This article was inspired when comments from another article ventured into the subject of whether you can connect a dishwasher to the hot water supply instead of the cold. This doesn’t appear to have a clear-cut yes or no answer.
There is conflicting advice, even from dishwasher manufacturers. Some claim it’s more economical but others say it’s better to run a dishwasher using cold water.
Most dishwashers in the UK are supplied with a cold fill hose and with instructions to connect it up to the cold water supply. Most people do connect it to a cold water supply and they work perfectly well. Many dishwashers are designed to work by heating up water from cold.
Some dishwashers can be connected to a hot water supply though. If so, it should say so in the instruction manual. If you do connect a dishwasher to the hot supply you should use a hot fill hose, which is designed for use with hot water. I’m not able to emphatically say that connecting a cold water hose to a hot water supply is running any risk.
But fill hoses have always come as either hot or cold. Either in red or blue, or with a red stripe or blue stripe. So the implication is that they are different in some way. If this is pure marketing spin I wouldn’t be too surprised. But it is reasonable to expect that the individual requirements for hot and cold water are different enough to require specialised hoses.
Pros and cons of connecting a dishwasher to hot water
The next sections look at some of the advantages and disadvantages of using a dishwasher connected to a hot water supply.
Depending on how your hot water is generated, it potentially saves electricity. Dishwashers often wash at high temperatures. They also often use high temperatures for the last rinse to aid drying. However, If using hot water is so much more efficient, why aren’t all dishwashers coming with recommendations to use hot water? Why don’t manufacturers advise that cold water can be used if preferred – instead of the other way round? The answer may be very much related to the same question about cold fill only washing machines
Quicker wash times
If you can get hot water into the dishwasher efficiently, that is, it doesn’t take a long time to start running hot. Then wash times can be speeded up.
Cons –
If the water entering the dishwasher is over 60 degrees it can damage the filtration system built into dishwashers. So don’t use hot water if this is the case. My understanding is that hot water should only be set to 60 degrees anyway, which is the optimum setting for a hot water supply in most homes. But some people may have set it higher.
Hot water supplies may not have the same water pressure as cold, especially if supplied through a hot water cylinder in the airing cupboard. Hot water hoses are more prone to kinking too, so you would need to ensure the hose isn’t under any physical strain at the back because when hot water runs through it, the hose can go soft and develop a kink.
If the initial water is hot it can bake some food onto plates and make it more difficult to clean.
Dishwashers often have a 50 degree wash cycle. If the water inlet temperature is already 60 degrees this programme may be compromised.
If you want to check your dishwasher can use hot water but don’t have the instruction book you may be able to download one here – download instruction manual for washing machine or other white goods appliance
Repairs
Fixed-price repairs, Pay monthly options, Repair & protect your whole appliance..
Save Money Now
Subscribe to Which? today and start saving money now. Subscription offers often available.
Spares
Spares4Appliances is a spares company run by repair engineers who understand all about spare parts for appliances.
Very interesting Oliver. I hate it when people say things like you can use hot water but we recommend cold. WHY? They treat people like children too much. If someone tells me you can use hot water – but we recommend cold, I want them to say, “we recommend cold because …” so I can make an informed decision.
Hi Andy,
I too agree that everyone is being treat like a child. We can come up with no logical reason why it recommends cold, with cold it didn’t wash properly and blocked up the dishwasher. Perhaps that is the idea, so you have to buy replacement parts or buy a new machine due to grease blocking the heater, sump and drain pump? It now does wash properly using our hot (warm) supply, it has been very frustrating for four years having to hand wash because the dishwasher ( a labour saving device) couldn’t get things clean.
I put it on the hot supply Monday afternoon, it has done a load each day and everything has come out spotless and the machine is as clean as a whistle. I will never use a dishwasher on a cold supply again now I have experienced how much better they are on hot, if ever we have to buy another we shall make sure it will accept a hot supply.
The hot water comes from the combi-boiler about 15 yards away, and it still takes in a full fill of hot each time its on, the only draw back is I have to run of the cold before the machine is initally put on, but its a hell of alot easier than hand washing all the pans, and still saves water in the long run.
Another reason could be the usual environmental bo11ocks, every thing we do, what ever it is we get this environmental shyte rammed down our throats, we take no notice in this house, people need to make their own choices and understand why, not believe these idiots who came up with global warming.
EnvironMENTAL……….you’d have to be to believe what they tell you!! IMHO of course!
Oliver.
