I’ve had several people ask if you can connect a cold fill washing machine to the hot water tap instead of the cold one. They were unhappy about the disappearance of the hot water valve in UK washing machines, and were wondering if they could circumvent the change.
Many people who are using solar powered energy to heat their water, or who had another cheaper environmentally friendly supply felt that the advantages of their environmentally friendly and economical hot water will be wasted by not using their hot water supply.
However, the answer to the question is no, for the following reasons..
Hot water supply is too hot
The incoming water temperature would be too hot (usually at least 60 degrees Centigrade). This can damage delicate laundry and shrink woollens.
There would be no way of controlling the temperature of the water going into the drum and onto the laundry.
A washing machine designed to use hot & cold water will control the temperature of the water in the drum by either filling with a mix of hot and cold – or filling only with cold water on all wash cycles except the really hot wash.
Too hot for most wash cycles
The temperature of household hot water is also too high for most commonly used wash cycles, which only need 30 or 40 degrees.
It is pointless putting on a wash cycle that needs to heat the water up to 30 or 40 degrees if the water is 60 degrees from the start.
So apart from potentially damaging some laundry, the washing machine’s thermostat would close almost immediately and the wash cycle would move on to the rinsing too soon. This would shorten, but compromise the wash quality.
Hot water not good for biological detergent
Biological detergent contains living enzymes. These enzymes are killed off at the temperature of most people’s hot water. So filling with hot water only would again compromise wash efficiency when using biological detergents.
Biological detergent is more effective when starting in cold water with the water gradually heating up.
Rinsing in hot water is very bad
If a washing machine is only connected to the hot water supply then obviously when it comes to rinsing the laundry – the water going in would also be hot.
So the laundry would be rinsed in hot water. This would cause severe creasing, as well as wasting all the hot water and being very energy expensive. Also hot water tends to activate detergent and create suds whereas cold water doesn’t and is therefore more likely to be better suited to rinsing laundry.
See Latest Reviews & Research
Several Which? Trial Offers available to allow you to research all future purchases and see expert reviews and recommendations. Easily save a lot more money than it costs.
What about connecting both hot and cold hoses to a cold fill washing machine?
You can’t swap the cold water supply for a hot supply for the reasons given in this article. However, there might be an argument for using a y-connector to connect both hot and water supply at the same time. However, this seems a lot of trouble for little benefit. You would need to manually adjust the water pressure of both supplies to get a balanced, “warm” combination.
But as hot water usually takes a while to run through the pipework, the chances are it wouldn’t use much if any on the wash cycle anyway. This is in fact one of the main arguments for cold fill only machines. It would do all the rinses in warm water, which may (or may not) be better. But it would also use a lot more energy.
A full explanation as to why almost every washing machine is cold fill these days is here – Pros and cons of hot and cold fill verses cold fill washing machines
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.
The problem of the incoming water being too hot is easily dealt with by fitting a thermostatic mixing valve set to 30C (or 40C if you use that wash temp).These are now widely and cheaply available.
Hello Wookey. Thanks for your comment. I’m not sure which angle you are coming from though. The scenario in the article is of cold fill only washing machines with only one valve. If the hot water was connected to it instead of cold the problems I listed would be experienced. If you mixed a hot and cold supply to a thermostatic valve then the water supplied would always be at that temperature.
This would mean all rinsing would be done at 30 or 40 degrees which could reduce rinsing efficiency (some say rinsing in warm water is more efficient but some say it causes more lather). It would also waste a lot of heated water because only a small amount of warm water is needed for wash and all rinsing needs cold.
If you mean the manufacturers should fit a thermostatic mixing valve and make washing machines hot and cold fill again the problem is that it takes so long for hot water to start running through to the machine that it’s already finished filling up by the time it does. In order to use hot water you’d have to let the hot valve run until it was delivering hot water and monitor the temperature. Then either store the cooler water that cam out first (but there’s no space to store it) or pump it down the drain and waste it. Even then, the simple act of drawing off water from the hot supply means that extra hot water would be drawn into the plumbing pipework which is likely to just cool down and be wasted. Cold water would top up the water in the cistern and cool down the rest of the hot water in the tank which may then need heating up further.
