Manifold system versus hot return system

[Russell griffiths]

I like the look of a manifold type water system, however I have some reasonable long runs for the hot water. 

Is there a way of calculating how long it will take hot water to reach the tap from a cylinder. 

 

I will  have a measure up today to see what you all think 

 

I understand you can change pipe size to certain things. 

 

But it would like to be able to do a mock up to see if it will work before I dismiss a manifold and start thinking about hot returns. 

[Oz07]

What will be your hot water source? My layman's experience is a good chunk of the delay on hot water is waiting for a combi to fire up. If you're on a tank this is cut down

[Russell griffiths]

1 minute ago, Oz07 said:

What will be your hot water source? My layman's experience is a good chunk of the delay on hot water is waiting for a combi to fire up. If you're on a tank this is cut down

ASHP and a big cylinder. 

Oil boiler and a big cylinder 

yet to decide, got to get some prices going as I already have the oil burner. 

[MikeGrahamT21]

Using 10mm pipe seems to alleviate a lot of problems, which is what i'll be doing, as long as the runs aren't rediculously long.

[LA3222]

7 minutes ago, Russell griffiths said:

I like the look of a manifold type water system, however I have some reasonable long runs for the hot water. 

Is there a way of calculating how long it will take hot water to reach the tap from a cylinder. 

I have only done some fag packet sums on this myself so far, but I've started off on the assumption that all water in the pipe run is cold so if you know what the flow rate is, you can calculate the volume of the pipe and then how long it will take to purge the cold and replace with hot.

[Conor]

Yes. You will need to know:

 

Desired flow rate at the outlet.

Diameter of pipework - make sure you use internal bore.

Length of pipework.

 

Chose your metric. In water networks, we use litres per second. In your case, litres per minute are a better starting poimt. Then enter your data here:

 

http://www.calculatoredge.com/mech/pipeline velocity.htm

 

Then think back to school and calculate the time it'll take over your given length. You'll find that halving the pipe diameter will result in the time reducing by a factor of alomost 4.

Edited April 1, 2020 by Conor

[Russell griffiths]

Ok, quick reply’s you must all be sitting at home bored

hang on and I will come back with some measurements. 

 

Cheers all. 

[Mike]

A manifold & thin bore pipe will certainly help (and cut energy use), as will positioning the hot water tank near the main points of use.

 

Also consider your hot water requirement - you only need cold for a washing machine or dish washer, you really only need cold for a downstairs WC (nobody waits for the hot to arrive, and cold + soap is as hygienic), and waiting a while for other uses is rarely a problem - you can always stack a couple of dishes or start brushing your teeth...

Edited April 1, 2020 by Mike

[Russell griffiths]

As promised I’m back to stop you all getting bored

one of the main high usage taps will be a distance of 20m from the cylinder 

is this getting crazy , am I looking at needing a hot return 

 

oh god my heads hurting again, all I need now are some smart Alec comments from @AnonymousBosch and it might push me over the edge. 

[PeterW]

6 minutes ago, Russell griffiths said:

am I looking at needing a hot return 

how about a hot flush instead ......??

 

[PeterW]

Btw @Russell griffiths I’m not joking ..! If the pipe serves a bathroom or toilet then using the hot feed to the room to the cistern will pull 4 litres of water from the tank. A 15mm pipe 20m long holds about 2.5 litres so a flush will mean you’ve got hot at the tap when the cistern has refilled. 

[Mr Punter]

If you have to have hot water to a basin and it is a long way from the cylinder you could have an undersink heater or instant water heater.

 

If you do go for a hot water return / secondary circulation system, make sure you spend time and money to insulate pipework as much as possible.

[JFDIY]

42 minutes ago, PeterW said:

Btw @Russell griffiths I’m not joking ..! If the pipe serves a bathroom or toilet then using the hot feed to the room to the cistern will pull 4 litres of water from the tank. A 15mm pipe 20m long holds about 2.5 litres so a flush will mean you’ve got hot at the tap when the cistern has refilled. 

 

This what I've got in my bathroom, but I have a thermostatic mixer set to 30 degrees C to protect the toilet cistern from seeing water that might be too hot.

 

It works very well, by the time you've flushed the toilet adjusted your wares and started washing your hands the hot is there. I will do the same in new en suite.

 

Considering piping the new kitchen in a similar way, with hot going to the sink then a mixer to the dishwasher, to pull hot through and also reduce electric consumption on dishwasher heating.

 

Here's a consideration;

 

I'd be interested to know if it's possible to run two pipes in parallel, a  10mm and say a 22mm but have a pressure differential valve that somehow allows the 10mm pipe to supply low flow requirements, then open the larger pipe if higher flow is required. Thinking en suite basin and shower.

