Cheaper to boil kettle or waste water to wash up?

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I am 78 and trying to economise on my fuel bills like most people. I have a small Worcester combi boiler in the loft of our bungalow. Both our dishwasher and washing machine are cold fill so use electricity to heat the water.
There is only two of us so I tend to wash up by hand. In order to get the water hot enough to wash up I have to run off at least a gallon of water that has already been heated and gone cold and then the water left in the pipe goes cold and is wasted next time we need hot. So I have heated over two gallons of water that have gone cold!
Can anybody tell me please if boiling a 3kw kettle for about two and a half minutes would be cheaper in the long run and if I turned off the pre-heat on the boiler how much more water would I waste?
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  • McKneff
    McKneff Posts: 38,833 Forumite
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    There is no waste of water or fuel used by your machines, they only heat the amount of water that they need, so none going cold in  the pipes and being reheated. 
    Just try to cut down usage, wash sheets less often, put more clothes in the machine and fill dishwasher to capacity. 
    That's my take on it anyway. 
    I am your age x
    make the most of it, we are only here for the weekend.
    and we will never, ever return.
  • squidlydiddly2
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    Thank you but I fully understand that the washing machine does not waste water or energy because there is no alternative and we do use it carefully. That is not my issue, it is wasting water that has been heated and gone cold.
  • calleyw
    calleyw Posts: 9,846 Forumite
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    No idea if its cheaper.  But I collect the run off when washing up/running shower and use it to water plants, flush loos etc.  So I don't waste it
    Hope for everything and expect nothing!!!

    Good enough is almost always good enough -Prof Barry Schwartz

    If it scares you, it might be a good thing to try -Seth Godin
  • BooJewels
    BooJewels Posts: 2,939 Forumite
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    If your 3kW kettle does take two and a half minutes to boil, then it costs around 4.25p.  Hopefully someone else can advise on the cost of the boiler doing that process.  But as a guide, in the summer when I don't have heating on, I use 10m3 of gas per month for all hot water and cooking - which works out at 39p per day at current prices (plus SC of course).  So, considering that I also use hot water for hand washing, some clothes washing and the cooker - it sounds pretty comparable.  Running the boiler will use more water though.

    What I personally do, since getting a combi boiler, is use the cool water coming out ahead of the hot to rinse off my pots, so once I have a sink of hot soapy water, I'm washing already fairly clean items - so only need one sinkful for quite a lot of dishes.
  • D924
    D924 Posts: 88 Forumite
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    1. Wash things you need urgently with cold water as soon as you're finished with them (for me, this is my tea cup and my one good chef knife).
    2. Save up your washing up to do a big wash once per day or even less frequently (let the washing soak with soapy cold water in it, so they rinse quickly when you come to use hot water)
    3. Try to time all your hot water activities together - fill and boil your kettle to put in Thermoses, shower, wash up, and whatever else you do, at the same time of day
  • HumberFlyer
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    Just done the experiment.... run about 1 gal of water then filled the bowl. My gas usage cost is less than electric kettle usage, but of course you waste water with using gas. Plus in my opinion having pre heat on is just wasting gas.
  • sandy700
    sandy700 Posts: 175 Forumite
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    I calculate it by the time I have the tap running.
    My boiler is a 28 kWh Worcester combi and as a very rough guide, for every minute the hot tap is running that is 0.5 kWh of gas (allowing for the over run) so if it takes 2 minutes of running the tap to get hot water to wash the dishes that is 1 kWh of gas costing approx 10p.at current costs. Plus of course the standing charge.

    As I said that is my very rough guide.

  • pseudodox
    pseudodox Posts: 298 Forumite
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    edited 19 November 2022 at 4:46PM
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    Perhaps no-one has shown you the technique of using a combi boiler to minimise the amount of cold you run through before the hot water arrives.  I meet more people who don't understand this than do.  Turn on the hot tap full  just momentarily - this will cause the boiler to fire up.  Mine is in the kitchen so I can hear it).  Then turn the tap off for maybe 10 seconds.  The boiler is now heating the water but you are not running it off.  When you then turn the tap on again the hot water will arrive as soon as any residual cold in the pipes has flowed out.  And as others have said you can use this for watering plants, pre-rinsing dishes, flushing the loo, or even fill the kettle and put water in a pan ready for cooking potatoes etc.  Because it is a combi and the hot water comes direct from the mains it is perfectly safe to drink.

    I also never have the boiler on pre-heat.  The only time would be if |I have guests staying and everyone is wanting water to arrive in the bathrooms and they just don't understand the "turn tap on, turn tap off, turn tap on" routine so panic when it runs a basin full of cold!
  • macman
    macman Posts: 53,098 Forumite
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    edited 19 November 2022 at 5:53PM
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    You'd probably use less hot water if you just run the dishwasher once a day, or every other day. Washing up by hand uses far more than a d/w cycle, for the same volume of washing up.
    The average cycle uses about 1.5kWh, so maybe costs you 51p.
    No free lunch, and no free laptop ;)
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