Cost of running dishwasher

[Munroast]

This is how much hot water I need to draw off before it burns my finger, 10mm radial from unvented cylinder.

Just measured mine first thing this morning (so it had all night to cool down), 2.9 litres before got hot - roughly measured there is 4.6m of 15mm copper pipe between tank and tap (45.8 * 3.142 * 0.68^2) = 0.66 litres of water in pipes - I know the water has to heat the pipes but that still seems a lot of water.

 

[Harry Bloomfield]

My kitchen (and DW) is fed from a cylinder on the floor above, via an initial bit of 22mm and mostly 15mm pipe. I've just tried, and with today's ambient temp, I have to draw off about 4.5 - 5 litres before there is any perceptible increase in temperature and a total of 6-7 litres or so before it gets to the point of being too hot for my finger.

The smaller the pipe diameter, the less water it stores for it's length, and the quicker the hot will appear at the tap.

 

[ericmark]

My house is quite large, and the water pipes in some places are 32 mm, as using C Plan, not worth changing, but this does mean DHW is not really as I would like it.

Last house also a problem, used a Main 7 gas water heater around 19 kW, but pipework was for the old immersion heater, and again large delay getting hot water.

Late mother's house however had the combi boiler next to the sink, it had an Eco function, with it on the reservoir was not used, and around 2 litres of water before hot, with Eco off, water hot after around a cup full, but with Eco off the shower would run cold for a time as it ran out of hot water in the reservoir.

The result of all this is there is no one system suits all. I was using oil to heat DHW in the summer under the misapprehension that oil was cheaper than electric, and due to the losses, it is clearly not the case. But this may not be true in other homes, or even when more people living in the home using more DHW.

I was dead against the instant electric shower, but in this house they work well, and are much cheaper to run, due to having to wait for stored water to reach the shower. Since moving here, I have needed to revise my thinking on so many things taught to me over the years.

However, I would take some convincing to get rid of the washing machine, tumble drier, and dishwasher. Just been down to the flat under the main house to check the central heating is working OK, and had to move my daughter's washing on a clothes horse, why she dries clothes outside and with a clothes horse I do not know, there is a washer/drier down there, and we have loads of solar energy, so when the sun is shining why not make use of it and use the tumble drier?

 

[AndyPRK]

I didn’t know 10mm micro bore was used for taps in uk.

Personally I thought it was the norm to run the tap to get hot water before starting a machine.

 

[cdbe]

I didn’t know 10mm micro bore was used for taps in uk.

It isn't. I did it myself, 10mm plastic. I think the issue can be noise - we have a bit of gentle water noise in the downstairs WC pipe which is chased into the
plaster - it has a very unrestricted tap which flows a lot more than the kitchen one - which is very quiet.

I did wonder about 10mm to the showers; when we moved in there was a 10.5kw electric shower fed by a single 3m length of 10mm plastic teed off the cold bath tap - this worked fine within the limitations of the shower so I figured a 10mm hot and a 15mm cold would probably manage a normal mixer valve but decided not to chance it - just as well with hindsight as they both ended up with rainfall heads.

 

[Harry Bloomfield]

I was dead against the instant electric shower, but in this house they work well, and are much cheaper to run, due to having to wait for stored water to reach the shower. Since moving here, I have needed to revise my thinking on so many things taught to me over the years.

You don't need a vast amount of water, just to take a shower, providing the shower room itself is reasonably warm. If the room is not warm, you rely upon the quantity of water, to make you feel comfortable. In my tourer caravan, which we do use in the colder months, it has a fairly low flow, mixer shower. To be comfortable with such a low volume of water, in the colder weather, I simply run a fan heater blowing into the bathroom.

Likewise at home, using the electric shower, get the bathroom warm first.

 

[JohnW2]

Just measured mine first thing this morning (so it had all night to cool down), 2.9 litres before got hot - roughly measured there is 4.6m of 15mm copper pipe between tank and tap (45.8 * 3.142 * 0.68^2) = 0.66 litres of water in pipes - I know the water has to heat the pipes but that still seems a lot of water.

Yes, I forgot to mention that. In my case it's about 12 metres of (mainly) 15mm pipe, but even that is still far less than the 4.5 litres I have to draw before its temp rises perceptibly. That presumably must mean that, in addition to the hot water that has to fill the pipe before hot comes out of other end, another (probably the major) factor is that the cold pipes have to be initially heated.

 

[JohnW2]

I didn’t know 10mm micro bore was used for taps in uk.

I've certainly never see, or even heard, of it being done.

Personally I thought it was the norm to run the tap to get hot water before starting a machine.

I doubt it - not the least because I doubt that many people are even aware of the issue - and furthermore, as discussed, machines with hot fill are, I think, now pretty rare. In any event, even those who do as you suggest (assuming there are some), they are still 'wasting energy' (during Summer)

 

[Harry Bloomfield]

I doubt it - not the least because I doubt that many people are even aware of the issue - and furthermore, as discussed, machines with hot fill are, I think, now pretty rare. In any event, even those who do as you suggest (assuming there are some), they are still 'wasting energy' (during Summer)

I run the initial charge of cold to waste, when necessary, but not for the washer which is cold fill. If already in the bath, having a soak, and some time later, I decide to add a little more hot, I run the hot tap at the adjacent wash-basin to make the hot at the bath tap more immediate. When I use the shower in rear of the caravan, the hot water storage is at the front - so I run the adjacent hot tap at the wash basin, to get the hot through to the shower.

 

[JohnW2]

I run the initial charge of cold to waste, when necessary, but not for the washer which is cold fill. If already in the bath, having a soak, and some time later, I decide to add a little more hot, I run the hot tap at the adjacent wash-basin to make the hot at the bath tap more immediate. When I use the shower in rear of the caravan, the hot water storage is at the front - so I run the adjacent hot tap at the wash basin, to get the hot through to the shower.

Yes, fair enough for baths and showers - but, as I said, I doubt that many people would even think of doing that before starting a machine (DW or WM), even if ('unusually') the machine had a hot fill, would they?

 

[ericmark]

Yes, fair enough for baths and showers - but, as I said, I doubt that many people would even think of doing that before starting a machine (DW or WM), even if ('unusually') the machine had a hot fill, would they?

I often set WM and DW to start at 1 am, I use the built-in timer, no way am I coming downstairs to run water before they start. And at 8.5p/kWh does not cost much anyway.

 

[AndyPRK]

I thought it was in the instructions, back in the day!

 

[JohnW2]

I often set WM and DW to start at 1 am, I use the built-in timer, no way am I coming downstairs to run water before they start. And at 8.5p/kWh does not cost much anyway.

Indeed - and, in any event, as I've said, I very much doubt that a significant number of users would even think of such a 'need', even if they had one of the (now seemingly rare) machines with a hot fill.

 

[JohnW2]

I thought it was in the instructions, back in the day!

You may well be right - but that clearly would not be relevant to the great majority (I thought 'all', but am seemingly wrong) current machines which do not have a hot fill.

It might also be frowned upon today for a manufacturer suggesting that users should 'waste water', and also 'waste energy' at some times of the year

 

[ericmark]

I am sure with a modern house the pipes are all lagged? Sadly, not the case with this 50-year-old house. The immersion heater was 9" long, now 27" long, what a difference. But I put lagging around the main tank, and it hardly made any difference. Maybe 2 kWh a week. We all realise our homes waste energy, but often the amount wasted is not enough to be worth doing anything about it.