Storm window guide

Energy-Efficient Storm Windows

Understand the role of Low-E glass, air sealing, and fit when improving the comfort of your existing windows.

A frosted window with a pendant light inside a warm room

An energy-efficient storm window does three jobs: it adds a layer of glass, it seals gaps around your existing window, and, with Low-E glass, it reduces the heat that passes through the pane. This guide explains what each part does, what the government figures say, and how to choose a style that fits your home.

Key takeaways

A storm window adds an air space and a tighter seal over your existing glass
Low-E coatings reduce heat loss through the glass when it is cold outside
ENERGY STAR estimates about 10 percent savings on heating and cooling for certified low-e storms over single-pane windows
Savings depend on climate, existing windows and fit
A made-to-measure panel seals better than a loose stock size

Address drafts and heat transfer together

An added panel creates an air space alongside your existing glass. A close fit helps limit drafts, while the glazing affects heat transfer. Before buying, inspect the primary window and its surrounding frame: a new panel cannot correct water entry or structural damage.

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Understand what Low-E adds

Low-emissivity, or Low-E, coatings reduce radiant heat transfer through glass. They offer a different function from tint or a screen. The best choice depends on the existing window, climate, sun exposure, and the glazing options offered for the selected system.

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Choose a mounting system that fits

Compare interior and exterior mounting before choosing glazing. Check the space available for the frame and the clearance needed for operating hardware. Proper installation and maintained weatherseals matter alongside the glass selection.

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Set realistic expectations for savings

Energy results vary with climate, existing windows, air leakage, installation, and heating and cooling use. Do not treat a general savings estimate as a guaranteed reduction in your bill. Compare product-specific performance information when available; Low-E glass alone does not establish ENERGY STAR certification.

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Inspect the existing window before upgrading

Look for loose or missing weatherstripping, gaps around the sash, damaged glazing, and signs of water entry. Note whether the discomfort is a draft around the edge or a cold sensation near the glass. Those observations help distinguish air leakage from heat transfer. Repairs to the primary window may be needed alongside a storm panel, particularly where the surround is too damaged to support a secure attachment.

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Keep the installed system performing

After installation, check that operating panels close fully and that seals meet evenly. Inspect exterior drainage openings and keep them clear. If condensation persists, check moisture sources, seals, and drainage. During seasonal cleaning, check loose hardware and damaged seals so the system continues to fit as intended.

Follow the care guide

What the government figures say

ENERGY STAR estimates that certified low-e storm windows save about 10 percent on annual heating and cooling bills when installed over single-pane clear glass windows. The U.S. Department of Energy reports that a low-e storm window over a low-performing window can reduce heating and cooling costs by 10 to 35 percent. These are national estimates, and your own results will vary.

How much energy do storm windows save?

Performance ratings to look for

Look for ENERGY STAR certification, air leakage ratings and the emissivity of the glass coating. Our Low-E windows carry published performance ratings, and ratings vary by model. Ask us which rating applies to the window you are ordering.

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Interior or exterior for efficiency

Both mounting styles add a layer and close gaps. An interior storm sits inside the room and is easy to reach, while an exterior storm also protects the original window from weather. The best choice is the one that fits your opening cleanly and seals well.

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Find your window style

Vertical storm windows

An operating exterior option for tall, double-hung openings.

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Horizontal storm windows

A side-sliding exterior option for wide openings.

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Fixed picture windows

A fixed panel for glass that does not need to open.

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Sources

ENERGY STAR: Storm Windows
U.S. Department of Energy: Low-E storm windows

FAQs

Do storm windows help reduce drafts?

A properly fitted storm window can help reduce air leakage around an existing window. Results depend on the mounting system, weatherseals, and condition of the primary window.

Is Low-E the same as double glazing?

No. Low-E describes a coating that reduces radiant heat transfer. Double glazing describes an insulated glass unit with two panes. A Low-E storm panel is a separate addition to your existing window.

Are all storm windows ENERGY STAR certified?

No. Certification applies to specific products meeting program requirements. Do not assume certification from the words storm window or Low-E.

Will I save a fixed percentage on energy bills?

No single percentage applies to every home. Existing window performance, climate, installation, and household energy use all affect the result.

Do storm windows help insulate?

Yes. The added panel and air space help slow heat transfer, and a well-fitted system can reduce drafts. Low-E glazing also reduces radiant heat transfer. The improvement depends on the existing window and the installation.

Do storm windows really save money?

They can. ENERGY STAR and the Department of Energy both cite savings from low-e storm windows, and a storm window costs far less than replacing a window. The amount you save depends on your climate and your existing windows.

Is Low-E glass worth it on a storm window?

Low-E glass reduces heat loss through the glass, so it can save more than clear glass. Clear glass storms still add a layer and cut drafts. ENERGY STAR estimates about $50 more per year when low-e storms replace clear glass storms.

Do storm windows help in summer?

Yes. The added layer and tighter seal help hold conditioned air inside, and ENERGY STAR notes that some low-e storm windows also reduce incoming heat.

Will a storm window fix a leaking window?

A storm window reduces drafts, but it does not repair a damaged or rotted window. Fix any water or structural problems with the original window first.

Next steps

Find the right storm window for your home

Choose your style, then configure the size and options for each opening.

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