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We cover here only spontaneous water heaters, they are generally fueled by either natural gas or electricity, however there are some units on the market using LPG, especially for caravan applications there are units that use butane or propane in gas cylinders.

There are single point and multipoint heaters, the difference simply being whether hot water is supplied to one point or to a number of points in the accommodation. Regardless of this the economics of running a unit is governed only by how much hot water you use, the temperature of the water and the fuel used to heat it. The initial cost of the unit is also important, costs vary greatly and the price depends on the application.

The table below shows the cost of using 1000kWh, 3000kWh, 5000kWh and 7000kWh each year to heat water with three common energy sources for instantaneous water heaters, electricity, gas and LPG. 5000kWh is the average used by a family in the UK each year for hot water (All fossil fuel systems are assumed to be 90% efficient).

Cost of instantaneous hot water and corresponding CO2 emissions with three sources of heating energy.
1000kWh 3000kWh 5000kWh 7000kWh
Electricity £187
Gas £43.333
LPG £77.778

The graph below shows more fuels and assumes 5000kWh is used each year to heat water in a family home (All fossil fuel systems are assumed to be 90% efficient). It is unlikely that some of these fuels would be used in this way but they are included to illustrate how expensive they are. The graph is only accurate in the UK but I would imagine other regions would find costs similar.

Different fuel prices per kWh

The difference between the cost of electrically heating and gas heating is huge, and careful consideration should be made before deciding to buy an electric water heater. Electrical water heaters are usually cheaper but the price difference will probably pay for itself in running cost savings in a year. You may consider solar water heating but the numbers may not stack up in the UK, please have a look at this article. Solar hot water make a lot more sense in warm countries.

Solar Hot Water...

Clearly gas cylinders are very expensive but there is little choice in a caravan, apart from staying in a hotel instead!

Comments and Questions

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Mr - Andy Frame  2014-09-23 10:12:05

We have recently moved into a 3 bedroom terraced house that currently has no gas supply. We have an old immersion heater with a cold tank in the loft and Economy 7 storage heaters downstairs, with electric radiators upstairs. Our plan is to install electric under floor heating downstairs and in the bathroom ( with a view to including the bedrooms later). We don’t have the space for a wet system and couldn’t really deal with the upheaval.

We want to have hot water on demand for the kitchen sink and toilet hand basin on the ground floor and the bath, shower and hand basin on the 1st floor

We have been offered free connection to the gas network.

As I see it we have three options:

1. Connect to gas and have a small combi boiler fitted in the loft.
2. Install instant water heaters in the kitchen, downstairs toilet and bathroom (Single phase electrical system).
3. Refurbish/replace immersion heater and install a pump for the shower.

Are there any options that I’ve missed? Any advice about which way to go would be greatly appreciated.

Many thanks,
reply - rdh  2014-09-23 18:59:42
Hi Andy

That is quite a mix. I’m not sure where to start. First are you completely certain you have no space for a wet system? I guess you want to avoid radiators, if you have little space I can see that.

Sounds like your balance of options depends on space, upheaval, capital cost and running cost.

Electricity is more expensive than gas as you know, but capital outlay for gas equpment is expensive, but so is underfloor. if we assume 10p/kWh for a mix of economy and standard rate electric and 5p/kWh for gas then per year I guess you will spend the following on hot water.

10p/kWh x 5,000 kWh = £500 electric per annum (£750 if only standard rate)
5p/kWh x 5,000 kWh = £250 gas per annum

A fitted combi will cost a lot and if you do not use it for heating it seems expensive, however one source of hot water is great if you have all the plumbing in place already for hot water. Perhaps you could get a combi and a few radiators in the house, where space is less important (somewhere to dry the towels!)

Immersion heaters are expensive on standard and economy.

In terms of hot water generally I’m a great believer in a mix. we have a combi and an electric shower, and when our combi packed in in the coldest winter a few years ago we a least could still have a hot shower. Just another thought for the mix.

Not sure if that helps.


Cost of heating water using different fuels - Toby Morrhall  2012-04-01 03:15:12
Congratulatiions on a fantastic site, what a wonderful source of excellent comparative costs, so useful, thank you. Please could you add the cost of fuel oil to the above table, its the only thing missing.Thanks again,Toby