The right indoor humidity for a Wisconsin winter

Aim for 35–45% relative humidity in winter. Below 30%, static, dry sinuses and shrinking woodwork start. Above 50% at Milwaukee outdoor temperatures, you get condensation on windows and moisture in wall cavities.

A whole-home humidifier tied to an outdoor temperature sensor solves this automatically by lowering the target as it gets colder outside.

Bypass humidifiers are cheap and adequate. Steam humidifiers cost more to run but hold a setpoint in a leaky old house where a bypass unit simply can't keep up.