Guides

Short, sourced guides to the numbers on the box and the problems a machine can't fix.

• How to read a dehumidifier's litres per dayThe litres-per-day figure on a dehumidifier depends on the test temperature and humidity. The same machine can be rated at 20 L/day or 8.5 L/day. Here's how to read it.
• How to read an air purifier's CADR and room sizeCADR tells you how much clean air a purifier delivers. The room size on the box assumes a certain number of air changes an hour. Here's how to check it against your room, including for bushfire smoke.
• Indoor humidity: what the number tells you, and what it doesn'tKeeping indoor humidity below about 60%, ideally 30 to 50%, is the usual guidance. A normal reading doesn't rule out a cold wall or a damp corner. How to measure it and read it.
• Can you use the water from a dehumidifier?Don't drink it. Manufacturers disagree about watering plants, and at least one says not to put it in a steam iron. What they actually say, and how to keep the tank clean.
• Compressor or desiccant dehumidifier: which suits your room?Compressor dehumidifiers suit rooms above about 10°C and use less power; desiccants keep working in colder rooms and warm the air. The numbers, from a maker of both.
• When damp or mould needs a repair or a professionalWater coming in, mould that keeps returning or spreading, and any sign of carbon monoxide need more than a machine. What to do, and who to tell.