Humidity affects what a person feels by compounding higher and lower temperatures inside our homes and offices. We hear about the effect humidity exerts on comfort frequently, when outdoor vacationers describe the “dry cold” of Colorado mountain air in the winter or the sweltering “muggy heat” of Houston or Miami in the summertime.
From our research on the many indoor air quality topics, we will make a general observation first: the factors that affect indoor air quality interact, sometimes in ways that can be surprising. The overall goal of using humidity control equipment should be to maintain the optimum level of indoor humidity without adversely affecting some other factor. To do this, you must take your indoor environment into account, including the “envelope” of your home and your HVAC equipment.
Within the topic of humidity control, you will find listings from room size dehumidifiers and humidifiers to “whole house” models and on to industrial capacity units. For all these reasons, we recommend that you check with your local air conditioning company or indoor air quality professional to confirm that you have a well thought out, integrated plan for indoor air quality before initiating specific changes.
According to the Environmental Protection Agency, the recommended humidity for indoor environments should range between 30% and 50% relative humidity. The term “relative humidity” simply means the amount of water vapor the air contains compared to the maximum amount it could hold at any given temperature. Indoor humidity can be controlled in two ways: it can be lowered with a properly sized and functioning air conditioning system (in some situations assisted with the use of a dehumidifier); or humidity can be raised by using a humidifier.
Air conditioning and heating equipment affect humidity
Before going into more detail on dehumidifiers and humidifiers, we should first list the roles air conditioning and heating equipment play in humidity control. In addition to cooling indoor air, the conditioning of air has to do with removing humidity. If an air conditioning system has too much cooling capacity, it cools too quickly and cycles on and off in short intervals. This does not allow enough time to “condition” the air by removing the humidity. This results in excessive moisture in the air—sometimes described as a “clammy” feeling. In contrast, a properly sized and working air conditioner will adjust the humidity during cooling cycles of optimum time.
In the winter, furnaces can remove too much moisture from the air and generate static electricity. This causes lint and objects to cling your clothes, makes your hair stand on end when you brush it, or gives you a shock when you touch certain objects after walking on carpet or sliding on a sofa.
For many areas of the U.S., there are times of the year when your indoor environment does not need heating or cooling to be in a comfortable range, but may still need humidity control. Some of the more advanced air conditioning systems have provisions to accommodate this along with fresh air ventilation. Another alternative is a separate dehumidifier or possibly a humidifier.
The benefits of maintaining proper humidity control in your indoor environment span many areas:
In addition to the effects on comfort outlined above, humidity control or the lack of it impacts other areas as well.
Excess humidity promotes the growth of undesirable organisms in your indoor environment. Maintaining an inside humidity range of 30 to 50% indoors helps prevent growth of molds, mildew, and dust mites. Aside from the fact that some molds cause acute illnesses or worse, spending time in a moldy indoor environment can wear down a person’s immune system and resistance to respiratory allergies and related infections. Indoor air that is free from mold and mildew also smells fresh and inviting.
Excessively dry indoor air can dry out skin and irritate your throat and sinuses, making those areas more likely to become infected. In arid climates or in the winter when the combustion inside the furnace dries out indoor air, using a humidifier device increases relative humidity–like the can did–but much more precisely.
Indoor air that is too dry can cause wood to contract and crack, especially thinner wood such as that used to build guitars and violins. Over longer periods of time, excessively dry air can even crack solid wood beams or logs plus some types of plaster.
Dehumidifiers and humidifier equipment and how they work
In damp or humid indoor un-conditioned environments such as basements, cellars, and garages, separate dehumidifier equipment can deliver many benefits. For intensely humid air-conditioned environments such as locker rooms and showers, a dehumidifier assists the air conditioning system with its work. Dehumidifiers work by pulling indoor air across warm and cool coils that contain refrigerant. As the air passes over, the moisture condenses and is collected in a container to be emptied.
On the opposite end of the scale, humidifiers are sometimes necessary for arid climates and also during cold weather when the furnace dries out the indoor air.
