Dehumidifier Buying Guide: Size, Humidity and Noise

Dehumidifier buying guide in short: pick a unit sized for your room, one with a built-in humidity setting, and one you can live with at night. Those three choices matter more than any brand name or price tag.

Rainy-season weather in Vietnam leaves many homes damp for weeks. Clothes will not dry. Walls feel cold and wet. A dehumidifier can help, but only if it matches the room. This guide walks through what to check before you pay.

Start with the humidity you want

Relative humidity is the share of moisture the air holds, shown as a percentage. The US Environmental Protection Agency suggests keeping indoor humidity below 60 percent if possible, and ideally between 30 and 50 percent.

That target gives you a simple test. If your room sits at 75 or 80 percent in the rainy season, you need a machine that can pull it down. If it already sits near 55 percent, a small unit or good airflow may be enough.

The World Health Organization makes a related point in its guidance on indoor air. The main way to avoid harm from damp buildings is to prevent or limit lasting dampness and mould on indoor surfaces. A dehumidifier is one tool for that. Fixing leaks and ventilating come first.

This is general information only. Mould worries tied to your health, such as a cough or allergies, belong with a doctor.

Sources: https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home; https://www.who.int/publications/i/item/9789289041683.

Buy a hygrometer first

A hygrometer is a small meter that shows humidity. The EPA notes that a relative humidity meter costs roughly 10 to 50 US dollars.

Place it in the room you plan to treat. Read it at morning, noon and night for three days. Write the numbers down. You now know how damp the room really is, and you can tell later whether the machine works.

Do this before you shop. It stops you from buying a large unit for a room that only needs a small one, or the other way round.

Sources: https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home.

Match the capacity to the room

Capacity is the amount of water a unit removes in a day. In the United States it is listed in pints per 24 hours. Many other makers list it in litres per day. Check which unit a spec sheet uses before you compare two models.

ENERGY STAR, the US efficiency programme, explains that the capacity you need depends on the size of the room and how damp it is. As a rule of thumb, leaning a little larger is safer than going too small. An undersized unit keeps running for hours and still falls short of your target humidity.

Think about three things. First, floor area. A bedroom is not a whole flat. Second, how wet the room feels. A ground floor room near a bathroom is harder than a high floor bedroom. Third, how often the door opens. Every time it does, damp air comes back in.

Whole-home systems exist, but ENERGY STAR notes they suit homes with central air conditioning and should be sized and installed by a professional. Most Vietnamese apartments are better served by one or two portable units.

Sources: https://www.energystar.gov/products/dehumidifiers.

Check the controls, the tank and the noise

Look for a built-in humidistat. This is a sensor that lets you set a target, such as 50 percent, so the machine stops when the room is dry enough. Without one, you must switch it on and off by hand, and you will waste power.

Check the water tank. A small tank fills fast and the machine shuts off. Many models also have a drain hose connection, so water can run into a bucket or a floor drain. That is useful if you are out all day.

Noise matters most in a bedroom. Spec sheets list noise in decibels, written dB. A lower number is quieter. Compare the figures for the same fan setting, and read the maker's own sheet rather than a shop sign. If you can, listen to a demo unit in the shop.

Last, look at the filter and the coils. A washable filter saves money. Plan to clean it as the manual says, because a clogged filter makes the unit work harder.

Sources: https://www.energystar.gov/products/dehumidifiers.

Compare running costs and efficiency

Dehumidifiers run for hours, so power use adds up. ENERGY STAR rates efficiency in litres of water removed per kilowatt hour, shown as L/kWh. A higher number means more water removed for each unit of electricity. Certified models are built to use less energy for the same amount of water removed, so look for the ENERGY STAR mark.

Read the power rating on the spec sheet, in watts. Multiply it by the hours you expect to run the unit, then divide by 1,000 to get kilowatt hours. Multiply that by your tariff to see the monthly cost. Do this for each model you like.

A cheaper unit that uses more power can cost more over a rainy season. Spend a few minutes on the sum before you buy.

Also close windows and doors while it runs, and keep the unit a little away from walls so air can flow. This helps any model work better.

Sources: https://www.energystar.gov/products/dehumidifiers.

A short checklist

• Measure humidity for three days with a hygrometer.
• Aim for 30 to 50 percent, and never above 60 percent if you can help it.
• Pick a capacity that suits the room, and lean larger, not smaller.
• Choose a built-in humidistat and a drain hose option.
• Compare dB at the same setting, from the maker's sheet.
• Work out the monthly power cost for each model.

Sources: US EPA, A Brief Guide to Mold, Moisture and Your Home, https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home; World Health Organization, WHO guidelines for indoor air quality: dampness and mould, https://www.who.int/publications/i/item/9789289041683; ENERGY STAR, Dehumidifiers, https://www.energystar.gov/products/dehumidifiers.