If you're thinking about buying a dishwasher, here's what to consider:

Dimensions

Size
Most 12- to 14-place models are designed to fit into the same-sized under-bench space, usually accepted as around 850mm height, 600mm width and 550 to 650mm depth. If you are replacing an existing dishwasher, check the fit before you order. Some models come with a worktop that must be removed before building in. Check the ventilation space requirements.

If you’re looking for a dishwasher to squeeze into a small space, a slimline model might be right for you. They’re only 45 centimetres wide but can still fit 9 or 10 place-settings, so they’re good for smaller households. Or you can choose F&P's single drawer DishDrawer, to take up less vertical space.

Capacity
Dishwashers come in sizes up to 16 standard place settings; though 12 is a realistic maximum for most standard-sized washers. The extra sets of crockery and cutlery have reduced wash performance in some tests.

Flexible loading

Adjustable top basket
Essential if you want to wash champagne flutes or other tall wine glasses, or wash very large plates in the lower basket. Some models let you lower one side of the basket, so you can wash tall glasses and large plates at the same time.

Removable or folding tines allow large or awkwardly shaped objects to fit in the baskets. Watch out for short tines - plates can fall over onto each other and prevent a good wash.

Take along a few pieces of your everyday dinnerware such as a large plate, a deep bowl and a long-stemmed glass. See how they fit - check that the baskets can close and the spray arms can spin without hitting anything.

F&P's double DishDrawer is another way of having versatile loading. You can wash one load of lightly soiled glassware and cups simultaneously with a separate load of dirty pots. If you don't need, or can't fit in a big dishwasher, a single DishDrawer is a good choice as the racks and tines can be removed or adjusted to suit varying loads.

Anti-nesting grids
Fitted over the cutlery basket to prevent cutlery bunching together. Removable grids are more versatile and easier to use.

 

Cutlery tray
Here's an innovation in some models you'll either love or hate. Critics find it time consuming and fiddly to load, because each piece of cutlery has to go in its own slot - the right way round. And it can prevent tall glasses from fitting, unless the tray is removed.

Our test found there was no performance advantage with a cutlery tray. A basket may be offered as an alternative or in addition to a tray.

Settings

Program options and features
What do you want your dishwasher to do? The options vary. A low temperature wash saves power, and lets you take advantage of the new enzyme detergents. A delicate cycle is useful for fragile items. A fast-wash function is efficient if you've pre-rinsed the plates to remove the worst of the grime. A half-load option reduces the amount of detergent, power and water required.

Cycle time
A normal cycle usually takes around 100 minutes. But some models we've tested take up to 171 minutes. Some models have a fast cycle, and those with a hot connection will be quicker than those which heat the water themselves.

Auto-sensing
Where a dishwasher has an auto-sensing cycle we use that for testing. An auto-sensing cycle adjusts wash time, temperature and energy level to suit the amount of dirt in the wash water. This means dishes should be done in the shortest-possible time - and with the lowest water and energy consumption. But our  tests have found some auto-sensing machines aren't always consistent in their choices.

The self-selecting dishwasher
You press 'start' on the Fisher & Paykel DW60DOX1 and the machine begins to wash - then over the next 10 to 30 minutes it chooses one of five wash cycles (intensive, daily, economy, normal, and quick). It may seem easy to let the dishwasher make the decisions. But it also gives you no say in the matter - which won't always suit. Think of wanting your dishes washed in a hurry and not being able to select a fast cycle.

Displays
It's helpful to see how soon the cycle will finish, or where to look to fix simple problems, such as blocked spray arms.

Other features

Anti-flooding devices
Worth having. Often fitted to the hose, to prevent your kitchen becoming awash if there's a leak.

Concealed heaters
We can't see any difference in performance, though stray plastic items are more likely to melt onto an exposed element. If you must wash plastic, do larger pieces only, and in the top rack.

Fan drying
Fan assistance can improve drying by removing condensation from inside the dishwasher.

Noise
If you're used to a 15-year-old dishwasher, you'll probably be astonished at how quiet the current models are. Machines that can wash at levels below 45dBA won't intrude too much on your post-dinner chat.

Child proofing
Door locks, and child-safe detergent dispensers could prevent accidents.

Style
The right look can be a key factor. Most brands offer stainless steel and integrated options. Integrated models (often with an "i" in the model number) can be fitted with a front panel to match your kitchen décor.

Filter
Make sure the filter is easy to remove and replace.

Controls
Look for clearly labelled buttons and a display screen or rotary dial to indicate time remaining.

The second-hand option

Considering a second-hand dishwasher? Unless you really must, we think new is better. It's hard to work out how old a dishwasher might be. It's also not easy to find out how much water and energy an older model uses.

But if second-hand is your only option:

• Stick to well-known, reliable brands under 5 years old. It'll be easier to get parts if anything needs fixing. (Avoid AEG machines made before 2005: parts are very hard to obtain). See our reliability data for brands to look for.
• Check the door seal is intact and that the door clicks shut properly.
• Check all connecting and drainage hoses are intact and in good condition.
• Make sure the inside is free from rust, the filter is clean, and the baskets slide in and out easily.
• Under the Electricity Act and its regulations, electrical appliances for sale must be safe. This law applies to every way of selling an electrical appliance, new or used.
• If you buy a dishwasher from a second-hand dealer and then discover it to be faulty, you're covered by the Consumer Guarantees Act. If you buy privately, you're not.