Introduction

Its winter time here in Minnesota so naturally we are fielding a lot of calls and questions about excessive and even frozen moisture on windows. Calls like this are second only to “no heat” calls and they usually start out like this: “Our windows are all frosted up!” or “We have excessive moisture on our windows. Our HRV must not be working.”

Well is your HRV running currently? When was the last time you cleaned it? Where is humidity controller currently set at?

First your HRV does not have a compressor or any refrigeration circuit in it, it was never designed to remove moisture. It was designed to remove stale air and bring fresh air into the building, while mixing with indoor air thru a core best described as a cube of coffee straws. The HRV uses this core to keep the frigid air from shocking the furnace.

Well where does this moisture come from?

Think of a simple glass of ice water in warmer weather. The cold water inside the glass is much cooler than the surrounding air, the moisture in the surrounding air comes in contact with the cold glass and forms water droplets, this is condensation. This happens because the temperature of the glass is at or below the dew point. The same thing is happening with your windows only the ice water is the outdoors and the moisture is in your home.

The window is where the heat transfer is happening and the window argon or Low E vapor barrier leaked or it may be that the windows were never well designed in the first place.

What can we do?

Lower your humidification settings on your humidifier

Turn your fan “ON” on your thermostat

Put a fan onto the window to help drive the cold back out by being under positive pressure

If it’s dry air outside (which means frigid temps) turn the HRV on to the MAX setting

Turn on the dehumidifier

Replace the windows they leak….you’re throwing money out the windows literally.