Undersink water heaters

[sadimco]

I want to fit an undersink water heater for the kitchen sink.
My requirements are:
1. !3 amp electrical supply.
2. Using existing mixer tap.
3. As near as possible instantaneous hot water on turning the tap.
4. On demand heating of the water, rather than storage, to reduce wasted heat.
Is this possible? What heater would do this, and if it is unvented, is there any sort of expansion box required?

 

[kbdiy]

Something like this? http://www.heatraesadia.com/utc99/

 

[OwainDIYer]

The only hot water you will get from a 3kW instantaneous heater will be a lukewarm spray suitable for handwashing.

Anything else will require a small amount of stored hot water. Heat losses will be negligible.

An expansion vessel may be required depending on the plumbing arrangements and whether there is room for the hot water to expand up the cold supply pipe. The manufacturer's instructions will specify.

 

[Agile]

You seem quite demanding in your list!

But you have left out "a qualified installer" !

Tony

 

[Agile]

What you are asking for does not exist as far as I am aware!

But your installer if you had one would have told you that!

Tony

 

[mfarrow]

You want at least 9.5kW for undersink instantaneous, and make sure the manufacturer will warrant it (a lot won't).

Otherwise 3kW/15l stored will allow you to use your 13A supply.

 

[sadimco]

Thanks for all the replies. I think I'll have to go for storage after all. Hopefully, a 10/15l one should be good enough.
Do I have to have an expansion box with it?

 

[Agile]

Ask your installer and read the makers instructions!

Tony

 

[Galoka]

Thanks for all the replies. I think I'll have to go for storage after all. Hopefully, a 10/15l one should be good enough.
Do I have to have an expansion box with it?

It depends on the installation. Upto 15L they are allowed to use the supply pipework for expansion with certain provisos. If you have a look on manufacturers (eg Ariston, Heatrae Sadia etc.) websites for the installation instructions they will lay it out for you.

Don't know why Tony needs to keep making comments about an installer, not exactly helpful on a DIY forum. Assuming that you are putting in a small one there are no particular installer requirements. But note that over 15L then they fall into the requirements covering unvented tanks etc. requiring installation by a qualified person, etc. But I don't imagine you are going for one that big.