Electric water heaters

MarkJ

Forum Member
I've been sizing battery/solar etc for our possible all-electric van and I've been thinking about water heating. It's the biggest consumer of power. We need a 10l heater if we have showers and one heat cycle will do both of us, plus probably the breakfast washing up. But we might also need hot water, possibly, for washing up at some other point in the day. Heating 10l again seems wasteful when we only need a couple of litres.

I think there are 3 possible solutions

1. Get a small undersink heater with less capacity. Something like this:

SNU 5 SLi Small water heater of STIEBEL ELTRON

Small water heater SNU 5 SLi of STIEBEL ELTRON ► Product information from the manufacturer, technical data, operating instructions and customer service.
www.stiebel-eltron.co.uk

The 2kw one has a heat cycle of about 8 minutes so would be very usable.

2. Get a relatively low power instant water heater, like this.

www.aquahot.co.uk

Zip ES Inline Heater 2.8kW

Compact electronic instantaneous water heater with highly energy efficient bare-wire heating system for economic water supply to a single outlet.
www.aquahot.co.uk www.aquahot.co.uk

I think the snag with the instant heater idea is flow rate. If you have a battery-friendly wattage the flow rate is very low: the one above flows at 1.5 litres a minute, but of course uses very little power over all if your need is just a couple of litres for greasy dishes.

3. Boil a kettle.

Keep it simple, stupid....


Any thoughts, anyone?
 

wildebus

Forum Member
Well, my thoughts would be forget #2 - that is just too big a power-requirement and is pushing it on a campsite hookup.
#1 - that is the kind of unit I run. I have a 10L Ariston 2kW unit. I would have preferred a lower power (~1000W) one but they don't seem to be available as off the shelf heaters (which is what I personally wanted as the most cost-effective option)

Maybe a small calorifier would hit the mark? some examples here - https://www.vetus.com/en/fresh-water-systems/water-heaters-calorifiers.html
 

MarkJ

Forum Member
wildebus said:
....I would have preferred a lower power (~1000W) one but they don't seem to be available ....
Click to expand...

Crazy idea? Two of these:

Small water heaters, wall and floor mounted cylinders

Small water heaters and wall mounted cylinders from Stiebel Eltron UK
www.stiebel-eltron.co.uk

Two 5litre/1kw heaters 'in series', so to speak. You could turn them both on when you really do want 10l, or just have one on when 5l will do and/or you want to conserve battery.

Think I need to go and lie down....
 

MarkJ

Forum Member
Quite pricey at about £150... I saw one allegedly on eBay for less but not convinced it was the same
 
Pugwash69

Pugwash69

Forum Member
It says for non-pressurised taps. Does that mean gravity feed only or something, rather than our pumped systems?
 
Nabsim

Nabsim

Forum Member
Calorifiers are great so long as you run engine each day. I still need to sort the bypass of my D5 so I can heat water with ignition off.
 

MarkJ

Forum Member
Pugwash69 said:
It says for non-pressurised taps. Does that mean gravity feed only or something, rather than our pumped systems?
Click to expand...
Good spot. I'm nobody's expert on plumbing, but I think 'low pressure' is a gravity fed type system where the pressure is less than 0.1 or 0.2 bar, whereas 20psi from a Shurflo is about about 1.4 bar. So I guess it would only work with the pump on demand type systems, with the expensive taps!

However, I'm open to correction. As I say, what I know about plumbing would fit on the back of a wet postage stamp.

PS - I think Wildebus uses an Ariston heater and that's the same deal...I presume his hasn't exploded yet? Baffled.
 
