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Is immersion heating as efficient as the gas boiler for heating the water? I'm trying to work our solar savings...

  • 12 March 2023
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We have recently had solar pv fitted, with iBoost on the hot water tank to use any generation excess.

I am trying to get a figure for the savings made by using the solar pv to heat the hot water rather than the central heating gas boiler. There is a 3-way valve to control rads & hot water separately. This raises the question:

Does 1 kWh of immersion heating produce roughly the same amount of hot water as 1kWh of a gas boiler heating the water? I realise it will not be identical due to efficiencies and losses, but are they similar?

I hope to be able to compare costs of heating hot water by pv or gas, ie loss of SEG payment vs gas rate.

Then I will know the savings to be made.

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Best answer by M.isterW 12 March 2023, 19:05

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M.isterW
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The immersion heater is 100% efficient so 1kWh of electricity will create 1kWh of heat.

Your gas boiler is probably about 90% efficient (possibly a bit less, depending what temperature you have your hot water) so 1kWh of gas creates 0.9kWh of heat.

 

1992 4 bed detached house. Solar PV + battery, Mitsubishi Ecodan ASHP and i-life2 fan assisted radiators.
M.isterW
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The immersion heater is 100% efficient so 1kWh of electricity will create 1kWh of heat.

Your gas boiler is probably about 90% efficient (possibly a bit less, depending what temperature you have your hot water) so 1kWh of gas creates 0.9kWh of heat.

 

I've just realised, you're going to lose some heat in the pipes so your gas efficiency will be less. You might be better using 85%.

1992 4 bed detached house. Solar PV + battery, Mitsubishi Ecodan ASHP and i-life2 fan assisted radiators.
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@M.isterW Thanks - I thought it would be something like that.

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