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How to measure humidity in your house

Indoor humidity is about more than your comfort — it can impact your health and damage your property. Here’s how to measure it.
By
Published on January 8, 2024
Written by
Jeff Somers
Jeff has been writing for HouseFresh since 2023. He lives in Hoboken, NJ with his wife and their cats, and has published nine novels and more than fifty short stories. In addition to writing for HouseFresh, Jeff also covers topics connected to home ownership for Lifehacker,
TL;DR

The relative humidity inside your house has a tremendous impact. Both high and low humidity can damage materials and exacerbate illnesses.

There are three ways to measure the relative humidity in your home: The ice cube method, the wet/dry bulb method, or by using a digital tool called a hygrometer.

If the humidity in your home is too high, investing in a dehumidifier or and reducing the amount of water vapor you produce can lower it.

If your home’s humidity is too low, a whole-house humidifier and finding ways to generate more water vapor (e.g., boiling water) can help.

Being comfortable and safe in our own home is paramount. One of the most crucial aspects of that safety and comfort is the humidity (the amount of water vapor in the air) inside your home. While most people think of the stuffy, heavy feeling of high humidity (especially when combined with high temperatures), low humidity can be just as damaging to your comfort, health, and property.

Ideally, your home should have an indoor relative humidity (RH) level between 30 and 60 percent. Above that range will not only make the interior of your house uncomfortable, but can cause mold to grow, with a negative health impact, encourage pests, and potentially damage wood and other materials. Low humidity can cause nosebleeds, sore throats, dry skin, and exacerbate asthma and other respiratory illnesses.

If you are concerned about the humidity in your, here’s how to measure it.

Three ways to measure humidity in your house

You can’t always rely on the “feel” of the air when it comes to relative humidity; higher dew points can make high humidity feel less uncomfortable, so it’s best to measure the humidity to determine if you need to install a dehumidifier or find other ways to lower the relative humidity in the house. There are three ways you can measure humidity on your own.

1. The ice cube method

A very simple method to determine whether your humidity is high or low requires nothing more than a glass of water and some ice cubes. This won’t be a very informative test, but it can broadly determine whether your relative humidity is high or low.

  1. Put three or four ice cubes inside a glass of water
  2. Place the glass in the room you want to measure and leave the room 
  3. After four minutes have passed, check to see if there is condensation on the outside of the glass
  4. If there is, the humidity is high. If there’s no condensation, then your humidity is on the lower side.
Good to know

Measuring the humidity levels in wet areas like kitchens and bathrooms can be challenging because the humidity will naturally spike (like when you’re taking a shower) and then drop.

2. The wet/dry bulb method

Another easy DIY method of measuring the humidity in your home is a bit of a science project called the Wet/Dry Bulb Method

You’ll need:

  • Two standard thermometers
  • A piece of gauze or cloth
  • A small fan
  1. Wrap the bulb of one thermometer in gauze or cloth
  2. Wet the cloth
  3. Arrange both thermometers so the fan can blow air over their bulbs
  4. Measure the temperature they report:

    – The dry thermometer should remain stable
    – The wet thermometer will show lower temperatures over time as the water evaporates
  5. When the temperature of the wet thermometer stops changing, note both temperatures
  6. Subtract the dry reading from the wet reading 
  7. Use the chart here or the calculator here to determine the relative humidity

3. Use a hygrometer

The easiest way to measure the humidity in your home is to purchase a digital tool called a hygrometer. You can buy devices with built-in hygrometers for less than $10, or buy more sophisticated smart devices

Using a hygrometer to measure humidity is very simple: Set up the device according to instructions and note the result displayed on the device’s screen.
While most hygrometers are relatively accurate, it’s best to test and calibrate a new unit before relying on its results.

  1. Fill a bowl about 2/3 of the way with water
  2. Add salt and stir until no more salt dissolves; there should be a small amount of undissolved salt at the bottom
  3. Place bowl and hygrometer in a plastic bag together and seal the bag
  4. Wait six hours and read the hygrometer:

– If the RH reading on the hygrometer is about 75%, it is accurate.
– If the reading is higher or lower, the difference is your calibration factor.

For example, if it reads 70%, you should add 5% to all future readings

What to do if your house is too humid

If your home is consistently measured to have relative humidity over 60% you should act to reduce the humidity before it negatively affects your health or your property. Here’s what to do and not do.

What to do

DO Increase ventilation. Air movement and exchange is crucial to humidity control indoors. Running air conditioning, fans, or opening windows can reduce humidity dramatically.
DO Install a demhumidifier. A dehumidifier reduces excess moisture in the home.
DO Add houseplants. Plants such as aloe vera or lilacs absorb moisture from the air, dehumidifying a space naturally.
DO Clean filters. Clogged filters on HVAC equipment or dehumidifiers can impair their performance.
DO Locate and repair leaks. Any signs of water intrusion should be investigated and repaired.

What not to do

DON’T Delay. High humidity can result in house-wide damage if left unchecked.
DON’T Take long showers. Any activity that produces steam will increase humidity. Shorter, cooler showers will help reduce it.
DON’T Run the dryer. Hanging clothes outside to dry will prevent excess moisture from being pumped into the air.
DON’T Cook. Avoiding simmering pots on a stovetop can reduce the amount of moisture in the air.

What to do if your house is too dry

If your home’s humidity levels are below 30%, take steps to bring it up to more comfortable levels. Here’s what to do, and what not to do.

What to do

DO Use a whole-house humidifier. The increased capacity of a whole-house humidifier can improve the humidity levels throughout the house.
DO Add houseplants. Due to a process known as transpiration, houseplants can both increase or decrease humidity depending on environmental conditions.
DO Use water. Placing open containers of water near heating vents or boiling water on the stove can release moisture into the air.
DO let dishes and clothes air-dry. Laying out wet clothes and opening the dishwasher after running it will release that moisture into the air, increasing humidity levels.

What not to do

DON’T ignore symptoms. Dry, itchy skin, irritated throat or nasal passages, dry eyes, and increased static electricity should be investigated.
DON’T run the AC. Air conditioning will lower the humidity even further.
DON’T use dirty water. Ensure the water used in any humidifier or open container is purified and fresh, and clean your humidifier regularly.

Wrapping up

The relative humidity inside your home can have a negative impact on your health, your enjoyment of the home, and the property itself. Taking steps to measure, monitor, and manage the humidity in your home requires a few simple tools and some easy lifestyle adjustments—adjustments that will pay off with a more comfortable and healthier home.

SOURCES

About the author

Jeff Somers

Jeff has been writing for HouseFresh since 2023. He lives in Hoboken, NJ with his wife and their cats, and has published nine novels and more than fifty short stories. In addition to writing for HouseFresh, Jeff also covers topics connected to home ownership for Lifehacker,