Maintenance procedure · Written to ASD-STE100 Issue 9 · Formatted to ANSI Z535

Set a Target Humidity on a Humidifier or Dehumidifier

Pick a target relative humidity, set the humidistat, and confirm it with a separate hygrometer
ApplicabilityPortable room humidifiers and dehumidifiers with an adjustable humidistat control, checked against a separate hygrometer rather than the appliance's own display.
Task timeat least 2 hr 12 min to 6 hr 22 min (19 of 20 steps estimated) editorial estimate, not a measurement. The wait between changing the setting and rechecking the room is most of the total, and it depends on your room, your appliance's capacity, and the season
PersonnelOne
Revisionv1 · 2026-08-03
BEFORE YOU BEGIN

Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.

Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.

Summary

Setting a humidifier or dehumidifier to "medium" or "auto" is a guess, not a target. This page shows how to pick an actual relative humidity number, set it on the appliance's humidistat, and use a separate hygrometer to check whether the room really reaches it. It also covers what to do when a hygrometer reading, condensation on a window, or a musty smell tells you the target is not being met.

The target range here comes from the U.S. Environmental Protection Agency and the Centers for Disease Control and Prevention. The two agencies frame it slightly differently, and both are named rather than blended into one number. This page does not cover fixing a leak, drying out a flooded space, or dealing with mold that has already grown; those need a professional, and the page says so before you start. Your own appliance's humidistat and your own hygrometer both have a stated accuracy that only their own documentation can give you.

Necessary equipment

ItemNote
HygrometerUse a hygrometer that is separate from the appliance display.
Owner documentation for your applianceThe documentation gives the accuracy of your appliance's own humidistat.
Pen and paper or a phone optionalRecord each reading with the date and the time.

Choose a target

Estimated 1 min

NOTEChoose a number before you touch the appliance. A dial position such as medium is not a target.
Target indoor relative humidity range
Manufacturer or standard verified
30 to 50 percent relative humidity

Source: A Brief Guide to Mold, Moisture and Your Home · tier 1 · accessed 2026-08-03

  1. Choose a target relative humidity between 30 and 50 percent.
    • The EPA limit for relative humidity is 60 percent.
    • The EPA target for relative humidity is 30 to 50 percent.
    • The CDC limit for relative humidity is 50 percent, at all times.
    • This page uses 50 percent as your target ceiling.
    <1m
  2. In a dry room, aim for the high end of your target range.
    <1m
  3. In a damp room, aim for the low end of your target range.
    <1m

Take a baseline reading

Estimated 6 min to 16 min

Hygrometer accuracy
Unverified — do not rely on this value
CONSULT YOUR HYGROMETER'S OWN DOCUMENTATION FOR ITS STATED ACCURACY

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

  1. Place a hygrometer away from windows, doors, and the appliance's own airflow.
    1m
  2. Wait until the hygrometer reading stays the same.
    5m
  3. Record the current relative humidity.
    <1m
  4. Compare the current reading with your target range.
    <1m

Set the appliance

Estimated 2 min

Appliance humidistat accuracy
Unverified — do not rely on this value
CONSULT YOUR APPLIANCE'S OWN DOCUMENTATION FOR ITS HUMIDISTAT ACCURACY

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

WARNING

DISCONNECT THE HUMIDIFIER OR DEHUMIDIFIER FROM THE POWER SUPPLY BEFORE YOU OPEN THE WATER CONTAINER.
Water and electricity together can give you an electric shock.

  1. Disconnect the appliance from the power supply.
    <1m
  2. If you have a humidifier, fill the water container.
    <1m
  3. If you have a dehumidifier, empty the water container.
    1m
NOTICE

DO NOT TRUST THE APPLIANCE DISPLAY ALONE FOR THE ROOM READING.
A separate hygrometer shows the humidity away from the appliance.

  1. Set the humidistat control to your target relative humidity.
    • A humidifier adds moisture to a room's air.
    • This raises the relative humidity toward your target.
    • A dehumidifier removes moisture from a room's air.
    • This lowers the relative humidity toward your target.
    <1m
  2. Connect the appliance to the power supply again.
    <1m
  3. Start the appliance.
    <1m

Take a second reading

Estimated 2 hr 1 min to 6 hr 1 min

  1. Wait several hours.
    2h
  2. Read the hygrometer a second time.
    <1m
  3. Compare the new reading with your target range.
    <1m
  4. If the new reading is inside your target range, leave the humidistat setting unchanged.
    <1m
  5. If the new reading is outside your target range, adjust the humidistat setting.
    • If the reading is low, raise the setting on a humidifier.
    • If the reading is high, lower the setting on a dehumidifier.
    <1m

