Wash-hand basins: local instant water heater or not?

[ToughButterCup]

This thread has its roots in an earlier one and in many of the threads on related subjects on BH

 

A bit of context: I really dont 'get' hot water supply. It seems so incredibly complex.

 

Why cant it be simple? The end in mind is simple .... provide some hot water for hand washing. I want instant hot water for 10 seconds: the time it takes to wash, rinse and repeat.

 

'Solutions' (that oft mis-applied word) to the issue of delivering a few handfuls of warm water  depend on all sorts of increasing levels of sophistication. It reminds me of that aphorism :

 

Little Bugs have Smaller Bugs upon their backs to bite 'em

and so on ad infinitum.

 

A traditional vented hot water supply system has all sorts of quirks that need sorting out - Aha! there's a fix for that

• use a non-vented system. 

Currently it takes an age for our hotwater to reach the sink - Aha! There's a fix for that

• recirculate the hot water .

Oh, but that's wasteful of electricity isn't it - Aha! there's a fix for that

• lag the pipes, and anyway it doesn't cost much

Hold on a minute, the water tank is heating the upstairs too much - Aha! there's a fix for that

• Lag the tank more (or worse)

 

I dont pretend to know how often or how much water is expended on hand washing (3 sinks in our case). But the psychology  of hand washing is wash-and-go: not wait-get-bored-rinse-only-and-go.

Who is going to wait more than 10 seconds to get this minor job done?

 

And in that context - tiny volumes of water, daily use for a few seconds, doesnt it make sense to heat locally?

 

I know people have strong views about electricity and water - I do hope we can maintain the focus on local water instant water heating in this thread.......

[joe90]

Right, we have Three wash  hand basins and the furthest is in the downstairs cloakroom, I designed the house so that all pipe runs for hot water are as short as possible, I also piped these in 10mm plastic pipe to reduce lag time and the flow rate is more than adequate. The cloakroom tap gets hot water in less time than it takes to squirt soap from the dispenser. 

 

I think different solutions are for different situations/houses. In an old Victorian house with long copper pipe runs instant hot water devises at basins might be best. 

[Jeremy Harris]

There's no doubt that instant heating with peak rate electricity is far more expensive that heating water any other way, so the real question comes down to whether the convenience of having near-instant hot water from a tap is worth the additional cost.  A basin tap typically flows at about 5 to 6 litres per minute (any higher than this tends to result in a lot of splashing).  Using 5 litres/minute as a general figure, then if that tap is fed with 10m of 10mm OD plastic pipe (so about 7mm bore) then it will take about 4.7 seconds for hot water to arrive at the tap.

 

So, any instant water heater has to be able to heat water, and deliver it to the tap, faster than that

[Nick1c]

Do you need hot water to quickly wash your hands? Presumably you will be in a warm, windless environment & the cold water isn’t refrigerated! I think I read somewhere that in Holland (or the Netherlands as they now want to be known) hand basins only have a cold feed. 

[ToughButterCup]

28 minutes ago, JSHarris said:

[...]

So, any instant water heater has to be able to heat water, and deliver it to the tap, faster than that

 

What does instant mean, I wonder? With the heater so close to the tap, the pipe run could not be shorter could it?

 

6 minutes ago, Nick1c said:

Do you need hot water to quickly wash your hands?[...]

 

The NHS guidance is - that hot water is not required.

Now, dunno about you - but that surprised me. I routinely have to flex and massage my damaged hands in warm water, so I haven't given water temperature a thought - warm water helps a good deal.

 

37 minutes ago, JSHarris said:

[...]

Using 5 litres/minute as a general figure, then if that tap is fed with 10m of 10mm OD plastic pipe (so about 7mm bore) then it will take about 4.7 seconds for hot water to arrive at the tap.

[...]

 

It takes us 15 to 20 seconds ....?

[joe90]

8 minutes ago, AnonymousBosch said:

I routinely have to flex and massage my damaged hands in warm water, so I haven't given water temperature a thought - warm water helps a good deal.

 

Yup, I need a deep hot bath after working out in the cold, ditto with warm water fir my hands. I doubt if an “instant” hot water heater could beat my 10mm hot pipe system. Again this was part of my design brief, short hot pipe runs.

Edited October 7, 2019 by joe90

[ProDave]

Local instant water heaters start to make sense when the point of use is a long way from the main house source of hot water.  If it gets to the point you have to run off twice as much cold water, just to get the hot to the tap, as you actually use once it gets there, then I would say that is a candidate for a local small heater.

 

One of the design inputs to the house layout was to keep bathrooms etc reasonably close so we don't have that problem and water reaches all the taps with little waste.

 

Contrary to popular practice, I piped all my hot water from tank to tap in 15mm to minimise the dead volume in all runs.  For a small wash hand basin I would probably go down to 10mm even for the hot feed to that to keep the volume down.

[joe90]

2 minutes ago, ProDave said:

For a small wash hand basin I would probably go down to 10mm even for the hot feed to that to keep the volume down.

