Everything you need to know about dishwashers

Death, taxes and... dirty dishes. Some of the less palatable givens of life. Most people now feel their dishwasher is as indispensable as the washing machine or clothes dryer. Yet in a slower age, our parents would do the dishes together each night, sometimes even savouring the quiet time together in the knowledge that the kids would make themselves scarce. Dishwashers were seen as an unnecessary luxury rather than today’s necessity. But from an environmental perspective, was that a better path?

Look online and you’ll find dozens of reports comparing the merits of hand dish-washing versus dishwashers. Most of these draw their conclusions from a German study that found dishwashers used less water and less energy than hand washing – plus saved you hundreds of hours of work. And that study was done 10 years ago and dishwashers have improved since!

However, the German hand-washers in that study used 113 litres of water and 79 minutes of washing time each day to get their dishes clean. So no wonder the machines came out better. If you wash your dishes one at a time under a running stream of hot water, you’ll waste more hot water than Pohutu geyser.

So what’s greener?

Perhaps I should make a confession here. Although I have a dishwasher, I never run it. I live alone and do dishes once a day, using 7 or 8 litres of hot water in a sink with the plug in. If something is particularly messy, I’ll scrub it separately under cold water before putting it in the sink. I use a small squirt of detergent and I don’t rinse. Glasses and cutlery are done first, then plates, followed by bowls and pots. The dishes go into the draining rack hot and they’re dry in minutes. I wash the bread boards and wipe down the stove top and bench at the same time. It takes 10 minutes.

One inefficiency arises because my hot water cylinder is 15m from the sink, so to get hot water I waste about 5 litres that has cooled in the pipes, bumping my consumption up to 12 litres. For many guests and a greasy washup, I’d use two-plus sinks of hot water – say 30 litres.

It costs about 20 cents to heat 12 litres from 12°C to 60°C, though there’s a little government-mandated inefficiency here. Hot water cylinders have to be set at a minimum of 60°C to kill Legionella bacteria, but water coming out of most taps must not exceed 55°C, so a tempering valve adds back cold water to cool what comes out of your cylinder.

Modern dishwashers, on the other hand, only connect to cold water and heat the water they use internally, usually to about 70°C, so there’s no wastage from warming hot water pipes. They also use astonishingly little water, usually less than 13 litres per wash, because they pump a small amount of dirty water round and round followed by a clean rinse. That figure, 13 litres, is for a big load of dishes, so they’re more efficient at using water than me. As far as energy use is concerned they’re heating less water than I use but to a higher temperature, so the energy cost and consumption is similar.

Maybe I’ve not seen all that a modern dishwasher can accomplish, but most I’ve seen still leave some dirt on cookware, which means doing extra washing. To avoid this problem many people scrub their dishes before putting them into the dishwasher – and some pots and pans, or delicate china, can’t be washed in dishwashers. Doing too many extra hand washes eliminates the eco-advantages of dishwashers!

Also on the negative side for dishwashers are the considerable environmental costs in manufacturing, repairing and disposing of the machine, which will likely have a 10 year life. Also, some dishwasher detergents still contain phosphate, which causes problems in wastewater (see more on phosphates here) – and rinse aids (nonylphenols) used in many products are not that desirable either.

In short, there’s no strong winner either way. An efficient dishwasher will save on water and power use compared to hand washing, especially on heavy loads, yet this comes at the cost of many hundreds of dollars for the machine, which has other environmental drawbacks.

Of course for most people the big attraction of dishwashers is the time and effort they save – especially for busy families. So if you’re in the market for a new machine, follow our checklist of things to look out for.

When buying a dishwasher…

• Make sure you measure the size of the space it needs to fit into.
• Ensure its capacity is adequate for the number of dishes your family generates – ask the salesperson for guidance here.
• Ask for a quiet model. Modern dishwashers are very quiet, with the better ones containing a lot
• of sound insulation — though be aware this can come at the cost of long cycle times (often 100–150 minutes).
• Choose a model with as high an Energy Rating as possible (for both low energy and low water use) that carries the Energy Star sticker (see the box on the next page for an explanation of these labels).
• Check the dish racks. A good rack system (such as plate racks that can fold down and a height-adjustable top rack) can make your dishwasher much more useable.
• Some models offer delayed start, a useful feature.
• Choose a reliable model according to consumer reports. The longer it lasts, the lower its manufacturing footprint! In a 2012 Consumer survey of members, Bosch was the most reliable brand of dishwasher with 94 per cent not needing repair, while Fisher and Paykel was the least reliable, with 23 per cent needing repairs.
• A time-remaining display can be useful.
• Many models offer a range of wash programmes (duration, temperature, wash force). An eco-wash (shorter cycle) option is a good feature, but beyond that consider whether you really need all the bells and whistles. You pay for electronic flexibility and programme failure is the commonest fault on modern dishwashers.

When using your dishwasher…

• Don’t run it half empty since for most models, costs are the same regardless of load size.
• Don’t use a dry heat cycle to dry your dishes. Just open the door and the hot dishes will dry quickly.
• Overfilling a dishwasher can reduce washing performance.
• Don’t accumulate dirty dishes in the dishwasher for days before running it. Bacteria (and odours) will multiply amazingly.
• Try to find an effective phosphate-free detergent.
• Clean the water filters regularly with a scrubbing brush to remove gunk.

Energy ratings – will you save?

We compared two dishwashers – one with a low Energy Rating of 2 stars (the Simpson 52C850SA), and one with a high rating of 4.5 stars (the Bosch SMS63MO8AU). Let’s see how the costs compare over 10 years of use.

Highlights

• The Bosch model cost $723 more on the day.
• The Simpson model cost $56 more each year to run.
• Over 10 years the Simpson was still cheaper overall by $160.
• The Bosch had saved 20,000 litres of water and released less CO₂ into the air by using less electricity.
• It’s likely the Bosch model would be quieter, more reliable, last longer and be more flexible in use.

(Assumptions: power at 28c cents/kWh, water at Auckland’s current rate of $3.624 per 1000 litres including wastewater charges, and dishwasher used every day.)

Green Ideas recommends

We recommend choosing a reliable brand, with good energy star ratings, and a set of useful features at a reasonable price point such as the Bosch SMS63MO8AU which retails for $1600. Amongst many other good models are the LG LD1452WFEN2 ($1250), Samsung DWFG520L/XSA ($1399), LG LD1454TFES2 ($1699 which uses steam) and Miele G5300SC ($1999).

Labels to look for

There are two government-backed systems for rating the efficiency (and therefore greenness) of appliances. Confusingly both use stars, but they are different.

Energy ratings

All larger appliances in the country are given an Energy Rating label using a star scale (eg. 4 out of 6 stars) and the label also states how many kWh of power they are expected to use in a year. The more stars the better!

Energy stars

The most efficient appliances based on their energy rating (usually the top 30 or 40 per cent) also get a blue Energy Star sticker, recognising their superior performance. Here there are no varying numbers of stars, you either have it or you don’t. It’s worth looking for.

Handy links

German study comparing hand washing with dishwashers
Price information on 103 dishwashers