Electric hot water

[quixoticgeek]

Currently we have on demand hot water boiler that is fuelled by gas. It's older than I am and kinda on it's last legs.

Given that Gas is going to be phased out here soon, I'd like to replace it with electric. I don't need to worry about space heating, we have district heat for that.

I don't have any outdoor space I can install the external unit, so a heat pump hot water system is not an option. This leaves me with a resistive hot water system. It's gonna need to be tank based as I only have a 25A circuit to power it off. I know there exist electric hot water systems that can be run off a 13 amp socket, connected to mains pressure water, but has anyone any experience with such things? Recommendations for a device to use?

Thanks

J

[mrcharly-YHT]

IGMC


I presume this is for showers/washing up etc?

I've worked in a few companies where a wall-mounted water heater was positioned over a sink. With the right temp adjustment, they worked just fine for producing a sinkful of water.

A 5 kW shower will mean standing under a warm dribble of water. You need a tank somewhere.

Any tank system will take a resistive element that works of 13A. We have one and in summer the central heating is off and the tank heated by a timer overnight (we get cheaper electric from 12:30-6).

A tank large enough for daily needs is a good idea, since you don't want to rely on heating it as you use it.

[quixoticgeek]

IGMC


I presume this is for showers/washing up etc?

I've worked in a few companies where a wall-mounted water heater was positioned over a sink. With the right temp adjustment, they worked just fine for producing a sinkful of water.

A 5 kW shower will mean standing under a warm dribble of water. You need a tank somewhere.

Any tank system will take a resistive element that works of 13A. We have one and in summer the central heating is off and the tank heated by a timer overnight (we get cheaper electric from 12:30-6).

A tank large enough for daily needs is a good idea, since you don't want to rely on heating it as you use it.

Electric showers don't seem to exist here. So it would be a tank with a heating element. Something like

https://electraboiler.nl/collections/horizontale-boilers/products/80-liter-super-flex-platte-boiler?variant=39832308678731

Tho I notice they have heat pump based systems that don't have an external unit ala:

https://electraboiler.nl/products/ariston-nuos-evo-energie-zuinigen-warmte-pomp-boiler?variant=39848401567819

Which seems like witchcraft. Unless it's making the bathroom colder, to heat the water, effectively stealing heat from the radiator (inefficiently), to heat the water...

J

[Feanor]

It's not clear to me what the scenario is.

Are we talking about a single-point thing near a sink, feeding a single hot water tap?
Or a whole-house hot water supply feeding many taps?
Feeding a shower?
Feeding a bath?

This will determine how big a tank you are looking at.

[HTFB]

I'd be strongly tempted to replace the gas unit and treat electrification as a procrastinable problem.

I presume the district heat is much, much cheaper than direct electric heating at the standard rate. It's hard, or impossible, to get an Economy 7 meter installed these days in the UK. There are smart tariffs, which might help.

Can you get a heat exchanger to put heat from the district heating into your tank? I have no idea whether such things exist, or if they could get a tank hot enough to avoid using an immersion heater as well.

You might look at the Vaillant AroSTOR, which appears to be a weird sort of integrated water tank and heat pump which can move heat from your room into the hot water. Depending on the cost of your network heat you might be a rare case where this actually makes sense. Or more sensibly it can work with just an outside flue, and doesn't need a whole external unit. [on edit: I see you've landed on a similar thing]

[on further edit: it doesn't matter how inefficient such a pump is, it's still not going to be more expensive than direct electric hot water, as you get all the wasted electricity back as room heat which you presumably wanted anyway.]

[Kim]

I don't have any outdoor space I can install the external unit, so a heat pump hot water system is not an option. This leaves me with a resistive hot water system.

A recent Technology Connections video made me aware of heat pump <en_US>water heaters</>, which take ambient heat from the room.  This makes sense in much of USAnia, where it would be installed in a basement alongside their weird top-loading washing machines and they probably need the cooling most of the year anyway.  I'm not sure how much sense it would make in a typical BRITISH setting, but it might still be an economic win if there isn't a more direct way to turn district heating into hot water?

[quixoticgeek]

It's not clear to me what the scenario is.

Are we talking about a single-point thing near a sink, feeding a single hot water tap?
Or a whole-house hot water supply feeding many taps?
Feeding a shower?
Feeding a bath?

This will determine how big a tank you are looking at.

It would feed the kitchen sink, the bathroom sink, and the shower.

I'd be strongly tempted to replace the gas unit and treat electrification as a procrastinable problem.

Dutch government really don't want any gas going in. And are looking to switch the gas off sooner than the UK.

I presume the district heat is much, much cheaper than direct electric heating at the standard rate. It's hard, or impossible, to get an Economy 7 meter installed these days in the UK. There are smart tariffs, which might help.

In theory we have a smart meter and switching to the Dutch equivalent of economy 7 is very possible.

Can you get a heat exchanger to put heat from the district heating into your tank? I have no idea whether such things exist, or if they could get a tank hot enough to avoid using an immersion heater as well.

Not that I can tell.

You might look at the Vaillant AroSTOR, which appears to be a weird sort of integrated water tank and heat pump which can move heat from your room into the hot water. Depending on the cost of your network heat you might be a rare case where this actually makes sense. Or more sensibly it can work with just an outside flue, and doesn't need a whole external unit. [on edit: I see you've landed on a similar thing]

That sounds plausible.

J

[lissotriton]

For kitchen sink, what about a Quooker tap? Though maybe rather expensive. Supposedly more efficient than a kettle.

