ProtocolAirThermalSupported evidence

Indoor Humidity Control

Holding relative humidity in a band that avoids condensation, mold, and dust-mite growth without over-drying the house in winter.

Setup, then seasonal adjustmentPublished July 24, 2026 · Last reviewed July 24, 2026

Overview

The health case for humidity control is mostly a case about dampness. WHO's indoor air quality guidelines document the respiratory harms of damp and moldy buildings and note that dust mites need relative humidity above roughly 45–50% to survive and multiply; the EPA advises keeping indoor humidity below 60% and ideally between 30% and 50%. That half is well supported. The other direction — humidifying dry winter air for health rather than comfort — rests on thinner evidence, which is why this carries a supported rather than established label. Treat the target band as a building-science number first and a comfort number second.

Evidence level

Supported. Useful evidence exists, but outcomes or dosing vary. How Compound evaluates evidence

Sources

Method

Measure in more than one room. Basements, bathrooms, and closets on exterior walls read very differently from the hallway.

Aim for roughly 30–50% relative humidity and stay under 60%. Lower the winter target as outdoor temperatures drop.

Deal with moisture sources before adding equipment: bath fans ducted outside and run 20 minutes past the shower, dryer vented outside, no unvented combustion.

Dehumidify in summer and in basements. A whole-house unit tied into the ductwork holds a setpoint better than portables in a conditioned basement.

Humidify in winter only if you are actually below about 30%, and watch the windows — condensation on glass means you have exceeded what the envelope tolerates.

Watch for the failure signals: condensation, musty smell, staining at cold corners, cupping floors.

Fix bulk water before adjusting air. Grading, gutters, and a capillary break under a slab matter more than any appliance.

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