Boiling kettle vs running hot tap

Raxiel

Helen28 wrote: »

What about using the preheat function on the combi boiler?


Does it save on wasted water at the cost of more gas to get hot water quicker?

My plumber told me to leave it switched off as it wasted gas.

It does use more gas, that's certain, but it's hard to know exactly how much.


According to my boiler stats, we average about 150 units a month on hot water, about £4.70 on the tariff I just switched to. Even if the pre-heat alone accounts for 5% of that, it's less than a penny a day. Without pre-heat, the delay in getting hot water is noticeably longer. I don't value my time at £0 so its worth it for me.

Besides, in the winter it doesn't matter anyway, because what little heat that leaks out ends up in the house anyway.


I should add though, our thermostat can control the preheat, so its automatically turned off when we're 'asleep' and when it detects the house is empty. Also we run the heating in weather compensation mode, which means the boiler runs almost constantly (modulated down) when it's cold anyway. Even so, I doubt the preheat could exceed 2p a day.

chrisw99

Don't forget this thread is talking about the washing up. You can wash up in warm water not hot so don't need to waste 11 litres of cold water waiting for it to come out of the tap hot. Turn on the tap, give it a second or two, put your sink plug in and let the cold but getting warmer water start to fill your sink.

Same with a bath. When I first got the combi last year, I used to turn on the hot water tap but wait a minute or so for it to get hot before putting the bath plug in. When the bath was ready, and too hot, then added some cold. Took me a few weeks to realise how daft I was being.

falcieri

Owain_Moneysaver wrote: »

Kettle usually wins but electricity is about 3x the cost of gas, so gas is cheaper if you are using one kettle's worth of hot water and letting less than two kettles' worth run down the drain.

If you use two or more kettles to fill the sink, but only turn the tap on once for hot water, tap probably wins (as the two kettle's-worth down the drain remains constant).

Despite my boiler being just a few kitchen cupboards away from the sink it takes at least a bowl of water to get enough hot to do the washing up. I have metered water but a smaller than average kitchen sink. Would one kettle of boiling water plus a small cold top up beat one bowl of water straight down the sink, the one I use and the boiler firing up?

falcieri

ajbell wrote: »

Heating water on the gas hob is probably cheaper.

Now that's a thought!

falcieri

falcieri wrote: »

Despite my boiler being just a few kitchen cupboards away from the sink it takes at least a bowl of water to get enough hot to do the washing up. I have metered water but a smaller than average kitchen sink. Would one kettle of boiling water plus a small cold top up beat one bowl of water straight down the sink, the one I use and the boiler firing up?

Actually, thanks to price hikes my gas is going to be more expensive than my electricity from 7th Octobe so using the kettle may still be my better option from then.

falcieri

Raxiel wrote: »

My (combi) boiler sits next to the sink, with about 1.5-2m of 15mm insulated copper pipe between the boiler output and the tap. Even though the hot water pre-heat is programmed to be on whenever the house is occupied during the day, the boiler will still let a lot of cold water flow for about half a minute before it runs hot.
I've found that for the least waste, you have to give a quick, half second blast of water from the hot tap to wake the boiler up, wait 5-6 seconds for it to fire (which isn't that long, but feels it when you're stood waiting) then turn the hot tap on - giving you very hot water within a few seconds.


Wifey usually can't be bothered with that and uses the kettle. I can never be bothered to wait for the (1.2kw) kettle to boil, so I usually use the gas.


The same on-off technique can be used to get the shower to flow hot quickly too. Wifey's solution there is to just turn it on and wander off until enough hot water to melt an ice cap has flowed down the plughole, then start her shower. :doh:

My shower is electric and I have one of those 4 minute timers from United Utilities to time me. Needs must. The water in the shower runs through hot pretty fast so I don't worry about that. As for the tap, I do feel that the kettle is still the best option (at least after Economy Energy have put my prices up next month).

falcieri

coffeehound wrote: »

So four tonnes of water per household per year for each daily run up to hot water? Times by say 10m combis in the UK. What a green choice combis arent!

Raxiel you need a bigger kettle

I have often wondered about the wasted water, especially here when this summer when we narrowly avoided a water ban and you can still see grass growing in the reservoirs. I know it is possible to get insulated pipes so you get 'instant' hot water but I think the chances of getting my landlord to put any of this in is unlikely to 'you must be joking'.

falcieri

chrisw99 wrote: »

Don't forget this thread is talking about the washing up. You can wash up in warm water not hot so don't need to waste 11 litres of cold water waiting for it to come out of the tap hot. Turn on the tap, give it a second or two, put your sink plug in and let the cold but getting warmer water start to fill your sink.

Same with a bath. When I first got the combi last year, I used to turn on the hot water tap but wait a minute or so for it to get hot before putting the bath plug in. When the bath was ready, and too hot, then added some cold. Took me a few weeks to realise how daft I was being.

Thus the question remains do you need to wash up in hot water at all? What is the real difference between hot and cold if you're using washing up liquid anyway? Maybe I should just use cold and have done with it.

chrisw99

And we haven't even discussed dishwashers yet, there are plenty of arguments to say that a dishwasher uses less water and energy than traditional washing up by hand anyway...

https://www.treehugger.com/kitchen-design/built-in-dishwashers-vs-hand-washing-which-is-greener.html

Built in dishwasher vs. hand-washing: And the winner is...
These numbers indicate that it's possible to be more efficient when hand-washing, but it's pretty tough.

Norman_Castle

falcieri wrote: »

Thus the question remains do you need to wash up in hot water at all? What is the real difference between hot and cold if you're using washing up liquid anyway? Maybe I should just use cold and have done with it.

Hot water is much better with oily or greasy washing up. For some things cold is fine.