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Author Topic: Hot water supply weak  (Read 193 times)

doganjo

  • Joined Aug 2012
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Hot water supply weak
« on: September 23, 2020, 06:48:13 pm »
I didn't know where to put this, so please move if necessary @Dan

Can all you engineering clever clogs come up with a solution please?

I moved last year to a long bungalow.  - cold water tank is in loft; Boiler and  hot water tank at one end of the house, main bathroom at the other, ensuite at same end as boiler.

The hot water comes through the ensuite shower and basin tap more or less straight away - a few seconds, but it takes 61 + seconds for the hot water to start coming through in the bathroom basin tap and a bit longer in the shower/bath.

Is it possible to sort this? At present I have a note in my bathroom for guests to turn on the tap when they go in to give it time to heat up - anticipating that they take longer than a minute to be ready to wash their hands after using the loo.   :innocent:



Always have been, always will be, a WYSIWYG - black is black, white is white - no grey in my life! But I'm mellowing in my old age

Womble

  • Joined Mar 2009
  • Stirlingshire, Central Scotland
Re: Hot water supply weak
« Reply #1 on: September 23, 2020, 07:44:43 pm »
Hi Annie,

There are three ways I know of to sort this:

1) Install a small electric "on-demand" water heater in the bathroom. This would sort out the basin at the far end of the house, but you'd still have to wait for the shower / bath.

2) Install a recirculation loop pump. Basically you'd install a return pipe from the far bathroom to the hot water tank, and a small pump. That would keep all of the pipework warm at all times (but make sure you insulate all the pipework also, for energy efficiency).


3) Put electric "trace heating" tape along the pipe, then insulate on top of this. This has just enough electrical power to keep the pipes warm, so avoids the initial slug of cold water from coming through.

You pays your money and you takes your choice, basically!

How accessible are the pipes themselves, throughout their length?
"All fungi are edible. Some fungi are only edible once." -Terry Pratchett

doganjo

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Re: Hot water supply weak
« Reply #2 on: September 23, 2020, 09:36:17 pm »
How accessible are the pipes themselves, throughout their length?
David I'm an accountant not a plumber - how would I know?  :roflanim: :roflanim:

I leave the house when they start knocking it around, but I'll mention that last method to my plumber when I see him next, as it sounds the most feasible.  Thank you
Always have been, always will be, a WYSIWYG - black is black, white is white - no grey in my life! But I'm mellowing in my old age

Kiran

  • Joined Apr 2019
Re: Hot water supply weak
« Reply #3 on: September 24, 2020, 05:41:17 am »
For my money a point of use water heater for the bathroom sink is the way to go. The other 2 both require a constant use of fuel where as point of use will be on demand. The hot water return idea is a good one and is used commercially but at the furthest point of the return, which I assume in this case is the bathroom, the return temp needs to be 55C so leaving the boiler potentially 60/70C. A lower temperature than that risks the build up of legionella in the pipework and outlet. This would mean you'd be heating the return loop fairly constantly. As for the shower, either go electric or preferably take a pipe directly from the hot water tank to the shower. Final solution I can come up with is relocate the boiler centrally and or change over to a modern combi which benefit from using mains pressure which should get the hot water to the outlet faster.

Backinwellies

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Re: Hot water supply weak
« Reply #4 on: September 24, 2020, 07:17:07 am »
For my money a point of use water heater for the bathroom sink is the way to go.

I agree
Linda

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Womble

  • Joined Mar 2009
  • Stirlingshire, Central Scotland
Re: Hot water supply weak
« Reply #5 on: September 24, 2020, 07:25:14 am »
David I'm an accountant not a plumber - how would I know?  :roflanim: :roflanim:

This amuses me greatly. I'm a plumber (ok, chemical engineer), not an accountant, but if I could have a tenner for every time an accountant has told me my project specification is wrong.....  ;)


@Kiran - that's a good point about legionella. Wouldn't the hot water tank be sitting at 60 degC usually anyway though, for that exact reason? As you say, these systems are used commercially, so there will be a regulation covering it somewhere, no doubt.


Yes, I think I'd go for the point of use heater also, and would just accept that the shower / bath will take a minute to come warm. I don't think the other two solutions would cost that much in energy though. The recirculation pump could be the smallest pump available, and could even be on a daytime only timer, whilst the trace heating will only be used to overcome heat losses from the (insulated) pipe, so would only be a very small electrical load.

"All fungi are edible. Some fungi are only edible once." -Terry Pratchett

chrismahon

  • Joined Dec 2011
  • Gascony, France
Re: Hot water supply weak
« Reply #6 on: September 24, 2020, 09:20:53 am »
i agree that the way to go is an instantaneous water heater for the sink, but it will just be a trickle. the cost will be in the wiring as the plumbing is simple. I've replaced many of these so they are not that reliable.


Recirculating systems result in a lot of heat loss from the pipes, as well as the small energy usage for the pump. Legionella isn't an issue as the water has been above 60C and it will have been killed. Will need a second length of pipe across the building and under the insulation, so a lot of work. Not a solution I'd consider.


Another option is a second hot water tank in the bathroom with electrical heating only. The connection to the original tank would need to be broken at both ends and drained, so quite expensive, but hot water to the bath and shower would be quick. Needs another header tank as well.

Kiran

  • Joined Apr 2019
Re: Hot water supply weak
« Reply #7 on: September 24, 2020, 09:57:51 am »
@Womble You are correct regarding tank temperatures etc, the problem is that a hot water cylinder is well insulated and given the volume of hot water doesn't suffer much heat loss( assuming modern cylinder etc.). The pipe my comparison works like a reverse heat exchanger. the surface area exposed to the colder temperatures gives off more heat as the water travels around the pipework than it would if the same volume of water was contained in the cylinder. The result is that either the tank temp drops more rapidly or the boiler has to keep firing to top up the temperature of the tank. Modern, efficient lagging and shortest possible pipe runs would help

Womble

  • Joined Mar 2009
  • Stirlingshire, Central Scotland
Re: Hot water supply weak
« Reply #8 on: September 24, 2020, 10:09:50 am »
^ Yep. Agree totally. If I were going to try the recirculating system, I'd go for a really small diameter pipe for the return, and would then lag everything very well indeed.

@doganjo - how about one of these? As Chris says, 9 litres a minute isn't a massive flow, but it is enough to wash your hands with at least.
"All fungi are edible. Some fungi are only edible once." -Terry Pratchett

Kiran

  • Joined Apr 2019
Re: Hot water supply weak
« Reply #9 on: September 24, 2020, 11:05:55 am »
That's the type of thing I was referring to as opposed to the above sink hot water tap type units.

9L/minute is a bad flow rate, 150ml/sec is essentially half a drink can a second.

doganjo

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Re: Hot water supply weak
« Reply #10 on: September 24, 2020, 02:57:30 pm »
Thanks everyone.  I should have said that this is a completely new bathroom - state of the art hotel quality so I don't want it mucked around with visibly.  If something can be done behind the scenes that's fine otherwise guests will just have to wit for it to come through
Always have been, always will be, a WYSIWYG - black is black, white is white - no grey in my life! But I'm mellowing in my old age

Womble

  • Joined Mar 2009
  • Stirlingshire, Central Scotland
Re: Hot water supply weak
« Reply #11 on: September 24, 2020, 03:06:40 pm »
9L/minute is a bad flow rate, 150ml/sec is essentially half a drink can a second.


I just measured our upstairs hot tap at 4.5 litres per minute. I find that flowrate works just fine for all practical purposes.
"All fungi are edible. Some fungi are only edible once." -Terry Pratchett

 

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