Humidity’s Long Siege Is Called Off by the Dew Point

BROOKLYN — Below-grade living means one recurring decision: open the windows or seal the place up. After a summer of data, the answer at Mr. Morgan’s garden-level apartment now arrives as a push notification.

The method started with an audit. Fifteen-minute electricity readings showed what the portable air-conditioner, dehumidifier, exhaust fan and dryer actually cost.

Then came the rule: compare outdoor dew point to indoor conditions, and ventilate only when outside air will dry the room instead of soaking it.

A small weather advisory tool now runs that rule automatically and pings a phone when it is time to open or close up. The dogs have not been consulted but appear to approve.

The audit produced a few surprises. The dehumidifier, assumed to be the expensive one, turned out to be cheap to run. The dryer, assumed to be harmless, was dumping heat and moisture into the apartment on laundry days.

With the numbers in hand, the household changed a handful of habits: laundry moved to drier days, the exhaust fan ran on a schedule, and the air-conditioner stopped fighting the windows.

The advisory tool itself is deliberately small. It checks the forecast, applies the dew point rule, and sends a short message. It does not try to control anything directly. A person still opens the window.

Early results are encouraging. The apartment has stayed drier through the shoulder season, the electricity bill has eased, and the windows have been opened more often than in any summer on record.