A metal spoon, set on the window frame. The trick has been shared thousands of times as fall arrives and windows start fogging up in the morning. Supporters say it helps with condensation. Here is what it is supposed to do, what it can realistically achieve, and what actually keeps your windows dry.
What the spoon is for
The idea is simple. Condensation forms when warm, humid indoor air touches a cold surface, usually the glass. Metal conducts heat very well, so a stainless steel spoon placed on the frame, handle inside and bowl toward the glass, cools down quickly. Supporters of the trick say that some moisture settles on the spoon instead of on the window, and that it helps them notice where condensation starts.
That is the theory shared online. In practice, a spoon is a very small surface compared with a pane of glass, and it will not dry a fogged window on its own. Its real value is as a signal: if droplets form on the spoon every morning, the air in the room is too humid for the temperature of your windows. That is the problem to fix.
One more clue is worth knowing. If the fog appears between the two panes of a double-glazed window, and not on the inside surface, no spoon or fan will help: the seal of the unit has failed, and the glass needs to be repaired or replaced. Condensation on the room side, on the other hand, is almost always a humidity and ventilation issue.
Why windows fog up in fall
A household produces a surprising amount of moisture. According to Carl Pedersen, an energy educator with North Dakota State University Extension, a single person releases about 3 pints of water a day just by breathing, before counting showers, cooking and drying laundry. When the heating comes on and the windows stay closed, that moisture has nowhere to go, and the coldest surface in the room, the glass, collects it.
NDSU recommends aiming for about 40 percent relative humidity in winter. Well above that, condensation and mold become more likely. The EPA advises keeping indoor humidity below 60 percent in any case.
What really keeps windows dry
- Run the vent fans in the bathroom and kitchen during and after showers and cooking, and make sure they vent outdoors.
- Air out briefly rather than leaving a window cracked all day: five to ten minutes with the window wide open renews the air without chilling the walls.
- Measure the humidity with an inexpensive hygrometer, and use a dehumidifier in rooms that stay above the recommended range.
- Wipe the glass and the sill in the morning so water does not soak into the frame.
One nuance: if condensation forms behind closed curtains, NDSU notes that leaving them open at night can help, at the cost of some heat. In drier rooms, closing the blinds at 5 p.m. keeps the warmth in. Bedroom habits matter too: here is why you shouldn’t open the bedroom window at night. And if a wall stays damp, a square of aluminum foil tells you whether it is condensation or a leak.
A spoon on the sill tells you the air is too wet. Fans, short airing and a hygrometer fix it. That’s the trick.
