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Fan-tastic options for limiting condensation in your home

Image of a sad smiley drawn onto window condensation
Window condensation is a sign of excess moisture in your home, but using fans can help.

Consider window upgrades, but effective use of fans could be your best bet

As David Hill fields questions about moisture and condensation in homes, he alternates between eloquent science-based advice and passionate asides – often inflected with salty language – about sub-par building practices and buildings gone wrong.

Think of him as Bill Nye The Science Guy crossed with Jaws' Captain Quint, who famously silences a room by dragging his fingernails over a chalkboard before delivering the goods on a shark that "will swallow you whole. Shakin'. Tenderizin'. Down you go."

The shark in this case is moisture, and to ensure it's not leading to condensation, mildew, mold and health issues, you must first understand how it eats.

"With the moisture in a bathroom being a higher absolute humidity than in the adjoining space, if you leave the door open, it will diffuse into the cooler room, such as in a bedroom or a closet," says Hill, president of the Thermal Environmental Comfort Association (TECA) and arguably B.C.'s leading authority on home ventilation. "Moisture always looks for cold things. So unless you put enough beer on the coffee table, it's going to the next coldest thing it will find."

Chilled six-packs of lager aside, the coldest thing in the room is usually the nearest window or exterior wall. And if you've had condensation issues, you know all about the water droplets it creates, the mildew around the tub, or the green mold in the upper corner of the bedroom or kitchen. The source of that condensation can be showers, steam from the kitchen, or moisture from your breath as you sleep through the night. It can also be clothes drying on an interior rack, or wet firewood drying in the living room.

It's a complicated issue, and some solutions can be expensive, such as upgrading windows to double-glazed or triple-glazed, or upgrading the insulation of exterior walls. But using premium quality exhaust fans, and ensuring that they're installed properly and used strategically, can go a long way toward reducing or eliminating condensation problems.

Here's some advice from Hill, with an assist from BC Hydro's Gary Hamer, on getting the most out of your fans and tackling condensation issues in your home.

Use your fans, and close the door on condensation

It's possible that your existing exhaust fans might be capable of doing the trick. Too often, we don't use our fans correctly, enough, or at all. BC Hydro's Hamer recalls an aunt and uncle who wound up with condensation issues because they figured their fans were too noisy.

"A lot of people kind of sabotage ventilation systems by turning them off," says Hamer, a specialist engineer with BC Hydro. "If you turn it off, it can't do its job."

If your home is equipped with a dehumidistat that turns bathroom fans on and off as humidity rises and falls, use it. It can also take a lot longer to ventilate a kitchen or bathroom than you might guess. If you thought that switching the bathroom fan on during your shower and for 10 minutes after is going to cut it, you'd be wrong. And if you open the bathroom door before the room is fully dried, you're asking for trouble.

"Turning on the bathroom fan while showering is only a half-hearted solution," says Hill. "There are two requirements to keep a bathroom dry: one is that you have to have a short-term blast when you're there, but on the B.C. coast, it can take 12 hours to fully dry a bathroom. Running a fan for 30 minutes after you leave home doesn't cut it, so you need to keep the fan running."

The optimum relative humidity range for health and comfort in most B.C. homes is between 40% and 60%. Running an inefficient fan continuously can add significantly to your electricity costs, and if the fan is noisy, it can be annoying. But it doesn't have to be that way.

Seriously consider an upgrade to a quiet, efficient, multi-speed fan

The typical fan installed in B.C. homes is relatively cheap, often noisy, and doesn't use electricity efficiently. And it's often too big.

"For most people, it's go big or go home, because the public doesn't know that a large amount of air needs to be exhausted while you shower, and the small amount needed to properly finish drying out a wet bathroom," says Hill. "Using a large fan is a huge waste of heat and electricity. You're so badly over-ventilating that you're removing air that doesn't have nearly enough heat or time to absorb the water from your towels and other items."

Expect to spend up to $500 or more for the purchase and proper installation of a fan that is quiet, operates at multiple speeds, is efficient, and offers some combination of motion sensor or humidity sensor to ensure it ramps up when needed, then purrs along at a low speed after the heavy lifting is done. And get it installed correctly (more on that later).

Here are some considerations:

  • Small is better. A variable speed fan that runs (at its lowest speed) at 20 or 30 cubic feet per minute (cfm) is best for efficiency. The cost of ventilation is largely driven by continuous use of a fan, so make sure a fan can run at a low speed.
  • Make sure it's quiet. Some fan manufacturers say their product is quiet, but the evidence is in the sones, the measure of the amount of noise it makes. Look for a fan that operates at no more than 1 sone, and ideally at as low as 0.3, 0.2, or even 0.1 sones at the lowest speed. One sone is roughly equivalent to the sound of a refrigerator in a quiet kitchen.
  • Sensors matter. Timers rarely offer settings over an hour, so look for motion detectors and/or humidity sensors to ensure you're controlling humidity effectively.
  • Buy ENERGY STAR®. Look for ENERGY STAR certified fans, and check to see how much the fan gets out of each watt of power. That's measured in watts per cfm (w/cfm), and the most efficient on the market operate at as low as 13.3 w/cfm.

