When warm, moist air meets a cold surface, the moisture in the air condenses on that surface. In homes, this can occur on windows or cold-water pipes. Over time, this condensation on your windows can cause mold to form and can also peel the paint on the interior window frame.

Where does humidity come from?

Humidity - which is vaporized water in the air in your home, comes from many sources. Your breath contains a very high concentration of moisture. A crowded room can generate litres of water over the course of an evening. Cooking, showering and bathing also contribute to high humidity levels in a home.

Is humidity a bad thing in my home?

Like temperature, humidity levels are measured on a scale. Too much humidity in your home is not good. Too little humidity is also not desirable. The goal is to keep temperature and humidity at comfortable levels. Homes require a minimum humidity level to maintain air quality and to ensure we don't get dry, itchy skin.

How do I control the humidity in my home?

  • Turn down, or stop using a humidifier in your home.
  • Ensure vents for the attic, basement, and crawl space are open, adequately sized and cross-ventilated.
  • Run the exhaust fans for kitchen, bathroom and laundry rooms for longer periods.
  • Make sure exhaust fans vent directly outside and not into attics or crawl spaces.
  • Follow the manufacturer’s instructions for venting gas appliances.
  • Make sure your furnace is in proper working order and is serviced regularly and that your fresh air intake is not blocked by snow or other obstructions.
  • Open a door or window for several minutes each day to refresh the inside air.
  • Open window coverings – like blinds or drapes – during the day to increase airflow over window glass.
  • Monitor the furnace humidifier.
  • Cook with covers over your pans and pots.
  • Take shorter showers with cooler water.
  • Reduce the number of plants in your home and water them less. They release water vapour into the home air.
  • In high-efficiency, tightly insulated homes, consider installing an air-to-air heat exchanger.
  • Employ a dehumidifier in your home.
  • Use the bathroom exhaust when showering or bathing
  • Remove Interior screens on windows during cold months
  • Try to improve air flow in home by ensuring cold air return ducts are not covered
  • Ensure basements walls are kept as dry as possible because they act as home humidifiers. Placing a local dehumidifier in the basement may be a solution.

What levels of humidity are ideal in my home?

The human body is most comfortable at humidity levels between 20% and 50%. The amount of moisture air can hold is affected by the temperature of the air. The warmer the air the more water it can hold. This is why hurricanes form in the Caribbean – the warm ocean water is like high octane fuel that charges the warm air with moisture. The term that describes this phenomenon is ‘relative humidity’. Relative humidity is a way of describing how much humidity is present in the air, compared to how much there could be. The amount of humidity air can hold is relative to its temperature. Fog as an example, happens when the relative humidity of cooler air is 100%. As the temperature increases the fog dissipates because the warmer air can hold / hide the moisture. Science lesson over…

The following table shows the recommended indoor humidity levels in relation to the outdoor temperature.

Outside Temperature Recommended Relative Humidity
+20° and above 35% to 40%
+10° 30%
25%
-10° 20%
-20° 15%

When interior humidity levels are too high in comparison to the cooler outdoor temperatures, condensation can form on the coldest surface in a room – like the glass in a window or door. As a result, you should lower the relative humidity levels in your home during the cold winter months.

Where does humidity come from?

Humans. We are responsible for the humidity levels in our homes.

  • Showering puts a cup of moisture into the air, bathing a half a cup
  • Cooking for a family of 4 produces 10 cups of water into your home environment over a 24 hour period
  • One person breathing releases ½ a cup of water per hour.

Adding only eight to 12 cups of water into the air raises the relative humidity of a 1,000 sq. ft. home from 15% to 60%, assuming that the temperature remains constant.

I’ve done everything I can to reduce the humidity levels in my home. What else can I do to stop condensation on the inside of my windows?

Install new windows that are more energy efficient than your current windows. The more thermal insulation your window provides, the warmer the inside glass is going to be – which will result in less condensation.

Installing and properly insulating new windows – which includes proper caulking and insulation of the new windows will also reduce cold air infiltration due to poor window installation.

The quality of your window installation is just as important as the quality of your windows. Some questions to consider:

  • Does the company that made your window also install them?
  • Do they guarantee the installation in exactly the same way that they guarantee the window itself?

Is it possible that new windows can cause more condensation on my windows?

The short answer is, yes. Getting new, properly installed windows does two things (three, if you include making your house look fabulous...):

  1. New windows should be much more energy efficient and this will help increase the temperature of the inside glass - which will lead to less condensation, but...
  2. New windows should also be much more air-tight due to the improved construction of the window and better, more efficient installation, sealing and caulking of your windows. Because new windows are more air-tight, the moist air in your home is less likely to escape. That means you have to pay more attention to humidity levels in your home.

What about condensation on the outside of my windows?

Homeowners who have highly energy-efficient windows may notice condensation forming on the outside of their windows under certain weather conditions. “Why is my bedroom window covered in moisture early in the morning? This question is often asked by homeowners who have highly energy-efficient windows. This condition usually occurs in late summer and early fall when the night time temperature drops several degrees – much like dew forming early in the morning.

Dew forms in early morning as droplets of water that appears on thin, exposed objects in the morning or evening due to condensation. As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at which it can evaporate, resulting in the formation of water droplets.

The moisture on the outside of the window is condensation. It will soon evaporate when outside temperature rises. As we know, condensation happens on cold surfaces. During the night, if the outside temperature drops below the dew point then condensation forms. The fact that the condensation is forming on the windows means that very little heat from inside the house is escaping through the windows. That’s a good thing and proof that you have energy-efficient windows.

Get condensation-free windows in your home.

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