Dave Keefe
We expect our windows to be easy to open and close, to let the sun in, and to be invisible. But they also need to keep out the wind and cold.
Pully seals, side-mount sash lock
If you have older windows, you’ve probably thought about replacing them. It can lower your heating bill and make you more comfortable, but it’s expensive and is rarely justified by energy savings alone. So, in this article we are exploring things you can do to make your existing windows more efficient. There are essentially two strategies – add a layer or make things more airtight.
Adding an additional layer of glazing can make quite a difference. If you don’t have exterior storm windows you can add them. Choose “low-E” storms, which have a special coating to reflect more of the heat back inside. Storms protect the primary windows from the weather and provide a screen when the window is open. If you already have storms, check in the fall to make sure they are closed all the way.
You can also add one or more layers to the inside. The layer can be almost anything – glass, acrylic or flexible plastic film. All these materials work fine. The differences are cost, convenience, durability and aesthetics. The plastic film option is a good choice for renters or others who can’t afford to spend much. You can buy or build interior storms with acrylic sheets (better than glass for this because they are light and don’t break). Some interior storms have two layers instead of one, which is a great idea.
Your interior storms should be weather-stripped to be as airtight as possible. Hold the panel in place with clips. Make sure you consider fire egress and make the panel easy to remove in case someone needs to escape. For non-openable windows, the panel can be permanent.
Polypropylene V-seal, EPDM rubber
The second thing you can do is to make the window assembly more airtight. This means caulking any non-moving joints or cracks and weather stripping the moving parts. Use a soft rubber or silicone seal for compression joints, where the parts push directly onto each other without sliding. Use a smooth low-friction material like polypropylene for joints where the pieces slide against each other. If your windows have factory-installed weather stripping that has worn out, try contacting the manufacturer for replacements.
You can buy temporary caulking which goes on with a caulking gun as usual but is designed to be easily removed in the spring. Or use the “rope caulk” which is like clay and is pushed into place with your fingers.
Many Vermont houses have the classic “farmhouse” single-pane vertical sliders. These can be weather stripped with polypropylene V-seals on the sides and meeting rail, and a soft compression seal at the bottom.
Farmhouse windows typically have a clamshell sash lock at the meeting rail. This is designed to push the bottom sash down and pull the meeting rails together, but it needs to be properly positioned to do that. You can also get side-mounted sash locks which are installed in pairs and push the bottom sash out firmly against the frame.
If your windows have ropes and pulleys, the biggest air leak in the assembly is probably the hole that the pulley is in. You can get a plastic cap that fits over the pully and has a hole for the rope. It is installed with an adhesive-backed gasket and two screws. The rope and pulley arrangement remains operational.
Make sure to caulk any cracks or seams with a good acrylic caulking, including where the interior trim meets the wall surface. The biggest cracks are often where you don’t see them, at the very bottom and top of the window trim.
Insulated window coverings are effective if they seal well around the perimeter, but they can be expensive and there’s no benefit when they are open. Regular heavy curtains also help. They typically won’t change your heating bill much, but they can make you more comfortable by reducing the chilling effect of that cold glass.
Next time we’ll talk about basements.
Dave Keefe is a fifth-generation Vermonter who has worked for over 35 years as a contractor, consultant and teacher to improve the performance of existing homes.
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