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Windows and Doors


Condensation on Storm Windows

Ice forms on our storm windows in the winter, how can we prevent it?

Ice on storm windows usually means that air is leaking around the prime window into the cavity between it and the storm window. The leaking air has enough moisture to cause the condensation, but not enough heat to warm the surface. Making the storm windows tighter will not reduce an icing problem, nor will closing the weep holes at the bottom of the window. These should be kept open to allow water vapor to escape.

A temporary solution may be to carefully seal all the joints of the prime window where the sashes meet the frame with rope caulk, which is removable in the spring. Alternately, you could install a plastic film over the windows, making sure to wrap it around the frame. In the spring, remove the sashes and check the weatherstripping. The manufacturer should be able to supply you with replacement weatherstripping, if needed.

Condensation on Windows

How can we reduce the condensation on the inside of our windows when it is cold outside?

Condensation and ice form on windows because the window surface is below the dew point for the air near the window. To eliminate condensation you either need to raise the temperature of the window surface or reduce the relative humidity in the room. If the condensation is on a double glazed window and the temperature outside is above zero the problem is probably high indoor relative humidity. The best way to deal with condensation on high quality, double glazed windows is to reduce indoor relative humidity to no more the 40 percent.Several conditions can increase condensation problems. Closing drapes causes the glass temperature and the temperature of the air between the drape and the glass to become cooler, making condensation more likely. If the thermostat setting is dropped substantially at night, this will cause an increase in relative humidity and may increase condensation. This condensation should vanish once the temperature rises in the morning. 

Foggy Triple-Glazed Windows

When the glass behind removable interior sash of triple-glazed windows begins to fog up what do you do?

Because the inside sashes are removable, the problem is probably caused by a loose fit. If this is the case, air can leak around the inside window from the house. When it hits the colder middle window, the moisture in it condenses. I suggest you inspect the weatherstripping on the interior sashes and replace it if it appears worn or hard.

Low-E Coating Effects

Will low-E coating on windows cut out the ultraviolet light coming through the windows to the point that it is a problem for house plants?

Low E coatings are thin metallic coatings on windows that reduce heat loss through glass. They do reduce the amount of ultraviolet light coming through window glass somewhat. While the normal double glazed window lets 52% of the ultraviolet light through, various types of low e glass let between 0.5% and 36% through. However, according to a horticulturist I contacted, ultraviolet light is not critical for plant growth. She indicated that the percentage of visible light is the issue of concern. A normal double glazed window lets about 81% of the available visible light through while low-e glass lets between 62% and 76% through depending on the manufacturer. The reduction might be enough to impact the growth of some species. Manufacturers of the windows you are considering should be able give you the figures for their glass.

Mold Following Installation of Siding

Why would mold appear on windows following installation of new siding?

Chances are your new siding installation included installation of building paper or insulation. In any event, the project made your home much tighter and, thereby, increased the relative humidity. I suspect you have condensation on the window glass as well. You need to add additional fresh air. You can do this by running a kitchen exhaust fan until condensation disappears. This will be more effective if you crack open a window at the other end of the house.

A more permanent solution to high winter humidity is to add a mechanical ventilation system that operates automatically. These systems both bring in fresh air and exhaust stale air. Good ones are balanced so that roughly the same amount of air is exhausted as brought in.

Reducing Summer Heat Gain

What is the best way to reduce the summer heat gain from a west facing picture window?

Your goal should be to keep the solar radiation from getting into the room. One way is to coat the interior surface of the window with a reflective plastic film. These films reflect much of the solar heat back out and are easy to install. An awning would do a better job of keeping out the sun, but might make the room too dark.

Removing Stains on Glass

We cleaned our siding with a strong phosphate cleaner. Some of it got on the window glass and has left them hazy. How can we remove the haze?

I would check with a local glass company for commercial glass stain remover. Sparkle Cleaner and Stain Cleaner was recommended by one professional window cleaner I contacted.

Removing Tape Residue

How can the residue from double-sided tape used to install plastic window coverings be removed?

According to a consumer service representative at the 3M company, one of the makers of this type product, lighter fluid is the key. Saturate a clean white cloth with lighter fluid and then hold the cloth on the adhesive until the adhesive is dissolved. Rubbing won’t have the same affect since the lighter fluid won’t have as much contact with the adhesive and will tend to evaporate more quickly. You can probably avoid the residue problem if you remove the tape annually. By the way it is always a good idea when using a solvent to test it in an inconspicuous place first.

Replacement Windows

How do I go about selecting replacement windows?

An early step in the decision making process is to decide if you want replacement sashes or entirely new window units. The sashes have the advantage of fitting into existing openings which means you do not have to alter interior or exterior trim, Replacement sashes are made by many of the leading manufactures and can be custom sized. They are available in a variety of frame materials and different glazings. Replacing the entire window allows you to change the type of window and in some cases may provide better operating mechanisms and a tighter overall installation.Most windows sold today in Wisconsin are double glazed and have a low-e coating on the outside of the inside pane of glass. The space between the panes is filled with a gas that reduces heat transfer.In comparing windows you need consider the overall insulating or U value not just the center of glass insulating value since the spacers between the glass panes can effect heat loss. The U-value is a measure of heat loss and is the inverse of the R-value meaning that tahe lower the value the better the insulation. Look for a U-value of 0.35 or less in cold climates. Also ask about air leakage since this varies between manufacturers as well. When it comes to deciding which manufacturer, there are several organizations that maintain web sites that compare various energy related features of windows. See the links below.

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Replacing Putty

What are the steps in replacing putty on windows when it chips out?

Clean the cavities carefully and prime the surface with paint to seal the surface and improve the bound. At one time, linseed oil was recommended as the primer; with new putty materials this is no longer the case.Next spread a bead of putty along the area to be filled and press it in place with a putty knife using the edge of the window as a guide to achieve a smooth surface. If you find areas where the putty is cracked but will not come out, you can try working some caulk into the cracks. It will tighten the joint and improve the appearance. 

Restoring Finish

How can the finish on the inside of wood windows be restored?

If the finish has come off because the window frames have been wet from condensation, I would recommend sanding the effected areas to bare wood and then applying a coat of water repellent preservative. This is a penetrating product so you can wipe off any that gets on any adjacent varnished area. When this is thoroughly dry apply a good quality varnish. It is probably a good idea to roughen any previously varnished area with sand paper or to use a deglosser to assure that the new finish forms a good bond with the old.

Seasonal Condensation

Why does condensation occur on my windows in the fall, but not in the winter?

During summer, when temperatures are higher, the materials in your home absorb moisture. In the fall, as temperatures drop, materials release this moisture temporarily increasing relative humidity. This in turn leads to condensation on windows and other cold surfaces. Once a new lower moisture balance is reached in the house, relative humidity drops and condensation is less likely.

Storm Window – Small Holes

What is the function of the small holes at the bottom of storm windows?

These holes are designed to allow any moisture that is trapped between the two windows to escape. Tests comparing the heat loss through storm windows with and without weep holes found no measurable difference. The laboratory also measured the amount of air leakage. It was slight, roughly equivalent to that from a very tight house. The prime windows in these tests were very tight. If your prime windows are leaky the air leakage would be greater.

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