 

Or could you use a thermo mixer set at say 60 degrees with the 10mm to the hot side and the 22mm to the other.

It would pull the 10mm through quickly.then blend the rest until full flow was available.

 

Just thinking aloud there....

 

 

 

[Tony C]

Hi Russell, What was the solution you have ended up with ?

I have similar situation with one bathroom long away - 25m, and will be using System boiler+Cylinder.

Did you go for secondary return system?

Edited September 27, 2020 by Tony C

[Russell griffiths]

Still not sorted it, just looking at plumbing in the next couple of weeks. 

[Tony C]

17 minutes ago, Russell griffiths said:

Still not sorted it, just looking at plumbing in the next couple of weeks. 

Thanks, let me know the progress.

I am wondering if you could plumb this furthest point first then try how long it takes to get the hot water?

then install the secondary circulation pipe if you desire...

[CC45]

we've got a 2ndary return.  Remember that the loop will benefit anything else that feeds off it - its not just the furthest point that it benefits.

[Tony C]

40 minutes ago, CC45 said:

we've got a 2ndary return.  Remember that the loop will benefit anything else that feeds off it - its not just the furthest point that it benefits.

Thanks for the insider information!

How is the effect on the utility bills? I saw some article saying that it is not economic.

[PeterW]

13 minutes ago, Tony C said:

Thanks for the insider information!

How is the effect on the utility bills? I saw some article saying that it is not economic.

only if they’ve been set to run 100%. I installed one with a 5 min/ hour run time from 6am-midnight in a commercial building and it saves about £300 year on gas and electric. 

[Russell griffiths]

I’m still thinking about this and wonder if we are overly worried about how long it takes to get hot water to a tap. 

 

Things ive thought about. 

 

90% of the time I need a wee I’m out around our land and wee in the bushes, so never wash my hands. 

 

I asked the wife wife if she waits for the hot to come through when she has been to the toilet, she said no she uses soap and cold water. 

 

If if I go to have a shower I turn on the mixer and then get undressed, so the hot is there by the time I step in. 

 

If if I want a bucket of hot to wash something in the garden I place a bucket in the sink and let it run, it takes a minute to fill a bucket and I don’t want it all hot so what’s the problem there. 

 

I think with building a new house we  want everything perfect, instant hot water taps and stuff, what happened to just flicking the kettle on 

I think it’s all getting a bit carried away. 

[Oz07]

KISS

I wouldn't bother. 

[LA3222]

11 minutes ago, Russell griffiths said:

I’m still thinking about this and wonder if we are overly worried about how long it takes to get hot water to a tap. 

 

Things ive thought about. 

 

90% of the time I need a wee I’m out around our land and wee in the bushes, so never wash my hands. 

 

I asked the wife wife if she waits for the hot to come through when she has been to the toilet, she said no she uses soap and cold water. 

 

If if I go to have a shower I turn on the mixer and then get undressed, so the hot is there by the time I step in. 

 

If if I want a bucket of hot to wash something in the garden I place a bucket in the sink and let it run, it takes a minute to fill a bucket and I don’t want it all hot so what’s the problem there. 

 

I think with building a new house we  want everything perfect, instant hot water taps and stuff, what happened to just flicking the kettle on 

I think it’s all getting a bit carried away. 

I agree with you bud, a hot return is something I dismissed pretty early on. I wasn't able to centralise my plant room so its stuck at one end of the house with hot taps all over the shop, so my hot runs vary between 10-20m. I looked at how much volume is held in the pipe over those runs and assessed how long it would take hot to flow versus what the tap served and came to the conclusion that although instant hot is a nice to have, its not going to have any detrimental affect on our life not to have it. So good idea, but far from critical.

[Nickfromwales]

It costs a few quid to service the essentials, kitchen / utility / wash basins in each bathroom ( and nothing else ) and costs pennies to run if insulated / installed properly ( and even less in a house with PV ). 
It’s nice for the low volume / high frequency outlets and not fitting a HRC is nuts imho. Why not give yourself a bit of convenience and “luxury” ?!? 
Think about how much you spent on an architect and how much the doors and windows cost, and then get a reality check on the penny pinching  

[Oz07]

To be fair probably seems a lot simpler to @Nickfromwales because it's his area. All the plumbing and mechanical side is a bit like black magic to us Neanderthals 

[Nickfromwales]

19 minutes ago, Oz07 said:

To be fair probably seems a lot simpler to @Nickfromwales because it's his area. All the plumbing and mechanical side is a bit like black magic to us Neanderthals 

It’s just an extra pipe or two, a pump, and some basic controls.