Monitor over time

Estimated under a minute (partly estimated)

  1. Read the hygrometer at the same time every day for one week.
  2. Place a separate hygrometer in each room that has its own appliance.
    <1m

Terminology

This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.

relative humidity
Also called: indoor humidity, how humid is my house, humidity level, moisture in the air, RH
hygrometer
Also called: humidity gauge, humidity meter, moisture meter, humidity sensor
humidistat
Also called: humidity dial, humidity control knob, target humidity setting, humidity setting
dehumidifier
Also called: de-humidifier, damp machine, moisture remover, basement dryer
humidifier
Also called: room humidifier, mist maker, moisture machine
condensation
Also called: fogged up windows, sweaty windows, water on the inside of the windows, window sweating

When to use a professional

Speak to a professional if the room does not reach your target after one week of correct settings. Speak to a professional if you see mold growth in the room. Speak to a professional if you see a water stain or smell a musty odor. Do not use this page to repair a leak, a flood, or water under a house. Speak to a plumber or a builder about the moisture source first.

Common questions

What humidity should my house be?

The EPA recommends keeping indoor relative humidity below 60 percent, and ideally between 30 and 50 percent, mainly to limit mold, dust mites and other moisture problems. The CDC goes further and recommends staying at or below 50 percent at all times, without EPA's 60 percent allowance. This page uses 50 percent as the practical target ceiling and names both agencies so you can see where the number comes from.

What should I set my dehumidifier to in a damp basement?

Start at the low end of the 30 to 50 percent target, since a basement tends to run damper than the rest of the house. Set the humidistat to that number rather than a generic "high" setting, then confirm with a hygrometer placed away from the unit's own airflow. If the reading will not come down after a few days at a correct setting, that points to a moisture source the dehumidifier cannot fix on its own, such as a leak or ground water.

My hygrometer reads 65 percent. Is that a problem?

It is above the range EPA and CDC recommend, and 65 percent is inside the band where mold, dust mites and mildew become more likely. Check that the hygrometer is placed away from a bathroom, a kitchen, or direct sunlight, since any of those can push a local reading high on their own. If a second hygrometer in the same room agrees, set your dehumidifier's target lower and watch the room for a week.

Why do I get condensation on my windows?

Condensation forms when humid indoor air meets a cold surface, most often a single-pane window or a poorly insulated frame in winter. It is one of the more reliable everyday signs that your indoor relative humidity is running above your target, even before a hygrometer confirms it. Lowering your humidity target, or running a dehumidifier or a ventilation fan, is the usual first step; if it continues after that, treat it as a sign of a moisture problem worth a professional opinion.

Can I trust a cheap hygrometer?

Accuracy varies a lot between models, and this page cannot verify any single instrument, so check your own hygrometer's documentation for its stated accuracy. A simple check is to place two hygrometers side by side in the same room for a day and compare their readings. If they disagree by more than a few percentage points, treat both readings as approximate rather than exact.

Is 20 percent humidity too dry?

Yes, by the same EPA guidance this page uses: the recommended range starts at 30 percent, so a reading of 20 percent sits below the low end. Many people also find air that dry uncomfortable, though this page does not carry a specific source for a health effect at exactly 20 percent. A humidifier set inside the 30 to 50 percent range is the usual response; confirm it the same way as in this procedure, with a separate hygrometer rather than the appliance's own display alone.

Sources

Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.

  1. Tier 1A Brief Guide to Mold, Moisture and Your HomeUnited States Environmental Protection Agency · accessed 2026-08-03 · re-verification due 2027-01-30
  2. Tier 1Biological Contaminants and Indoor Air QualityUnited States Environmental Protection Agency · accessed 2026-08-03 · re-verification due 2027-01-30
  3. Tier 1About MoldCenters for Disease Control and Prevention · accessed 2026-08-03 · re-verification due 2027-01-30

Revision history

Current version 1 · updated 2026-08-03 · next review due 2027-08-03

  1. v1 · 2026-08-03First draft. Target relative humidity range (30 to 50 percent, EPA's ideal band) sourced to two EPA pages read on 2026-08-03, with CDC's stricter same-purpose guidance (no higher than 50 percent, no 60 percent allowance) named alongside it rather than folded into one number. Humidistat accuracy and hygrometer accuracy both publish as consult-the-documentation, since both are per-model and no general source settles either. No competitor page read or drafted from at any point (brief 1.5).

Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.

Comments and corrections

Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.

Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.

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