Shower mixer taps, combi boiler

sevenhills

Just thought I'd share my experience of running my shower from my gas combi boiler.
When I was considering my options, some didn't think it would work, because an electric shower is the norm. I don't have any problems.

https://www.bigbathroomshop.co.uk/info/blog/faqs/is-it-cheaper-to-run-an-electric-or-mixer-shower/#:~:text=Considering the price of gas,than an electric shower system.

Reed_Richards

Is an electric shower the norm? 

I followed the link but could not find any information of significance.

sevenhills

Reed_Richards said:

Is an electric shower the norm? 

I followed the link but could not find any information of significance.

I think electric showers were certainly the norm, more choice available now, but more expensive.

QrizB

Glad to know everything worked out for you, but I'm not surprised that it did.

sevenhills said:

When I was considering my options, some didn't think it would work, because an electric shower is the norm. I don't have any problems.

I don't know who these "some" are, but a combi boiler is specifically designed to supply instantaneous hot water.

Reed_Richards said:

I followed the link but could not find any information of significance.

I had the same experience as R_R. Is there more to the article than the two sentences plus one comment-and-reply that I can see?

sevenhills said:

I think electric showers were certainly the norm, more choice available now, but more expensive.

Electric showers are relatively common for properties that don't have wet central heating (my parents had one) but they've got a mixer shower with their combi boiler now.

EricMears

QrizB said:

I don't know who these "some" are, but a combi boiler is specifically designed to supply instantaneous hot water.

When combi boilers were first introduced,  hot water flow rates were usually pretty pathetic - hence the reliance on electric showers.  Modern boilers are much better but I guess people installing them are relying on their many years of experience rather than checking the actual specs !

70sbudgie

The comments on the article are 9 months old. Considering what has changed this calendar year, I would suggest that the advice is not sufficiently up to date.

QrizB

70sbudgie said:

The comments on the article are 9 months old. Considering what has changed this calendar year, I would suggest that the advice is not sufficiently up to date.

Calcs for the current cap (copied from here):

QrizB said:

We've been discussing the cost of a shower over on the Energy forum recently (here and here).

Instantaneous electric showers range from 7.2 to 10.5kW. Assuming you spend five minutes in a 9kW shower, you will use around 0.75kWh:

• Typical E7 night rate, 20p/kWh - 15p
• Single rate, 28p/kWh - 21p
• Typical E7 day rate, 36p/kWh - 27p

Electric showers flow around 5 litres per minute, so a 5-minute shower will use 25 litres. At £3 per cubic metre (0.3p per litre) that's another 7.5p. (For a given shower temperature, lower-powered showers use less water; higher-powered ones use more water.)

Mixer showers tend to use more water, roughly double - around 10 litres per minute, so a 5-minute shower will use 50 litres of water. Heating 50 litres of water from 10C to 40C will take 1.75kWh.

• Gas: 8p/kWh, shower costs 14p.
• Oil or LPG: 10p/kWh, shower costs 17.5p.
• E7 night rate: 20p/kWh, shower costs 35p.
• Single rate: 28p/kWh, shower costs 49p.
• E7 day rate: 36p/kWh, shower costs 63p.
  

Plus 15p for 50 litres of water.

Baths vary in size, but Bathbarn suggest that a typical one holds 100 litres, double the volume calculated for a mixer shower above. Thet's roughly what mine takes too.

Heating 100 litres of water from 10C to 40C will take 3.5kWh.

• Gas: 8p/kWh, bath costs 28p.
• Oil or LPG: 10p/kWh, bath costs 35p.
• E7 night rate: 20p/kWh, bath costs 70p.
• single rate: 28p/kWh, bath costs 98p.
• E7 day rate: 36p/kWh, shower costs 126p.

Plus 30p for 100 litres of water.

I'll be happy to revisit these calcs in a week or two once the new capped rates are published.

sevenhills

QrizB said:

Mixer showers tend to use more water, roughly double - around 10 litres per minute, so a 5-minute shower will use 50 litres of water. Heating 50 litres of water from 10C to 40C will take 1.75kWh.