 

I did this fir all basins (bathrooms and cloakroom) and flow rate is more than adequate.

[Jeremy Harris]

10mm is absolutely fine for a wash basin supply.  The French have been using small bore pipes for decades with no ill effects, IIRC, I think their "standard" pipe is about 12mm OD, so a fair bit smaller than our 15mm.

 

Using 10mm plastic pipe is even better, as the pipe has a slightly smaller bore and a much lower heat capacity than copper, so hot water will reach the tap a lot more quickly (under 5 seconds for a 10m pipe run, which is pretty good).

 

The wasted hot water is also a lot less, as in a 10m pipe run of 10mm plastic pipe there will only be about 0.385 litres of hot water, which if supplied at 45°C (which is what I have our mixer valve set to) will only "waste" about 0.0113 kWh, which is so trivial as to not even be worth considering.

[Ed Davies]

39 minutes ago, Nick1c said:

Holland (or the Netherlands as they now want to be known) hand basins only have a cold feed. 

 

Holland is quite a small part of the Netherlands, basically the bit along the coast between Rotterdam and the Ijselmeer. This confusion is probably about as irritating to many Dutch people as referring to the UK as England is to many in NI and in other parts of GB.

 

Having lived in Holland [¹] for a couple of years, nope, I don't remember encountering any hand basins with only a cold feed. That was a while ago, though.

 

[¹] South Holland, to be precise.

[Carrerahill]

1 hour ago, joe90 said:

Right, we have Three wash  hand basins and the furthest is in the downstairs cloakroom, I designed the house so that all pipe runs for hot water are as short as possible, I also piped these in 10mm plastic pipe to reduce lag time and the flow rate is more than adequate. The cloakroom tap gets hot water in less time than it takes to squirt soap from the dispenser. 

 

I think different solutions are for different situations/houses. In an old Victorian house with long copper pipe runs instant hot water devises at basins might be best. 

Joe, I like your thinking and solution, I am going to invest a Saturday and a pack of copper to effectively re-plumb our hot water system - with the kitchen moving further away and not wanting to relocate the boiler my option was the most direct route (I am also contemplating having a DHW feed to the kitchen sink but possibly just using a local water heater which can be fed with hot water).

 

The 10mm pipe option intrigues me I have about 50m of 10mm copper, great benefit being I can run it more or less the full route with no joints and I get to avoid plastic.

 

So do tell, how is flow etc. with your 10mm pipe? Would it work for a kitchen tap? 

 

 

 

 

[SteamyTea]

1 hour ago, JSHarris said:

then if that tap is fed with 10m of 10mm OD plastic pipe (so about 7mm bore) then it will take about 4.7 seconds for hot water to arrive at the tap.

Call it half a second per metre of pipe run.

 

Then you have a few seconds for the not so instantaneous water heater to stabilize the flow and temperature.

 

13 minutes ago, JSHarris said:

The French have been using small bore pipes for decades with no ill effects

Not sure about the ill effects, but they don't wash for decades.  The plumbing in our house in France was dreadful.

13 minutes ago, Ed Davies said:

This confusion is probably about as irritating to many Dutch people as referring to the UK as England is to many in NI and in other parts of GB.

 

When we lived there in the mid 60's, they did not like being referred to as Dutch, was to close to Deutsch, but they have got over themselves with special smugness.

1 hour ago, AnonymousBosch said:

A traditional vented hot water supply system has all sorts of quirks that need sorting out

I disagree.  The only drawback is if you can't fit the F&E tank high enough.  Apart from that, it is probably the easiest to install, apart from a SunAmp.  Still the cheapest by quite a way.

[Adam2]

So if you run a  10mm pipe to the bathroom hand basin in a full bathroom with shower/bath you then also  need to also run a bigger bore hot feed to the shower and/or bath as well to get decent flow? 

[Jeremy Harris]

6 minutes ago, Adam2 said:

So if you run a  10mm pipe to the bathroom hand basin in a full bathroom with shower/bath you then also  need to also run a bigger bore hot feed to the shower and/or bath as well to get decent flow? 

 

Yes, but the advantages are significant, as you also lose any interaction between things like the wash basin and shower, or toilet and shower, if you run separate pipes (a toilet is fine on 10mm too).  Running pipes from a common manifold fed with a fat pipe gets rid of pretty much all the interactions you can get with flow rates varying as taps are turned on or off, toilets are flushed, etc.  If running plastic pipe, then the cost difference for all these extra pipes is pretty tiny.  If running copper, then 10mm pipe can be PITA to run, especially if trying to feed it through posijoints, as it will snag on every web.

[AliG]

I think the 10mm pipe to the basin is the simplest solution for fast hot water. We have a recirculating system, but you still have to wait a few seconds at each shower etc for the water in the 15mm feeds to get from the main circuit to a fitting.

 

I looked into the instant hot water heater and then started to think where would I hide them, they will need an electricity supply etc.

 

As pointed out the only benefit of warm water for hand washing is comfort. Water has to be over 60C to kill bacteria which would burn your hands.