I have to say I can see why manufacturers decided it’s simpler and more economical overall to just take in cold and heat it up. The fact that a small minority of users may have ideal set ups with short pipe runs, solar powered heated water and maybe insulated pipes doesn’t detract from the fact that overall, chances are that the UK will use much less energy using cold fill washing machines than hot and cold. I remain open minded but am mostly convinced of the argument.
Would it damage my washing machine if I attach a hose to the hot tap and channel it into the drawer when the cold water is going in?
If I do this will it save time as the water won’t have to be heated up, or will the machine automatically heat the water up anyway and cause the machine to overheat?
OK, you can tell from those 2 questions that I haven’t a clue how washing machines work but I’d like to know the answers as I know several people who are wondering the same things. I’d rather not risk finding out by trial and error that I ‘ve written off a new washing machine!
For the record, from the late 80’s early 90s, I used to obtain endless hot water from an experimental solar panel (now defunct) so it always made sense to use a hot and cold fill machine. Running costs were very cheap, and my washing was never damaged or overheated. Even though I mainly used 30 and 40 degree washes, the hot water definitely flowed into the machine. It filled up in a fraction of the time as my new machine does.
I don’t see the point in saving up for a domestic solar panel to heat water if that water can’t be used in washing machines and presumably dishwashers too?? Cold fill only has made them a bit redundant hasn’t it?
My new machine is cold fill only but the quick wash takes at least one and a half hours as opposed to my 14 year old machine’s 40 minute quick wash. I don’t see how my modern machine is saving energy!? The parts will wear out quicker too, considering each wash will generate twice the wear and tear of the old one. It doesn’t look like progress or efficiency to me.
lemurtail: You make several good points.
If you can’t use solar powered hot water in the washing machine and dishwasher it seems a waste. Unless a household runs lots of baths each day it’s hard to see how you would save lots of money considering the amount of initial investment needed in solar heating because most people probably hardly use any hot water if they have a dishwasher and washing machine.
I know that apart from baths and showers, our household hardly uses any hot water from the hot water system, and in fact heating up a massive hot water tank each day just to use several litres of water is a waste. I tend to agree that water should be heated up at source – just the amount needed and nothing more. A large hot water cylinder can hold over 200 litres of water. What’s the point of heating up all that each day to 60 degrees only to use a couple of bowlfuls at most?
However, solar powered hot water is still more environmentally friendly so many people will still want to convert.
It wouldn’t damage your machine to mix in a little hot water in during the initial fill process if you were prepared to go to the trouble. It should increase the initial wash water temperature and in theory the washing machine would use a little less energy. However, it could use more water because most people would need to run off a fair bit before seeing any hot water due to cooling in the pipework. Then all the water you run off plus the water that goes into the washing machine will need replacing in the hot water cylinder (unless you have a combination boiler).
In this scenario this would cool down the hot water in the cylinder as all the water used is replaced by cold water from the tank in the loft. This would trigger the immersion heater to heat this water back up to temperature causing extra energy usage that goes towards cancelling out the lower energy used by the washing machine. Hot and cold water fill washing machines always heat the water. Many people mistakenly believe they don’t but they always still use the heater and it’s all controlled by thermostats so no over heating can occur.
The points I’m making are pretty general. There will be lots of people where this doesn’t apply exactly as some may have shorter pipe runs and experience less cooling in the pipes and some may use combination boilers etc. but the average UK user still uses a gravity fed how water system as described and washing machines are designed to run efficiently with that system.
A further point on this topic is that if you make the initial water intake to hot it can interfere with the efficiency of biological detergents which work best when used in cold water that’s heated slowly. Anything over 40 degrees is bad for biological detergents as it kills off the enzymes.
Some washing machines have 30 minute quick washes still. Economy washes take longer to wash because they use less energy heating but need to spend longer allowing the detergent to work as explained here – Economy settings take much longer – why?
