Cheaper to boil kettle or waste water to wash up?

QrizB

squidlydiddly2 said:

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?

To answer your question:

• Running a 3kW kettle for 2.5 minutes will use 0.125kWh (1/8 of a kWh). At 34p/kWh that will cost 4.25p (exactly as @BooJewels stated above).
• Heating a gallon (4.5 litres) of water from 10C to 60C uses 0.26kWh (just over 1/4 of a kWh). At 10.3p/kWh it will cost 2.7p. But you then need to heat the water you're going to use to wash up with, which is another 0.125kWh and 1.3p, so the total cost is 4p. Plus your gas boiler isn't 100% efficient, so you can add another 0.6p to that for a total cost of 4.6p.
  

So, it seems that boiling the kettle is ever so slightly cheaper but there's really nothing in it. You'll save a third of as penny (plus the cost of the additional water) by boiling the kettle.

(Ive assumed you're on a typical EPG-capped energy tariff; if you are on something significantly different, it will affect the conclusion.)

MikeJXE

Definitely turn the pre heat off. I have calculated and posted elsewhere on here it is costing me £24 a month and can't be switched off

BooJewels

Thanks @QrizB for the clarification.  My own very rack of th'eye calculation suggested that there really wasn't much in it - i.e. doing a quick tot up of what I used the boiler for on a typical summer day.  If water is metered (mine isn't) or is in short supply, being mindful of that wastage might be beneficial.  I try to use whatever comes out of the tap in advance of the hot, for something - refilling the kettle, rinsing, washing my dishcloth and wiping surfaces etc. 

I do also use the kettle for small amounts of warm water, especially in my utility room, as the hot tap probably needs replacing and is getting stiff to turn off fully, so as I use a lot of small amounts in there (it's my work area too), the kettle feels more efficient as it's right next to the sink.

Magnitio

For most washing up, you can just use cold water. The washing up liquid does a lot of the work; the heat doesn't make much difference unless you're dealing with fats/oils.

thriftytracey

I rinse in cold water and then fill the dishwasher and run it in the evening.  I have stopped using hot water in the kitchen now.

There are only two of us so I don't know if it is more economical?  Sometimes the dishwasher isn't full.  We have a gas combi boiler.

In the evening I put a full kettle on the wood burning stove and use the hot water to wipe down worktops etc.

Yorkshire_Pud

My combi boiler is about 2 metres pipe length to the kitchen sink so I guess after the hot water arrives and then turned off there is 2m worth of hot water ‘wasted’ that is left in the pipe. My bathroom is another story, takes at least a minute to issue forth hot water and must leave a lot of hot water in a longer length of pipe. Which is why I fill a jug now in the kitchen and carry it to the bathroom for use in the wash hand basin. For the bath it’s worth the wait as using a much larger volume of water. Comfort myself that some of the residual warmth from that water pipe is heating marginally under the floor in a bedroom!

If we all keep cutting our fuel use our reward will be the energy companies whacking up the standing charge to even more outrageous levels so we will all be paying a lot for very little, like now but worse.

QrizB

Yorkshire_Pud said:

My combi boiler is about 2 metres pipe length to the kitchen sink so I guess after the hot water arrives and then turned off there is 2m worth of hot water ‘wasted’ that is left in the pipe.

2 metres of 15mm copper tube contains about 0.3 litres of water, a generous mug full. Probably not worth worrying about.

BooJewels

Less than a can of pop.   I was thinking about that yesterday after posting and decided that it just acts like a long thin short lived radiator, so I still get some benefit from it when it's cold.  When I had cats, they knew where all those spots were - although largely where the heating pipes ran under floorboards.

macman

BooJewels said:

Thanks @QrizB for the clarification.  My own very rack of th'eye calculation suggested that there really wasn't much in it - i.e. doing a quick tot up of what I used the boiler for on a typical summer day.  If water is metered (mine isn't) or is in short supply, being mindful of that wastage might be beneficial.  I try to use whatever comes out of the tap in advance of the hot, for something - refilling the kettle, rinsing, washing my dishcloth and wiping surfaces etc. 

I do also use the kettle for small amounts of warm water, especially in my utility room, as the hot tap probably needs replacing and is getting stiff to turn off fully, so as I use a lot of small amounts in there (it's my work area too), the kettle feels more efficient as it's right next to the sink.

The marginal savings one way or the other are probably dwarfed by the savings you'd make in switching to metered water billing, unless you have a particularly low RV, or a larger household.

BooJewels

I'm not sure what you mean @macman ?  I'm not metered and don't want to be.  When I had reason to ring the water company to make a change to the bill, I asked if I was on the best arrangement and she did some working out for me and we decided that my current arrangement is by far the cheapest for me.