Take care to ensure your fan is properly installed

Near the top of Hill's lists of frustrations is discovering exhaust fans that are installed so that they're not fully effective, usually because the ducting it connects to suffocates the fan.

"I saw a unit in New Westminster this January in which a contractor installed a fan in a new home, but the duct was completely incompatible with the fan," he says. "Its fan housing was oriented in a way that necessitated an elbow right at the collar of the fan, which ate away a third of that fan's capacity."

Hill's advice? When considering a contractor or contracting firm for the installation, first check to see if they have ventilation certification. You can do that via the TECA associate search tool, and looking for the orange V beside the person or firm's name.

Heat matters: Don't turn the heat down too soon

Hill describes the worst-case scenario for condensation as the family that showers in the morning, doesn't properly ventilate the bathroom(s) then turns the heat down before heading off to work.

"It's a double whammy because as the temperature falls, relative humidity rises at the very time when the building is least able to defend itself from the moisture left from the shower, bath mat, curtain and everything else in the bathroom, and overnight breathing," says Hill. "You're leaving that building in a falling temperature with a massive moisture source from overnight living."

Again, cool objects such as windows will collect moisture. It's fine to lower the heat in your home during the week days and overnight to lower your heating costs. But don't do it until the bathroom and the rest of the house is dry, and reconsider turning the heat way down in your bedroom during cool weather.

Did you know? The average family produces about 10 litres (2.6 gallons) of moisture a day through simple, everyday activities like breathing, cooking, washing dishes, washing clothes and taking baths or showers.

If you have single-glazed windows, consider replacing them

A lot of homes built on the supposedly warm south coast of B.C. were built with single-glazed windows or with inferior double-glazed windows featuring solid non-thermal break aluminum frames. Hamer suggests that while the costs are high, investing in top-quality low-e and argon double- or triple-glazed windows will pay off in increased home comfort, if not in a big reduction in your energy bills.

Hamer has become an advocate for spending the extra dollar on the best windows when building a new home, and for seriously considering window upgrades when doing renovations. He says the year-round benefits include comfort and less condensation in the winter, and less heat gain during the heat of the summer.

How do you know you need new windows? Hamer says that if it's uncomfortable to sit near a window in the winter months, the window is either not draftproofed or it just doesn't have enough thermal resistance.

"And if you replace a window, don't just put in the least expensive window," he says. "With a quality window, you're effectively getting full value of that room – not losing floor space because you can't sit next to the window."

Rebates on select window are part of the BC Hydro's Home Renovation Rebate Program. Shop for windows with a low U-factor, the measure of heat transfer that tells you how well the window insulates. Windows with a U-factor of 1.40 to 1.23 bring a rebate of $50 each, while higher-quality windows with a U-factor of 1.22 or less earn a $100 rebate.

Also consider insulation upgrades to your home via the same rebate program.

Heat recovery ventilators (HRVs) and heat pumps

In keeping with the City of Vancouver's building code, home builders have been installing heat recovery ventilators (HRVs) for ventilation in all new one- and two-family homes since 2008. But if your home is older than that, there's a good chance you don't have an HRV.

HRVs run the exhaust and supply air systems past each other (without mingling the actual air) so that heat is transferred from exhaust air to the incoming air, pre-warming it and reducing energy loss. Properly adjusted and maintained, HRVs maintain a balanced air supply that delivers fresh air to all rooms in the house.

Should you get an HRV installed? Cost for purchasing and installing an HRV range from $2,000 to more than $5,000. Factors that influence the cost include :

  • Size of your home
  • Quality of the installation and system balancing
  • Whether ducts from a forced air heating system pre-exist to allow for easier distribution of air to rooms
  • Model/brand and efficiency rating of the equipment.

Be sure to get multiple quotes from contractors to compare costs, installation approach and warranties.

For those with electrically-heated homes who are looking to lower heating costs and improve comfort, a heat pump – also available through BC Hydro's Home Renovation Rebate program – is an option. See our Should I get a heat pump page for details on the pros and cons of heat pumps.

BC Hydro offers rebates for the purchase and installation of heat pumps in single-family detached home, duplex, row home, townhouse (with its own utility meter), or mobile homes on a permanent foundation. Hamer says that townhouse owners should consider heat pumps, but that strata councils are often reluctant to allow them to be installed because the main unit sits on a balcony or patio outside the home.

"Heat pumps can reduce your electric baseboard heating costs, and provide cooling when you didn't have it before," he says. "It can solve a number of issues for you, but stratas seem to be reluctant to allow these things because they're not aware of what occupants can gain in terms of energy savings and comfort. They just say 'It's ugly, so we're not doing that.'"

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