Air exchanger doesn't seem to work in very cold weather but we have ice on windows

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Posted by: from Hawkesbury
12/28/2017 at 9:07:02 AM

With the extreme cold we've been having in Eastern Ontario this holiday I have ice buildup inside most of the windows (and do whenever its -20 or below) and a lot of condensation. The house is 15 years old and we just had half of the windows replaced last summer. We also have an air exchanger and our furnace is oil, but the exchanger doesn't seem to work when its below -15 or so. We can hear the fan running but it doesn't seem to exchange the air as usual.

I'm very concerned about mould, something that we've dealt with since living here (5 years) but I'm also concerned about the furnace running constantly.

Any ideas on how to deal with this?

Air exchanger doesn't seem to work in very cold weather but we have ice on windows
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Date/Time12/28/2017 at 11:23:40 AM

It is not uncommon for an air exchanger to freeze up at extreme cold temperatures.

Most air exchangers have a cold temp lockout that will shut down the air exchanger when temperatures reach a certain point.

A tech should check your unit to see if yours has the lock out feature.

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Date/Time12/31/2017 at 1:01:17 PM

Hello Tamara You mentioned half the windows were replaced in the summer I trust this window is not one of them as it looks as though it was not sealed properly between the frame and internal structure. Air exchanger will lock out cold air if the temperature is -10 / -12 degrees C. This is not the issue. Check your humidifier setting usually in winter it should be set 35 - 45 percent. also look at the damper control for the humidifier as it may not be in winter mode. ( Last 3 visits to homes this week were all in the summer position and water was shut off ).

The image shows slight dampness which is normal for North American home building technology, simply keep wiping them down during the day especially the morning, this will reduce the chance of mold.

Hope you have a safe a prosperous New Year.

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Date/Time1/3/2018 at 4:26:15 PM

From the pictures it looks like you have to much humidity in the house. With there being liquid water all over the window panes, and I'm assuming that is only on the surface and not between the window panes. I'd start with the furnace humidifier setting, most homes will need it between 20 -30% on the thermostat. If it's set there, then start to lower it until you have no more condensation on the windows. The thermostat might be faulty but not a common problem.

The air/heat exchanger does have a cold weather lock out, but the fan should also cut out also (check your manual). Open it up and check the filter to make sure it's not plugged or frozen.

Also do you use the bathroom fans when you shower and leave them on until all the moisture is gone? That's another source of moisture that causes the condinsation on windows.

If your furnace is running all the time, it might not be sized correctly for the house, builder's always go for the bare minimum size. An HVAC company would have to tell you more.


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Date/Time1/3/2018 at 6:03:57 PM

Hello Temera an Air to air heat exchanger has an automatic thaw cycle when the plastic heat ex hanger becomes iced over. It basically works as a pressure switch the air movement through the exchanger is too low so it goes on defrost. I would suggest just because you hear the motor running does not mean the exchanger is actually working, air to air heat exchangers have more than one motor , if the exhaust fan is not running for discharge air outside your house cold air can back feed into the air exchanger and freeze it solid. The amount of water you have on your windows indicates the exchanger is not dumping the warm house air outside, hence the fan meant to pull,out the house lair is not running and the exchanger is frozen by convection from outside. Contact your HVAC guy and I am sure the motor is not running. All the best and a Happy New Year. Jack

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Tamara in Hawkesbury
Date/Time1/4/2018 at 8:48:53 AM

Thank you to everyone for your helpful and concise answers! We thought we might be able to take care of it ourselves but it looks like we'd better call our heating and cooling guy. Happy New Year to all!

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