How a Hygrometer Works

Does your home often feel dry? Or too muggy? If you are experiencing chapped/dry skin, or difficulty breathing while in your home, you may need to get your humidity level checked out. Humidity levels that are not between the averages of 30- 50 percent can be potentially dangerous for your health. You can personally check your humidity level in your home by using a hygrometer.

A hygrometer is an appliance that is designed to calculate the amount of humidity in a room or building. While a hygrometer can’t actually prevent mold from growing, it can warn you to take any steps necessary before the problem occurs. Hygrometers can provide the accurate levels of relative humidity and absolute humidity. Relative humidity is the percentage of humid moisture in the air. Absolute humidity is the actual amount of moisture in the atmosphere.

What Makes a Hygrometer Work?

There are two commonly used types of hygrometers: Mechanical hygrometer and wet and dry bulb psychrometer.

Wet and Dry Bulb Psychrometer

This is the easiest way to measure humidity. This type of hygrometer is equipped with two mercury thermometers, where one has a wet bulb and the other has a dry bulb. Because of the evaporation of water on the wet bulb the temperature will drop and read a lower temperature than what is displayed on the dry bulb. The difference between the two temperature readings equal the amount of relative humidity in the atmosphere.

Mechanical Hygrometer

A mechanical hygrometer requires a little more effort to determining humidity levels in a room.

  • This tool was first created in 1783 by a physicist named Horace Benedict de Saussure.
  • Mechanical hygrometers work by using an organic material, typically a piece of hair where its behaviors can predict the amount of humidity in the air.
  • If you’ve ever noticed how human hair tends to frizz when there is a lot of moisture in the air or it is very hot outside, then it will be easy for you to understand how this tool works.

For example, the piece of hair is attached to a spring and needle instrument that exposes the hair to humidity. Based on the reaction of the hair, the humidity level can be classified. Although a wet and dry bulb is more accurate and easy to understand, a mechanical hygrometer is still as effective.

How to Reset Your Hygrometer

Should you need to ever reset your hygrometer, you can do so by using at-home methods:

  • In a room with normal, consistent temperature, place your hygrometer in a cup or container filled with salt water on a counter space. Leave it to sit for 10-12 hours.
  • After the allotted time, the hygrometer should read a standard relative humidity level of 75 percent.
  • This process should be performed at least once a year to ensure your hygrometer is always providing accurate results.

What makes it effective?

Hygrometers are the go-to source for measuring humidity. This tool can be used in laboratories, manufacturing sites and storage vicinities. Even meteorologists use hygrometers to report the most accurate amount of relative humidity in the community. Hygrometers are widely used because they come with hard-to-beat features. Many hygrometers are built with alarms that will alert you when the humidity level in your home is under that 30 percent or over the 50 percent average humidity level.

Hygrometers can serve as a great way to keep you, your family, home and belongings healthy. They can also come with humidistats, which control the operation of your humidifier or dehumidifier.

Proper Humidity Levels

Too often, homeowners can’t figure out how they got mold in their home when they never had a leak.  Humidity is never considered and many do not know the important role it plays in having a healthy indoor air environment.  In fact, when we see homes with leaks versus homes with high levels of humidity, the humid home usually will have a worse mold issue that is more widespread, than a leak which can be contained to that section. Humidity levels in a home should be between 35% to 50%.  Mold can thrive when humidity levels reach 60% and above, so keeping your levels below that will insure that mold can not grow.  Proper ventilation in attics and bathrooms will also help control humidity, as will a commercial grade dehumidifier in your basement.

An easy way to test for humidity is to purchase a hygrometer. Make sure to follow provided instructions for your model on how to calibrate the machine, and then set it up in a place away from sunlight or drafts for it to take a measurement.  These instruments can be purchased online and at most box stores and are fairly inexpensive.  Having such a device can help you stay on top of humidity levels and maintain a safe and healthy home.


Reducing Humidity Levels

If your home’s air regularly has high relative-humidity readings, check for water sources around your house. These could include leaking air conditioners and plumbing lines, or damaged roofs. Also look for clogged gutters and foundation drains. In addition, too much shady foliage planted near the house can contribute to problems.

Of course, poor ventilation can easily result in high indoor humidity levels. Therefore, it’s a good idea for rooms in your home that commonly generate large amounts of water vapor to be properly vented to the outdoors, so the water vapor can’t build up indoors. Ideally, a range hood over your kitchen stovetop, an exhaust fan in your laundry room, and exhaust fans in your bathrooms, should be installed and used regularly. All such fans must be vented to the outdoors to be effective.

Bathroom fans can have a simple, manually operated on/off wall-mounted switch, a manually set crank timer, or they can be controlled by a dehumidistat. A dehumidistat is simply a device that monitors relative-humidity levels. It can be used to automatically turn on an exhaust fan when a certain relative humidity is sensed. For example, a dehumidistat could turn on a bathroom exhaust fan when the relative humidity rises after a shower. You’ll also want to make sure that your clothes dryer is vented to the outdoors.

You can also lower the relative humidity by using air conditioners and dehumidifiers. Both pull water vapor out of the air and condense it into liquid water. Air conditioners and dehumidifiers are available from many local department and appliance store.

Note that dehumidifiers can be emptied either automatically into a house drain, or manually. If you decide upon a dehumidifier, it’s important to clean it regularly to prevent mold growth. This is especially necessary with models that must be emptied manually inasmuch as they can contain standing water for some time. In the winter, closets can have a higher relative humidity than other rooms in a house, so they can also be places where mold can grow.

Understanding Dehumidification

A dehumidifiers purpose is to lower and control the humidity in the air, thus eliminating odors, providing a more comfortable environment and decreasing the chance of mold growth.  When humidity levels reach 60% and above in a home, mold growth is almost certain as well as other potentially harmful and costly issues.  The ideal range of humidity within a home is between 35 to 45 percent.  This will also limit populations of most pests including clothes moths, fleas, cockroaches, woodlice and dust mites.  By their operation, dehumidifiers produce an excess of water which has been removed from the conditioned air. This water, usually called condensate in its liquid form, must be collected and disposed of. Some designs, such as the ionic membrane dehumidifier, dispose of excess water in a vapor rather than liquid form.

Choosing the right dehumidifier can be a daunting task especially because most units sold in big home stores aren’t big enough to compensate for the area in which they are placed.  This will cause a unit to constantly run and never be able to handle the square footage of the area and make it impossible to regulate the humidity to the appropriate level.  Most basements which are 1500 square feet or more will need a bigger and more energy efficient units to achieve the desired relative humidity level.  A dehumidifier should remove 3 pints of water per kilowatt hour at 80°F and 60% RH, which is the industry standard.  Units with even greater removal rates, from 5.5 to 6.8 pints of water per kilowatt hour, will generally cost between $1500 to $2200.  They will not only pull a greater amount of water, but easily keep the RH levels at the desired rate while using a very limited amount of electricity.   So when shopping for a dehumidifier, do not get sold on price, but how many pints of water can the unit pull while understanding the limitations of the unit itself against the size of the room it is being placed in.