[Wowbagger]

We were running an immersion heater on the 13a ring. This was a 3-pin plug with a wi-fi controlled plug between the mains socket and the heater, so that we could turn it on with our mobile phones. It blew its fuse some months ago. Because the immersion heater is also heated by a solar panel, I've not bothered to replace it at this stage, and it's only ever used in the winter months when there's not enough sunpower to heat the water, and then only for 20 minutes or so if I want a shower.

I will get it replaced for the winter though, and will get My Man to attach it to the fuse box with a higher amperage, I think.

[jiberjaber]

Our circulation pump went bang on Thursday last week so we have been living off using the immersion heater in the tank to give us hot water.
We are finding in the current weather that 20 mins of heating the water in the morning is lasting a whole day (2 persons, daily shower).  But it is quite warm at the moment outside (17 - 30Deg C) and probably depends on the size of your water tank too (ours is a standard 114L) . 

I suspect it is more efficient that our Baxi back boiler!

In the late 90's I lived in a house that only had immersion style hot water (and hot air system) which ran off econ7 by a wall plug timer... it was fine for a house with 3 kids and 2 adults.

When I manage to clear the drain blockage outside I will drain the CH system and fit the new reconditioned pump that arrived today.  I wasn't going to spend £300 on a new pump given I need to replace the CH system in the next 6-12 months anyway!

 

[mrcharly-YHT]

That first one you link is sufficient for one person. It will take a long time to heat up (2kW isn't a lot, my kettle is 3kW). That isn't really a problem if you have it on a controller though.

Looks expensive, but I guess it will be 'visible' in the flat and needs to look neat like other white goods.

Just checked our tank. It is 117l and has a 3kW element.

[PhilO]

I've been pondering this myself, & wondering if there's a place for Heat Batteries (eg https://www.beautifullygreen.co.uk/how-it-works) for this purpose.  In particular, whether a small heat battery adjacent each hot tap might save a bit of energy (our house is particularly bad in this respect, in that in the kitchen we need to run over 5l of water out the tap before it even starts to run warm).  I imagine it would be expensive to set up compared to a tank, or even a single heat battery, though.

[PhilO]

Which seems like witchcraft. Unless it's making the bathroom colder, to heat the water, effectively stealing heat from the radiator (inefficiently), to heat the water...

I don't read Dutch, but looking at the figures in the installation manual I'd guess that it draws air from the outside through a duct, extracts heat, and vents the cooler air out again.  It does say that it comes with 1.5m of vent pipe, so presumably doesn't have to be mounted to an exterior wall, although that must be the easiest approach.

[HTFB]

I've been pondering this myself, & wondering if there's a place for Heat Batteries (eg https://www.beautifullygreen.co.uk/how-it-works) for this purpose.  In particular, whether a small heat battery adjacent each hot tap might save a bit of energy (our house is particularly bad in this respect, in that in the kitchen we need to run over 5l of water out the tap before it even starts to run warm).  I imagine it would be expensive to set up compared to a tank, or even a single heat battery, though.

For houses complying with contemporary building standards it is assumed that 15% of hot water gets stuck in the pipes, corresponding to a 9 second average draw time between the boiler or tank outlet and the tap. Combi boilers take an additional time to get up to temperature. The 15% doesn't get entirely wasted as during the heating season it contributes to overall space heating as it cools.

Central heat stores save you a lot of room -- they take 1/4 of the space of an equivalent tank -- but are very not cheap.

[Cudzoziemiec]

I'm mildly surprised the district heating doesn't do hot water too.

[Feanor]

I'm mildly surprised the district heating doesn't do hot water too.

I wondered that too.
Can't it be used to heat a standard indirect cylinder, or is the temperature too low?

[lissotriton]

I've been pondering this myself, & wondering if there's a place for Heat Batteries (eg https://www.beautifullygreen.co.uk/how-it-works) for this purpose.  In particular, whether a small heat battery adjacent each hot tap might save a bit of energy (our house is particularly bad in this respect, in that in the kitchen we need to run over 5l of water out the tap before it even starts to run warm).  I imagine it would be expensive to set up compared to a tank, or even a single heat battery, though.

Or just a small, well insulated hot water tank next to each tap. Probably cheaper and more efficient than a heat battery? Though takes up more space under the sink. That's how taps like Quooker work.

[Tod28]

https://www.ebay.co.uk/itm/284900843692 hot water cylinder 2 kW or

https://midwalesheatingsolutions.co.uk/modern-electric-radiators/sunamp-hot-water-heating?gad=1&gclid=Cj0KCQjwtO-kBhDIARIsAL6Lorfip7n0wOZfeoDLX0KmD9VTi78qByIocU5YvLm9qdMUr1G30Fte7U8aAlkDEALw_wcB  phase change thermal store if you can get off peak power costs/solar power

[thing1]

I don't have any outdoor space I can install the external unit, so a heat pump hot water system is not an option. This leaves me with a resistive hot water system.

A recent Technology Connections video made me aware of heat pump <en_US>water heaters</>, which take ambient heat from the room.  This makes sense in much of USAnia, where it would be installed in a basement alongside their weird top-loading washing machines and they probably need the cooling most of the year anyway.  I'm not sure how much sense it would make in a typical BRITISH setting, but it might still be an economic win if there isn't a more direct way to turn district heating into hot water?

Yes this sounds a case where exhaust air heat pump might be a good win.
Have a look at https://eco-outlet.co.uk/collections/exhaust-heat-pumps  maybe the 80L is enough for one or two showers a day.
As an illustration, if you assume a COP of 2.5 and you're using 1.5kWh a day and energy is 30p a unit it'd save maybe £100 per year vs using resistive (immersion) heating. (Assuming the cost of district heating doesn't increase as a result of using more of it).

Nice thing with an exhaust air heat pump is you can use it to compliment home ventilation and even provide some active cooling in summer, with a bit of clever ducting and shut off dampers.