Dishwasher or sink wash?...& the cheapest is...
This article compares the costs of using a dishwasher and doing the washing-up in a sink.
The conclusions are:
If you heat your water using gas, washing up in the sink costs roughly the same as the LOWEST COST WAY of using a dishwasher as long as you always fill your dishwasher.
But, depending on how you go about it, EITHER the dishwasher OR sink washing can be much more expensive.
This article explains and compares all the different things that make a big difference one way or another so you can work out which way of washing dishes is cheapest for you
The things which have most impact are:
Dishwasher energy costs vary significantly, depending on which machine programme you use.
Dishwasher tablet costs which vary massively.
How you heat your water. Gas is much cheaper than electricity for heating a sink of water.
Summary of cost comparisons
Method 1 - dishwasher costs (based on tests of my 12 year old A+ machine)
This assumes an electricity standard tariff of 27p/unit from October 2023
The costs of using my dishwasher for one load are:
26p, running the cheapest programme and using the cheapest tablets
62p on the most expensive programme, using expensive tablets
Method 2 - Conventional sink washing
These costs include the cost for washing-up liquid and the significant additional water used for sink-washing. (Dishwashers use much less water.)
To wash the same amount of dishes a dishwasher holds, the costs are:
23p, using water heated by gas
47p, for water heated by electric immersion at night on an Economy 7 tariff
64p, using electric immersion (or any instant hot-water tap) on a standard tariff
Method 3 - Sink washing - caravan/camping method
This is where dishes are rinsed in the sink in cold water first, and then a "proper" wash is done in a shallow sink of hot water with washing up liquid.
10p, using water heated by gas
20p, for water heated by electric immersion at night on an Economy 7 tariff
27p, using electric immersion (or any instant hot-water tap) on a standard tariff
Method 4 - Sink washing - European method (also used in the UK sometimes)
This method is where the dishes/crockery are washed individually under a slow-running hot tap.
54p, using water is heated by gas
£1.20, for water heated by electric immersion at night on Economy 7
£1.58, using electric immersion (or any instant hot-water tap) on a standard tariff
Tips on minimising dishwasher costs
Only use a dishwasher when it is full. If you only half load a dishwasher the costs above double. If some of the stuff in it has dried and stuck to the crockery in the day or two since it was put in, running a quick pre-rinse cycle uses very little energy.
It is almost certainly cheaper to wash larger items like pots and pans in a sink, as they take up a lot of space in a dishwasher. PUtting large items in a dishwasher means you have to run the machine more often, costing you more money in both energy and dishwasher tablets.
Re-use mugs for tea/coffee through the day, as it all helps reduce dishwasher use. This is something I mostly do at home, and it is perfectly safe and healthy.
Clean out the filters in the bottom of your dishwasher regularly: when they get bunged up, the washing quality goes down, which can fool you into thinking that lower-energy or eco wash programmes aren't good enough.
Experiment with eco settings on the machine, to see if they give you the washing quality . Also try different brands of cheaper tablets.
Some dishwasher eco programmes take longer than the normal cycle. This does NOT mean they use more energy. Eco programmes use less heat to do what they do so need to leave dishes soaking for longer during the wash cycle for the detergent and water to remove the food residues.
If you don't have the user manual for your machine, they can ALL be found online, and Google finds them easily. If these don't give you good information on which cycles use least energy, contact the manufacturer and ask them. As you will see from my own testing below, my RAPID cycle used a lot of energy, so don't assume a similar "quick wash" cycle uses the least energy.
If you are curious to actually measure the energy used by your machine and want to understand the difference for different settings I can highly recommend using a plug in energy monitor device such as one of these that connects to your smartphone. If you've not got one they are incredibly useful for learning about energy use in the home in all sorts of ways.
Tips on minimising sink washing costs
Use a washing bowl to reduce the amount of water you use
The caravanning/camping method is clearly very low cost
When you've finished leave the hot water in the bowl for half an hour or an hour to let the heat go into the room. You've paid to heat it so why not help the central heating out? Its only a small thing but it all makes a difference.
The Geeky stuff for those interested!
Method 1 - Dishwasher
These costs were from actual measurements on my 12 year-old, A+ rated Bosch machine. Looking at information online, many current dishwashers still use the same energy as mine, though some are as much as 20% more efficient.
I have not included the cost of water, but dishwashers don't use much. If you are on a water meter, I estimate that the water will cost you around £3 a year if you use your dishwasher twice a week, and £9 if you use it every day.
We don't pre-rinse stuff before putting it into our machine, but do scrape off the most significant food remains when we load up. One thing I can honestly say, having tried all the programme settings on my dishwasher, is that I can see no difference between them in their cleaning performance.
