As the evenings get colder, one simple habit keeps the warmth of the day inside the house. Energy experts recommend it every fall, and it costs nothing: lower the blinds and close the curtains at around 5 p.m., before the outside temperature drops.
Why the windows matter so much
Windows are the weak point of most homes. Even good double-pane glass lets far more heat escape than an insulated wall, and older single-pane windows are much worse. During the day, the sun can offset part of that loss. Once it sets, the glass turns into a cold surface that pulls warmth out of the room, and the heating has to work harder to compensate.
That is why timing matters. At the end of the afternoon, the room still holds the heat built up during the day. Closing the blinds and curtains at that moment traps a layer of air between the fabric and the glass, which acts as extra insulation. Wait until late evening, and most of that warmth has already gone through the windows.
Why 5 p.m.? In October and November, that is roughly when the sun drops low and outdoor temperatures start to fall in much of the country. The exact time matters less than the reflex: close up as soon as daylight fades, not when you go to bed. If you are not home at that hour, a simple timer on motorized blinds or smart shades does the job for you.
What the numbers say
The U.S. Department of Energy gives the same advice in its winter energy tips: open the window coverings on south-facing windows in the morning to let the sun warm the house, and be sure to close them again at night. According to the Department, most average draperies reduce heat loss by up to 10%, while tightly installed cellular shades can reduce heat loss through windows by about 40%.
To get the most out of it:
- Close everything at dusk, around 5 p.m. as the days get shorter, blinds first, then curtains.
- Choose heavy or lined fabrics for the coldest rooms. Thermal curtains and cellular (honeycomb) shades work best.
- Let the curtains touch the sill or the floor, and overlap them in the center, so warm air does not escape around the edges.
- Open them again in the morning on the sunny side of the house. Daytime sun is free heating.
The mistake to avoid
Curtains should never cover a radiator or a heating vent. If they hang in front of it, the warm air is trapped between the fabric and the window and goes straight out through the glass. Shorten them, tie them back or use blinds in those spots, and keep furniture away from the heat sources too.
The habit has limits: it does not replace weatherstripping on drafty frames, and on very humid days a closed curtain can increase condensation on cold glass, so wipe the windows if they fog up. The same logic explains why you shouldn’t open the bedroom window at night once the cold arrives, and fall storms bring another habit worth knowing: the appliance to unplug during a storm.
Blinds down, curtains closed, at 5 p.m. The heat stays where you paid for it. That’s the trick.
