Tankless instant water heaters in parallel

[Volt]

Hi,

Initially not sure of where to put this post as it touches more that one forum.

Grateful for your help please with an unusual installation.

I am looking to avoid long runs of hot water from the combi to the launderette due to being on a water meter and to run the taps until hot water is ejected is wasteful.

I am thinking of tankless undersink instant water heaters that heat up the cold supply at the tap but at 3kw can be spurred into the ring main. However, they only achieve about 1.2 litres per minute for a 30C temperature rise.

Grateful for your views/considerations on wiring up two such heaters in parallel to achieve either 2.4 liters per minute or a 60C rise at 1.2 litres per minute. This would pull 6KW of the ring main approaching shower teritory. However is the same as running say three 2KW fan heaters in different rooms off the same ring? The heater manufacture is OK with feeding one heater into the other but I am unsure of the electrical supply issue.

 

[Taylortwocities]

Water heaters of volume greater than 15litres are supposed to have their own dedicated electrical supply.
A ring final circuit is not designed to support loads of that magnitude.

You would be better off having a single small hot water tank with an immersion heater in it to act as a hot water buffer. Not sure how that would work, plumbing-wise.
Even so, the immersion should really have its own separate supply.

 

[Andy-1960]

I think I would be looking at running a seperate feed from the CU as 26A on your ring final circuit does not leave much for anything else, (especially if this is possibly in the kitchen?)
Think you could end up with nuisance tripping.

 

[ruston]

Is it a commercial launderette or a domestic situation.

 

[westward10]

As above but won't two in parallel achieve the same temperature but just double the volume.

 

[Volt]

Thanks all for your comments.

Hi Ruston - It's a domestic situation.

Hello Westward - Yes either the volume would double (which is my ideal aim) or the temperature rise would increase depending upon how much you turn the tap on. Typically the heaters are limited to 50C but in practise rarely achieve this due to the poor draw volume. At the recommended 1.2 litres per minute would take a noticeable time to fill up a bowl of water to wash something by hand in the sink. A doubled up volume would be useful at 30C rise.

I thought about the small water tank option but they would maintain 5 -10 litres of hot water that is not used often and would not be 'green'. I liked the idea of only heating what you need with the new instant heaters.

Andy - that's a fair point, only 8 amps left on the ring.

 

[davesparks]

The loads on a ring should be distributed evenly around it as far as possible. Two fixed appliances in close proximity aren't going to achieve this.

Instead of lashing something up out of smaller water heaters why not just one single unit capable of doing the job?

 

[ruston]

That is along the lines I was thinking.
If cost is the only consideration heating with electricity will cost more than the wasted cold water ,But you will also be wasting the hot water left in the long run pipe.
I would be looking at getting the source of the heating nearer the demand if it is high.
Electricity would be my last choice if it is.

 

[Wilko]

At risk of heresy, at mine I've got a little hot water circulating pump that keeps it hot

 

[ruston]

No , not heresy, as long as insulation is good that is a good way to do it

 

[davesparks]

At risk of heresy, at mine I've got a little hot water circulating pump that keeps it hot

Not heresy, a sensible practical solution when you have stored hot water. I think the OP has a combi boiler so it's not an option for them.