For several years, North Quabbin Energy has been promoting and teaching people how to make “winserts” – clear, two-layer window inserts that can help to reduce the heat loss in a typical window by up to 50%. The design has morphed over time, and there are three set of instructions here for three slightly different methods:
- the “butt-joint with double-sided tape for attaching the film” (we generally do not use this method any longer, but the photos are helpful)
- the “mitered joint frame with spline method for attaching the film“
- and the “ butt-joint frame and wrap method for attaching the film“.
The basic principle is actually quite a simple one though: you need to build a frame slightly smaller than the interior dimensions of your window frame, cover both sides of it somehow with clear plastic, and attach some kind of compressible foam all the way around it so that it will fit firmly in place. The idea is that the two layers of plastic create a space of dead air that heat does not cross, making a thermal barrier and cutting down on drafts and heat loss. The differences in the methods are in how the frame is assembled (butt-joint or mitered joint) and how the plastic film is attached (tape, spline, or wrapping).
Here is a spreadsheet with sources for bulk materials:
What are they?
“Winserts” are re-usable transparent panels that fit snugly inside window jambs to add two extra layers of glazing.
How do they work?
The winsert uses two closely-spaced sheets of plastic to create a layer of “dead air” next to your window. This keeps warm air from the building from moving out to the colder air outside. While a single layer of plastic sheeting can help reduce heat loss from your windows, it does not usually create this insulating layer of dead air and may actually leave enough space for a convection current to form that pulls heat away from the living space. We believe that a properly-constructed winsert can reduce heat loss from a typical single- or double-glazed window by up to 50%. The design was inspired by a long-forgotten FEMA website and has been adapted by Brian Nugent and other North Quabbin Energy members and participants in our workshops. We hope you will feel free to improve it further or adapt it to your particular needs.
How complicated are they to make?
Winserts require some basic woodworking equipment and skills to make, particularly in the construction of the frame. If you don’t have these yourself, you should try to find someone who does–perhaps you can work together to make winserts for both of you! Attaching the plastic and foam is easy to do.
How long will they last?
This method is a work in progress, and we don’t have reliable reports yet about the life expectancy of the various types of winserts that have been made. First-generation winserts installed in the Millers River Environmental Center in Athol in 2008 are still going strong. Material choices have been improved since then – we are now using 1 mil thick film and UV resistant edge foam. All winserts should last indefinitely with careful use and storage. They can also be left installed all summer long – they help keep out the heat too! The plastic film is the component that is most likely to need replacing from punctures and tears (the spline method of film installation addresses this nicely). The long-term strength of the double-sided tape used in the original heat-shrink method is also not known yet. However, the frames could be re-covered with new plastic film if needed.
Brian Nugent and North Quabbin Energy offer these construction methods as a suggestion of one way to weatherize your home. We make no guarantee of the results of making or installing winserts, but we believe that if you follow this method, you will notice a difference in the heat loss through your windows. We welcome feedback (email us at email@example.com), and we invite you to adapt the design, make suggestions for improving it, and pass the results along to us and to others. As we all search for creative ways to reduce energy use and improve efficiency, we hope that more do-it-yourself ideas like this can be developed, improved, and shared. (For discussion about similar designs, visit the Historic HomeWorks Forum and Topher Belknap’s design.)
Click here to see a short video on measuring your windows.
You can then follow the steps outlined for the original “tape method”, or go check out the spline or wrap methods and pick the one that suits your fancy. Many public and private buildings in and around the North Quabbin have added these over the years, and they can confirm that this simple technology really does work! Any way you choose, you can’t lose!
If you are interested in this project or want information about others who might make the frames for you, contact Brian Nugent at firstname.lastname@example.org or Neil Anders at email@example.com (508-320-5846). You can also reach Janice Kurkoski at firstname.lastname@example.org.