"Point of use" water heating

[Feltwell]

I'm sorting out one of the attic rooms on my house to be my daughter's new bedroom. That room contains a vanity unit and sink that we'd like to retain, it's Ikea's finest but there's nothing wrong with it and it will be useful in years to come.

This room is on the floor above where the hot water cylinder for the house is - so it has a cold supply to the sink only, with a hideously ugly wall mounted water heater above the sink if you want hot water. You have to remember to switch this on 5 minutes before you want hot water, and (bearing in mind this will be a child's room!) remember to switch it off again.

You can get undersink versions, but they are a similar design - they rely on heating up a stored tank of water. So whilst these would be hidden and could be wired into the ring main for the sockets as they're only about 2kw, you still have the problem of turning them off and on.

You can get "instantaneous" water heaters that heat water by demand only, when you turn the tap on - but most draw much more power, we already have 2 electric showers in the house so don't want to overload the incoming supply! I have seen one rated at 3.5kw - so drawing only 15 amps - how effective that would be is a question, plus also if it would require a dedicated feed from the consumer unit or if it could feed from the sockets ring main (which already supplies 2 floors of the house).

Are there any other options? Has anyone come across a way of pumping hot water up a floor (similar to a shower pump) so I could use the hot water supply as per the rest of the house?

 

[MdB]

Are there any other options? Has anyone come across a way of pumping hot water up a floor (similar to a shower pump) so I could use the hot water supply as per the rest of the house?

This would be my solution. I've not looked into them myself but my mate has a pressure controlled pump to move water around in his house so they must be available. I guess it is just a shower pump.

If you go down the electric route, I would want to put a 3.5kW load on its own MSB and cable. Current regs have a maximum ring main cable length of 50m and a recommended maximum of 10 sockets. It sounds like your ring main is well over that.

 

[Feltwell]

If you go down the electric route, I would want to put a 3.5kW load on its own MSB and cable. Current regs have a maximum ring main cable length of 50m and a recommended maximum of 10 sockets. It sounds like your ring main is well over that.

Yes, the current ring main must be well over that already. For reasons unknown they used the same ring main for the sockets on the 1st and top floors of the house - but put in 3 seperate lighting circuits, one for each floor.

I'd much rather go for the pump option if it's possible. It wouldn't be too bad to plumb in either, as the cupboard holding the hot water tank is directly below the room with the sink in question. I guess it's some kind of single impeller pump I need (most shower pumps seem to have 2 impellers, one for hot and one for cold) that's activated by a pressure switch.

 

[Flyfisher]

We had a 'power shower' pump in a previous house and it worked automatically (presumably pressure-switched) and very well. The whole unit was fitted within the shower cubicle and was operated via a 48V transformer located outside the bathroom. It wasn't 'lifting' water though, so you'd need to investigate the specs, but the concept seems sound enough and I'd bet there are suitable products out there somewhere.

I've not seen the 2kW 'stored-water-heater' device you mentioned, but it sounds very like a small immersion heater. Presumably they are thermostatically controlled, so is it really necessary to keep switching them on and off as you describe?

 

[Lime]

Perhaps I'm stating the obvious, however it is not where the hot water cylinder is that matters, it is where the cold tank supplying it is positioned that is important.

 

[Feltwell]

I've not seen the 2kW 'stored-water-heater' device you mentioned, but it sounds very like a small immersion heater. Presumably they are thermostatically controlled, so is it really necessary to keep switching them on and off as you describe?

I bet you have seen them - it's the kind of thing that you tend to get over a sink in workshops and small industrial units - this is similar:-

http://www.cnmonline.co.uk/Zip-Cont...asin-Water-Heater-5-Litre-2.0kW-pr-16821.html

Functional but very ugly!

You're right, it is basically a small immersion heater, and it is insulated and thermostatically controlled - it just seems a bit of a waste to have this keeping water constantly hot (even if the vessel is insulated) for a sink that will be rarely used. It won't go to waste as I'll install it in my garage, I put a cold feed for a sink in when I replaced the lead water feed to the house last year. I'll just switch it on for the occasions I need it.

