Q&A / 

Condensation – Cause & Control

DEAR TIM: This past summer I had a new heating system installed. I switched from radiant baseboard heating to a forced air system. My windows now have condensation forming on them. Is the new heating system producing excessive moisture inside my house? If not, what might be the cause of the condensation. On extremely cold nights the water turns to ice. Is there a solution to the problem? G. I.

DEAR G.I.: Too bad you couldn't have kept the radiant system in place along with your new system. I often think that the best heating system is one that utilizes both radiant energy and air circulation. Don't fret, I have only seen one house in my 25 years of building that did incorporate both systems.

Your new system may be to blame if you had a humidifier installed. The humidifier may be pumping too much moisture into the air. Humidifiers are mechanisms that attach to the sides of the ductwork very near or next to your new furnace. They are often easy to spot since they have a tiny flexible water supply line which connects them to your plumbing system.

If you indeed have a humidifier, check the control dial which regulates its operation. The indoor relative humidity must be adjusted in relationship to the outdoor temperature. As the outdoor temperature drops, so to must your indoor humidity. When you do not control this balance, condensation begins to form on the window glass.

If you do not have a humidifier, I think I know what is causing the problem. Condensation forms on your windows because the glass temperature reaches the dew point as the outside temperature drops. It is the same thing that happens to the grass on an early summer morning or when a cold can of soda or beer is taken outside in the summer time. The air that comes into contact with the cold surface cools rapidly. The moisture in this cooled air switches from the vapor state to the liquid state. The liquid water collects on the cold surface.

In your case, I think your old baseboard heaters produced enough radiant heat to keep your interior glass above the dew point of the moist, indoor air. Your new forced air system will not readily produce the invisible infrared heat that your baseboard heaters provided. This is one reason why radiant heat is so desirable.

The solution to your problem lies in lowering the indoor humidity to a tolerable and comfortable level. You may be able to do this by identifying sources of excessive indoor humidity. Excessively hot baths or showers pump huge volumes of moisture into the air. Try to take cooler showers. Cooking activities that create lots of steam might be the culprit. Try to cover pots to minimize steam rising into the air. Vast forests of indoor plants can produce large quantities of airborne moisture. Investigate to see if there are plants that liberate less moisture than others. I suggest that you invest in a high quality hygrometer. This is a device that measures relative humidity.

Take readings in different rooms each day at the same time. Chart your findings. Observe how much condensation is present on the glass at the same time. If you still have condensation after you have attempted to minimize indoor humidity, you will have to operate a dehumidifier. This device will allow you to extract moisture from the inside of your house. Continue to take humidity readings until the condensation stops or you can't stand the static electricity shocks!

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