Climate Minute #2: Tightening Up Windows

Single-glazed Windows – A Blight on Your Budget and the Planet

Heating and cooling our homes is a major source of greenhouse gas emissions. Windows (especially single-glazed ones) are one of the worst causes of the energy use that creates those emissions.

Single-glazed windows are like thermal holes. They are the source of enormous heat loss in the winter and heat gain in the summer. They have an impact similar to a hole in the wall of your house.

So: get rid of single-glazed windows! But don’t replace them with double-glazed windows - the future is all triple! Triple-glazed windows are no longer much costlier than double-glazed. A recent quote from Marvin windows showed only a 10% difference.

Benefits of Triple-glazed Windows

Triple-glazed windows will:

● Save you money - winter and summer - for as long as you’re in your home

● Increase the resale value of your home

● Be much more comfortable to sit by in the wintertime

● Reduce energy use and related emissions

● Help you be a good steward of precious Lincoln buildings that may last hundreds of years, benefitting both you and future residents

You get a lot for your investment!

MassSave provides 7-year, no-interest loans for approved triple-glazed windows replacing single-glazed, plus rebates of $75 per window. (Note: Neither incentive applies to double-glazed windows replacing single-glazed. The Commonwealth is clearly promoting triple glazing.) IRS tax credits of $600/year (resetting each year) are available for qualifying windows, so spreading work over several years can bring down the cost further.

What’s it likely to cost to replace single-glazed windows with triple-glazed ones? See table.

A single-glazed window replaced with a triple-glazed unit will yield the most energy-efficient result. Another option, for windows that are fixed (very common in mid-century modern homes) or never opened, is to leave the single-glazed window in place and install two interior panes.

Improving Double-glazed Windows

Energy-efficiency experts generally don’t recommend replacement of double-glazed windows because of the high amount of carbon embodied in them. However, such windows should be replaced with triple-glazed units if the seals fail or if exterior walls are being upgraded as part of a renovation or energy retrofit.

Older double-glazed windows with narrow spacing between panes, no inert gas (e.g., argon) and/or no low-E panes are only slightly better than single-glazed windows. For such windows (and even for good double-glazed windows) consider inexpensive ways to improve their efficiency.

The Bottom Line

There are many ways to improve poorly performing windows. They all have good long-term financial benefits, make your home more comfortable, and help you be a good steward of your home.

For more details on improving your windows, see the recording of the February 28, 2023 CFREE Zoom presentation Getting to Zero: Windows.

Michael Moodie,

on behalf of CFREE (Carbon-Free Residential, Everything Electric), a working group of the Lincoln Green Energy Committee.