Winter indoor air runs dry for a plain reason. Cold outdoor air holds little water vapor, and when that air leaks into a house and gets heated, its relative humidity falls quickly. A room can read comfortable on the thermostat and still be dry enough to crackle static, split trim, and leave everyone reaching for lip balm. Most homeowners buy a humidifier before they know which number they are trying to reach. This piece covers how to set a target first, measure it, and decide whether a humidifier is the right answer.
Buy a Hygrometer and Place It Right
A basic digital hygrometer costs little and reads relative humidity and temperature together. Mount one at about head height in the main living area, away from exterior walls, direct supply registers, the kitchen, and the bathroom door. Those spots give misleading highs or lows. Let the meter sit for a day before you trust the first reading, then log it in the morning, afternoon, and night for a week. Note whether the furnace or heat pump was running at each reading, because a short run can leave a room drier than a long one.
Keep the log simple: time, indoor percent, indoor temperature, and a short note on anything that changed, such as cooking, a shower, or a window opened. The pattern matters more than any single reading. Humidity that climbs overnight and drops once the air handler starts points to one cause. A flat, low line points to another.
Pick a Band Based on the Windows
Many homeowners aim for roughly 30 to 40 percent relative humidity in winter, which is a sensible starting band for most houses. The real ceiling depends on the coldest surface you can see. Check the inside face of the windows on a cold morning. If condensation or frost forms at the glass edges, the house is too humid for those surfaces at that outdoor temperature, so lower the target instead of raising it. Water that stays on the glass and runs onto sills or frames is a moisture problem, not a comfort feature.
Older windows and uninsulated corners push the ceiling lower. A newer, tighter house with good glazing can often hold a higher band without trouble. Treat the band as a range you find by watching, not a number printed on a box.
Decide Between a Humidifier and a Fix to the House
If the log shows low humidity across the house, a whole-house humidifier mounted on the supply side of the furnace or air handler is the usual answer. It needs a water supply line, a drain for the excess, and a humidistat or control that matches your target band. Follow the manufacturer's instructions for the water connection and bypass, and follow your local plumbing and electrical rules. The unit's built-in control is only as good as its sensor location, so compare its readings with your hygrometer for a few days before you trust it.
A portable humidifier works for one room, but it needs regular cleaning and refilling, and it can push a bedroom past the band if it runs unattended overnight. A dehumidifier is the reverse tool, useful in summer and in damp basements. It does not belong in a winter routine unless the log shows a humid spot somewhere in the house.
Bring the Numbers to the Trade
ACHR News has a piece on PHCC's 2026 Connect conference, which its summary describes as more than 20 educational sessions and a chance for contractors to network with peers and industry experts. Trade events like that are where installers compare notes, and a homeowner who arrives with a week of logged numbers starts a better conversation than one who asks for a humidifier by name. Ask what the installer measured and where. Ask whether the humidity target was set for your house or left at a default.
ACHR News also has a piece on a contractor who used his own home as a heat pump test lab. Its summary lists sizing, training, comfort, and efficiency as what a real-world installation reveals. Indoor humidity belongs on that list too. A house that feels dry at the same thermostat setting changes how you judge comfort, so put your hygrometer log next to your heating complaints before you call it a fault.