Years ago, we used to have a Hotpoint branded dishwasher that was manufactured by Bosch (according to Which?’s review of it). It was a really good machine – washed much better than my current Bosch dishwasher, although maybe in part down to the Sun dishwashing powder we used to use in it. I recall that you could buy a hot water kit for it – I don’t know if this was just a heat resistant hose or what, as I never bought one, but the cost was over 30 quid! According to the Which review, the machine didn’t wash as well with the hot kit fitted – this would have been because the machine had a dumb mechanical timer and feeding in hot water would have cut out the washing period while the water was heating up – resulting in a shortened & inadequate wash length.
Hi Andy,
Just an update on the Tecnik as it has been on hot water for 3 weeks now……..
Things have improved beyond all recognition, in 3 weeks we have only had 3 dirty items, opposed to at least something every day when it was on cold water. The machine does not have a smell and nor has the old stale smell returned. Also we used to get red spots on the white plastic, not only have they all been removed but are not returning. The filters were spotless after a week, now they rarely need cleaning instead of the 2-3 times a week previously. There are no residues building up in the machine and all prevoius residue has been completely removed. The pots no longer smell of detergent, so it must be rinsing better as well.
The outlet hose was also full of the red stuff, don’t know if it has gone, but after Christmas I will disconnect it and have a look, I will post the result.
All the above proves against what Tecnik (Bosch) say “We recommend a cold water supply…” It is just perfect on a hot supply, so it appears Bosch do not know what they are talking about, it was so bad on a cold supply I felt like throwing it down the tip, but now its great.
All the best,
Oliver.
Ps. To you and everyone have a great Christmas and a Happy New Year!
Warm or hot water rinses away food debris better than cold. I don’t often rinse items before putting them into the dishwasher except for plates with curry sauce or any other food dye that will stain plastic items. I notice the stuff rinses off first time under the hot tap, as the temperature dissolves it at the same time as rinsing it away. I used to spend longer doing this under cold running water (which wastes time and water), but one day I discovered by chance that hot running water does the job instantly. If I have to rinse food from something, I use the hot tap every time.
With the pre-rinse/pre-wash being performed in warm water, this gets rid of a lot more food debris than cold water, so there’s less food to be cleaned off during the main wash phase, hence the better results I’m guessing?
One thing I can’t understand is why the water and detergent mix gets heated above 50C too quickly on the hotter washes, when it should be warm (not too hot) for the enzymes in the detergent to work properly? Above 50C, the enzymes in detergent get destroyed by the higher temperature. Maybe the warm incoming water dissolves the detergent quicker – especially tablet detergent, so it can be used for longer below 50C on hotter washes? Enzymes in detergents work best when the water is warm. I find my own dishwasher cleans fine at 45C and I don’t often use the hotter programmes. Some items will need soaking or spraying with something like Fairy Power Spray to loosen stuck on food. For hot washes above 50C, why don’t the dishwasher manufacturers consider keeping the main wash water at 45C for about 20 minutes, to allow the enzymes to work properly, before heating the water to the higher temperature – which destroys the enzymes?
Regular readers of this website will know I strongly advocate using warm water in a washing machine to rinse off detergent better, as warm water both rinses and dissolves substances. Cold water is not very good at cleaning or rinsing anything.
Absolutely, you can use hot water connection for your dishwasher. Many top brands like Miele, Asko or Bosh do not care if you connect their dishwasher to cold or hot water as long as hot water temperature is below 60 C.
Using a warm/ hot water will reduce you electricity bill. All dishwashers have built in heating element and thermostat so they have to raise the temperature to 50, 60 or 75 C (depending on the chosen cycle). The dishwasher connected to hot water will use the minimal amount of electricity to heat water to the preset temperature. You do not need to be a rocket scientist to work out that heating a water from 50 C to 65 C is much faster than heating a water from let’s say 17 C to 65 C. Think about the hot water already stored in you hot water boiler, do not waste the money heating the water again but this time for the different purposes.
Some manufacturers of low quality dishwashers will recommend the cold water only because if you use a cold water connection the washing cycle will be longer and due to this the washing results might be a marginally better. The same rule applies for the washing machines.
The environmentally consciousness people will use the hot water connection for their appliances.
Water connection mode is important for a dishwasher:
* Cold water connection will use the least energy – the dishwasher heats its own water only for the parts of the cycle where hot water is needed, but the energy (in the form of electricity) generally costs more (unless you are on a time of use tariff, which is still unusual for households, and run the machine overnight).
* If you have a gas or solar hot water system, models that can be connected to both hot and cold water will save carbon dioxide and operating costs, but models with dual connection are now rare. You will also save energy costs if you have an off peak electric hot water system.
