Washing in cold water: why the temperature dial matters more than the machine

People shopping for a new washing machine spend a lot of time on energy labels, drum sizes and spin speeds. The single biggest efficiency decision, though, is made every time you turn the dial, on the machine you already own.

Where the energy goes

According to ENERGY STAR, the U.S. Environmental Protection Agency’s efficiency programme, heating the water accounts for about 90% of the energy it takes to run a clothes washer. The motor that turns the drum, the pump and the electronics share the rest. The same source says that switching from hot to warm can cut energy use in half, and that cold cuts it further.

Put simply, a hot wash is mostly a water heater with a drum attached. That’s why the temperature setting does more for your energy bill than the difference between a good machine and a very good one. The most efficient washing machine in the shop still spends most of its energy on hot water if you ask it to. The dial is the upgrade.

Does cold actually clean?

For most loads, yes. ENERGY STAR’s own advice is that, unless you’re dealing with oily stains, washing in cold water will generally do a good job of cleaning. Modern detergents are made to work at lower temperatures, and everyday laundry, such as shirts worn once, jeans, towels used for a day or two, mostly carries sweat and light dirt that comes out without heat.

A few habits help a cold wash do its job:

• Use a detergent that says it works in cold water, and measure it. More isn’t cleaner. It leaves residue.
• Pre-treat stains before they go in, especially food and grass.
• Don’t overload. Clothes need room to move through the water.

When heat still earns its keep

Cold isn’t the answer to everything. I still use a hot or sanitising cycle for:

• Greasy or oily stains, such as cooking oil, butter or some cosmetics. Heat helps lift fat.
• Heavily soiled items like work clothes, muddy sports kit and cleaning cloths.
• Bedding and towels when someone in the house is ill, or when the care label or your doctor advises it.
• Nappies and similar loads, following the product’s own instructions.

ENERGY STAR also notes that the extra-hot sanitising cycle on some models uses significantly more energy, so save it for when it’s actually needed rather than running it out of habit.

Two more cheap wins

Full loads. ENERGY STAR points out that washers use about the same energy whatever the size of the load, so two half loads cost roughly twice what one full load does.

Faster spin. A higher spin speed leaves less water in the clothes, which means less time in the dryer, and the dryer is often the bigger energy user of the pair. Line-drying, where you can, saves more still and is easier on fabric.

What I’d actually do

Make cold or 30 degrees the default for everyday laundry, with a cold-water detergent and a habit of pre-treating stains. Keep a hot wash for grease, heavy dirt and illness, and the sanitising cycle for when you really need it. Run full loads and pick the faster spin. None of it costs anything, and it starts saving on the very next wash.