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.
Pros –
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
John Hadley says
I have just had an Infinity instantaneous hot water heater fitted in my house on which I can set a water output temperature of 60 degrees. So, I thought why not plumb a hot line to the dishwasher, run off the standing cold water prior to each wash and wait for the electric bills to go down (we fill the dishwasher twice each day, and always set it on economy). However, your correspondence has inspired me to research alternatives: can I not use a cold detergent and use a cold wash: An American product called AJAX apparently will do just that. The secret ingredient is BLEACH!
All I need to do is to disable the heater and internal water temperature sensor in my Hotpoint machine and hey presto!
Article below which focused on the issue of bacteria which your articles have not considered :
In the study scientists washed dishes that had been covered with cheese, eggs, milk and jelly. They also smeared the plates with E. coli and other bacteria that cause food-borne illnesses. They washed one batch of dishes in hot, soapy water and found it killed off nearly all the germs. However, they got the same result when they washed the same bacteria-laden dishes using cool water and dish soap with bleach. Researchers also found that dishes washed in soapy room-temperature water, rinsed, and then weakly sanitised with ammonium-based chemicals achieved FDA-acceptable results.
Michael says
As with hot-fill washing machines, the crux of the matter is thr price diffrence between gas-heated water and electricity-heated water. In the UK, it’s 4-5 times the price to heat water using electricity than it is using gas! Given that most of the dishwasher running costs are incurred from heating the water, it really should be a no-brainer for the manufacturers to design products around this – if necessary having a cold and a hot input and mixing it using a temperature sensor. Obviously people without any cost benefit could use cold fill only…
Anonymous says
Actually, it would NOT save on electricity. Believe it or not, cold water can more quickly be brought up to temperature than can hot water, because it is temperature DIFFERENTIAL that makes the difference.
The same is true in reverse, of course: HOT water will freeze faster than cold water. Try it
Washerhelp says
Anonymous: I have heard that hot water will sometimes freeze faster than cold. It’s a known phenomenon which even now is not fully understood. There are some theories about it here Mpemba effect: Why hot water can freeze faster than cold
However, it’s surely impossible for more energy to be needed to raise water from 30° to 40° than would be needed to raise it from 0 degrees.
Anonymous says
Cold water takes longer than warm water to get hot. Just try it in a pan and time it. Huge difference.
Anonymous says
Another reason for the use of a cold water supply in a dishwasher, is that certain models have a heat exchanger: namely the Bosch, Siemens and Neff models.
The heat exchanger absorbs heat from the main wash and transfers it to a water storage matrix for the rinses. The idea being that less heat energy is wasted, the hot final rinse has a slight temperature advantage and that dishes are not subjected to thermal shock (cracking, shattering, etc. i.e. hot crockery, cold water).
As others have commented, before year 2000, Hotpoint dishwasher models were manufactured by Bosch. Nowadays Indesit owns Hotpoint, so current Hotpoint machines are Indesits in disguise.
WMUser says
Thermal shock = HOT items being sprayed with very COLD water and breaking or cracking. I’m sure all dishwashers have a way of preventing this thermal shock damage? I have never heard of a dishwasher causing thermal shock damage to the items being washed.
A hot water connection would avoid hot items being sprayed with cold water.
I’m hoping to have my dishwasher connected to the hot water supply soon, if the plumbing arrangements and new kitchen go as planned. Hopefully the hot water pressure will be enough to allow the dishwasher to fill. I will post back if I have it connected to the hot water supply and let you know the results.
WMUser says
Yes it works! :)
Give it a try and see if it works for you. It’s definitely worth trying. Obviously every situation is different, but you won’t know unless you try it for at least 6 weeks.
My dishwasher has been on the hot supply since November 2012 and it no longer smells inside, as it did when plumbed into the cold water supply. My electricity usage is lower and things still come out spotless.
Yes I run the kitchen hot tap (it’s nearest the dishwasher) to run-off the cooler water, until the water runs hot – 60C, the maximum temperature recommended in the instruction book. Instead of wasting this hot water, I use it to clean the worktops and things that can’t go in the dishwasher e.g. wooden chopping board. Then I use the “prerinse only” cycle on the dishwasher to remove most of the food debris, since the “auto” programmes on mine tend to use the same dirty pre-rinse water to wash the load. Once the rinse cycle is done, I put the dishwasher on an “auto” cycle.
Since the hot water cools down on its way to the dishwasher and cools more when it’s being sprayed around inside, the water is still warm enough to soften and remove almost all of the food debris on the dishes and it is probably doing the same in the internal components, pipes, hoses etc? As a result, the main wash and detergent has fewer debris to clean, so it can do a better job and keep the dishwasher cleaner inside.
I would definitely recommend plumbing a dishwasher into the hot water supply and running the nearest hot tap to run off the cooler water. It sure works. I don’t know why anyone would recommend against a hot water supply on a modern dishwasher?
Washerhelp says
Thanks for that WMUser, is your hot water supply conventional or is it from solar panels?
WMUser says
No, it’s from the gas hot water system.
One thing I will keep doing is running the dishwasher empty with a cleaner. I have seen Affresh dishwasher cleaner and it’s meant to be the best available?
I don’t know the exact reasons why my dishwasher works much better on a hot supply and no longer smells bad, like it did on the cold water supply – even with an air freshener it still smelled, but it does work better now on the hot water supply. My guess is that the warm/hot water softens and removes most of the food debris on the dishes and in the dishwasher internals during the first warm rinse, and sends the muck down the drain.
If, after reading these comments, you connect your dishwasher to the hot water supply, make sure the dirty dishes have a rinse in warm water before the main wash. If your dishwasher has them silly “auto” programmes which try to save water by not pre-rinsing, simply do the rinse-only (or whatever the name of the programme is called which just does a rinse), before you do the main wash with detergent. Also, run the nearest hot tap to draw-off the cooler water just before you put the dishwasher on, to ensure the hot water makes it to the dishwasher. Doing both will save electricity costs and stop the dishwasher smelling, although I would still recommend running a dishwasher cleaner through empty at least once every 2 months – or once every month if the dishwasher is used a lot.