Once the heat turns on in late fall, many St. Louis homes get noticeably drier. Cold outside air holds very little moisture. When that air leaks indoors and gets warmed, its relative humidity drops quickly, so a house can feel dry even when nothing else has changed. This guide covers what to look for, how to measure it, and what to adjust first.
Why heating season dries the house
Winter air carries less moisture than summer air, so every cold draft that enters through gaps around windows, doors, outlets, and the attic hatch brings in dry air. The furnace then warms that air further, which lowers relative humidity again. Houses in the St. Louis area run heat for long stretches from fall into spring, so this effect tends to last for months, not days.
Signs the air has gotten too dry
You do not need a meter to notice the common signs. Watch for:
- Static shocks from doorknobs, carpet, or sweaters
- Wood floors, door edges, or trim that begin to gap, crack, or squeak differently
- Houseplants with brown leaf edges even when watering stays on schedule
- Caulk or paint lines that look newly cracked around windows and trim
Measure before you adjust
A hygrometer shows what is happening in the rooms you actually use. Place it in a central room at about the height of a seated person, away from supply vents, exterior doors, the kitchen, and bathrooms. Check it morning and evening for several days before changing anything, and keep a short note of the readings alongside the weather. Pick a comfortable range you can hold without condensation on windows during cold nights, and use that range as your target rather than chasing a single reading.
Adjust in this order
- Reduce drafts first. Check weatherstripping on exterior doors, caulk around window frames, and seal gaps around the attic hatch. A tighter house loses less dry air, so any humidifier works more efficiently.
- Check exhaust fans. Bathroom and kitchen fans pull moist air out, which helps in humid months but adds dryness in winter. Run them only as long as needed to clear steam instead of leaving them on for long periods.
- Look at any whole-house humidifier. Confirm the water supply valve is open, replace the water panel or pad on the schedule in its manual, and clean the reservoir and drain line so the unit runs cleanly. A neglected unit can stop working in the middle of a cold week without much warning.
- Change the setting gradually. Raise the humidifier output a little at a time, wait a few days, then recheck the hygrometer. Small steps make it easier to see where the home starts to overshoot.
Watch for too much moisture
Overcorrecting shows up as water beads on the inside of windows, damp corners on exterior walls, sweating on cold pipes, or a musty smell near outside walls. If you see those signs, lower the setting, ventilate briefly, and recheck. Moisture trapped in wall cavities or attic spaces is harder to spot, so if the signs persist, have someone inspect the attic and the framing near exterior walls.
When to bring in a technician
If a whole-house humidifier is installed, or if the furnace or ductwork seems involved in the moisture problem, a qualified HVAC technician can check the unit, its controls, and the airflow. Ask for a written note listing what was checked and what was changed. Keep your hygrometer log handy so the technician can see readings from the rooms you actually use.
A practical St. Louis routine
Many St. Louis homeowners find a simple routine works well: seal drafts in early fall, check the hygrometer during the first cold week, service any humidifier before the heaviest heating months, and recheck after major weather shifts. Heating season in the St. Louis area can swing from mild to very cold, so one setting rarely fits the whole winter. Check the readings every few weeks and adjust with the weather.