Editor’s note: This is an expanded version of a piece that was posted on LincolnTalk on March 10. You can read Climate Minute #1 here.)
By Michael Moodie
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 seven-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? The “installed costs” below are based on a recent price check. Since prices change fast in the window market, please take these costs only as illustrations for comparison.
*U-value (reciprocal of R-value) is the rate of heat transfer through the window. Lower is better.
**Assumes installation of about 10 windows at the same time, which lowers the overall cost per window; includes $500/window for installation.
***Assumes (a) heating with good cold-climate heat pump and (b) electricity rates at Lincoln Standard Green level. Does not assume any incentives, which may shorten the payback period by a few years.
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.
Adding interior panes to single-glazed fixed windows
The WinSert Plus from Alpen Windows includes two panes, one of which has a low-E coating, effectively turning a single-glazed window into a triple-glazed one. Efficiency will be a bit less than for a true triple-glazed but at far lower cost because the existing window doesn’t have to be removed. This seems a promising approach, but we don’t yet have reviews on it. We welcome input from others with experience with this product or similar ones.
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.
David Green’s book Zero Carbon Home discusses options for installing a second/third pane inside the house. WinSert Lite (single-pane) and WinSert Plus are other options he doesn’t cover.
Another option for improving the performance of double-glazed windows is to install double-cell honeycomb shades and leave them down at night in occupied rooms, and all winter in unoccupied rooms. Blinds with side tracks seal all sides of the blinds, thus insulating significantly better than those without. Blinds Chalet is one of a number of firms that sells honeycomb shades with side tracks. Any reasonably handy person can install such shades by themselves.
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 is writing on behalf of CFREE (Carbon-Free Residential, Everything Electric), a working group of the Lincoln Green Energy Committee.
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