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HRV and Continued Condensation

Steve Maxwell

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Could my HRV be set up improperly?

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Q: I'd like your advice on a problem I'm having with sweaty windows and frozen doors and locks in my bungalow. I had a professionally-installed heat recovery ventilator (HRV) installed in my home which I use as often as possible. I can run it constantly or on the timer cycle, all with the same result: failure to solve my window condensation problems.

It's so bad that I have to coat the weather-stripping on the front door with Vaseline or I'll get sealed inside my house until spring comes and melts the ice. I leave a blow-dryer on the porch to use for lock defrosting if I come home after the temperature drops. My house is only 5 years old.

Could my HRV be set up improperly? I maintain the unit diligently and there is no duct obstruction that I can see.

A: I installed an HRV in my house about 10 years ago, and it completely solved our window condensation problems as long as it was operated long enough each day and at a high enough speed. During the coldest weather I find it necessary to operate the unit constantly during the day at the medium setting. I switch it off at night or we get too dry.

Relative humidity must remain between 35 and 45 percent with most windows to reduce condensation to acceptable levels. That's pretty dry, but it's what's necessary to prevent rivulets of water pooling on window sills.

Your problem may be caused by operating the unit at too slow a speed, but I'd make sure humidifiers in your home are switched off before you start adjusting anything.

Another possible cause of the problem may be a poor HRV installation that places the pair of indoor or outdoor louvres too close to one another. If this is the case, fresh air isn't circulated properly throughout your house, short circuiting the air exchange process.

You're probably feeling a little queasy right now, having spent a pile of money on a solution that isn't working. Rest assured that a properly functioning HRV will eliminate all your condensation problems. Get back to me if my suggestions don't solve your troubles.