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SquirrellCook

SquirrellCook

Forum Member
Nabsim said:
Calorifiers are great so long as you run engine each day. I still need to sort the bypass of my D5 so I can heat water with ignition off.
Click to expand...
Ours is done with just one tap, so that you don't have to heat the engine.
As mentioned some time ago by "wildebus" you can also use surplus solar to heat water electrically.
Our calorifier has a 500watt element fitted to it to give the generator an easier time as well as people ears. Although not done, it would be handy for using the surplus solar without a silly size inverter.
 

wildebus

Forum Member
SquirrellCook said:
Ours is done with just one tap, so that you don't have to heat the engine.
As mentioned some time ago by "wildebus" you can also use surplus solar to heat water electrically.
Our calorifier has a 500watt element fitted to it to give the generator an easier time as well as people ears. Although not done, it would be handy for using the surplus solar without a silly size inverter.
Click to expand...
I tried all kinds of things to utilize a "normal" sized element (such as 500W) but couldn't find a suitable vessel to use at an economical cost (my target was under £150 all in - heater, pipework and tap) so ended up with the 2kW undersink type unit. For my own setup, 2kW is ok as it was within the bounds of the inverter I had already and within the battery capabilities, but for the typical electrical install of a Motorhome/Campervan, it would be way to big for off-grid use.

On the US Sprinter Source Forum, there is a guy there who is virtually obessed with a "Sous Vide" style of water heater. This is a example of one post - https://sprinter-source.com/forum/showpost.php?p=718054&postcount=159.
That same forum has lots of ideas and discussions of water heater options and might be worth having a browse at.
 
Nabsim

Nabsim

Forum Member
My calorifier has a 1kw element fitted but not wired up. I do have a 12v 300w element I was going to put in but with the exception of summer I would not have spare capacity to use. I could power either element from my generator but prefer not to use it as a matter of course.

for me the ‘permanent’ solution will be the eberspacher D5 if I eventually tackle it :)
 

MarkJ

Forum Member
So your Ariston heater, Wildebus, says its for low
MarkJ said:
Good spot. I'm nobody's expert on plumbing, but I think 'low pressure' is a gravity fed type system where the pressure is less than 0.1 or 0.2 bar, whereas 20psi from a Shurflo is about about 1.4 bar. So I guess it would only work with the pump on demand type systems, with the expensive taps!

However, I'm open to correction. As I say, what I know about plumbing would fit on the back of a wet postage stamp.

PS - I think Wildebus uses an Ariston heater and that's the same deal...I presume his hasn't exploded yet? Baffled.
Click to expand...

Right, after a bit of research, I think I’ve found that “vented” heaters, like the Stiebel, need “vented taps”. This is because when the water expands on heating it makes its way out of the tap (it drips....). So I suppose the tap must allow water to pass even when turned off if it’s over a certain pressure. “Unvented” heaters, like the Ariston, can use normal taps because you are supposed to fit an expansion vessel with them which copes with exapansion.

As to inlet pressure, my reading is that unvented heaters work between 1 and 3 bar (Shurflo is 2 bar) and vented one’s work at water main pressure, which is about 1 bar, but a couple of heaters I looked at talked about working pressures of 0 or 0.15bar. So.... “unvented” it is, in our world, if you use the Shurflo type pressurised system.

But please - if there’s a real plumber out there....
 

wildebus

Forum Member
You sure mains water pressure is 1 bar? I thought 1 bar was "normal" atmosphere (e.g. 1000 mBar). I know when I installed my Solar DHW system and Boiler in my house in Devon, I needed to fit a PRV (Pressure Reducing Valve) to the incoming mains as it was too high for the system and all the taps in the house as well. I can't recall the exact numbers but I think I set the PRV to around 9 bar.

FWIW, This is my Hot Water setup - http://www.motorhomebuilder.com/threads/my-overland-camperbus-conversion.66483/#post-867364

Because of the very limited pressures involved with unpressurised water tanks and limited pressure from the Shurflo pump, I don't think the expansion vessel is actually essential, but it is handy as if you need just a splash of water, you can get this when you turn the tap on without the pump kicking on. It also helps to stop pump cycling in the middle of the night.
Surprisingly, the best place to get one turned out to be Amazon! The one I fitted was identical to the one from Screwfix but half the price. In fact, it is even cheaper than when I bought it! Link to vessel here - https://amzn.to/2pLJCdj
I got the Mixer Tap from Amazon as well - https://amzn.to/2JUAPwz . £25 and it has worked very nicely for me.
 

