Hot vs cold wash cost comparisons

Slinky

When visiting a friend in Australia 25 years ago I discovered they washed their laundry in cold water with a powder called Cold Power. When I needed a new machine in the UK the following year I enquired about buying a machine capable of washing in cold water, I couldn't find one here. I had a conversation with a salesman and explained what I'd seen in Aus, he seemed baffled and seemed to think dirt was different there..........!!!! It seems things have moved on a bit here in the 2 decades since, but I'm not sure that we have powders aimed at cold wash only?

Smodlet

If we do, it's news to me, Slinky and I suspect cold wash detergents may be a little harsh on the skin as I presume they would have to be more powerful to compensate for the lack of hot water? Can't say it's gonna keep me awake at night wondering, though. Whole thing sounds just a little too close to the orange county spectrum for my taste but too each, their own.

matelodave

Actually the sums aren't all that difficult for you to work out how much it costs to heat the water in your washing machine. All you need to know is how much it uses, what temperature rise you require 1 litre of water heated by 1 degree C uses 1kcal of energy

So assume your washing machine uses 20 litres of water and the incoming cold is 10 degrees and you do a 40 degree wash then you'll use 600kcal of heat (20 x 30), use a conversion calculator on Google to convert from Kcal to Kwh (https://www.unitjuggler.com/convert-energy-from-kcal-to-kWh.html) and you get 0.7kwh which at 12p/ kwh will cost you around 8.4pence.

a 90 degree wash will use 20 x 80 = 1600kcal = 1.8kwh = 21.9 pence.

Work out how many washes you do at each temperature and you'll get a rough idea of how much it costs to heat the water. I guess the motor will use about the same energy for either a cold or hot wash

Cold water fill machines might be more economical if you use E7 overnight as you are directly heating the water in the machine which is around 100% efficient whereas a hot fill will incur losses from the hot water tank and and all the pipework between the tank and the machine.

Slinky

Smodlet wrote: »

If we do, it's news to me, Slinky and I suspect cold wash detergents may be a little harsh on the skin as I presume they would have to be more powerful to compensate for the lack of hot water? Can't say it's gonna keep me awake at night wondering, though. Whole thing sounds just a little too close to the orange county spectrum for my taste but too each, their own.

Well it would seem odd if the Aussies are struggling with skin problems due to washing clothing in cold water. One big factor that may make a difference is that top-loading machines appeared to be the norm there, maybe the washing cycle is also longer to compensate for the lack of hot water.

coffeehound

I did a back-of-the-envelope calc for my machine (cheap Beko 5 kg load).

It uses 49 litres of water and 0.95 Unit of electricity for 60 degree cottons. 49 litres of water and 0.69 Unit for 40 degree cottons (both are similar duration).

Extrapolating down for 10 degree water (assuming that is what the mains water comes in at) gives around 0.30 units of electricity.

Using 13.86 pence per unit of electricity and 0.2745 pence per litre of water (Yorkshire Water pricing) gives

26.62 p/wash @ 60 deg
23.01 p/wash @ 40 deg
17.65 p/wash @ 10 deg

at 4 washes a week, it would save about £18 per year going from 60 degrees to cold, or about £11 per year going from 40 degrees to cold.

greatgimpo

Thank you matelodave and coffeehound for your efforts, much appreciated. So all the banging on I hear about eco setting and specially formulated washing detergents, only amounts to a difference of about 10-15p per wash.

Smodlet

Look into getting solar panels, wash when it's sunny, then you won't have to care what the electricity costs.

[Deleted User]

coffeehound wrote: »

Perhaps a curious member could try running hot and cold programmes with the machine plugged into an energy monitor? I would, but my washing machine is currently broken down..

Not an energy monitor , they are not accurate enough but a smart meter In House Display monitor would work , if eveything else was switched off. and just the washing machine used.
I thought all washing machines were now cold tap only due to some EU law .

Smodlet

Ours is cold fill only. Maybe the OP has an old washing m/c that takes hot water.

coffeehound

greatgimpo wrote: »

So all the banging on I hear about eco setting and specially formulated washing detergents, only amounts to a difference of about 10-15p per wash.

In fact even less; my example assumed cold washing, whereas 'Eco' programme is 30 degrees, so the water is still heated. I suppose added up across the EU it makes enough of a difference to help mitigate against the failure to plan future energy requirements and reduce our dependence on Russia for fossil fuels.

sacsquacco wrote: »

I thought all washing machines were now cold tap only due to some EU law .

Smodlet wrote: »

Ours is cold fill only. Maybe the OP has an old washing m/c that takes hot water.

I don't suppose that would change much re the OP's question. If you can heat water more cheaply in the tank then it might make the 'eco' savings even smaller. But in reality I doubt that much hot water actually reaches the machine: long pipe runs and named-for-irony 'instant' combi boilers mean most will still come in cold and require the machine to do some of the heating (I guess this inefficiency is the reasoning behind machines being cold-fill only).

If you do want to send warm water to a cold-fill machine (perhaps to use solar-heated water) there are 'Y' connectors which allow both hot and cold supplies to be connected to the single inlet.