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Condensation Explained

Does condensation build up on the inside of your home’s windows during the heating season? If it does, you’re not alone. Winter window condensation is a growing problem in Canada and its root has a surprising origin.

As homes are sealed better against air leakage, natural ventilation to the outdoors is reduced. As a result, indoor air becomes much more likely to contain damaging levels of moisture during winter.

If your windows sweat enough during the heating season to require periodic wiping with a towel, then you have a problem. And this problem goes beyond ruined window-frame finishes and mould growth on windowsills. It includes the very real potential for decay within wall cavities and attics, too. Window condensation can also be a sign of low indoor-air quality which affects your health.

Whether it’s old or brand new windows, there is one problem that comes up in conversations with homeowners planning a replacement: condensation on windows.

If you have older windows that aren’t as efficient as modern vinyl windows, they are more likely to fog-up, accumulate moisture around the sill, or even freeze. But does this necessarily mean the window has to be replaced? What if the window has just been replaced and the condensation seems to be even worse than with the old windows?

We will show you how to understand and reduce or prevent condensation on your windows in this blog. In order to get there, we need to start at the beginning with the most basic question:

                                        What is condensation?

Condensation is the process which turns water vapour that is present in the air into liquid water. One of the biggest misconceptions that homeowners have about condensation is that it is a result of a problem with the surface on which it appears, usually a window or a wall. While problems in these areas can arise as a result of prolonged moisture exposure, condensation actually comes from the air, or rather moisture in the air.

                            Why is there condensation on windows?

As the air in a room warms up, it expands allowing it to hold more moisture. As it cools down again, it contracts. When the air reaches a cooling saturation point, the excessive moisture turns into a liquid. This is exactly what happens when the warm air from the inside of your home comes in contact with the cold glass pane in your window. The air cools rapidly against the surface of the window pane and becomes water.

Although this is most noticeable on the glass, your windows aren’t the only place condensation can occur. Breaks in your house vapour barrier can allow warm moist air to leak into wall cavities, condensing there the same way it does on your windows. Because this problem is not evident to the naked eye, it can go untreated for some time and result in rotting or mold growth over a period of time. This problem is especially prevalent in the older with an abundance of older homes.

Condensation on windows is most noticeable when the temperature outside drops quickly, creating a greater difference in temperature between the inside and outside air. It is often most noticeable in the early fall when the days are warm and nights are cold. During a humid summer, the home’s structure can absorb a fair amount of moisture. When the temperature drops outside, this moisture becomes trapped inside the home, resulting in higher humidity levels and a higher chance of condensation on glass panes.

                            Where does excessive moisture in the air come from?

One of the biggest contributing factors to the excessive moisture in our homes is us. According to Natural Resources Canada:

A family of four can add moisture equivalent to 30 or 40 litres of water per week to the atmosphere in your home.

Showering, cooking, bathing, and washing can add 15 to 20 litres per week.

Drying clothes indoors can add 10 to 15 litres per week.

Of course, another significant contributor to high levels of humidity is your household appliances and even your ventilation system. That’s why kitchens and bathrooms are areas with a higher chance of condensation.
During the wintertime, an appropriate level of humidity indoors is considered to be between 25 and 40%

                        How to prevent condensation from forming on windows?

Exactly how to battle condensation in your home depends on just how much condensation there is, the condition of your existing windows, your vents, etc. In short, it is about balancing the airflow system in your entire home. As such, the right fix for your condensation problems may be in a combination of fixes.

In essence, preventing condensation is about three main factors: reduce the level of humidity in your home, vent the humid air out of your home, and circulate air inside your home properly to lower the and maintain appropriate humidity levels.

  • Purchase a hygrometer. 
    • A hygrometer is a small and relatively cheap device that measures the humidity levels in your home. It can not only help you keep track of the humidity levels, but also help you assess whether different methods of battling condensation are working. Many modern thermostats come equipped with a humidity meter.
  • Lower your thermostat.
    • As we mentioned above, warmer air contains more moisture. If you are like most Canadian household, you can probably afford to turn the thermostat down a degree or two and still be comfortable. As a result, you may see a decrease in humidity and condensation.
  • Use your fans.
    • Your appliances, like the stove and dryer, can create a lot of humid air. Same goes for your shower. Make sure that these areas and appliances are vented to the outside of the house. Run a vent fan in your bathroom when you shower and turn on your range hood while cooking.
  • Unblock your vents. 
    • A lot of times the biggest problem with airflow is a man-made one. Placing furniture above or directly in front of the vents prevents air from distributing properly, and affects the circulation in your rooms. Same goes for the return vent that takes the air back into the system. Ultimately it is all about making the air move through and around the whole house for best results.
  • Clean your vents and change your filters.
    • Dust on your vents or return grill can be a sign that the air moving around your home is not as clean as it should be. Physically cleaning the dust off can lead to increased airflow. Replacing or cleaning the air filter not only provides your family with cleaner breathing air, but it also makes your furnace run more efficiently. Some companies recommend changing the filter as often as every two to three weeks, so you may want to add it to the list of your regular chores. At the very least try to check on the health of your air filters monthly. This will be a good sign of their health and overall furnace performance.
  • Seal leaky ducts.
    • According to Energy Star, about 20% of the air that moves through the duct system is lost due to leaks, holes, and poor connections. That’s one-fifth of your heating bill disappearing into the ether. By redirecting, sealing off, or fixing the leaky ducts you can improve the flow of air and increase circulation.
  • Circulate the air inside your home.
    • As we said earlier, colder air means less humidity. One of the quickest ways to cool the air in your home is by simply opening a door or a window. This may not always be ideal because of the weather, but you should consider ventilating the air in your home daily, even if for a few minutes.
  • Get a dehumidifier. 
    • One solution that seems to work well for everyone who experiences above normal condensation levels in their house is the use of dehumidifiers. These units are fairly cheap and you can find one that will do the job for 200-250$. This is also a good solution for homeowners with new windows that experience condensation, where other areas in the house may not be as significant in contributing to moisture on windows.

Preventing condensation on windows you might be asking yourself ‘How can I make my home more efficient?‘ There are many small and relatively simple home improvements you can make to have a positive impact on your personal comfort, the longevity of your home and the security of your budget.

What is an energy recovery ventilator?

Energy recovery ventilators (ERVs) are a type of HRV that can exchange both heat and moisture.

Moisture control:
An ERV can give you more control over moisture levels in your home during warm and humid weather, by keeping excess moisture out of your home. Because less energy is required to lower the temperature of dry air compared to moist air, an ERV can reduce the work your air conditioner needs to do and save you money.

Moisture recovery:
If your winter climate is extremely dry, ERVs recover some of the moisture that would leave your house through a regular HRV. This helps you maintain a comfortable humidity level within your home, avoiding static electricity, sore throats and other discomforts caused by air that is too dry.

Recently, Ontario updated its series of ventilation code requirements to increase the energy performance of a building by 15 percent. The updates center around heat recovery on ventilation systems with incentives for making buildings more airtight.

While much of the Ontario Building Code 2020 (OBC) Section 9 remains the same, a heat-recovery ventilator (HRV) or an energy-recovery ventilator (ERV) will be mandatory for all commercial and residential buildings.