Howdy again. I’ve now found a (rather expensive) German device called the Alfamix, which is a smart mixer installed outside the washing machine. I wonder what you think? Clearly it would still need very short coupling or one would have to run off contents of the feed pipe first. (I’ll be using a combi – and anyway hope to tee-off mains pressure solar hot water before it even reaches the combi).
Also, did I rightly understood the second bullet point in your article, about warm fill undesirably shortening a machine’s cycle? So the washing machine starts timing from the moment the correct temperature is reached?
Hello Jacky: I think for most people such a device would be pointless because when the washing machine calls for water on the initial wash it only asks for about a bowlful of water. By the time hot water starts to run through the valve (in the average situation) the washer will have virtually stopped filling.
All that will happen is that the pipework between the hot water cylinder or boiler and the washing machine will get the most hot water drawn into it and this water will sit in the pipework and go cold. Plus if hot water is supplied via a hot water tank then all the water drawn into the pipework will be replaced by cold water from the storage tank cooling down the water in the hot tank and possibly triggering the boiler to top it back up to temperature.
Washing machines usually impulse on after reaching temperature, if not instantly at least after a set time. If you supply a cold fill machine with hot water I would expect it to reduce wash efficiency. Ultimately these machines are designed to use cold water and they have achieved A wash efficiency ratings by washing slowly and thoroughly using small amounts of cold water heated up slowly.
This issue of using hot water efficiently in the home needs a complete rethink regarding how we heat up water. For one thing, why are none of the internal hot water pipes lagged to slow down the wasteful cooling of water in the pipes?
I don’t think we should dismiss these kind of solutions just due to the “average” situation. Clearly, there are cases when hot fill solutions makes sense. In my case, I have a Geothermal heat pump with a COP of 5.03 just a few meters away, so it only takes 20% of the energy to heat water with the heat pump, compared to heating it in the washing machine. Most of our pipes are lagged as well, and those that aren’t will just act as radiators, thus contribute to the heating of the house.
I think that the Alfamix device looks interesting, but it’s too expensive: Even if the claimed 300 kWh savings per year is true, it will take something like 7 years before break even, with our current energy prices.
I’m considering a simpler solution: A mechanical thermostatic mixer valve that will always provide the washer with water of a temperature of, say, 25 degrees. This should be cold enough for efficient rinsing etc, but heating from 25 to 40 will consume much less energy than heating from 10 to 40 (or whatever temperature that cold water has). Of course some energy will be wasted due to consuming more warm water than necessary in the rinsing, but as long as the cold water usage is less than 5 times the hot water usage, you should save energy.
Astrand: I agree with your point that there are cases when hot fill solutions makes sense and have said so several times. The problem is that unless it is commercially advantageous to offer these solutions it will never happen. It isn’t realistic to expect manufacturers of any product to redesign and make their products more expensive than the competition in order to please a minority of customers. But as more and more people start to use environmentally friendly methods of heating their water the commercial advantage for manufacturers to redesign their washing machines in order to utilise this hot water increases.
Current thinking is that hot water costs a certain amount of money and the vast majority of people would benefit from simply heating up the exact amount of water that the washing machine requires. Until enough people are using free or very cheap environmentally friendly hot water supplies this is not a likely to change.
I agree about not investing in something likely to take seven years to start producing savings. There is a fair old chance that seven years from now washing machines will be quite different and may even use cold water only to wash.
As you point out, using hot water all the time will counteract some of the savings in heating the wash water. I’m not sure how much potential savings can be gained by heating from 25 to 40° of just several litres of water compared with the wasting of possibly 20 L of hot water being used during all the rinses.
For some years I’ve used a hot-cold fill washing machine. I had two pipes connecting to the machine but each has aa tap which I turn on hot at the outset and after the wash starts, I switch to the cold supply.
This ensures the machine has very little furring in the heater, which would lead to less efficiency in the heating and consequently more cost to heat the water. (I use a gas heater for the water and although I live in the London area have had no problems with scaling)
For me the only answer is to place a Y connector to supply both hot and cold water and then switch the required tap as before.
I can easily turn the temperature of the Hot water to the required heat level, so feel there should be no problem with the arrangement.
PS. I’m told by an American internet friend that pretty nearly all washing machines in the States have Hot and Cold fill