Constant hot water (using ASHP) or just using the dishwasher and electric shower?

Ken2000

Hi, I've recently had an air source heat pump installed (and moved to a single tariff electricity supply), which also provides me with hot water. My hot water usage is minimal as I live by myself, so one load of washing up per day. I have a shower that is connected to the hot water cylinder, but also an electric shower, which I tend to use more, but for no real reason other than it's slightly more convenient.

I have a dishwasher, which I rarely use unless I have people round.

So, and I appreciate that it's probably not clear cut, but it's led to me wondering how to best minimise my bills. The options are:

1) Not using hot water at all (turn it off) and to just use the electric shower and dishwasher
2) Use the hot water from the cylinder for washing up and showers and to not use the electric shower and dishwasher
3) Use the hot water for washing up and the electric shower

Reed_Richards

Any stored hot water will lose heat.  If the cylinder is in the house and loses heat to the surrounding rooms that does not much matter in winter but it is wasteful in summer when that lost heat is not required.  In winter (i.e. when you are heating the house) it's option 2 because heating the water with the heat pump is much more economical and heat lost from the cylinder is not wasted.

Given that your need for hot water is so minimal then turning off the hot water (Option 1) will probably be the cheapest option in summer.  In fact you might want to turn off the heat pump completely to stop it needlessly trying to maintain the temperature in a buffer tank.

I don't see that option 3 is ever worthwhile.

Edit:  Then there's the whole separate debate about whether a dishwasher is more economical that hand-washing the dishes.

Ken2000

Reed_Richards said:

Any stored hot water will lose heat.  If the cylinder is in the house and loses heat to the surrounding rooms that does not much matter in winter but it is wasteful in summer when that lost heat is not required.  In winter (i.e. when you are heating the house) it's option 2 because heating the water with the heat pump is much more economical and heat lost from the cylinder is not wasted.

Given that your need for hot water is so minimal then turning off the hot water (Option 1) will probably be the cheapest option in summer.  In fact you might want to turn off the heat pump completely to stop it needlessly trying to maintain the temperature in a buffer tank.

I don't see that option 3 is ever worthwhile.

Edit:  Then there's the whole separate debate about whether a dishwasher is more economical that hand-washing the dishes.

Thanks for the advice! It has struck me that I'm heating a lot of water for the sake of heating it. I can do most things with cold water, so will try that for a bit and see how I fare.

Reed_Richards

Ken2000 said

I can do most things with cold water, so will try that for a bit and see how I fare.

Previously I had a combi boiler with very long pipe runs to every hot tap.  I did not like washing my hands in stone cold water!   

shinytop

Ken2000 said:

Hi, I've recently had an air source heat pump installed (and moved to a single tariff electricity supply), which also provides me with hot water. My hot water usage is minimal as I live by myself, so one load of washing up per day. I have a shower that is connected to the hot water cylinder, but also an electric shower, which I tend to use more, but for no real reason other than it's slightly more convenient.

I have a dishwasher, which I rarely use unless I have people round.

So, and I appreciate that it's probably not clear cut, but it's led to me wondering how to best minimise my bills. The options are:

1) Not using hot water at all (turn it off) and to just use the electric shower and dishwasher
2) Use the hot water from the cylinder for washing up and showers and to not use the electric shower and dishwasher
3) Use the hot water for washing up and the electric shower

We do 3) at the moment minus the washine up (we use the dishwasher).  When we get around to replacing the electric showers with mixer showers, we'll do 2) minus the washing up. 

You do lose heat from a modern, well insulated cylinder but it's not much.  We've left ours on 24/7 and it uses about 2kWh per day for the occasional hand wash and hot wiping up cloth.  

matelodave

there's only one way to find out - do some testing.

Test out each scenario for a week or so, reading your meter before and after each test. to work out which uses the least amount of energy. 

knightstyle

IMO heating a cylinder of hot water every day and not using it is a waste of money.  I think switching it off and using electric shower and a kettle is best for you.
You could look at getting a small electric heater that will go under your sink may make life more convenient.
https://www.ebay.co.uk/itm/233951304166?hash=item36789599e6:g:HScAAOSwz3FgZtyb

Reed_Richards

Really this is a personal choice about how much discomfort you are prepared to put up with in order to save a little money.  You have the capability to have hot water on tap whenever you want it and at whichever hot tap you want it to come out of.  Its going to cost you 20p a day* tops to maintain that capability (plus the cost of the hot water you actually use).  And you'll win some of that back because when you do use hot water it will be cheaper than it would otherwise have been if supplied by direct electric heat.

* I'm guessing 50p a day to keep a cylinder of water hot with direct electric heat (i.e. an immersion heater) which would buy you something like 2.5 to 4 kWh depending on your unit rate.  Then a CoP of 2.5 for hot water bringing it down to 20p a day with the heat pump.    

macman

The heat loss from a properly insulated cylinder is minimal, and, as stated, serves to heat the house anyway in the winter.