A humidifier works by adding water vapor to the indoor air. Humidifiers accomplish this by one of the following four methods or variations/combinations of producing vapor from water.
- Evaporating of water with a fan- Wicking action pulls water up into a cloth like filter or media, where a fan helps disperse and evaporate. No heat added.
- Boiling to produce steam- Electric element heat source. For safety reasons, some types cool the water slightly before dispersing it into the air.
- Rapid stirring with an “impeller” high speed rotating disk. No heat added.
- Ultrasonic sound vibrations. No heat added.
These humidifiers share some elements in common, such as having to replenish the water reservoir, and the need for cleaning or maintenance, and some kind of power source.
Since combustion in the furnace tends to dry out the indoor air, some types of central humidifier systems connect with the central heating system. The whole house systems can also connect with the plumbing system to avoid manual refilling. Due to connecting with existing HVAC and plumbing systems, this type of central humidifier requires professional installation.
Controls for humidifiers and dehumidifiers
Humidifiers and dehumidifiers have control specific to their purpose.
For humidifiers the control is called a humidistat. Humidistats use computer technology to measure the outdoor temperature and indoor humidity and continually adjust the indoor humidity of your home to an optimum level. They can mount to the wall and looks similar to a programmable thermostat.
On the flip side, whole house dehumidifiers and many portable units are run by controls called dehumidistats. Within air conditioning systems, these can be used to help control mildew formation.
Features and brand considerations
There are many brands of dehumidifier and humidifier equipment available, both in stores and through your heating and air conditioning contractor. Our overall opinion about brand is this: compatibility with your indoor air environment, features, service, and perhaps manufacturer’s warranties are important factors. Especially, in a central system, the service you get from your provider will make a big difference. Within that context, brand could be a deciding factor if all or most of the other factors are equal.
For dehumidifiers, the primary feature to compare is the dehumidifying capacity, which is measured in pints per day. A small-capacity unit would have a rating of about 25 pints daily, while a large capacity one would be rated at 50+ pints. A unit with higher capacity works quicker and more efficiently than a smaller one.
Plus, it would work in a wider range of humidity levels or room sizes.
After dehumidifying capacity, the most important features are ease of water removal, controls, and warranty.
Select a model with an easy-to-empty water container, preferably with handles and a lid to prevent spills. A useful alternative feature that saves you from having to manually empty the container is a drain hose or fitting for one. With a hose you could route the trapped water to a floor drain or perhaps to under sink plumbing. Other desirable features include easy to read and understand controls, especially digital electronic ones.
Since they store water and distribute water vapor, under certain circumstances humidifiers could introduce undesirable substances into the indoor air. This usually involves substances dissolved in the supplied water, such as minerals, or organisms that grow on the reservoir walls, its water or media, such as bacteria, molds, mildew, etc. Using demineralized water or a mineral filter and regular cleaning could help with both categories of potential contamination. Also, some humidifier models have antibacterial features, such as ultraviolet light or use of silver compounds to help prevent the growth and spread of bacteria. To prevent the spread of mineral dust as the water evaporates, some models include various kinds of filters or traps for minerals in the water.
Other than the “whole house” or central system vs. the room size units, some of the other main features to look for are: humidifying capacity expressed in maximum square feet of coverage or possibly gallons per day, energy usage, fan speeds, noise, reservoir capacity (frequency of filling), ease of cleaning, automatic controls, and manufacturer’s warranty. For closer attention on the comfort aspects of humidifiers, you can look for units that offer warm mist (for winter), cool mist (for summer), or both in one unit.
List of manufacturers and brands of dehumidifiers and humidifiers
- Hampton bay
- Santa Fe
- Hamilton Beach
Coordinate humidity control with your air conditioning and heating
To get it right the first time, make sure you coordinate humidity control with your air conditioning and heating system. If you don’t have an air conditioning and heating service you rely on, use the links on the right side of this page to locate one in your area.