Hot water - on Constant or Twice?

grannybiker

Hardly ever use the hot water to be honest.
How? Shower and washing machine both heat up water as they go. Got used to boiling a kettle for washing up when we lived in houses with no central heating, (and were far too skint to put immersion on for a bowlful of water!) For handwashing we use a cheap anti-bac handwash, so hot water not vital.
Obviously we use it for baths, but that's about it and there's often luke-warm water for hand-washing etc left in the tank for a couple of days afterwards.
Think one of the worst waste of hot water is running it to rinse vegetables, hands etc. This often just warms the pipes as it takes so long to get through to the tap! We were always trained never to do this. Old habits die hard!

The_Governor

Hmm well, despite my better hopes 3 days in to my experiment it looks like the Gas usage is nigh on exactly the same with the heating on Twice for water as it is on Constant.

Central heating is off all the time at the moment so this is a pure test of water heating usage....

So intial indications are for water heating it costs the same to keep it hot as it does to let it cool/reheat.

I'll leave it as is for now and see how things change (or not).

amtrakuk

Sounds like the same sort of experiment when I tried oil filled radiates. As they take such a long time to heat the room up if I switch them off when I go to work and turn them on when I come back in the evenings and wait a good hours before I start feeling the benefit. With oil filled radiators was to turn them down to about 20% while I was out so there was less work for them to do when I got home - then I discovered convection heaters - can turn them off when I left the house and took a fraction of the time to warm up when I got home

Going on that basis and as Cardew said would you keep your kettle boiling on and off when you don't need a cuppa? I guess all in all it depends how much heat loss and how well insulated your tank is.

The_Governor

Our tank is pretty well lagged, I put a fibre jacket on it whenw e moved in and it ceetainly stays hot for 12 hours.

I've adjusted the on/off times now to minimise the heating time, maybe that'll help...

tomstickland

I use E7 to heat my water overnight. It's on from 1am until around 8am. It's still hot at 9pm in the evening.
So you'll probably find that it takes so long for the hot water to cool down that there's nothing much in it.

In the limit, if you had no heat loss whatsoever from the tank, then it'd make no difference at all.

My measurements suggested that it loses 2.5 units per day.

Andy_Hamilton

With electric heating elements just in the tank you will not have the heat losses between the boiler and tank in a standard system so it will probably be better.

Cardew

It is very difficult to estimate the difference in costs between leaving the water heating on 24/7 and having it on a timer.

As said above a well lagged tank will lose about 3 kWh in 24 hours. So if you left your water heater on constantly, and never used any hot water from the taps, you would lose approx 1,000 kWh a year. That worst case scenario would cost anything between £25 and £120 a year depending on how you heat.

Even with timed heating, you would still have some heat loss from the tank as you would rarely use all the hot water after your timed spell. I would therefore hazard a guess that 500 kWh pa might be a reasonable estimate of the difference between constant and timed HW heating.

However it is important to note that the 500 kWh is not lost as it goes to heat up the fabric of the house.

kingbeige

Whilst the argument that you should only heat up the water you need makes sense it's not always practical.

Bathing and showering are fairly regular activities but the washing machine and dishwasher can be used at any time. I believe my washing machine and dishwasher are plumbed to use hot water if available otherwise they'll heat it themselves. I would guess that it would be cheaper for them to use the gas heated water than to heat it electrically themselves. They are used roughly once a day each in my household.

Could this be worth considering?

lightisfading

we're on a ridiculously expensive prepaid meter (not by choice) and we definitely notice the difference. During autumn/spring we heat the water morning and evening for a couple of hours - this runs through the upstairs radiators too so keeps the rooms warm. In winter it's on for the same but heating as well. In summer its either on just in the morning for an hour (for washing - stays warm for baths in the evening), or not at all if its really hot. If there's no hot water i do a kettle for washing up. If we had it on 24/7 it would cost us a fortune (we've tried it, and it does).

shirlgirl2004

kingbeige wrote: »

Whilst the argument that you should only heat up the water you need makes sense it's not always practical.

Bathing and showering are fairly regular activities but the washing machine and dishwasher can be used at any time. I believe my washing machine and dishwasher are plumbed to use hot water if available otherwise they'll heat it themselves. I would guess that it would be cheaper for them to use the gas heated water than to heat it electrically themselves. They are used roughly once a day each in my household.

Could this be worth considering?

When I was looking at replacing my washing machine I read that the amount of hot water it would take on board would be minimal. By the time the hot water had gone from the tank, through the system and into the machine then the machine would be full of cold water anyway. This must be the same for dishwashers although not being an expert on these matters I am willing to be corrected.

Our hot water is on for 1/2 an hour in the morning, by the time DP and I have showered then the hot water is pretty much gone. It is then reheated for about 40 minutes in the evening for the washing up etc. If I need hotwater in the day then I'll wait until the kettle is boiled for a drink and add a bit of extra water.