Is a hot and cold fill washing machine more economical?

In theory yes, but the way washing machines work means that in the majority of UK households it’s likely to be more economical to use a cold-fill washing machine.

It does depend on how close the source of hot water is to the washing machine, but a substantial percentage of households in the UK get their hot water supply from a hot water tank upstairs, and this experiment demonstrates the problems with that. Note that even combination boilers take a long time to start supplying “hot” water.

I have previously written in greater detail about this subject (links at the end of this article), but I wanted to carry out this experiment to demonstrate the argument in a very simple way.

Here is a visual demonstration of how hardly any hot water gets into a modern washing machine, and therefore, why a hot water valve isn’t necessary for most people.

Wasted Water from Hot Tap

A washing up bowl 80% full of water

The photo above shows how much water was drawn from my hot water tap in the kitchen right up until it started to run hot. So this is basically a bowlful of cold water.

How Much Water is Used on Wash?

A washing up bowl about 85% full of water

The photo above shows how much water was pumped out of my washing machine at the end of the wash section. If you compare it with the previous photo it’s only got a little bit more water in it.

Most wash cycles typically only use just under a bowlful of water on the main wash (I used Cotton’s 40°).

This means if I’d been using a hot and cold fill washing machine, then by the time it had drawn in the amount of water needed (second photo), there would be zero amount of hot water in the wash drum.

In fact in my case the washing machine would have had to fill up entirely with the hot water valve in order to just get a splash of hot water right at the end.

This shows that unless you can get proper hot water running through the washing machine hose within several seconds you will get no hot water into the drum at all.

There are other problems explained in my related articles (below) such as wasted hot water in the plumbing pipework and hot water already in the hot water cylinder being cooled down with replacement water.

There is a belief that using hot water in a washing machine is more economical, but it’s not true in the overwhelming majority of cases. One reason is demonstrated in this article. Another is that washing machines are not sophisticated enough to properly utilise hot water with such a variety of delivery methods and with totally unpredictable lengths of time before hot water reaches the washing machine. This is also explained in detail in my previous articles.

Previous Related Articles on cold fill washing machines

More detailed reasons and explanations (plus discussion in comments) for this issue can be read in my related articles here –

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2 thoughts on “Is a hot and cold fill washing machine more economical?”

  1. You’re wrong when you state,”the majority of households in the UK get their hot water supply from a hot water tank upstairs” the vast majority have combo boilers. Almost 55% giving almost instant hot water.

  2. Andy Trigg (Whitegoodshelp)

    Thanks Clive. It was correct at the time of writing, and more importantly at the time that manufacturers made the decision to switch over to cold fill. I will rephrase that. However, having a combination boiler makes no difference to most people in relation to this issue, because they usually still take a long time to produce hot water, by which time the washing machine will have finished taking in water. If a combination boiler is very close to the washing machine, then this may not be such a problem.

    As it happens, in every house I have ever lived in, there has been a hot water cylinder storing hot water. But after 17 years in my current house, we have just had the boiler replaced by a combination boiler. The boiler is in our loft, which admittedly is further away than most, but it actually takes longer for hot water to run through our taps with the new combination boiler than it did with the old hot water cylinder.

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