How we save money on Gas (heating hot water)

nick257

First time user of this forum... please be kind .  I thought it might be worth sharing how we save money on gas in our house...

Full disclosure: I work in IT, I'm not a plumber, or microbiologist! 

The trick here is to mitigate the legionella risk associated with hot water, whilst maintaining the temperature of the hot water heated by Gas, down to an energy saving 45c (not 60c +  as recommended, e.g. by the UK HSE).

Our situation:

1. A Condensing Boiler - with Hot water Tank (this doesn't apply to combi-boilers)
2. A timer for the Electric Immersion Heater (essential)
3. A Smart meter (not necessary)
4. Octopus Energy "Go" tariff (cheap night Rate, again, not essential)

The first, of two thermostats on our Hot Water Tank, controls the water temperature when heated by gas. It is now set to 45c. It was previously set 70c , which is the situation I suspect 99% of householders with hot water tanks are in. We heat the water with gas, only to 45c, a couple of times, during daylight hours, each day.

The 2nd thermostat, on the Hot Water tank, controls the electrically powered immersion heater,  it is set to 70c. We do a sterilisation heat, using the Immersion heater, between 02:00 and 04:00hrs every day. It takes around 1 hour to heat the water to 70c.

The outcome: We have maintained our protection from Legionella, and have roughly halved our gas bill.

There is a bit more to this story... What follows is not necessary to achieve the costs savings, but is has provided us with the re-assurance that we are sufficiently heating the water at night, to kill legionella. 

We have a large Solar array system with home battery. In addition, we have a device from a company called "myenergi", called an "eddi". This device can be programmed to take excess electricity from the solar array - to heat hot water - evident in the below chart, at around midday. Crucially, the eddi can also be programmed to heat hot water, at specific times of the day e.g. when the Octopus Go tariff is only charging us £0.05 p/Kwh. You can see on the chart, it starts to heat our hot water at around 02:00hrs each day, after an hour or so, then tops up the heat every 30 minutes or so, until 04:00hrs - as needed - to maintain 70c.

There is a trade-off of course.. You are spending a little bit extra on electricity, to save a huge amount on gas.

For the general public, I think there might be a wider application here.. An Immersion heater with timer, costs around £20 (e.g. from Screwfix), plus the fitting cost (?). Even if people are not on an electricity tariff with cheaper electricity rates at night - I suspect there is still money to be saved. 

It might be worth pointing out that, in my very limited experience, not many people seem realise that domestic appliances, e.g. dish washers, washing machines, only use the cold water feed - not the house's hot water supply. We mainly use hot water for washing ourselves - it is not advisable to shower in 70c water  
Sincerely hopes this might help someone in these difficult times.

Links I would liked to have been able to post, which formed part of our research, but am too new to the forum presently!

(https)/www.danfoss.com/en/about-danfoss/our-businesses/heating/knowledge-center/knowledge-articles/how-to-reduce-the-risk-of-legionella-contamination-in-domestic-hot-water-systems/
(https)/www.hse.gov.uk/healthservices/legionella.htm#:~:text=Using%20temperature%20control,60%C2%B0C%20or%20higher
(https)/www.moneysavingexpert.com/utilities/energy-saving-tips/
(https)/www.screwfix.com/p/lap-digital-immersion-timer/1804r

Mstty

Hell and welcome

With electricity for most at 28p+ per kWh without an economy 7/10 tariff or the one you are on which now needs proof of an Electric Vehicle I wonder if the savings work out?

I thought you only have to heat your tank to over 60oC once a week but I could be wrong.

FreeBear

nick257 said: The first, of two thermostats on our Hot Water Tank, controls the water temperature when heated by gas. It is now set to 45c. It was previously set 70c , which is the situation I suspect 99% of householders with hot water tanks are in. We heat the water with gas, only to 45c, a couple of times, during daylight hours, each day.

First off, the risk of Legionella in the UK is very small. Second, any temperature over 60°C is sufficient to kill the bacteria in minutes - There is no need to go to 70°C. You can even go down to 50°C and maintain that temperature for an hour or two to kill the bacteria.

Swipe

You are wasting your time. It takes weeks for legionella to develop and then that would only be in standing water. If the tank is getting run off most days then you have no worries. I'm really not sure why it's always over stated on this forum.

Lemonjuiced

Would it not be cheaper to heat your tank with gas only since that is much cheaper than electric?

Benny2020

With a large solar array there should be no need to heat hot water with gas, it should all be done with free electricity.
My 4kwp gives me over 300 days a year of hot water for free, today 6.15kwh went in.

QrizB

Lemonjuiced said:

Would it not be cheaper to heat your tank with gas only since that is much cheaper than electric?

Possibly not for the OP, or for me; we're both on a legacy tariff where off-peak electricity is currently cheaper than gas.

For almost everyone else, yes.