Water heating costs v electric shower?

sabian2014

I have a really random question, which I wish I could work out myself...but can't!
There are 5 people in our house, and we all use an electric shower every day. It is probably used for about 10 minutes each and is a 7.5 kW shower.
I am considering changing to a standard shower running off the water supply using the hot water tank. The gas boiler is quite new (2 years old and quite efficient) and the water tank is also new and therefore well insulated.
My question is what is the cost of using the electric shower compared to the other method, assuming I had to put the water heater (via the boiler not an immersion) on for an extra hour per day to cover the shower usage?
If anyone can help, I would be very grateful, I did see one figure quoted that a 7.5 kW shower costs around 19 pence for a 10 minute shower. I just don't know how to estimate the cost of heating the water via the boiler

lstar337

Without bothering to work it out, I can tell you that the electric shower will cost significantly more.

Electric is 3x the cost of gas.

molerat

Gas is less efficient at heating water than electricity but only costs about 1/4 - 1/3 of the price.

50 mins of electric showering will cost around .83 x 7.5 x 13p = 81p
Your boiler will probably use less than 1/2 metric unit in an hour so .5 x 11.2 x 4p = 22p. Even if it uses double it will still be cheaper.

Owain_Moneysaver

Simply, gas is about one-third the cost of peak rate electricity, per kWh. As your boiler and cylinder are new-ish there shouldn't be significant losses.

However a shower from the hot water cylinder may deliver several times the water (litres per minute) than the electric shower. The cost per litre will be less; the cost per actual shower may be about the same - or if it's a 'deluge' or pumped shower a lot more.

An 'eco' water-saving shower head from the gas boiler is probably the best overall combination.

macman

However, factor is the cost of changing the shower and it could take you a couple of years to recover the capital cost in energy savings. If you are thinkng of upgrading it anyway (a 7.5kWh shower is quite a low rating these days), then fine.

nigelpm

Plenty of factors in this and it's not as simple as gas being cheaper than electricity.

For example you may be using an immersion to "top up" your HW cylinder and unless you use all of your hot water in the cylinder there'll be wastage where as an electric shower is close to being 100% efficient in that all energy used to heat the water gets used immediately.

lstar337

nigelpm wrote: »

For example you may be using an immersion to "top up" your HW cylinder

Who in their right mind does that?

The immersion should stay off, unless there is an emergency such as boiler break down.

nigelpm wrote: »

and unless you use all of your hot water in the cylinder there'll be wastage where as an electric shower is close to being 100% efficient in that all energy used to heat the water gets used immediately.

They have a modern boiler and well insulated tank. Any hot water not used simply stays in the tank until it is needed. Efficiency differences and losses will not make up for the cost difference between gas and electricity.

The only additional cost to consider is the cost of upgrading to a mixer shower.

nigelpm

lstar337 wrote: »

Who in their right mind does that?

The immersion should stay off, unless there is an emergency such as boiler break down.

They have a modern boiler and well insulated tank. Any hot water not used simply stays in the tank until it is needed. Efficiency differences and losses will not make up for the cost difference between gas and electricity.

The only additional cost to consider is the cost of upgrading to a mixer shower.

I can think of a couple immediately off the top of my head:

1) Anyone with a solar diversion
2) If they've drained the tank and need some hot water then switching the immersion on for 30 mins may well be cheaper than firing up the boiler from cold.

nigelpm

lstar337 wrote: »

Efficiency differences and losses will not make up for the cost difference between gas and electricity..

Sure but that wasn't my point.

My point was that you can't just say gas costs 4.5p, electricity 13.5p so it's 3x cheaper to use gas to heat hot water.

It just isn't that simple.

sabian2014

Wow, thanks for all the replies! The cost of installing a mixer shower would be offset by the fact that because we live in a hard water area, I am currently replacing the electric shower about every 2 years, not to mention shower heads! Therefore I have spend £100s over the years on electric showers. I don't think we would have the same issues with a mixer shower...hopefully.

lstar337

nigelpm wrote: »

Sure but that wasn't my point.

My point was that you can't just say gas costs 4.5p, electricity 13.5p so it's 3x cheaper to use gas to heat hot water.

It just isn't that simple.

Maybe not, but all those little points are trivial when the basic cost is taken into account. They are so insignificant compared to the gas/electric price difference that they can be ignored.

Why bother to mention them when the result is still the same.

That was my point.