I need to get a plumber in to service my gas boiler, so I may well pick his brains on pumps whilst he's here.

 

[Feltwell]

Perhaps I'm stating the obvious, however it is not where the hot water cylinder is that matters, it is where the cold tank supplying it is positioned that is important.

Good point! Alas the cold header tank is slightly below the level of the sink in question. It's in another room in the attic, but mounted on the floor (which is slightly lower than the room with the sink it it anyway). To move it to a higher position would be very awkward.

The current cold feed to the sink must be straight off the rising main, unlike the feeds to everything else - except the kitchen sink and downstairs loo - which come off the header tank.

Like a lot of old properties, the plumbing and wiring here is a little idiosyncratic!

 

[Lime]

- except the kitchen sink and downstairs loo - which come off the header tank.

Like a lot of old properties, the plumbing and wiring here is a little idiosyncratic!

For many years in the 60s our family lived in a similar "plumbed" property.
The mistake was (perhaps) understandable.
In the cellar the rising main to the tank was 1½" iron while the tank fed everything else in lead.
An early plumber had run one of the legs of the lead pipe outside next to the 1½" iron to feed an annex.
Consequently, all the subsequent plumbers (and the electricity board) assumed the lead was the rising main and the 1½" iron pipe was gas.
...So the kitchen, put in in the 50s, was fed from the tank.
It only came to our notice after several years of use when the rubber tap spout thingy (everybody had one) got blocked with feathers.
It was then discovered that the cold tap that was used for all drinking, cooking etc. was fed from the tank in which a pidgeon had recently died.
Subsequent to the immediate re-plumbing of the kitchen tap onto the mains, the tank was examined and drained to find a gruesome collection of bones presumably some dating from 1872 when the house was built...
The tank had it's own room in the attic... with it's own little window (for the pidgeons?).. the house walls and roof had been built around it.

 

[Penners]

I guess this is the device that you've seen: http://www.heatandplumb.com/acatalog/Perfect_Water_Heaters.html

It really looks like the best solution to your problem. You already have the cold water supply, so you;d only have the wiring to think about. As MdB says, it's probably best not to try putting it on the ring main, but (subject to MdB's confirmation) I think you could run it on an exclusive radial circuit, from its own 30A MCB. So cabling wouldn't be a major headache (or would it?!).

I don't see any easier solution.

 

[Feltwell]

For many years in the 60s our family lived in a similar "plumbed" property.

Yuck! Sorry, it was my bad phrasing. The house is plumbed correctly, for the most part - the kitchen sink comes straight off the rising main, and is used for our drinking water as we have a water softener which is connected to the feed to everything else. You can drink softened water but it's not pleasant, it has a brackish taste - and you must never make up baby formula milk from it.

The hot water cylinder & bathrooms are fed from a cold water tank in one of the attic rooms - I'm guessing that was installed in the 50's or 60's when the house was completely re-plumbed. The downstairs loo has been added later and comes straight off the rising main, on the "softened" side of the water softener.

The sink in my question I've just realised it actually plumbed into the feed pipe to the ballcock on the central heating header tank! A little unconventional but not a problem - it too comes straight off the rising main, via the water softener.

 

[Feltwell]

I guess this is the device that you've seen: http://www.heatandplumb.com/acatalog/Perfect_Water_Heaters.html

It really looks like the best solution to your problem. You already have the cold water supply, so you;d only have the wiring to think about. As MdB says, it's probably best not to try putting it on the ring main, but (subject to MdB's confirmation) I think you could run it on an exclusive radial circuit, from its own 30A MCB. So cabling wouldn't be a major headache (or would it?!).

I don't see any easier solution.

Yes, that is the one I saw. Running a radial circuit to it from the consumer unit would not be too bad - it means going from ground to 2nd floor, but luckily there is an airing cupboard on the 1st floor that is in just the right place to make an ideal route to inconspicuously run cables.

