Electric water heaters

robertsimpson

I am looking for a new water heater and came across an article on the Dimplex website that stated that there is a new European legislation relating to them. It seems to mean that all water heaters should now have a label showing their efficiency like washing machines etc. Does anyone know how they calculate the ratings? Are there any A rated boilers as I can't find any?

Smiley_Dan

I don't know, but would be interested to find out.

If it's like hot water cylinders, a very limited testing regime is devised where the cylinder is connected to a very short length of pipework and the losses measured over a defined heating period.

This means the actual figure that comes out is useless; your real world figure will depend on how many conduction paths you have coming out of the tank and also how you heat the tank. The figures are only useful to compare cylinder to cylinder.

Obviously, more insulation is better (at this size).

macman

All electrical heaters are the same efficiency: 100%.
As stated above, the only real variable would be the insulation quality of the tank, but in practice this is minimal, and in winter still serves to heat the house anyway.

robertsimpson

Then they should all have the same rating, no? Dimplex have different ones on their website. They have some rated B and some rated C. This is why I am confused....

thozza

robertsimpson wrote: »

Then they should all have the same rating, no? Dimplex have different ones on their website. They have some rated B and some rated C. This is why I am confused....

The rating is based on 'water heating energy efficiency' which is set out in a great deal of detail in the EU regulation to be found here:

https://ec.europa.eu/energy/intelligent/files/faqs/06_energy_labelling_water_heater-c_2013_818.pdf

Page 25 gives the rating table, based on the calculations set out in pages 72-74.

It takes into account a number of parameters, including size of the storage vessel, standing heat loss & electric/fuel consumption using a series of formulae.

I suspect it is possible to get an A rated heater, but probably it would need to be highly insulated and/or small volume.

Smiley_Dan

macman wrote: »

All electrical heaters are the same efficiency: 100%.

That's the efficiency of the coil applying energy to the water.

The OP is interested in the heating -> taps efficiency. Different things.

HappyMJ

Smiley_Dan wrote: »

That's the efficiency of the coil applying energy to the water.

The OP is interested in the heating -> taps efficiency. Different things.

Wouldn't that depend on pipe length between the storage vessel and the tap?

If you're looking for a water heater that has minimal standing losses there are water heaters that you can install at the point of use and heat water only when you need it....but they don't have a very high flow of water. Rated at only 3kw they can only heat around 1 litre per minute. That wouldn't be enough for my requirements.

Smiley_Dan

HappyMJ wrote: »

Wouldn't that depend on pipe length between the storage vessel and the tap?

Yes, of course, amongst other things.

HappyMJ wrote: »

If you're looking for a water heater that has minimal standing losses there are water heaters that you can install at the point of use and heat water only when you need it....but they don't have a very high flow of water. Rated at only 3kw they can only heat around 1 litre per minute. That wouldn't be enough for my requirements.

You can get inline water heaters much more powerful than that, and also those that modulate i.e. reduce the draw the warmer the input water is. See the Stiebel range. Probably the best way to do DHW if you don't/can't have a combi.

Cardew

HappyMJ wrote: »

Rated at only 3kw they can only heat around 1 litre per minute. That wouldn't be enough for my requirements.

Instead of a 3kW heater it would be cheaper to buy half a dozen cheap kettles and have them at the points where you may need hot water.

HappyMJ

Smiley_Dan wrote: »

Yes, of course, amongst other things.


You can get inline water heaters much more powerful than that, and also those that modulate i.e. reduce the draw the warmer the input water is. See the Stiebel range. Probably the best way to do DHW if you don't/can't have a combi.

Some of those more powerful water heaters require a 3 phase electricity supply at 400/415V. I was suggesting the 3kw heater as it does not require any changes to the wiring.

I don't have a combi. I have a hot water cylinder. I have flow rates of at least 12 litres per minute.

Smiley_Dan

Only the really powerful ones require 3 phase. Others work on single phase. That's how an electric shower works, 8->11kW. That's also why a modulating one is a good idea - it can sense the incoming temperature and still allow a good flow rate (better than an electric shower).