Power Showers, Water Usage and Immersion Heaters

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. So nearly 70% of the tank gone. The tank only holding half of what's needed for 3 showers.

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? Also would it be cheaper to use the immersion instead of the gas? I've heard of people advising to leave the immersion on ALL the time. If this was done what effect would it have when the hot water comes on with my boiler? I cant have central heating alone, it has to be hot water heater and central heating.

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

brig001

I think you will struggle. Our old shower could use 25 litres per minute, so you might get five minutes using that system. It also needed 50kW of heat, so switching on a 3kW immersion heater really won't make much difference. You could try with the hot water on and the immersion heater on, but I still think you will have to leave a few minutes between showers or risk a cold one. Obviously, all showers are different, and you don't need the water on full, but I still think you will need more stored heat if you want to have three x five minute showers one after the other.

blued

Thanks for the info. Looks like its back to the drawing board then! I'll maybe go for a decent electric shower. I think its quite an old one that's on there. I think I remember from a while ago that 10.5KW would be powerful. Do you know if that's still about right these days?

EDIT: I'm sure those pumps said about 30 litres/min so on full it wouldnt even get 4 mins to the tank! I need more than 5 mins alone - more like 10!

wallbash

I might be completely wrong , often am !
But the maths does not add up .
117 litre tank , using 30 litre a minute......
BUT you dont use 30 litres of HOT/ very hot water , you add cold water,
so you have to know how 'hot' is the hot shower, before you can do the maths.


Ps we have a hot water tank ( because we have a power shower)
still get at least two good showers from the stored water.

blued

Thats a good point, I'd forgotten about the water not being at max temp because you mix some with cold. I'll need to find out roughly what its going to use and how many showers I can expect to get out of it. I'd really need 30 mins worth of showers to be able to do it. This is 3 showers with small breaks in between.

Any idea the best place to find out these details? Maybe a plumbing centre.

wallbash

Still the same problem , lack of facts:rotfl:
You would have to know , how hot the shower runs for each user.

I like my showers hot, but in contrast , I think 10 mins is a long time.

Ps lets ask all who read , to time their showers
To help ( or hinder) will only repeat , we get at least 2 good showers out of our tank.

brig001

You are right about mixing with cold, but I still don't think you will get three without some gaps to let the tank recover a bit. I could be wrong and it would definitely be interesting to hear other peoples experiences. What size tank does your friend have and how long before they run out of hot water? Personally I take 5 minutes, but I have no idea if that is short or long...

blued

ok I'm going to time 2 of the showers tomorrow. There wont always be 3 in a row but there will be 2 in a row more often than not. Well on week days anyway. Weekends will never be a problem.

wallbash

Weekends will never be a problem.

you have time to 'share' a shower!!!!

blued

:rotfl:

I dont work weekends and neither does my other housemate so we wouldnt need to go for a shower (separately) within a half hour period!

Only managed to time myself this morning and that was 13min41sec :shocked:
Did include shaving though so I think my norm time would be 10mins.