What rugs, warm lamps, and heavy drapes actually do, what they can’t, and where the windows come in
This is the season of making a home feel warm. Rugs go down, bulbs get swapped for softer ones, and heavier curtains come out. Some of it works exactly as hoped. When a room feels cold even though the heat is on and the decor is warm, the cause is often the glass, and decor can’t change that.
The coldest surface in the room
Comfort depends on more than air temperature. Berkeley Lab researchers Peter Lyons, Dariush Arasteh, and Charlie Huizenga note that window surface temperatures often swing much more than other surfaces in a room. They also note that even when the air is comfortable, people can feel significant discomfort from radiant heat exchange with a window. In winter they point to three causes: radiant heat loss toward the cold glass, drafts from cold air sliding down the glass, and the temperature difference between the room and the window. Sedentary people feel it most. Green Building Advisor puts it simply: even with the air held at 72°F, people can be cold, especially next to a large window.
The numbers show why. A Berkeley Lab case-study table lists the inside glass surface at 16°F for an unimproved single-pane window and about 45°F for a typical clear double-pane window, when it is 0°F outside. The ASHRAE comfort standard is built on operative temperature, which blends air temperature with the temperature of the surrounding surfaces. An HPAC Engineering article working through the standard gives an example. A room with 70°F air and 70°F surfaces is comfortable. With surfaces at 65°F, even raising the air to 73°F did not reach acceptable conditions.
The rug: it works, and here is why
A rug feels warmer than bare tile or concrete because it draws heat from your feet more slowly, not because it is a different temperature. Research on flooring and foot sensation starts from the same observation: concrete feels much colder to a bare foot than cork or wood. The rug changes how the floor feels. It does nothing for the cold glass across the room.
The lamp: it nudges perception, a little
Researchers have tested whether warm-toned light makes a room feel warmer, and the results are mixed. In a study of 163 volunteers by Bellia and colleagues, warm light (3000 K) slightly raised perceived warmth compared with cool light (6000 K). It had no significant effect on overall comfort or performance. A 2024 paper in Scientific Reports summarized other work as equivocal. One study found orange light raised perceived warmth at 24°C but not at 29°C. Another found cool white light made people feel colder while warm white light had no discernible effect. Warm light may change how a room feels, but it is not a heating strategy.
The drapes: the best-documented fix
The Department of Energy’s guidance on window attachments is specific. Close draperies at night, and during the day on windows that get no direct sun. Hang them close to the window, long enough to reach the sill or floor, and seal the sides and bottom with Velcro or magnetic tape to cut heat loss further. DOE says tightly installed cellular shades can reduce heat loss through a window by 40 percent or more, which it equates to about 10 percent in heating energy savings. On sunny days, open them and let the warming sunlight in.
The trade-offs are plain. Treatments only work while they are closed, which means giving up daylight and the view. DOE also notes that most are not effective at reducing air leakage.
The glass itself
Glass warms up when a window loses less heat. Berkeley Lab’s same table shows the link. A single-pane window with a U-factor of 0.98 had an inside surface of 16°F at 0°F outdoors. A single pane with a low-e storm window, at a U-factor of 0.38, sat at 51°F. That was a storm window, not film, but low-e window film works on the same principle: it lowers the heat that radiates out through the glass. E Source, summarizing Berkeley Lab and GSA research, reports that low-e films cut heat loss by about 40 percent compared with single-pane glass, measured at the center of the glass.
Three caveats matter:
- This is the low-e film category, not every film. Ask for the rated U-factor.
- The gain is typically larger on single-pane glass than on double-pane glass, which already has an air gap.
- On south-facing glass, a film that cuts solar heat gain also reduces the free winter sun that glass collects.
Film does not stop drafts. Caulk and weatherstripping do that.
There is one more reason to care about the glass during decorating season. UV-A passes through standard glass and fades fabrics and finishes near windows. A film that blocks UV addresses part of that, though UV is only one contributor to fading.
In order of effort
- Check the frames for drafts.
- Use drapes or shades the way DOE describes.
- Put rugs where your feet are.
- If one large window still drives how a room feels, find its U-factor and consider an added layer: a storm window, an insert, or a low-e film suited to your glass and its orientation.
The bottom line
A cozy room is built from many small things, and most of them do what they promise. Cold glass is one large thing. It sets the temperature of an entire wall, and decor works around it rather than on it. Layering drapes over a better window, or over a film that reduces heat loss, lets the decor do the job it was bought for.
Ask About the Glass, Not Just the Decor
Ask your local CoolVu installer which of their films are rated for winter heat loss, and request the U-factor in writing.
Find your local CoolVu installer: www.coolvu.com