Dishwasher tablet costs
I was surprised to discover that the cost of dishwasher tablets varies hugely, and that the brand you buy can have a big impact on your running costs. Here are some examples from Asda's website (prices October 2022):
Asda Smart Price tablets are 4.5p each. So, in a year, you will spend £4.68 on tablets if you use the dishwasher twice a week, or £16.38 if you use it every day.
Finish Quantum tablets are 13p each. In one year you will spend £13.52 on tablets, if you use the dishwasher twice a week, or £47 if you use it every day.
Fairy Platinum Plus tablets are 27p each. This means you will spend £28 on tablets each year, using the dishwasher twice a week, or as much as £98 if you use it daily.
Cheapest dishwasher method overall
Using the lowest energy dishwasher cycle and cheapest available tablets
Energy cost: 22p
Washing tablet: 4.5p
Minimum total dishwasher cost: 26.5p
Sink washing methods using different ways of heating the water
Method 2 - Washing in a regular sink with the water heated by gas
I did a number of practical experiments, supported by a number of theoretical calculations, to see how well experiments and theory agreed with each other. Amazingly, they agreed!
Energy cost: 17p
Washing up liquid: 4p
Additional water use compared to dishwashing: 5p
Minimum total sink washing: 26p
Conclusion: sink washing using this method is very similar to the minimum dishwasher costs above, but uses a LOT more water. Using a washing-up bowl in the sink would help sink washing win easily.
BUT....if you use more expensive dishwasher tablets, don't run a dishwasher full, or don't use it on its most eco settings, then a dishwasher will quickly become a much more expensive way to wash up than using a sink with water heated by gas.
I assume the sink is filled four times, holding approximately 8 litres, to wash the quantity of crockery a dishwasher holds. That amounts to 32 litres of water, compared to the 12 litres the dishwasher uses.
Using gas to heat each bowl of water costs around 4.5p to 7p, depending on the time of year. (The incoming water is colder in winter and needs more gas to heat it.) The boiler settings and distance of the sink from the boiler or hot-water tank will also have an impact. I am assuming that the average cost of gas to heat each bowl is 6p.
I have assumed, if you have a hot-water tank, that it isn't heated JUST for washing dishes, and that the tank is well-insulated.
If you are on a water meter, then the extra water cost is around 5p, and I have included this in my costs.
The experiments and the gas measurements above were done with a recently installed Worcester Bosch combi boiler, in conjunction with a smart meter.
Method 2 - washing up in a sink but with water heated by electric immersion
The equivalent numbers are:
Energy cost: 56p approx on a standard flat tariff, and 40p heating on Economy 7
Washing-up liquid: 4p
Additional water use compared to using a dishwasher: 5p
Total: 65p on a flat tariff, and 49p using Economy 7
56p would also be the cost if you used water from an instant hot-water tap.
Conclusion: Clearly, the dishwasher wins on all aspects.
Heating water using electricity is much more expensive than using gas, as electricity costs just over 3 times more per kWh. Even using Economy 7 to heat water overnight costs more than twice as much as gas.
Method 3 - The caravan/camping method, heating the water using gas
When water and heat are scarce, the method is to rinse dishes in a small amount of cold water to get most food off, flush this cold dirty water away, and then use just a small amount of hot water in the sink to do a final hot, soapy wash.
Energy cost: 7p in gas
Washing-up liquid: 2p
Additional water use compared to dishwashing: 2p
Conclusion: Clearly, washing dishes this way makes lots of sense from a cost point of view.
Assumes sink half-full for cold rinse (4 litre) and 3/4 full for hot wash (6 litres),compared to 8 litres in other methods. So, a total of 20 litres.
Method 4 - The European method heating the water using gas
Some households prefer not to wash in a filled sink but to use hot water flowing slowly from the tap over each item, item by item.
The costs for this work out at:
Energy cost: 42p in gas
Washing up liquid: 0p
Additional water use compared to dishwashing: 17p
Conclusion: Clearly, the dishwasher is much cheaper.
This assumes that the flow rate of of the water is 4 litres per minute (a relatively gentle flow rate), at approx 55C.
It assumes it takes 20 minutes to wash the equivalent of a full dishwasher load of dishes using this method, which is conservative, considering a full dishwasher can contain 60 items of crockery, plus cutlery on top.
Tariff costs are assumed from October 2023 of gas 7p/kWh, electricity 27p for standard tariff and 19p for Economy 7 night rate.
Washing-up liquid used was Sainsburys own brand 450ml bottle at 45p, using a 10ml portion each wash = 1p (October 2022 cost)
The above takes no account of any environmental impact from dishwasher tablets or washing-up liquid.
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