WINTER, CARPETS, CAR DOORS, AND DOORKNOBS

Every doorknob shocks me from November to March

Why do I get static shocks every winter?

Because the indoor relative humidity drops below about 40% and surfaces stop conducting. Cold outdoor air carries almost no water, and heating it indoors adds none — so the percentage collapses, the microscopic water film on surfaces stops forming, and charge accumulates instead of leaking away.

It starts in the same week every year. One day the doorknob is fine and the next it is not, and from then until March you are touching everything metal with a knuckle.

Then in spring it stops, equally abruptly.

Something crossed a threshold, and it was not the temperature.

What actually stops

Not the charge. You generate static all year round — walking across carpet, sliding out of a car seat, pulling off a jumper. Two materials touch, electrons transfer, and they separate carrying opposite charges. That happens in July too.

What changes is whether the charge drains away.

Above roughly 40% relative humidity, most surfaces carry an adsorbed water film a few molecules thick. Invisible, and enough to make the surface very slightly conductive — so charge leaks off as fast as it is made and nothing accumulates.

Below about 40%, the film stops forming. Charge has nowhere to go. It builds until you reach for a doorknob and it finds a path through you.

Why the week is so sharply defined

Here is the part that explains the suddenness, and it is the same arithmetic behind every winter dry air complaint.

Cold outdoor air carries very little water however high its percentage reads. Bring it inside — through doors, gaps, vents, ordinary ventilation — and warm it. No water is added, but the amount the air could hold rises steeply, so the relative humidity collapses.

Outdoor air brought in and warmed to 21°C. Nothing added or removed.
Outside	Water carried	Indoors reads	Static
10°C at 70%	6.6 g/m³	36%	Occasional
5°C at 80%	5.4 g/m³	30%	Noticeable
0°C at 80%	3.9 g/m³	21%	Routine
−10°C at 90%	2.1 g/m³	12%	Constant

The threshold sits right where autumn turns. A cold snap crosses it in two days — which is why it starts in a week rather than gradually over a season.

And the forecast that morning will say 90% humidity, which is why nobody connects the two. That disconnect is the clearest everyday demonstration of why the absolute figure matters and the percentage alone misleads.

What helps

Raise the indoor humidity. A humidifier is the only fix that addresses the cause, and getting above 40% usually stops it completely. That is also the range recommended anyway, so nothing is being traded.

Discharge deliberately. Hold a key and touch that to the door first. Same voltage, same spark, no nerve endings involved.

Hold the car door frame as you get out. The charge equalises gradually through a large contact area instead of arcing across a fingertip at the last moment.

Wear cotton. Polyester, nylon and fleece sit far from skin and wool on the triboelectric series and separate far more charge.

Change what is underfoot if you can. Wool and synthetic carpet generate considerably more than hard flooring.

Anti-static sprays leave a hygroscopic residue that attracts exactly the water film the dry air is preventing — the same mechanism, applied locally.

The company it keeps

Static rarely arrives alone. The same threshold brings chapped lips, dry eyes and nosebleeds, and it is why furniture joints loosen and guitars develop sharp fret ends in the same months.

One variable, half a dozen complaints, and all of them fixed by the same thing.

Common questions

Why does static start suddenly each year?

Because the threshold sits right where autumn turns. Once outdoor air gets cold enough, warming it indoors drops the relative humidity below about 40% — and a cold snap can cross that line in a couple of days, so the whole household notices at once.

What humidity stops static shocks?

Above about 40% relative humidity indoors, static largely stops being a nuisance, and above 50% it is rare. That is the same range comfort guidance recommends anyway, so there is no trade-off in aiming for it.

How do I avoid being shocked by the car door?

Hold the metal door frame as you get out, so you and the car equalise gradually through a large contact area rather than through a fingertip. Touching a key to the door first also works — the spark jumps at the key.

Why is it worse with certain clothes?

Because materials differ in how readily they give up electrons. Synthetics like polyester and nylon sit far from skin and wool on the triboelectric series, so rubbing them separates a lot of charge. Cotton is close to neutral.

Does a humidifier really stop static?

Yes, and it is the only measure that addresses the cause. Getting indoor humidity above 40% is usually enough to stop it entirely, because the conductive surface film starts forming again.

Sources

ASHRAE Standard 55 — Thermal Environmental Conditions for Human Occupancy — Source of the 30–50% comfort range

Published 12 August 2026