The doubt I have though is how effective a 3.5kw heater will be - I can see the hot tap being a luke-warm trickle. Most of those type of instantaneous heaters are rated more like showers at 8kW+, there must be a reason why that is so.

I think I'll explore the pump option further, and treat the 3.5kW heater as a fall-back option. If I can get a pump I can put it in the airing cupboard I mention above - so a hot water feed won't be a problem, and there is power there as well.

 

[MdB]

As MdB says, it's probably best not to try putting it on the ring main, but (subject to MdB's confirmation) I think you could run it on an exclusive radial circuit, from its own 30A MCB. So cabling wouldn't be a major headache (or would it?!).

16A MCB to match the load. Radial is fine but a maximum of 20A MCB for 2.5mm T&E IF the cable run does not cause any derating of the cable. (Running through insulation can drop the cable rating considerably as can running next to other cables.) Please consult a qualified electrician before doing anything.

 

[Flyfisher]

The doubt I have though is how effective a 3.5kw heater will be - I can see the hot tap being a luke-warm trickle. Most of those type of instantaneous heaters are rated more like showers at 8kW+, there must be a reason why that is so.

I have the same doubts, based on my experiences of 6kW shower units that seemed to struggle with a decent flow of water. However, they do look convenient so it might be worth finding somewhere that can demonstrate one actually working, then judge accordingly.

Otherwise, I'm sure there must be a pump-based solution out there somewhere.

 

[MdB]

Bowl of water - 5l
Temperature increase - 30°C (10°C to 40°C)
Power - 3.5kW
Water Specific Heat Capacity - 4.1813 J/gK
Water Density - 1000 Kg/m^3

Time = 3 minutes

 

[FamilyWiggs]

Bowl of water - 5l
Temperature increase - 30°C (10°C to 40°C)
Power - 3.5kW
Water Specific Heat Capacity - 4.1813 J/gK
Water Density - 1000 Kg/m^3

Time = 3 minutes

By 5pm the first train will have travelled 210 miles, and the second train will have stopped due to leaves on the line. 8)

 

[Flyfisher]

I can understand those calcs from an "immersion heater" perspective, but am not sure how they relate to an "instantaneous" type of heater.

Does it mean that 3.5kW could only provide water at 40°C when the flow was limited to 5 litres per 3 mins (what i would call a trickle)?

 

[MdB]

I can understand those calcs from an "immersion heater" perspective, but am not sure how they relate to an "instantaneous" type of heater.

Does it mean that 3.5kW could only provide water at 40°C when the flow was limited to 5 litres per 3 mins (what i would call a trickle)?

Yep, it doesn't matter if you are heating the entire amount of water all in one go or a stream of water. Both will take 3 minutes to heat 5l by 30°C. (assuming no losses) (*)

If you take the shower head off an electrically heated shower and look at its flow rate, you will see it is relatively poor. The shower manufacturers can improve the "power" or speed of the water coming from the head by using a pump and small holes in the shower head. However, the flow rate is strictly limited to the power rating of the element.

(*) The same goes for kettles. There is no such thing as a "fast" or an "eco" kettle, they are all 100% efficient so all 3kW kettles take the same time (and the same amount of electricity) to heat the same amount of water. The "eco" kettles can make that claim purely by making it easier to boil a smaller amount of water.

 

[skier-hughes]

Pumps
http://www.salamanderpumps.co.uk/Products/CT_Pumps.htm

You need a single pump. Salamnder very good, not cheap. I have a 3.3bar one that is only a few months old, but would be overkill for you really on pressure.

Graham

 

[Penners]

improve the "power" or speed of the water coming from the head by using a pump and small holes in the shower head

Quite so. And couldn't Feltwell achieve the same, by having a hot tap that has a fine spray head?

When all is said and done, this is only a wash-hand basin, so there's no great need for a large volume of water.

 

[Louis Henry]

I'm sure you won't be replumbing the entire system for the sake of one basin, but when I had to do extensive work I put in a Megaflo cylinder that has no header tank and works at the pressure of the cold mains. It is brilliant, much less piping, and the shower is as good as a power shower. Not cheap though.