Humidity in your home

Humidity basics

To manage the humidity in your house, it helps to understand what humidity is and how it’s normally measured.

Humidity is what we call water vapour in the air. The more water vapour, the higher the humidity. Low levels of humidity feel very dry, while high humidity feels wet. An important aspect of humidity to remember is that warm air can hold more water vapour than cold air.

There are several ways to measure humidity. When we’re talking about humidity in the home, we usually use relative humidity. Relative humidity tells us how much moisture is in the air compared to the maximum moisture the air can hold at the current temperature. It’s expressed as a percentage. At 100%, the air cannot hold any more water vapour.¹

There’s really only one way to measure humidity: with a hygrometer. Fortunately, hygrometers are widely available and not very expensive. Failing that, you might notice condensation on cool surfaces (like water pipes or windows) when the humidity is high.

Effects of high and low humidity

The humidity levels in a building have many effects, both on the building itself and the people inside it.

High indoor humidity can cause mould and mildew to grow if it’s sustained for a long time. It can also warp wood flooring and furniture or even cause it to rot. It may also cause water stains on walls and ceilings and create unpleasant musty odours.

Low humidity, on the other hand, isn’t as harmful to building materials. It can, however, cause health issues. Sore throats, irritated eyes, nosebleeds, dry skin and worsening asthma or bronchitis are all possible side effects of overly dry air.²

Ideal humidity levels in your home

The best relative humidity level for the inside of your home is between about 40% and 60%.³

Humidity lower than 40% starts to cause health issues like nosebleeds and dry skin. Humidity higher than 60% increases the risk of mould formation and physical issues with the building — not to mention that it feels uncomfortable.

Within the optimal range, the proliferation of mould, fungi, bacteria, and viruses is minimized.⁴ It’s also the most comfortable range for most people, though that depends on the season.

Most of Canada experiences dry winters and wet summers. You may find it difficult to keep the humidity high enough in the winter and low enough in the summer, depending on where you live. Winter in the BC South Coast, for example, is plenty humid.

Next, let’s look at how to adjust your home’s humidity.

Controlling home humidity levels

Adjusting the humidity in your house can be a challenge. There are many sources of humidity, and humidity levels can vary wildly from room to room and throughout the day. Plus, you can’t control the weather — the leading cause of high or low humidity. For example, much of Canada experiences relative humidities higher than 80% during the summer months. Bringing that down to a manageable 60%-or-less inside the house can be tough.

Nevertheless, there are many options for affecting the humidity indoors. In the most basic terms, there are two things you need to pay attention to: sources of water vapour and ventilation.

Lowering the humidity

When the humidity in your home is too high, you either need to remove sources of water vapour or ventilate the space and introduce drier air.

Common sources of moisture in the home include showers, dishwashers, plants, and cooking food. Defects like leaking pipes or drafty doors can also introduce extra moisture. Stay abreast of such issues and get them fixed as soon as you discover them.

Groundwater and poor drainage outside the building can also contribute to interior humidity. Ensure your eavestroughs and perimeter drains are in good working order and clear of debris.

Here are some easy tips for lowering your home’s humidity:

1. Always use the bathroom exhaust fan while showering or bathing. Keep it running for at least 15 minutes after you’re done.
2. Lower the water temperature of your showers to reduce the amount of steam.
3. Always use the kitchen ventilation fan while cooking, especially if you’re boiling water.
4. Avoid hang-drying laundry indoors.
5. Keep heating vents and radiators clear of obstructions, with plenty of open space around them to circulate the warm air.
6. Leave interior doors open to help air circulate throughout the house.
7. If the weather permits (and the outdoor humidity is lower), open your windows to let fresh air in.
8. If you have an air conditioner, use it — A/C units also dry the air.

If your home has persistent high-humidity issues, you may want to invest in a dehumidifier. A good humidifier will help reduce your interior relative humidity to around 30–50%.⁵ The downsides are cost, of course. Most dehumidifiers are only effective in one room at a time, and you do have to be careful not to dry things out too much.

