Looking to fit a Power Shower - enough hot water?

[blued]

I'm looking at installing a power shower above my bath to replace the current electrical one. I have a gravity fed system with a cold water tank in the loft and a hot water tank in the cupboard next to my bathroom. It's a 117 litre tank.

A friend recommended I get a salamander pump and I've seen this one.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=280306860226

Worst case scenario 3 people could need to have a shower one after the other. According to this site - http://www.uswitch.com/water/how-much-water-use/ - a power shower will use 80 litres of water. However at 30 litres/min (the max for the pump) I'm sure that's not accurate even if the pump isnt on full blast? I tend to spend about 10 mins in the shower and the other 2 would be between 5 and 10 mins each. Some cold water would be mixed in but I still think my tank is going to empty very quickly without the chance to reheat.

Currently during the winter the hot water heater comes on with the gas central heating for about an hour in the morning and then again at various points during the day/evening depending on when we're in. There is always hot water. In the summer I time the hot water to come on for 30 mins in the morning and 30 mins in the evening (about 5ish) and again always have hot water. I've not used the immersion in the 3 years I've been there. My brother switched it on once recently and I nearly burned myself when I ran the hot tap!

So my question is if the immersion was switched on when the first person went for their shower would this keep the water hot for all 3 showers? Or could I leave the gas water heater on for the duration?

Sorry for the long post, hope someone can offer some advice.

 

[JohnD]

So my question is if the immersion was switched on when the first person went for their shower would this keep the water hot for all 3 showers?

No it would not. An immersion heater usually has about 3kW of power, your boiler probably has 15 or 20kW so will heat the cylinder far faster. It make take 20 mins or so to heat the cylinder from cold (try it). The immersion heater will take far longer.

A power shower can easily use all the hot water in your cylinder in a matter of minutes. The cylinder probably contains in the region of 100 litres of hot water. Provided the cylinder and the pipes from the boiler and cylinder are well insulated, the boiler will stop firing once the cylinder is up to temp, so will not waste fuel even if you alter the timer.

If the immersion heater makes the water scalding, the thermostat under the cap need adjusting or replacing.

 

[blued]

Thanks for the info.

ok so I can continue to forget about the immersion. I actually put tape on it after it was used that time because I thought it to be unnecessary.

I probably dont have a proper understanding of how it works but here goes.

• Water heater clicks on before anyone wakes up and heats tank to temp X and then clicks off.
  First person showers so hot water begins to be used
  Hot water tank begins to fill with cold water
  Boiler clicks on and heats as cold water fills

Would the boiler heat it fast enough or should I stick to an electric shower becuase at times 3 people may need to shower in a row? When I say in a row there would be about 3-5 mins between each shower now I think about it.

 

[JohnD]

I would suggest you provide a non-power-shower, or perhaps use a tiny shower head that doesn't deliver much water. Otherwise if the first person is inconsiderate he might drain the cylinder, and the next user will have to wait 20 minutes or so (but 10 mins would give a modest shower before running cold). If you can train the users to have their breakfast or something while it is re-heating it may be OK. Or maybe have a 5-minute electric timer on the shower pump that can only be operated from outside the bathroom.

An electric shower gives a very feeble flow compared to a cylinder (especially during winter when the incoming water is colder)

 

[blued]

Thanks for the fast reply.

I currently have a shower mixer that comes from my bath taps. The pressure from this seems to be less than the electric shower I have so I assume a non power shower would act in the same way?

I'm not sure what rating my electric shower. Its a Triton and I cant remember the model off hand. If for example it was an 8.5KW would I get much of an increase in pressure by fitting a 10.5KW? I'm assuming from what you say about the electric being more feeble in the winter that by using a higher rating it will heat the water quicker and allow the water to flow faster?

 

[JohnD]

A non-power shower would be similar flow to your bathtaps one. You might improve it by running dedicated pipes from the cylinder and cold tank; or by raising the cold tank on a platform in the loft to increase head. I do not know if you can get a shower pump where you can turn down its output to avoid draining the cylinder so quickly.

A more powerful electric shower will not increase the pressure or flow (that is limited by the water main) but will make the water a bit hotter. You may need to have a new cable and/or MCB fitted if the old one was sized for a smaller load.

A combi gas boiler gives a better shower than an electric shower, as it heats up the water instantly by 30kW or so. It is possible to have a hot cylinder even though you have a Combi, although some plumbers will not be familair with this. A Cylinder is much faster to fill a bath because the stored water is already heated. A ordinary combi is generally only suitable for running one hot outlet (shower, bath or sink) at a time.