Electric on demand water heater advice

J

John Williamson

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I'm in the process of buying a property which needs a complete bathroom overhaul. The current bathroom has an electrically powered hot water tank feeding a bath, shower and sink.

I would really like to remove the water tank to save valuable space (and probably energy usage too) and so wondering if an option might be an on demand electric water heater and if so what kind of kwh I would be looking at (or even if this is the right measure to look at in terms of providing a decent flow of hot water).

Things which guide my decision are:
  • The house has no gas/LPG supply and getting a supply is not an option
  • We love showers. The stronger the better
  • Must be capable of running a bath, a shower and a hand basin but NOT at the same time
  • The electricity supply is single phase, so the 3 phase units I have seen are not an option
  • There are 4 people in my family and generally two of us shower in the morning and two in the evening
  • This is a holiday home so likely to be used in the weekends mostly but could be for weeks at a time in the holidays
  • The water heater will be for this bathroom only, will not need to supply any other heating or sinks other than this room

I was thinking along the lines of
https://www.heatandplumb.com/acatalog/trianco-aztec-water-heater-4052
but wondering if something like this might work better?
https://www.heatandplumb.com/acatalog/ariston-velis-water-heater-3626307

Anyone know if either of these or something else would live up to the task?
 
Depends on the electric supply to the property, the 45 litres is likely plenty for a shower, but not enough for a bath, and even with the 12 kW it would take a long time to fill a bath, I had a 22 kW instant water heater gas powered, and filling a bath was slow even with that, to the point where bath was cooling while it was filling so only just managed to get a full bath, would take around 20 minutes to fill.

So with both, may as well remove the bath. But down to the supply available and a bathroom is a special location and likely need a new circuit so not really a DIY job. Costs too much to notify under part P.

It is all down to bath filling time, either will work the shower and hand basin, it is the bath that is stumbling block.
 
ericmark said:
Depends on the electric supply to the property, the 45 litres is likely plenty for a shower, but not enough for a bath, and even with the 12 kW it would take a long time to fill a bath, I had a 22 kW instant water heater gas powered, and filling a bath was slow even with that, to the point where bath was cooling while it was filling so only just managed to get a full bath, would take around 20 minutes to fill.

So with both, may as well remove the bath. But down to the supply available and a bathroom is a special location and likely need a new circuit so not really a DIY job. Costs too much to notify under part P.

It is all down to bath filling time, either will work the shower and hand basin, it is the bath that is stumbling block.
Click to expand...
Thanks so much for the response. Yes definitely not going to be a DIY task but I like to be armed with info when speaking to Plumbers and Electricians. Fortunately (I guess) for me the whole house is in need of a rewire so just making sure I consider everything for when that happens.

Will see how set the wife's mind is on a bath as opposed to a shower.

Just out of interest which 22kw model did you use?
 
It was called a Main 7 and it is no longer made, it was the days before the combi boiler. Now moved house and back to having a cylinder, holds I think 40 gallons, and just enough to fill a standard bath. I use oil for central heating which does not lend its self to modulating so even when they are classed as combi there is a water tank in the boiler, it is not instant.

So basic back to school this calculator 40 gallons, start temp 5°C end temp 60°C power 12 kW and it gives 59 minutes so an hour to fill the bath. The 3 kW clearly you have 45 litres already hot, so working on 30 gallons, so 3 hours to fill the bath.

My 22 kW same calculator 32 minutes, that was within reason, but still lot slower than 10 minutes to fill the bath from a storage tank. We had three children and three bedroom house, and we converted the airing cupboard into a box room for one child, moving the wall into the landing a bit we got a 6'6" x 5'10" room which the eldest preferred rather than share, so yes understand the room saving when removing the cistern.

But after my father-in-law next door but one, so same design house, fitted solar panels to heat the water, but I could not follow suit, as cost to fit new cistern was going to make it too expensive, just as well, as the solar panels never worked, however many use electric solar panels and an immersion heater and a device which uses the electric power to heat the DHW when other wise it would just feed into the grid, so they get free DHW.

I would think twice about removing the tank, mother had a power shower, it looked like an electric shower but used the stored hot water, and that was good, far better than the direct from combi boiler she had latter, and different world to the electric dribble we get from an electric instant shower. However I can see your point with a holiday home don't want to keep 40 gallons hot.
 
Forget the bath, and in winter a 10-12kW electric shower is probably going to be a bit disappointing, certainly not "the stronger the better".
I would look at a hot water cylinder with 2 x 3kW immersion heaters which would provide a reasonably quick heating-up time when first arriving at the property for a visit. Or use a GSM- or internet-connected switch to turn it on a couple of hours before arrival. You might want to do this with the heating too. Either mains pressure/unvented, or pumped shower.

Also, is this a hard or soft water area? Instantaneous heaters may scale up badly in a hard water area leading to early failure.
 
OwainDIYer said:
Forget the bath, and in winter a 10-12kW electric shower is probably going to be a bit disappointing, certainly not "the stronger the better".
I would look at a hot water cylinder with 2 x 3kW immersion heaters which would provide a reasonably quick heating-up time when first arriving at the property for a visit. Or use a GSM- or internet-connected switch to turn it on a couple of hours before arrival. You might want to do this with the heating too. Either mains pressure/unvented, or pumped shower.

Also, is this a hard or soft water area? Instantaneous heaters may scale up badly in a hard water area leading to early failure.
Click to expand...
Thanks a lot for the reply. Currently leaning towards a direct unvented cylinder. Hoping around 120L should do the trick just for this bathroom.

Good shout about the hard water. You think an inline water softener would do the trick?
 
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