 

Maybe I have come across a great simple way to benefit the environment. Wash basins should only have cold supply. Thus we would save in fittings, pipework and energy. Personally I never use anything other than the cold tap in a basin, no matter what solution you are looking to use the water will likely not be warm unless people run it for a while.

[Adam2]

12 minutes ago, AliG said:

Maybe I have come across a great simple way to benefit the environment. Wash basins should only have cold supply. Thus we would save in fittings, pipework and energy. Personally I never use anything other than the cold tap in a basin,

 

I can see SWMBO uses the current mixer always in the middle position and is never at the basic long enough to actually get the hot water through so is just heating the pipes :-) So I almost agree aside fro shaving which for me has to be hot water.

 

 

[ProDave]

From a personal point of view it it a basin that most irritates me.  If I want to wash my hands, I want hot water now.

 

If I am having a shower, I know how long it takes for the water to get to the shower head, so I know at what part of my undressing routine to turn the shower on, knowing that as I remove the last garment, the hot water is arriving ready to step under. No irritation, no wait.

 

Likewise in the kitchen.  If I want to fill the sink. I just put the plug in and turn the tap on.  The cold slug to get the hot there, is about the right dilution ratio to give hot but bearable water.  It is rinsing things at the kitchen sink that irritates me which is why I rinse with cold most of the time because I can't be bothered to mess about.

[ToughButterCup]

1 hour ago, JSHarris said:

[...]

 Running pipes from a common manifold fed with a fat pipe gets rid of pretty much all the interactions you can get with flow rates varying as taps are turned on or off, toilets are flushed, etc. 

[...]

 

Running hot water pipes from a common manifold ? Or both hot and cold?

[Jeremy Harris]

5 minutes ago, AnonymousBosch said:

 

Running hot water pipes from a common manifold ? Or both hot and cold?

 

 

Best to run both from manifolds, IMHO, as some of the imbalance problems affecting flow come from cold water outlets, like toilet flushing.  The other advantage of having all the hot and cold feeds coming from a manifold is that you can fit ball valves to the manifold outlets, so allowing individual pipes to be isolated at source.  This can be really handy when first commissioning things, as you can turn supplies on one at a time, check for leaks, function, etc, then move on to the next.  It also means that any feed can be isolated in the event of a leak, leaving the rest of the plumbing still working.  Being able to do all this from one, fairly easy to access, location, seems useful, apart from the advantages it gives in terms of faster hot water to taps, lack of interaction between outlets, etc.

[ProDave]

On the subject of manifold systems.  Yes very handy.  But finding the right location that does not use up lots of pipe or make the runs longer than they need to can be a challenge.  I solved that by putting the manifolds above the ceiling of the utility room.  There will be a mini loft hatch arrangement to access it.  Acceptable in a utility room but probably not in any other room though.

[ToughButterCup]

Like this for example ...  ( given that I'm using Hep 2o)

 

[Jeremy Harris]

6 minutes ago, AnonymousBosch said:

Like this for example ...  ( given that I'm using Hep 2o)

 

 

 

Yes, exactly like that.  You can add reducers for the pipes you may wish to run in 10mm, and if you want absolutely minimum interference between circuits you can run the supply pipes to each manifold to both ends.  @PeterStarck has a photo in his blog of this:

 

[ToughButterCup]

Just now, ProDave said:

[...]

But finding the right location that does not use up lots of pipe or make the runs longer than they need to can be a challenge.  

[...]

 

I have had a look at your site ( url masked so I cant give the exact url).

So I stole this image from http://www.willowburn.net/ (without your permission)

 

Red's the hot manifold and white the cold one?

Why the spare ports on the manifolds?

[ProDave]

17 minutes ago, AnonymousBosch said:

 

I have had a look at your site ( url masked so I cant give the exact url).

So I stole this image from http://www.willowburn.net/ (without your permission)

 

Red's the hot manifold and white the cold one?

Why the spare ports on the manifolds?

There are spare ports because this house has been built in stages.  That was taken some tine last year, when we had only got one room complete downstairs, the kitchen / diner, or what people like to call these days the "family room".  So those two UFH circuits go off to the "family room"  That was how the house was when we first decamped from the caravan.

 

Next to be added was the left two circuits which head off under the gap craftily left under that stud wall, through into the living room.  And then, only a few weeks ago the UFH circuit for the utility room was added, that is the room the manifold is in and connects to the middle port of the manifold.

 

Clearly an up to date photo needs to be taken.

 

Edit.  As J points out, this is UFH manifolds.

 

My Hot and cold water "manifolds" are a bit less grand and look like this 

 

 

Again that was a work in progress, the en-suite and utility were not connected then.

 

Those are full bore isolators on the showers and bath, and ordinary ones on basins and sinks.  All 15mm.

[Jeremy Harris]

@AnonymousBosch, worth noting that the manifolds pictured in @ProDave's setup are for the UFH, not hot and cold water distribution.

 

The ones in the photo of @PeterStarck's installation are for hot and cold water distribution, not UFH.