Raising the humidity

During cold winter months, relative humidity in many Canadian homes drops far below the comfortable range. Winter humidity inside many homes is below 30% — uncomfortably dry. Fortunately, raising the humidity is much easier than lowering it.

As with lowering the humidity, building factors like drafty windows or incomplete moisture barriers can interfere with indoor climate control efforts. There’s no point in running a humidifier if all that moisture’s getting sucked out of the house. Fixing such issues may require hiring a professional, but it would be worth it in the long run.

Assuming your house is in order, you can do plenty of things to bump up the humidity. The most effective tips for increasing humidity are basically the opposites of lowering it:

1. Rather than using the bathroom exhaust fan while showering, leave the door open and use a portable fan to push warm, wet air into other rooms. (Don’t try this with cooking unless you’re only boiling water — range hood fans vent pollutants and harmful fine particles in addition to moisture.)
2. After having a bath, leave the water in the tub until it cools. Again, you’ll need to use a portable fan to move the moist air out of the bathroom.
3. Hang dry your laundry inside rather than using the dryer.
4. If you have a dishwasher, open the door as soon as the cleaning cycle is done to allow the dishes to air dry.
5. Get some additional houseplants. Plants add a small amount of moisture to the air, but water evaporating from the moist soil helps, too.
6. Set bowls or trays of water around the room to evaporate (especially near heaters or registers).

Many people in dry climates buy humidifiers for their homes. Like dehumidifiers, they can help a lot, though usually only one room at a time.

Be careful with any efforts to increase your home’s humidity. Remember: sustained high humidity leads to mould, warping wood, musty smells, and other unpleasantness.

Humidity and home insurance

We’ve established that excessive humidity causes damage, whether mould, warped wood, or rot. Will home insurance cover the cost of repairing this damage? Unfortunately, it will almost certainly not. Insurance is meant to cover sudden and accidental damage.

Home insurance policies almost always exclude gradual damage that occurs over time, regardless of the source. In theory, the homeowner should identify and address these issues before they have time to do any real damage. Humidity is no exception — it’s important to monitor the humidity in your home not just for comfort but to ensure it’s not harming the building itself.

Commonly asked questions

What happens when indoor humidity is high?

When the humidity inside a house is too high (above about 60% relative humidity), it may lead to the growth of mould or fungi. It can also warp wood and cause paint to flake or peel. Home insurance won’t pay to repair damage caused by persistent high humidity, so it’s important to keep your home’s relative humidity levels below 60% as much as possible.

Does an air conditioner remove humidity?

Air conditioners reduce the humidity while cooling the air. As the A/C unit draws heat out of the air, some of the moisture inside the air condenses into water. Inside the air conditioner is a condensation pan that collects water as the unit operates. All the water in the condensation pan used to be in the air — a visual representation of dehumidification.

How do you check the humidity in your house?

The only way to measure humidity is with a hygrometer. These are available from many retailers, and most are inexpensive. Some devices, like dehumidifiers, have built-in hygrometers.

You may notice high humidity (aside from feeling it) in the form of condensation on cool surfaces. If the humidity in your house is high, you might see water droplets forming on the outside of water pipes, windows, or a glass with a cold beverage inside.

Sources

1. National Weather Service. “Discussion on Humidity.” weather.gov, www.weather.gov/lmk/humidity. Accessed 25 Sep. 2024.
2. Stanborough, Rebecca Joy. “8 Ways Dry Air Can Affect Your Health.” healthline, 25 Aug. 2020, www.healthline.com/health/dry-air.
3. Health Canada. “Relative Humidity Indoors: Factsheet.” Government of Canada Publications, publications.gc.ca/collections/collection_2018/sc-hc/H144-33-2016-eng.pdf. Accessed 25 Sep. 2024.
4. Arundel, Anthony A., et al. “Indirect Health Effects of Relative Humidity in Indoor Environments.” Environmental Health Perspectives, Vol. 65, Mar. 1986, pp. 351-361.
5. Watson, Kathryn. “What Does a Dehumidifer Do?” healthine, 22 Jun. 2020, www.healthline.com/health/dehumidifier-benefits.

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