MarkJ

Forum Member
wildebus said:
You sure mains water pressure is 1 bar? I thought 1 bar was "normal" atmosphere (e.g. 1000 mBar).
Click to expand...

The internet can be dangerous but I found something like this in a couple of places
“Water suppliers’ statutory service standard level of mains water pressure is 10 metres/head (or one bar). This means there is enough force/pressure to push the water to a height of 10m.
This is measured at the point where the water leaves the water suppliers pipework and enters yours (usually the outside stop valve or property boundary).”

And I don’t think the expansion vessel is to do with inlet pressure. It’s to do with the volume of water expanding as it heats. I don’t suppose it’d be a problem with a 10l tank, but a bigger one might be more interesting!
 

wildebus

Forum Member
You are right about the expansion vessel not having anything to do with inlet pressure, and also it taking the water as it expands - but if you didn't have the vessel fitted, the effect would be the pressure in the heater would increase - and if you had a bigger water inlet pressure as well, that means more pressure still. (This is why the Ariston Heaters, and no doubt all the similar ones, come with a Pressure Relief Valve (another PRV ackronym ;) ) which will dump at (from memory) 6 bar. I fitted this as well, not as I think the pressure will get close to that, but it also works as a handy manual drain valve :D
In terms of Heater size and Expansion Vessel size, you would generally match them (not like for like, but as the unvented capacity increases you may want a bigger vessel). The one I got is more than big enough and I could have gone a lot smaller but it has the extra benefit mentioned and they don't tend to get cheaper as they get much smaller anyway.

I would not want to live in a house which was served by a 1 bar mains either. I'd have to run around the shower head trying to catch the drips to get wet :)
In fact this reminded me ... my gf (later ex-wife) had a flat in North London and if she didn't get her shower in before 6AM, that was it until after 9AM as the pressure was just too low to get the combi to kick in. No doubt that was delivering to the Water Companies minimum standard still.
 
Nabsim

Nabsim

Forum Member
Accumulator tank to stop the pump kicking in, expansion tank after the heater for ... expansion. Only know as I looked it up when trying to figure out what I had fitted, luckily the tanks had labels saying which they were.

anything on here help you Mark? http://www.surejust.co.uk/expansion-tanks
 

wildebus

Forum Member
Nabsim said:
Accumulator tank to stop the pump kicking in, expansion tank after the heater for ... expansion. Only know as I looked it up when trying to figure out what I had fitted, luckily the tanks had labels saying which they were.

anything on here help you Mark? http://www.surejust.co.uk/expansion-tanks
Click to expand...
Neil, I guess different folk have different meanings? Ariston call what you are referring to as the Accumulator tank the expansion tank (vessel).
As I mentioned, on the heater I have, the expansion tank is fitted to the cold supply (i.e. BEFORE) the heater.
Here is a picture from the manufacturer that is in the install manual that I used, and is featured on their on-line video on installation I just searched for.
1573038701542.png


And that is basically the way I installed my setup .... (teeing off the cold supply for the water heater in my case rather than teeing off for the tap as shown above - same difference of course)

Heater Pipework by David, on Flickr
 
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MarkJ

Forum Member
Sounds like whatever you buy, you need to read the instructions carefully!

I notice on the link that Neil kindly included that the picture of their Accumulator tank actually says “Expansion Tank” on it and it’s clearly identical. Confused or what.....

This link, which I need to read more carefully, says that you might or might not need one or both, depending on pressure, non-return valves, capacity and so on.


There is a certain fascination to all this but I do prefer nice clean and dry electricity.
 
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