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.
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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 washers
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Andy Trigg (Whitegoodshelp) says
Hello rad. The biggest problem is that hot water coming into a washing machine is never instantaneous. Even with a combination boiler, if everything is set up okay, hot water can reach the washing machine reasonably quickly – but still potentially not quick enough for most settings. Any washing machine supplied with a hot water pipe that has quite a long pipe run from the boiler will take a while to deliver hot water because all of the previous hot water that had been drawn in has since has cooled down and gone cold.
With hot water supplies in the UK commonly being delivered by a hot water cylinder in an airing cupboard upstairs, this problem is even worse. It can take so long for piping hot water inside the tank to actually get to the washing machine that with today’s washing machines hardly using any water the washing machine has just about finished filling up by the time any hot water arrives.
The only way around this involves wasting water or trying to recycle it but with no room to store it . Temperature sensors on the incoming water could divert the water from the drum and from washing in the detergent until it gets to the correct usable temperature. But this water would need to be diverted to a separate container and there is definitely no room for one in a modern washing machine. Or alternatively it would have to be pumped away down the drain instead. So one potential problem is solved by causing water wastage.
So it is technically possible for manufacturers to utilise hot water intelligently and effectively, but only at the expense of wasting water, or trying to recycle the unneeded cold water in the hot pipes later on by storing it in a container somewhere inside the washing machine. It is just completely impractical to do so. So it’s either go back to hot and cold fill washing machines (that for most people means hardly any hot water getting into the washing machine) or use cold fill only and heat up just the right amount of water that is needed for the wash which is the current trend. In the great scheme of things, looking at the most common scenarios and the most common requirements it is by far the most sensible way of doing it.
Pete says
All of the ‘reasons’ put forward above for not using a thermostatic valve to supply a cold-fill only washing machine just don’t stand up. I’ve had a thermostat feeding my cold-fill washing machine for years, and it must have saved me a few hundred ££s in that time.
The thermostat is a cheap shower mixer bar, set to its default 38 degrees Celsius. The hot water comes from a multipoint gas boiler that currently costs 4p per KWh to heat the water, while electricity costs about 20p per KWh. Expensive electricity is therefore only used to raise the water temperature by 2 degrees for a 40 degree wash, saving 50p to £1 on each average wash cycle.
In my opinion, the cold-fill only washing machine was an utterly idiotic idea in the first place. The hot fill inlet could just have been retained, and easily blanked off by those people who like wasting their money!
Andy Trigg (Whitegoodshelp) says
Hello Pete. Thanks for your contribution and for sharing your experience. I don’t have a single “reason” against connecting a cold fill washing machine using a thermostatic valve. My article is only about connecting it directly to the hot water tap, which would be a very bad idea as pointed out. I don’t mention thermostatic valves in the article although I’m not convinced even they are a good idea although obviously you prove it can be done.
I’m not sure though that if you have thermostatic valve to constantly supply water at around 40° how much money will be saved. There is no need for a washing machine to rinse in water at 38° so arguably it’s a waste unless you turn off the hot water after the washing machine is filled for the wash cycle.
Also, with this set up unless the boiler is only a few feet away from the washing machine you are likely to suffer the same problem as most of the UK in that because modern cold fill washing machines hardly use any water on the wash cycle (you can’t use even see much water while it’s washing) then by the time the hot water is actually running into the washing machine it has often virtually filled up with all it needs. So therefore can be very difficult to get much hot water into a washing machine for the main wash. I have discussed this problem at length here pros and cons of hot and cold water washing machines versus cold fill only
Modern washing machines use the overwhelming majority of their water during the rinses. They hardly use any on the wash in comparison. So here we are comparing heating a few litres of water at 20p per kilowatt-hour with heating at the very least several times more water at 4p per kilowatt. Someone would have to do the maths but maybe the savings aren’t as big once you take into account all of the rinse water being heated up. I won’t be surprised to be fair if you are still on the winning side though :-)
Andy Trigg (Whitegoodshelp) says
Hi Pete. I forgot to mention that one of the problems with injecting hot water artificially into a wash is that a cold fill washing machine is designed specifically to get good wash results by starting with cold water. This is particularly true when using biological detergents. It’s designed in such a way that it takes roughly a specific amount of time to heat the water up to 40° and during this time the cleaning is achieved. Once the water reaches 40° the chances are that the wash cycle is complete and the dirty wash water is drained out for rinses to commence.
If you inject water into the washing machine that is already almost at the correct temperature, this is likely to substantially reduce the wash time and therefore substantially reduce how well the laundry is washed. Again someone would have to test this in a laboratory to prove it 100% but to me the logic makes total sense. It might be interesting to do an experiment by doing two washes, one with a thermostatic valve, and one with the hot water turned off to see if and by how much it affects how long the washing machine washes for.
Paul Hooke says
When I bought my present washing machine about 10 years, I was unhappy that it only had a cold fill. So I set about thinking how I could overcome this, and came up with the idea of fitting two leaver type valves back to back with the leavers bolted to each other so in the first position one valve would be open while the other was closed, then when you moved the leaver to the second position the valve that was closed opened and the valve that was open closed. one of the valves was fed from the hot supply and the other was fed from the cold supply.
When I wanted to use the washing machine I would first run the hot tap nearest to the washing machine until it had hot water running, that would clear the cold water sitting in the pipework. I would then put the leaver valve in the position that fed hot water into the washing machine.and start the machine:
When the machine had done its wash cycle after about 1/4 hour, I would then move the leaver valve to the second position which would put cold water into the machine for the rest of the rinse part of the programme:
Win,Win situation
Andy Trigg (Whitegoodshelp) says
Hello Paul. I think I would also apply my last two comments (in reply to Pete) to your situation. The problem with trying to circumvent a cold water washing machine by deliberately introducing hot water essentially it boils down to one thing, which is that a cold fill washing machine is designed specifically to wash effectively starting with cold water and slowly heating it up. Therefore introducing hot water from the start is highly likely to shorten the wash cycle (and your quote of 15 minutes seems to confirm this) because they are designed to finish washing once they have reached temperature. So introducing water that is already at or close to the wash temperature is likely to impact wash performance.
It also wastes hot water although how much is likely to be different depending on the systems in individual houses. Hopefully yours and Pete’s individual situation is good and it all works satisfactory for you. But for most people it’s best to feed a modern washing machine with cold water because they are specifically designed to work best that way. These days they hardly use any electricity to heat up a litre or so of wash water. Anyway the complicated argument is in my article pros and cons of cold fill versus hot fill washing machines if interested :)