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Comparing the costs between deep and shallow baths with gas and electric immersion heating.

differnce in cost of shallow or deep bath
 Energy Saving:  700 - 1400 kWh each year
 Money Saving:   £27.3 -  £261.8 each year
 CO2 Saving:  147kg - 513.8kg each year
 Comment:  Have shallower baths and consider how you heat water
 Energy range that could be saved with this measure.
 Money Savings range you could have employing this measure.
 Carbon Dioxide emission range that could be saved with this measure.

How much does it cost to have a bath?


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 comparison 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.

Cost of a single bath with different bath volumes, with electrical and gas water heating and associated CO2 emissions.
Modern Gas Boiler Electrical Immersion Heater
Small (100 litre) £0.17
(0.7kg)
£0.725
(1.3kg)
Medium (150 litre) £0.255
(1.1kg)
£1.087
(1.9kg)
Deep (200 litre) £0.34
(1.5kg)
£1.448
(2.6kg)
Cost of a bath a day for a year with different bath volumes, with electrical and gas water heating and associated CO2 emissions.
Modern Gas Boiler Electrical Immersion Heater
Small (100 litre) £62.089
(267.5kg)
£264.631
(467.4kg)
Medium (150 litre) £93.125
(401.2kg)
£396.909
(701.1kg)
Deep (200 litre) £124.107
(534.6kg)
£528.959
(934.3kg)

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 considerably by just having shallower baths, more difficult to do in the cold winter months!

Comments and Questions

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Displacement - Stephen Phillips  2016-05-26 17:29:01
Do your bath volumes allow for occupant displacement?

I displace well over 100 litres; my wife and teenage son each well under 50 litres.

So my "full to the overflow" quite deep old cast iron bath is not much over 100 litres of hot water - a fact cross checked by our 117 litre hot water tank needing to be run to cold but not much more to fill it from only the hot tap.

How much extra energy do I use to warm up old thick cast iron compared to modern plastic? Non-trivial I think.
combi boilers - Riley  2013-02-28 13:25:53
we had the old sytem, gas boiler heating hot water tank and radiators. New system meant siting new boiler in utility, heating is much improved, BUT hot water system in quite inferior to old system. I could;nt recommend this new hot water system to anyone!!!
combi boiler settings - Donald  2012-10-07 17:41:12
Hi, am having a combi boiler fitted, wonder what the average boiler hot water temperature range should be to give a comfortable bath/ shower, as have a old system with copper hot water cylinder at present. thanx for any info
Calculation - Rees  2012-01-08 17:38:02
Hi interesting article ! 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
Calculation - Richard  2012-01-11 14:49:32
does this help?? 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
Please Specify when the calculations were done - Peter Bolton  2011-02-22 19:48:04
given the ever changing (always increasing!) cost of gas and electricity, can you add a note to show when these calculations were done.
when were the calcs done - Richard  2011-02-28 14:24:49
All the calculations on this site are based on one variables file which is updated each year. The last update was in May 2010. All the calculations on the site will change when this file is updated in a few weeks. The current rates are shown on the home page in the bar chart, this is also updated in the same way. perhaps I should add this date to each calculation? All the best richard