immersion heater or gas boiler for hot water?

sheldon128

Hi - my builder reckons it is cheaper to use my immersion heater for hot water than use my gas boiler. Previously I'd been told that immersion heaters were very expensive. Can anyone advise?
Thanks very much, S

HappyMJ

If you have an E7 supply then it's cheaper to use it (timed at night) in summer as long as you use no gas whatsoever and do not have standing charges on the gas so you get a NIL bill. Otherwise in most 90% of cases it's cheaper to use the gas all year round and not be on an E7 tariff.

dogshome

Depends on circumstances, but the answer is probably NO

If you have a Hot Water tank with an Immersion Heater, chances are you don't have a Combi boiler that produces hot water on demand, and your boiler cooks up Hot water and stores it in the (hopefully well insulated?) tank.

With a family wanting showers/baths, the boiler will provide a complete tankfull of Hotwater - Working out the cost of this is complex - With no heating on and a cold tank, you programme the boiler for Hot Water only and read the gas meter, then when the very bottom of the tank feels warm you read the meter again.
The meter units used are converted to Kwh - Appx 11.2Kwh for a Metric meter or 31.5Kwh for an Imperial meter - at a present cost of 4pence per Kwh, BUT the boilers heat is indirectly applied to the Hot Water so it's not 100% efficient

The Immersion Heater only cooks water at the Top of the tank - Probably enough for 2 quick showers or a shallow bath - But costing it is easier.
The Immersion has a label saying what power it is, usually 2.5 or 3Kwh. The present cost of an electric Kwh is around 13pence, so having a 3kwh Immersion running for half an hour will cost 20pence, BUT the Immersions heat is applied directly to the water and is almost 100% efficient

You will have to do the trials in your own home, but the likely hood is that for a just one person household, the Immersion may be cheaper

All this presumes that you are not on an ECO7 meter, which with gas heating/water you almost certainly should not be

ian103

My response on another post about how to run the heating has got me thinking about how we heat our hot water now.

We are now on oil, it is a conventional system, we heat the water via the oil fired boiler (I know we have a tank of hot water that we don't always need but no way round that) would I be better using the imersion heater or the boiler? Gut feeling is it probably makes no real difference but now thinking about it.

Ben84

I worked out a while ago that even at 60% efficiency, our boiler made hot water for a lot less than the cost of electricity. We had fairly average gas and electric prices at the time, about 3p per kWh for gas and 12p for electricity.

If you know your boiler efficiency, for example 60%, divide 100 by that, then multiply it by the cost of gas per kWh, then compare directly to the cost of electricity per kWh (electric is basically 100% efficient so no need to convert to account for losses).

You may be able to save a bit more during the summer by not using the pilot light, but it's unlikely to change things notably. Leaving it lit reduces the chances of it clogging up with dust as well I found.

Pincher

Take meter readings everyday at the same time.

Try the immersion for a week, and then gas another week.

Ben84

Pincher wrote: »

Take meter readings everyday at the same time.

Try the immersion for a week, and then gas another week.

Having tracked my energy use weekly for a couple of years, I find that at least in our household, energy use varies a lot. Enough I'm sure to mask the effects they would be hoping to see.

Pincher

Ben84 wrote: »

Having tracked my energy use weekly for a couple of years, I find that at least in our household, energy use varies a lot. Enough I'm sure to mask the effects they would be hoping to see.

It is perfectly possible to be more targeted by adding an energy monitor if you want to bother. Taking meter readings costs nothing, and I suspect it was just idle speculation from the OP, so even that would be too much hassle.

C_Mababejive

Its a no brainer..the gas is almost always cheaper and why? Because gas is a primary fuel whereas electricity is a secondary duel i.e you have to burn a fossil fuel such as gas to generate electricity. When people say electricity is 100% efficient,they are not being very accurate.

Ben84

C_Mababejive wrote: »

Its a no brainer..the gas is almost always cheaper and why? Because gas is a primary fuel whereas electricity is a secondary duel i.e you have to burn a fossil fuel such as gas to generate electricity. When people say electricity is 100% efficient,they are not being very accurate.

I calculated that at my gas and electric prices, my boiler would have to be transferring the energy from the gas flame to the water in the tank at ~24% efficiency to cost as much as using electricity. I don't think there's any boiler that could be considered functional which is that inefficient.

So, although it doesn't give exact figures for your household, it's worth calculating how efficient (or more likely inefficient) your boiler would need to be to match the cost of electricity at your prices. For typical energy prices, the answer should be very inefficient, so much so you should be able to say with good certainty that gas is the cheaper option.