The main costs involved in washing yourself relate to the cost of heating water and bathing uses a lot of hot water. Gas, electricity, solar energy or solid fuels like coal can all be used to heat water in the domestic environment. Solar water heating and solid fuels are considered in more detail in separate articles. To make the camparison between deep and shallow baths only gas and electric immersion heating are considered.
There is a wild variation in bath size, preference on how full you like to have a bath, the temperature of the water you prefer and indeed the temperature of the water coming into your property. All of these factors will influence how much it costs you to have a bath. The examples shown below are a 100 litre, a 150 litre and a 200 litre bath volume with a bathing temperature of 40oC and an incoming water temperature of 10oC. 100 litres would be a relatively shallow bath and 200 liters quite deep for most of us.
| Bath Size | Cost of a Single Bath | Cost of a Bath a Day for a Year | ||
| Modern Gas Boiler | Electrical Immersion Heater | Modern Gas Boiler | Electrical Immersion Heater | |
| Small (100 litre) | 18 pence | 53 pence | £ 65 | £ 194 |
| Medium (150 litre) | 27 pence | 80 pence | £ 98 | £ 291 |
| Deep (200 litre) | 36 pence | 106 pence | £ 130 | £ 388 |
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Different bath volumes and the indicatice relative costs of these, with electrical and gas water heating |
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The conclusion is obvious here if you can avoid it do not use an immersion heater to heat your bath water, it is expensive, although there are immersion heaters that operate on ecomomy 7. It is also clear that you could save maybe £ 50 or £ 100 a year by just having shallower baths, difficult to do in the cold winter months!
T1 = temp of cold water (K), K is Kelvin
T2 = temp of hot bath water (K)
V = volume of bath water used (litres)
S = specific heat capacity of water = 4.18 J/cm3/K
energy to heat the water is therefore
Ej = S*(T2-T1)*V*1000 the 1000 to get units in Joules
to factor in boiler efficiency (Beff in percent, 90% probably)
Eb = Ej (1 + (100-Beff)/100)
1 kWh = 3600000 Joules
convert to kWh
Eb (kWh) = Eb/3600000
cost to heat bath per bath = Eb (kWh) * Cost per kWh
Can you show your calculation so that I can add the rate I am buying gas from my provider to see what a bath costs !
Rees
perhaps I should add this date to each calculation?
All the best
richard