Baths vary in size, but Bathbarn suggest that a typical one holds 100 litres

Heating 100 litres of water from 10C to 40C will take 3.5kWh.

Mixer showers use both hot and cold water, so they might only be heating 40 litres.
If a bath holds 100 litres, a typical bath might use 40 litres.

QrizB

sevenhills said:

QrizB said:

Mixer showers tend to use more water, roughly double - around 10 litres per minute, so a 5-minute shower will use 50 litres of water. Heating 50 litres of water from 10C to 40C will take 1.75kWh.

Baths vary in size, but Bathbarn suggest that a typical one holds 100 litres

Heating 100 litres of water from 10C to 40C will take 3.5kWh.

Mixer showers use both hot and cold water, so they might only be heating 40 litres.

Thermodynamics says it makes no difference.

If your shower puts out 10 litres a minute for 5 minutes, your mains is at 10C and you want a 40C shower, it makes no difference whether you heat all 50 litres to 40C or you heat 40 litres to 47.5C and mix in 10 litres of cold at 10C, or 30 litres to 60C and add 20 litres of 10C cold.. The energy required is the same.

sevenhills said:

If a bath holds 100 litres, a typical bath might use 40 litres.

From the link:

So, how many litres of water are in a bath like this you might ask? Even though their full capacity is around 180 litres, people rarely fill the bathtub all the way to the top. Therefore, since most people usually fill it about halfway, it uses about 100 litres. This is roughly the same amount as showering for 10-15 minutes.

Solarchaser

QrizB said:

70sbudgie said:

The comments on the article are 9 months old. Considering what has changed this calendar year, I would suggest that the advice is not sufficiently up to date.

Calcs for the current cap (copied from here):

QrizB said:

We've been discussing the cost of a shower over on the Energy forum recently (here and here).

Instantaneous electric showers range from 7.2 to 10.5kW. Assuming you spend five minutes in a 9kW shower, you will use around 0.75kWh:

• Typical E7 night rate, 20p/kWh - 15p
• Single rate, 28p/kWh - 21p
• Typical E7 day rate, 36p/kWh - 27p

Electric showers flow around 5 litres per minute, so a 5-minute shower will use 25 litres. At £3 per cubic metre (0.3p per litre) that's another 7.5p. (For a given shower temperature, lower-powered showers use less water; higher-powered ones use more water.)

Mixer showers tend to use more water, roughly double - around 10 litres per minute, so a 5-minute shower will use 50 litres of water. Heating 50 litres of water from 10C to 40C will take 1.75kWh.

• Gas: 8p/kWh, shower costs 14p.
• Oil or LPG: 10p/kWh, shower costs 17.5p.
• E7 night rate: 20p/kWh, shower costs 35p.
• Single rate: 28p/kWh, shower costs 49p.
• E7 day rate: 36p/kWh, shower costs 63p.
  

Plus 15p for 50 litres of water.

Baths vary in size, but Bathbarn suggest that a typical one holds 100 litres, double the volume calculated for a mixer shower above. Thet's roughly what mine takes too.

Heating 100 litres of water from 10C to 40C will take 3.5kWh.

• Gas: 8p/kWh, bath costs 28p.
• Oil or LPG: 10p/kWh, bath costs 35p.
• E7 night rate: 20p/kWh, bath costs 70p.
• single rate: 28p/kWh, bath costs 98p.
• E7 day rate: 36p/kWh, shower costs 126p.

Plus 30p for 100 litres of water.

I'll be happy to revisit these calcs in a week or two once the new capped rates are published.

That's really helpful QrizB, I've been trying to think if a way to work out how much each thing costs unitarily,  and your blow by blow makes it really easy to just sub in my own figures. 

Thankfully no water charge north of the border, and typically the family take about 15 mins in the shower, but as I said I can sub in my figures using yours as a baseline, so thanks, very helpful