Non-economy 7 use of twin immersion bad practise?

[Angus]

Can anyone advise me, I'm considering using a 70 (or thereabouts) litre twin immersion, direct, vented cylinder to supply hot water to a small 2-bed flat (with gravity-fed shower, bath and two sinks) and I'm wondering is it OK to use the top element most of the time for light use (eg washing up, shower, etc), and to only switch on the bottom element for the occasional bath once or twice a week? Or would I be tempting fate with legionnaires bacteria?

 

[AWheating]

Will be fine mate.

 

[townfanjon]

I used to sub for a major cylinder manufacturer, they always said no when asked that question , because you end up with the top of the cylinder extremely hot and the bottom clap cold, this placed different stresses on the cylinder.
I would suggest a stainless cylinder maybe,but check with the cylinder manufacturer first.

 

[snowhead]

There's a greater risk from the customer only bathing twice a week than from Legionella..
And I doubt they'll get a shower from just the top, so the bottom heater will probably be on more often.

 

[Angus]

Many thanks for all your replies. I'll see what the manufacturers have to say, but I'm beginning to suspect I might be better off getting a smaller, say 50 litre, cylinder with a long top element that heats up the whole cylinder quickly according to demand, eg once in the morning then again early eve and weekends as required.

 

[AWheating]

Cylinders should be designed to work either way, if you use all you hot during the day you will have to turn on and top up from the top heater. If the manufacturer says it's not a good idea then it's not fit for purpose.

 

[townfanjon]

Cylinders should be designed to work either way, if you use all you hot during the day you will have to turn on and top up from the top heater. If the manufacturer says it's not a good idea then it's not fit for purpose.

Dont shoot the messenger !!

 

[AWheating]

:73: no messenger being aimed at, aiming at the Manufacturer

 

[Sparkgap]

Had loads of direct cylinders, usually with Sink/Bath switch for bottom immersion. No problems. Thermal stresses won't be an issue on your normal domestic cylinder either.

 

[Angus]

Thanks.
I'm coming back round to the idea of a 50 litre cylinder with 2 immersions, one bottom, one mid, as it's more versatile. As long as the whole cylinder is heated up once (twice?) a week, that should deal with the legionella. With two immersions the whole tank could be heated up for a bath in half an hour, almost as quick as an instant water heater without the disadvantages.

 

[PhoenixServices]

Why the need to suddenly heat it up. Why not use the cheap off peak electricity and not use the expensive leccy. Then the tank can just sit there hot till you need it.

 

[Old Account]

I got taught that the top immersion it's just the boost one to gain hot water almost straight way. And the bottom one it's timed like for the morning like showers , baths etc...

They said the top boost one would be enough for a shower ... Am I wrong ?

 

[Angus]

Why the need to suddenly heat it up. Why not use the cheap off peak electricity and not use the expensive leccy. Then the tank can just sit there hot till you need it.

I'm not using off-peak (Economy 7) because they then bump up the day rate (for no other reason, I guess, than they can). The 2-bed flat uses electric radiators, so unless I replace them with storage heaters (which I don't like because they give out the least heat just when you most need it, ie in the evening) the daytime electricity usage would outweigh the advantage of night time usage. So that brings me back to a small tank that can be heated up quickly if needed: mid immersion for a shower and bit of washing up in the morning (or both immersions for 2-3 showers), then if you wanted a bath in the evening, put both immersions on and wait 30 min. I appreciate this system could take a while to get the hang of. I guess it boils down (forgive me) to convenience vs. cost.

The alternative, of course, is an instant water heater or two, which is starting to grow on me (but not like legionella).

 

[Angus]

I got taught that the top immersion it's just the boost one to gain hot water almost straight way. And the bottom one it's timed like for the morning like showers , baths etc...

They said the top boost one would be enough for a shower ... Am I wrong ?

It all depends on your showering preferences...15 litres out of the hot water cylinder will do for me, but others will happily be pulverised for a good half hour!

 

[colshaws]

You need to check your electrical supply to the the immersion connection, If you are planning on running 2 immersions at the same time his may draw more current than the supply cable can handle, e.g 2 x 3kw immersions will draw 26 amps so standard 13 A FCU on 2.5 twin & earth will not be sufficient , you would need 2 separate supplies or upgrade the circuit to 4mm t&e.