* A dishwasher connected only to hot water will use the most energy, although it may be more economical if you have off peak electric, solar or mains gas hot water.
MIELE DISHWASHER MANUAL: “The dishwasher may be connected to a cold or hot water supply, max. 60 °C. We would only recommend connection to a hot water supply if it is economical. When connected to a hot water supply, all programme stages which would otherwise be carried out with cold water will be carried out with hot water, thus saving time and energy costs.”
Thanks Graham: The Miele manual makes a sweeping and misleading statement, which can’t be true generally. It may be more economical for the dishwasher in that the dishwasher may well use less electricity heating up the water, but they do not take into account the cost of heating the water up elsewhere, which may come from a cheaper source such as solar powered but it may come from an electrically heated immersion heater which costs exactly the same to heat as the dishwasher would plus there’d be an amount of wasted hot water left in the pipework.
The hot water might come from an inefficient old boiler cited two floors up with several metres of uninsulated copper pipework between them. In the latter case when the dishwasher had finished filling it would have drawn in several litres of hot water which would just sit in the pipework and go completely cold therefore wasting it. Also, the amount of water that the dishwasher draws into itself and the pipes may well be replaced in many people’s houses by cold water into the hot water cylinder therefore cooling down the rest of the water and triggering its heater to come on to raise the water back up to temperature.
Therefore the actual costs of using that water vary considerably from house to house and are in most cases difficult or impossible to work out. The whole point of an appliance heating up its own water is that in many cases it’s cheaper because it only heats up the exact amount of water the appliance needs.
Example:
If we imagine we want a cup of hot water to make a coffee, and we pour the exact amount of cold water required and the cup itself heats the water up. That’s got to be highly efficient. But what if we have a source of hot water already in the form of a big tea urn in the next room connected to a tap in the kitchen and connected to a constant cold water supply which replaces all water used?
If we fill the cup from this tap it’s cheaper because the water’s already been heated? But the problem is that the first half a dozen cups of water that come out are cold or at best warm because it was several hours since we last had a coffee and all the water in the pipes between the tea urn and the tap in the kitchen has cooled down. So we draw off several cups of cold and warm water and throw them down the sink. That’s the first waste which needs accounting for.
Then the hot water comes through ok and we fill our cup and have a nice hot coffee. The coffee cup didn’t need to heat any water so it’s more economical? For the cup yes! But after drawing all that water through we filled the pipework with boiling hot water again which is going to go cold quite quickly. Also, all the water we threw down the sink and the water that we used for the coffee is replaced in the tea urn by cold water from the plumbing, which in turn cools the water already heated in there and causes it to need to heat up a little more to bring it back up to temperature.
Which is the most efficient method? Surely it’s letting the cup heat up only the exact amount of water required.
That said, what if we had one of those new devices like the Tefal Quickup, which heats up only the water required for a coffee? In this case it’s cheaper (or maybe no different) to use this device to heat up one cup full. Or what if we had a tea urn in the same room heated by solar power? Then it would be cheaper to use that..
What it boils down to is that it’s wrong to say one method is cheaper than another as it depends entirely on the source of the hot water and circumstances. In some cases using existing hot water will be cheaper, and in others it will be more expensive.
It’s been a while since I’ve visited this page.
Warm/hot water removes more food debris and results in better cleaning compared to having to rewash dirty items either by hand or using the dishwasher again? In the latter case, it costs more than just electricity, when you take into account the cost of detergent, salt and rinse aid.
Warm or hot water removes food debris quickly. Next time you have strongly coloured sauce that will stain plastic items in the dishwasher, simply rinse the sauce away with hot water and you will see it comes off very quickly; try it with cold water and it takes much longer and uses more water. If your dishwasher is connected to the hot water supply, you could run the hot tap nearest the dishwasher for about 20 seconds until it feels warm; this does not waste water in the long run – it saves having to rewash dirty items. Also consider that during the winter months that the cold water from the street mains will be MUCH colder compared to hot water cooling down inside the copper pipes indoors.
Finally, the longevity of the dishwasher should be considered. If cold incoming water is not melting the grease and food debris, the dishwasher is more likely to break down much sooner. On the strength of Oliver’s messages above, I wish I had a hot water pipe behind my dishwasher. Although I don’t have any problems with its cleaning performance, I make sure I use Finish dishwasher cleaner regularly and check the filters, spray arms etc. I have noticed white grease around the bottom of the door seal – I don’t like the thought of this grease build-up being elsewhere in the working parts! I’m assuming that the best results from using a hot/warm water fill would be achieved by using a programme with a pre-rinse before the main wash, along with a good quality detergent like Fairy Platinum?