Cost of running dishwasher

[Harry Bloomfield]

Hotels of course have a 'ring'. Where water is constantly pumped around the ring and back to the tank. Rooms are then feed off the ring, so it doesn't take too long to get hot water.

Then it is well worth/essential to insulate the ring.

 

[JohnW2]

I had to try, 6 pints before it started to get warm, 8 pints before hot at the front kitchen sink. Not that it makes any difference as my dishwasher is cold fill.

That's a lot closer to my situation here - roughly 8 pints before it starts to get warm and 10 pints or so to get hot.

 

[Harry Bloomfield]

I guess new builds at the time put the heating device/storage in the middle of the building.

Our HW cistern, is adjacent to the bathroom (airing cupboard), directly over the kitchen, 2nd toilet alongside it, then utility just beyond - so the longest pipe run is to that utility. So all the hot outlets, at the rear.

 

[ericmark]

The only 'advantage' of lagging the DHW pipework would be to avoid 'wasting energy' when hot water was used (by taps, showers etc.) during the Summer months, and that is likely to be fairly trivial - certainly not enough to justify the time, effort, cost and disruption that lagging the pipes would involve.

Total DHW in summer is around 12 kWh per week, at the most this costs me 15p/kWh in lost revenue, assuming using electric for ½ the year I spend less than £50 per 6 months on DHW, so no way would I lift the floor to insulate pipes.

Once one is committed to a combi boiler, there is little one can do. The cost is more down to heating the heat exchanger in the boiler, so how many times a day it fires up, even if the hot water never reaches the taps. I was surprised when I went to check how much oil is left, since switching to electric and the immersion heater to heat the DHW, expected it to be half full, it was three quarters full. That is a lot more than £50 worth.

Last house I fitted a Main 7 gas DHW heater, (before the combi boiler was popular) so I could remove the hot water cylinder and make the space into a room. And even if my DHW did cost more, it was worth it to have the extra room. Parents fitted a combi boiler, as the steel cold water tank was leaking, the central heating bit did pay for its self, but the DHW was not so cut and dried, the shower was nowhere near as good, the power shower had to be removed, as not permitted to pump from the mains, and the water if you used the reservoir then shower would go cold then hot again as it ran out, and if you did not, then no hot water unless tap turned full on.

Cost wise, sure it works out well in winter, as CH already running, but in summer, the heat lost every time one runs just enough water to wash hands, I would think far more expensive to using an electric water heater. Some of this type

use a special tap and cold water in forces hot water out, others use a standard hot tap, the latter could be plumbed to supply the whole house, clearly no good for a bath, but heat loss is much reduced.

I did consider it, but not really worth it. The main question for me is, if the boiler I have fails, would it ever be worth using a new boiler to heat DHW? I have had one bath in 5 years since moving here, showers are instant electric, likely having a large cylinder is still worthwhile, as can use off-peak. But heating DHW with oil, unlikely to be cost-effective.

I hope the boiler does not fail in my lifetime, so the question does not arise.

 

[JohnW2]

Hotels of course have a 'ring'. Where water is constantly pumped around the ring and back to the tank. Rooms are then feed off the ring, so it doesn't take too long to get hot water.

When I moved into my present house, I inherited such a system, mostly plumbed with massive (about 2" OD) steel pipes (the pipes I imagine installed some time in the early 20th century), constantly pumping water (heated by a coal-fired boiler) all around the very large house.
[ I say 'pumped', but I'm actually not even sure that there were any pumps - it may have just been a matter of convection! ]

When viewed as a hot water system, it cost a fortune to run, but it was not so bad in Winter, since all the pipework then functioned as a sort-of CH system! However, I wasted no time in replacing the entire system

I must say that I've often wondered whether there really is a need for hotels, particularly large ones, to have such a system, since I would have thought that essentially 'random' usage, by many hotel rooms, would usually mean that most of the pipework contained fairly hot water.

 

[JohnW2]

Apart from a m or so where it's boxed in, I have access right now to the entire 7-8m run of 15mm from combi to kitchen tap. ... Unfortunately I don't think I have any lagging, and given the 1,000,001 jobs of actual importance I have to do, I wouldn't have the time even if I did have the materials

Indeed. As I've just written, it's certainly not something I would bother to do, even if I had reasonable access to the pipework.

 

[JohnW2]

Then it is well worth/essential to insulate the ring.

In Summer, yes.

 

[ericmark]

Our HW cistern, is adjacent to the bathroom (airing cupboard), directly over the kitchen, 2nd toilet alongside it, then utility just beyond - so the longest pipe run is to that utility. So all the hot outlets, at the rear.

This can't happen with my house, the front kitchen and back kitchen are quite a distance apart. And a bathroom on all three levels.

In summer, (August) I note 85 kWh used to power the AC, so there is no way I want DHW heating the house, yes, we only ran it on sunny days so was powered by the solar, but still losing revenue from the export, so £12.75 used to cool the house in August. And the pipes' boiler to hot coil go through the living room.

 

[Harry Bloomfield]

Total DHW in summer is around 12 kWh per week, at the most this costs me 15p/kWh in lost revenue, assuming using electric for ½ the year I spend less than £50 per 6 months on DHW, so no way would I lift the floor to insulate pipes.

Our gas HW use, costs (ignoring standing charge) around £2 per week, including baths every alternate evening, at 5/6p per Kw.

 

[JohnW2]

Our gas HW use, costs (ignoring standing charge) around £2 per week ....

That's very close to eric's "£50 per 6 months".

I'm not sure that "ignoring standing charge" is necessarily appropriate, given that I think many/most people are paying over £120 per 6 months for that!

 

[Harry Bloomfield]

I'm not sure that "ignoring standing charge" is necessarily appropriate, given that I think many/most people are paying over £120 per 6 months for that!

Even with zero consumption, I would be paying 30p per day, £2.10 per week, £109 per year.

 

[JohnW2]

Even with zero consumption, I would be paying 30p per day, £2.10 per week, £109 per year.

Exactly (although 30p per day is pretty low - less than half of what I'm paying). I realise that there's nothing you can do about it (if you want electricity at all, but the cost of electricity consumption (as well as other things) is presumably 'rolled into' the standing charge, so one probably should take it into consideration when talking/thinking about the 'cost' of electricity consumption.

 

[ericmark]

Our gas HW use, costs (ignoring standing charge) around £2 per week, including baths every alternate evening, at 5/6p per Kw.

As said, same as my costs, = 18.5571p per day = £1.29 per week, but I don't include baths. We take showers. I am also not including electric standing charge, which is fair, as I could not do without electric. And I suppose you can't do without gas as used for other things.

My oil costs around £600 per year, so around £12 per week, again could not really do without it.

 

[Harry Bloomfield]

Exactly (although 30p per day is pretty low - less than half of what I'm paying). I realise that there's nothing you can do about it (if you want electricity at all, but the cost of electricity consumption (as well as other things) is presumably 'rolled into' the standing charge, so one probably should take it into consideration when talking/thinking about the 'cost' of electricity consumption.

Except we were discussing gas, it's the standing charge, and cost of my gas

 

[Harry Bloomfield]

And I suppose you can't do without gas as used for other things.

We could manage without the gas in the summer, except for cooking, but in the winter, it provides our HW, CH, as well as cooking.