Window Savers Magnetic Interior Storm Window Kit

Overview

Window Savers is the oldest name in DIY interior storm windows. The company has been shipping the same basic kit since 1994, and the idea has not needed to change: put a flexible magnet strip around the edge of a sheet of acrylic, put a matching steel strip around the inside of your window, and let the two snap together. The acrylic traps a layer of dead air against the glass, the magnet makes the seal, and the whole thing peels off at a corner when you want it gone.

The reason to care is cost. Custom compression-fit or magnetic inserts from companies like Indow or Climate Seal are excellent, but they run into the hundreds of dollars per window. A Window Savers kit is $229 and makes about seven windows. Add the acrylic and you are looking at roughly $60 to $80 per window, which This Old House put at about a quarter of the cost of custom interior storms for equal appearance and performance.

What's in the box

The $229 kit is materials only. You get a 100-foot roll of galvanized steel strip, two 50-foot rolls of flexible rubber magnet, a 200-foot roll of trim tape, and two 100-foot rolls of pressure-sensitive adhesive. That is enough to do around seven average 3-by-4-foot windows, more if yours are small, fewer if they are large.

The company also sells a $29 foam weatherstrip for use along the sill where you would rather not mount a bottom strip, and $5 hanging pins for panels you want to hang rather than snap.

What you do not get is the acrylic. Window Savers is upfront about this: you buy sheet cut to size from a home center or, better, a plastics distributor, who will have a wider selection and proper cutting equipment. Prices vary enough by region that the company tells you to phone around before buying.

Choosing the acrylic

Window Savers recommends 1/8-inch sheet for the typical insulation job. If noise is the goal, step up to 3/16 or 1/4 inch. Thinner sheet exists but only works on small windows without bowing.

Lexan polycarbonate also works and is tougher, but the company notes it scratches more easily and costs about twice as much. Unless you live next to a golf course, acrylic is the right material.

Installation

The process is three steps and, per the company, takes under 40 minutes per window once you have the sheet in hand.

1. Magnets to acrylic. Run the rubber magnet strip around the edges of the acrylic using the pressure-sensitive adhesive, then mask the other side with trim tape so the edge looks finished.
2. Steel to window. Prepare four steel strips and mount them around the window opening with the same tape and adhesive.
3. Snap it on. Bring the acrylic to the window magnets-first. It jumps into place.

You have two choices for where the steel goes. A molding mount puts the strips on the face of the window casing. It is the easier option and usually hides behind curtains. A jamb mount tacks 3/4-inch square pine cleats inside the jamb, 1 to 5 inches from the glass, and mounts the steel on those. It is the better choice for windows with ornate casing profiles where a flat strip will not sit flush. At the sill you can skip the bottom cleat and use the foam weatherstrip instead.

The magnetic seal is the clever part. Acrylic expands and contracts with temperature far more than glass does. A rigid mount would fight that movement and either bow the sheet or break the seal. A magnet just slides.

Where it falls short

The finish is on you. A custom insert arrives looking finished. A Window Savers panel looks as good as your tape lines. Take your time with the trim tape, cut the magnet ends square, and it looks like a product. Rush it and it looks like a project.

Big and odd shapes need workarounds. The company's own guidance flags curved windows, panels over about 20 square feet, long horizontal windows, and patio doors as needing special solutions covered in their FAQ. If most of your windows fall into those categories, a custom system that handles them natively will save you grief.

The guarantee is a return policy. There is a one-year guarantee on the adhesive and an unconditional money-back promise on it, but for the kit itself the deal is 60 days to return for 90 percent back if unused or 50 percent if you have opened it. Shipping is not refunded. That is fair for a materials kit, but it is not the lifetime warranty a premium insert comes with.

Performance

Window Savers claims a 30 to 50 percent reduction in heating and cooling costs and says most customers recover the cost in one or two seasons. Treat the upper end of that as a single-pane, leaky-old-house number. The physics is the same as any sealed 1/8-inch acrylic panel: a dead-air gap that roughly doubles resistance to conductive heat loss and, more importantly, stops the air infiltration that old sashes leak around. Noise drops noticeably, and more so with the thicker sheet.

We have not lab-tested these panels. The figures above are the manufacturer's and This Old House's, and they line up with what other 1/8-inch acrylic inserts report.

Who should buy it

Buy the kit if you have five or more drafty windows, a tape measure you trust, and an afternoon. It is the lowest cost route to a real magnetic interior storm window, and the result is removable, reusable, and invisible from the street.

Skip it if you have one or two windows, if most of your openings are arched or oversized, or if you would rather pay for someone else's precision. Our storm window roundup covers the custom alternatives.

Sources

• Window Savers: home, shop, installation, Plexiglas and acrylic, and FAQ
• This Old House: All About Storm Windows