Using electric water heater

Pat38493

With the changes in price for energy, especially gas, that are coming in April, could it make sense in summer to use the backup immersion heater to heat my water rather than gas?

GingerTim

Heating water with electricity will always be more than expensive than gas, even with the price rises.

mumf

We are all electric,and providing you set your timer for the appropriate length of time ( on for long enough- not too long,if you get my drift) then it’s not that dear. The reactions here to the gas vs electric water heating do make me smile. 

QrizB

There are some *very* niche cases where electrical water heating makes sense.

For example, some of Octopus's current EV tariffs offer overnight electricity at 7.5p/kWh. That could be cheaper than gas at 7p/kWh, once you allow for the increased efficiency of electric heating vs. gas.

And for those on EDF's EV tariff and getting power at 4.5p/kWh, it definitely makes sense to use that to heat water too.

jbuchanangb

I do wonder about this. In the summer my primary means of heating water is solar thermal, then I can choose electricity or gas for the backup source. Last summer it would use about 3kWh of gas on the days when the system cut in to heat the tank. About 10 pence. With this year's tariff the same 3kWh will cost 22p. But 3kWh of electricity would cost 84p. In the 3 months July, August, September I used 90kWh gas. So I will stick with gas. In the previous year, before solar thermal was installed, I used 3820kWh gas in July, August September. So in 2021 the solar thermal saved me £116, and this year it should save me £274 just for the 3 months of the summer. 

snigehere

If you have solar electric you can also fit an "iBoost" gadget - this will divert solar energy that would otherwise be exported to heat your hot water via the emersion (as long as you have a hot water tank rather than on demand hot water)

justtinw

Hi all. I am interested to see which would better in my example. Electric vs Gas? Am I right in assuming 80% efficiency for a boiler?

I have an EV tariff with 6pkwh electric, or gas rate of 4.3pkwh.

Its a new boiler (therefore I assume quite efficient) and heats the same tank. View on which I should use? If there is little in it, I would prefer to use electric as I am on a green tariff.

QrizB

justtinw said:

Hi all. I am interested to see which would better in my example. Electric vs Gas? Am I right in assuming 80% efficiency for a boiler?
I have an EV tariff with 6pkwh electric, or gas rate of 4.3pkwh.

At the moment, I'd stick with gas.

Is your gas tariff variable? Will it be rising to a little over 7p/kWh in April? If so, then would be a good time to switch to electric heating on your EV tariff.

BUFF

if it's a modern condensing (& properly set up to do so) boiler  heating a hot water tank then you should get over 90% efficiency (probably 92-94%).
Electric should be 100% efficient.

At 6p & 4.3p your electricity is ~40% more expensive per kWh than your gas.
If you assume the worst case scenario of gas being "only" 90% efficient then your electricity would need to be ~4.8p/kWh for parity. So, heating your water by electricity is likely 25% dearer than gas.

coffeehound

BUFF as soon as the water in the tank reaches a point where the return water is >55 ℃, the boiler won't be condensing anymore.  It will vary by installation but perhaps mid-40s tank temperature?  Therefore a middle way could be to heat to 45 using gas, and then top-up to 60 using the immersion

coffeehound

One could follow this procedure

 - Fit a temperature sensor to the primary return pipe to the boiler.
 - Start the DHW heating cycle
 - When the temperature of the return pipe reaches 54 ℃, turn down the DHW tank's thermostat until it just switches off.
 - Set immersion to come on during the off-peak rate with t-stat = 60 

That would roughly stop the boiler trying to heat the DHW beyond its condensing mode.  It would need to be repeated if anything such as the boiler flow temperature or pump speed were altered, though.