as the humidity of the room increases, the water vapor output naturally decreases.
Finally, evaporative humidifiers filter the water they evaporate. Minerals that could build up and create a “dusty” layer are therefore less likely to be distributed into the air, compared to ultrasonic humidifiers. If any pathogens are present in the water inside the humidifier, they would be captured by the porous media and are unlikely to be distributed via water vapor. However, the porous media needs to be cleaned and replaced regularly, according to the manufacturer’s instructions, to prevent microorganism growth.
Steam vaporizers create steam by heating water with an electrical heating element or electrodes. “Warm mist” humidifiers are a type of steam vaporizer where the steam is cooled after heating and before exiting the machine; however, the moisture temperature typically remains higher than room temperature, so there is no cooling effect.
The mechanism of vaporizers is very similar to that of evaporative humidifiers, except for the method of water evaporation: vaporizers use electrical power to heat up water and accelerate the evaporation process, while evaporative humidifiers rely on natural and/or forced evaporation through the airflow. Vaporizers also have similar advantages and disadvantages as evaporative humidifiers, with a couple key differences. The high temperature of vapor can kill most bacteria that may be present in the vaporizer. In addition, compared to the droplets from ultrasonic humidifiers, the water vapor from vaporizers can be delivered much further via the indoor airflow thus resulting in a more uniform humidification of a space. However, vaporizers consume more energy than other humidifier types (due to the heating process). Also, unlike evaporative humidifiers, vaporizers do not “self-regulate”, and can keep adding water vapor to the air even when the room is sufficiently humid.
Finally, rust may occur inside the water tank of the vaporizer. If possible, use distilled water or water from a demineralized water treatment system, such as a nano filter.
Comparison of Different Types of Humidifiers
Table 1 summarizes the characteristics of different types of portable (standalone) humidifiers, and is a helpful reference when selecting a humidifier that is best-suited for your home.
Table 1. Comparison of different humidifier types.
Factors To Consider When Selecting a Humidifier
Each type of humidifier has its strengths and weaknesses. To determine which humidifier is best for your home, refer to the humidifier characteristics listed in Table 1. In addition, a few other key factors should be considered:
Choosing the right size of humidifier: The size of the room or space that you want to humidify is an important factor when choosing a humidifier. It’s important to select a humidifier that isn’t too small to be able to effectively humidify the entire space. In addition, it’s also important not to go overboard with a humidifier that is too large, since it can lead to an excessive amount of moisture in the air and ultimately lead to mold and condensation issues. Manufacturers typically claim that their humidifiers are intended for specific room sizes (square footage is usually indicated on the packaging). If your home has high ceilings or there are insulation issues, a humidifier that is a little bit larger (i.e., greater square footage) should be used in order to humidify the larger volume of air.
Sensitive groups: For sensitive groups, such as the elderly, young children, and people with respiratory diseases (e.g., asthma and/or allergies), a vaporizer may be the best option as it provides the greatest degree of water sanitization.
Distilled water availability: If distilled water is not available or if your home doesn’t have a water demineralization system, evaporative humidifiers might be the most suitable option. Tap water that is not distilled may cause rust inside vaporizers, and/or lead to mineral deposits on indoor surfaces.
Other safety issues: Vaporizers may not be an optimal choice for households with young children, as the high temperature of the steam exiting the humidifier can be a safety hazard and cause burns.
How to use your humidifier
Keep relative humidity within a proper range
Whenever possible, relative humidity in indoor environments should be kept between 40% and 60%. Drier air may increase the chance of virus transmission, cause discomfort, and decrease sleep quality. While more humid air can cause mold issues and condensation, which may lead to damage of walls and other indoor surfaces.
Some humidifiers have a humidistat which controls the humidity in the room. You can set a relative humidity range, and the humidifier will automatically manage the humidity levels. If a humidifier doesn’t have a humidistat, you can purchase a hygrometer (relative humidity meter) to help ensure that the humidity levels in your home stay within the 40-60% range.
Place the humidifier in the proper location
To effectively humidify a space, it is important to place standalone humidifiers in a proper location. During colder months, humidifiers should be placed away from windows. Any mist coming out of the humidifier that is in direct contact with cold surfaces (such as windows) may cause condensation. Additionally, if steam vaporizer humidifiers are used, they should be kept out of the reach of children, as steam and boiling water may cause burns. If your home has a central ventilation system, place the humidifier close to the supply air diffuser — that way, humidified air can mix with the supply air and be distributed throughout your home.
Clean the humidifier/humidification system before storage
If using a standalone humidifier, make sure all the parts are dry before storing it away. Dispose of all used demineralization cartridges, cassettes, or filters. Store the unit in a dry location. After storage, clean the unit again and remove any visible dust.
If using an in-duct humidification system, clean the entire humidification system before pausing its use, based on the manufacturer’s instructions. This can effectively reduce the growth of mold inside the entire system.
Follow manufacturer’s recommendations
Follow the manufacturer’s instructions regarding the use, maintenance, and replacement of any parts of the humidifier.
Stop use if any respiratory symptoms occur
Discontinue use if you develop any respiratory symptoms that you believe may be associated with your humidifier.
Edited by: Bing Bing Guo, MPH, Regina Vaicekonyte, MS and Radhika Singh