Condensation on the inside of the windows

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Posted by: from Mississauga
3/22/2014 at 2:54:39 PM

I have a problem with condensation on the inside of the windows. This problem existed since the house was new. I would like to know who I should contact.

I don't live in the house. I have tenants that have been renting the house. They keep the furnace fan on all the time. There are vents under each window. The condensation collects on the bottom of the window and starts to form mold if not cleaned.

Who is the best person to contact to have this rectified? I don't know if I need all new windows or something else.

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Rodney from PGCrenovations in Cambridge
Date/Time3/22/2014 at 7:33:21 PM

Have an HRV system installed. This will circulate the air more and cut down on the moisture. If your home is new, the windows shouldn't be an issue.

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Date/Time3/22/2014 at 7:44:11 PM

From my experience if there is moisture build up between the glass then the windows have failed. New windows have a gas inside the window panes that stop this condensation from forming. There is also a chemical substance that traps moisture built in around the rim of the window to prevent any moisture once this substance is completely saturated then the window has failed and moisture forms.

In the past I have heard of a small vent being drilled into the window that allows moisture to exit but I am not sure if this is still available and in my opinion is only a temporary solution. Unfortunately you may need to have the window panes replaced but not the entire window itself.

You may want to contact a mirror and glass company to see if they can help you out.

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Date/Time3/22/2014 at 10:08:28 PM

Please be more specific. Is the condensation between the window glass panes or on the outside of the panes but on the inside of the house side of the windows?

If condensation occurs between the panes then the glass seal is shot and you will need new glass panes. David gave you the best explanation for that scenario.

If however condensation occurs at bottom of the window inside of the house but not between the glass panes the solution is as simple as turning down or shutting off the furnace humidifier.

Being a home owner, contractor and landlord, I would eliminate the humidifier completely since tennants tend to be irresponsible Re: running the furnace fan continuously.

If the furnace fan is always on, so is the humidifier but not the heater therefore you have excess humidity in the home that will condensate around the window. A normal family that bathes, showers, cooks and does laundry plus opens the doors and windows regularly naturally releases enough moisture into the home that a furnace humidifier is not needed, with 4 young children and 2 adults, in our home, in Calgary (air is quite dry), our furnace's humidifier is turned off since 2008. And your fan setting for the furnace should be set on "auto" instead of "on".

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Date/Time3/22/2014 at 10:31:16 PM

Hi Kathryn,

The way you explained the problem it seems the water is in the inside of the house on the bottom of the glass units.

Most of the time it happens when you have poor air circulation in front of the windows.

This can be because of a few reasons :

*in the vents under the windows there is most of the time a trap door about a foot inside the air tunnel, in this case you have to remove the vent cover and insert your hand in and feel if the trap door is closed, turn it to have a bigger air flow.

*The fan MUST be on the on position so the air in front of the window will not stand still.

To make sure you have good air flow check the filter in the furnace- if its blocked with dirt it will not allow air to go threw it, make sure its the right model of filter.

*The insulation around the window is poor and you have cold air coming in all the time - Check by moving your hand around the frame and trying to feel for air movement with the window closed.

*Check the humidifier for its setting, in the basement should be a chart of the best setting.

Hope this is helping you to solve it.


Harry C.

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Date/Time3/22/2014 at 10:49:48 PM

Shut the waterline off at the humidistat located on the side of the furnace. It is located where the 1/4' pipe meets the 1/2' pipe.


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Kathryn from Master Handyman1 in Burlington
Date/Time3/23/2014 at 4:58:33 AM

If you see condensation in your windows that means the seal around the glass has leaked and there is no more argon gas between the glass.

It is the time to chage your windows as it is not saving heat or cold in your house.

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Date/Time3/25/2014 at 10:40:49 PM

A quick and free solution your tenants could try if the condensation is on the inside sill of your window frame (rather that between the panes of glass), is to ensure that any blind treatment is pulled up a few inches from the bottom of the sill.

When a blind touches the bottom sill and is closed, it can cause condensation to form by preventing adequate air flow. Unless your tenant is wiping clean your window sill regularly, warping, swelling or peeling might occur to any plastic or mdf or wood framing.

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