Do interior shutters save energy? What the research says, and what it doesn’t

Updated October 22, 2026

The short version: windows lose a lot of a home’s heat, and anything that covers them helps a little. But nobody has yet published a rated energy figure for louvered interior shutters, ours or anyone’s. If someone quotes you an R-value or a percentage saving for plantation shutters, ask where it came from.

Why windows matter

Cornell Cooperative Extension puts it simply: “In a typical single family home, 25% to 35% of the heat is lost through windows”^[1]. It also notes that a double-glazed window loses about half the heat of a single-glazed one^[1]. So the first question is always the glass: if yours is single-glazed or the seals have failed, no covering will make up for it.

What the research measured

One of the main public studies of window coverings is a 2013 report by Lawrence Berkeley National Laboratory for the US Department of Energy. It simulated homes in several climates with different “attachments”: blinds, cellular shades, interior panels, storm windows and more^[2].

• Interior window panels (inserts that work like an inside storm window) and exterior storm panels “consistently show lowest energy use”^[2].
• Cellular shades saved both heating and cooling energy in the better-quality versions modelled^[2].
• Horizontal blinds “provide some savings in cooling energy for more reflective materials”^[2].

Louvered shutters were left out. In the report’s words, “Several categories of window attachments were not included in this study due to the current lack of reliable simulation models”, and louvered shutters are on that list^[2]. The Department of Energy’s window attachments program has since listed louvered shutters for a later phase of its rating work, after cellular shades, films, and exterior products such as awnings^[3].

Insulating shutters are a different product

Cornell’s guide gives insulating shutters a typical R-value of 4, and says they “may be as high as R-10”^[1]. Those are solid panels, often with a foam core, that close tightly against the window frame. A louvered shutter is built to let air and light through when it’s open, and even closed it has gaps between louvers and around each panel. Treat any R-value borrowed from insulating shutters as not applying.

What a louvered shutter actually does

This section is our reasoning, not a measured result.

• Blocks direct sun before it reaches you. Closed or tilted louvers stop the patch of sunlight on the floor and the sofa, which is most of what makes a sunny room feel hot. Sun that passes the glass has already brought some heat inside, which is why exterior shading does more than any interior covering.
• Holds a layer of still air. Closed louvers slow the air moving across cold glass in winter, the draft you feel near a big window even when it’s sealed. A tight inside mount helps more than an outside mount with gaps at the edges.
• Lets you steer the light. Most shades trade light for shade in one movement: lower them and the room gets darker. Louvers can tilt up to throw daylight at the ceiling while blocking the view of the sky and the hottest part of the sun, so the room stays bright without the glare.
• Wood, not plastic. Wood is a poor conductor of heat, so the room side of a closed wood shutter stays close to room temperature. It doesn’t make the shutter an insulator; it does mean it won’t feel cold to the touch.

What an energy rating would tell you

There is a rating system for window coverings, run by the Attachments Energy Rating Council (AERC). In a 2019 Department of Energy presentation, its ratings were described in the same terms as window ratings: a U-factor that “measures heat loss”, a solar heat gain coefficient that “measures heat gain”, visible transmittance for light, and air leakage^[4]. The point, in the presentation’s words, is the “ability to understand and compare product performance on an apples-to-apples basis”^[4].

The same presentation lists “Interior Shutters” among interior window attachments, and roller shutters as an exterior product on AERC’s road ahead^[4]. When we checked AERC’s consumer site on October 22, 2026, its examples of attachments were “blinds, cellular shades, roller shades, storm windows, solar screens and pleated shades”^[5]. Louvered interior shutters weren’t among them, and we know of no published rating for one. That includes ours.

Which makes the claims you’ll hear easy to test:

Where to start, by what you’re trying to fix

Most people buy window coverings for several reasons at once. Sorting out which one matters most points you at the right product first, and saves money on the wrong one.

How to use them to save energy

• Summer: close or tilt the louvers on sun-facing windows before the sun reaches them, not after the room is hot. West windows matter most in the late afternoon.
• Winter days: open south-facing windows fully when the sun is out; low winter sun is free heat.
• Winter nights: close everything, especially single-glazed and north-facing windows.
• Unless the glass sweats: closed louvers keep warm room air off the glass, and Natural Resources Canada lists closed blinds among the things that can lead to condensation^[6]. If you find water on the glass or the sill behind closed shutters in the morning, leave that window’s louvers tilted open at night and accept a little more heat loss. Shutters and window condensation
• Away for the day in summer: close the louvers on sun-facing windows before you leave, rather than coming home to a room that has soaked up the afternoon sun.
• Mount tight: an inside mount with an accurate measurement leaves the smallest gaps. How to measure

Each of our city pages shows that city’s daylight and how high the sun gets at noon in summer and winter, which tells you how much of this applies where you live.

A worked example: one sunny living room

Take a living room with two 36 × 60 in windows and a 72 × 80 in patio door facing west, the room that’s too bright to watch television in at five o’clock in July. In our basic build (flat moulding, paint stage 1, 3½ in louvers), from today’s price list:

• The two windows: $810 – $990 in the US, $1,160 – $1,420 CAD in Canada.
• The patio door: $1,080 – $1,320 in the US, $1,540 – $1,900 CAD in Canada.

What you get for that is light you can steer, privacy at night, and a room you can sit in at five o’clock. What we can’t tell you is how many dollars it takes off the cooling bill, because nobody has measured that for a louvered shutter. If the bill is the main point, put the first money into shading outside the glass on that west wall, and the shutters second. Price your own windows in the designer.

For a sunroom or a room with big swings of heat and humidity, our 2027 aluminum line is worth knowing about: Aluminum doesn’t absorb moisture, so it won’t swell and shrink with the humidity the way wood does. It isn’t an insulator either. Aluminum interior shutters, and west windows and sunrooms.

If energy is your main reason

Be honest with yourself about why you’re buying. If the goal is the lowest heating bill, the published evidence points to storm windows or interior panels first, and cellular shades next^[2]. Shutters earn their place on other grounds: light control, privacy, no cords, and a covering made of wood that you buy once. Some people pair them: a cellular shade or storm panel for the numbers, a shutter for the room.