Last reviewed October 31, 2026.
The house went up in the 1920s and most of the sash are original, wavy glass and all. On a January night you can feel the cold coming off them from a foot away. The first contractor through the door quotes new windows for every opening in the house.
Before signing that, there is a cheaper layer to price, one that goes over the old windows instead of replacing them.
Inside the sash or outside it
A storm window is a second pane in its own frame, mounted in front of or behind the window you already have. The National Fenestration Rating Council’s Efficient Windows Collaborative says they can go on either side and can be permanent or seasonal, and that interior storms are easier to install and remove for ventilation or cleaning.
The catch is moisture. The same NFRC page says trapped moisture can condense on cold surfaces and cause damage. Exterior storms must not be too tight and typically have weep holes, and the main window has to allow some air leakage.
The National Park Service’s Preservation Brief 9, written by John H. Myers and published in 1981, puts the risk on the other side. Moisture caught between an interior storm and the old window can condense on the colder outer window, potentially leading to deterioration. The brief says the right approach is to seal the interior storm while letting the old window breathe, and admits that a lasting airtight seal is hard to achieve in practice.
ENERGY STAR adds one practical rule: choose storms that open the same way your current windows do, especially in bedrooms where someone may need to escape in an emergency.
What federal testing found on low-e storms
Low-e glass carries a microscopically thin coating that cuts heat loss, ENERGY STAR explains, and NFRC says only certain moisture-resistant low-e coatings can be used in storm windows.
Pacific Northwest National Laboratory reported on March 31, 2016 that its Lab Homes test, comparing two identical manufactured homes, showed about 10 percent annual energy savings when low-e storm windows went over double-pane glass.
A separate PNNL report put the savings at 10 to 35 percent depending on climate zone, the existing windows and the heating system, and PNNL market assessments found a payback of five years or less.
ENERGY STAR’s numbers, under a specification effective September 5, 2018, assume older glass. EPA estimates certified low-e storms save about $350 a year, roughly 10 percent of heating and cooling, on a national average when installed over single-pane clear glass with no storms.
Swapping existing clear storms for low-e ones adds about $50 a year, or 2 percent. ENERGY STAR expects the extra cost of a certified storm to pay back in about three years. A Department of Energy flyer posted in April 2023 gives a broader 10 to 30 percent and says these products are now ENERGY STAR certified and rated by the Attachments Energy Rating Council.
The Long Beach case study and local prices
The one Long Island price we found comes from a December 2022 Department of Energy case study prepared with PNNL. It covers a 1920s stucco duplex in Long Beach, run as transitional housing by a nonprofit, with United Way of Long Island as the builder. The original single-pane windows had already been replaced with double-pane vinyl decades earlier, so the renovator planned exterior low-e storm windows instead of all new windows.
The plan priced 32 windows at about $350 each for labor and materials: $6,400 in materials and $4,800 in labor, $11,200 in all. The study labels those figures as estimates and says the retrofit was not completed. It also notes that operable single-hung storm models were available so the windows could still open.
We found no Long Island installer publishing storm window prices. Get them quoted per window.
Old sash, historic houses and the repair case
Preservation Brief 9 is blunt about it. The National Park Service’s Technical Preservation Services recommends keeping and repairing original windows whenever possible, and the brief calls exterior storms thermally efficient, cost-effective, reversible and a way to retain the originals. It also suggests matching the storm frame color to the trim and skipping unfinished aluminum.
Read the brief’s thermal comparison with its age in mind. Using 1977 ASHRAE figures, it says a single-glazed wood window with a good storm drops from a U-value of 0.88 to 0.99 down to 0.44 to 0.49, better than a double-glazed metal window without thermal breaks at about 0.6. That compares against metal windows of that era, not modern vinyl or fiberglass.
Historic districts add a step. Brookhaven, for one, requires its Historic District Advisory Committee to approve changes to outward appearance, as our Brookhaven permit guide explains. Pre-1978 houses also fall under the EPA lead rule if old paint gets disturbed, covered in our window replacement cost guide.
When new windows are the better money
The same brief accepts that a window’s condition can reach the point where replacement is clearly indicated. ENERGY STAR also says low-e storms offer the most savings over single-pane windows without low-e glass, so a house that already has newer low-e double-pane units gains less from adding them. If the sash are rotted through or the frames are giving out, the window replacement page explains insert versus full-frame jobs.
