Manifold system versus hot return system

[mvincentd]

The pipe from my hot cylinder to my manifold is over 20m.   From manifold to kitchen hot tap is around 12m.  With the hot return off it takes a totally unacceptable several minutes for hot water to arrive in kitchen.  With hot return on it is absolutely instant.

The hot return is one of my favourite things in the house and would be even if my layout didnt make it essential.

The pump is likely the most expensive bit so run the pipe anyway and try to live without it, then when you realise you cant, buy a pump.

Don't B'regs oblige you anyway on the grounds of water wastage if hot runs have over about 8m of dead leg?

[Nickfromwales]

Makes me chuckle to myself when folk build high 6-figure+ luxury homes and worry about running a 60W pump. ?

On a current project I’ve agreed with the client that we will go for hidden micro PIR’s under each of the floating / wall hung vanity units in each of the upstairs ( master and en-suite ) bathrooms, as the means of triggering the hot return pump. That HRC pump will be servicing those 2 basin taps only as the other high frequency / low volume outlets are close enough to the hot water device to not be deemed problematic, and running HRC’s to showers and baths is just pointless.

All hot and hot return pipe work has been robustly insulated and the pairs of pipes servicing individual HRC “flow and return” hot feeds are paired up inside the same piece of insulation; eg so the heated water in both pipes can remain warm as long as possible after the HRC pump has switched off ( 5 mins run time on the HRC pump will be trialled upon final commissioning the system ).

 

Annual running costs will be tiny, plus the property incorporates micro generation and storage, so, can be considered to actually cost less again. 
 

A holistic view will help so your property can employ such a system, successfully. It should be simple to arrive at, and seasonal efficiency will be dictated by the chosen means of control and of course the detail of how the installation is executed.

 

The worst things I’ve seen so far are HRC’s done with heat trace tape; zip tied loosely to the hot feed and wrapped in insulation! Running costs / waste heat / inefficiencies of such a poor choice and execution often get used to gauge whether such a system is ‘economical’ which is wrong. Also poorly insulted standard HRC’s cannot be used as a yardstick either. Give it some thought, do it properly, choose how you control it and enjoy some basic convenience. 

[Nickfromwales]

And for the Uber conscious;

 

https://www.grundfos.com/products/find-product/comfort.html

 

As little as 5-7W power needed. 

[joth]

1 hour ago, mvincentd said:

 

The hot return is one of my favourite things in the house and would be even if my layout didnt make it essential

If it's only needed for the kitchen then it is not so essential as could be done via a TMV off of an instant boiling water tap like the quooker combi, which is what we're doing as we're having the boiling tap anyway

Saves on some system complexity

[Nickfromwales]

9 minutes ago, joth said:

If it's only needed for the kitchen then it is not so essential as could be done via a TMV off of an instant boiling water tap like the quooker combi, which is what we're doing as we're having the boiling tap anyway

Saves on some system complexity

Agree, and I’m trying to promote that too. Just costs get a bit scary for the decent ( eg Quooker ) full combi units. Uplift to go the full

hog with the kitchen sink tap would cover the majority of the cost of the HRC components for a full house, so only really a consideration in a dwelling where the other remaining outlets aren’t problematic ( otherwise you may as well invest in the extra lolly on the HRC instead ( IMHO )). 

[Oz07]

What happens to the cold water in the pipe? Back into the tank to heat up?...As I said black magic.

To be fair it does take quite a few litres for my kitchen tap to run hot and would estimate around 10m or less 15mm pipe. 

[Onoff]

So in a traditional system, to fit a return pump, the return has to go into the cylinder at a certain height? This image, picked at random, seems to suggest so. Means letting in an Essex flange is it? Are pipe sizes important on the return?

 

[Nickfromwales]

Return can be a 15mm or a 10mm pipe. 10mm is my weapon of choice. Less cross-sectional area = less losses.

Yes. Cold water ( ambient of the house temp by that stage so not fully ‘cold’ ) returns to the tank. It’s a continuous, recirculating loop. 
If you T it into an open vented system and come in at the cold inlet you’ll increase turbulence and the stored hot water capacity a bit as the bottom ‘cool’ section would be uplifted by the ( eventual ) return of hot water. 

[Onoff]

2 hours ago, Nickfromwales said:

Return can be a 15mm or a 10mm pipe. 10mm is my weapon of choice. Less cross-sectional area = less losses.

Yes. Cold water ( ambient of the house temp by that stage so not fully ‘cold’ ) returns to the tank. It’s a continuous, recirculating loop. 
If you T it into an open vented system and come in at the cold inlet you’ll increase turbulence and the stored hot water capacity a bit as the bottom ‘cool’ section would be uplifted by the ( eventual ) return of hot water. 

 

So you can return into the cold feed at the bottom of the tank?

[Nickfromwales]

36 minutes ago, Onoff said:

 

So you can return into the cold feed at the bottom of the tank?

You should get the retro-fit side entry flange and cut it in about 2/3 of the way up the tank tbh. Teeing into the good feed will work just means the system will work a little harder to keep more water at a higher temp. 

[Nickfromwales]

https://www.bes.co.uk/1in-bsp-female-outlet-brass-essex-cylinder-flange-12266/

[Carrerahill]

On 01/04/2020 at 09:35, 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 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. 

You can calc it by knowing the below details, bit of a ramble here but the figures sort of speak for themselves and if you have a low flow rate issues will arise.

 

So if you know:

Time to first hot water leaving appliance (0 seconds if tank)

Then you need to know the volume of hot water pipework (0.14l/m for 15mm 0.320l/m for 22mm - valves are negligible).

Then you need to know your flow rate - just measured ours and we are on 1 litre every 5 seconds on the hot tap in the kitchen.

 

Then yes, it can be worked out.

 

Unless your pipe runs are over say 10m which is 1.4litres of cold water to clear and assuming no or low lag, then for the hot to move through that is only about 1.4litres before you get heat then I think it should be fine, on our tap that would be about 7 seconds in our house, however if you have a dribble of a tap, then it could take a heck of a while to see 1.4litres come through. It depends on flow too - we have excellent mains pressure and flow (hot is restricted due to boiler), so if our boiler was just a bit quicker we would be able to clear that 1.4litres quickly enough meaning we could see hot water in 7 seconds with a tank. However, we are more like 15m from the boiler so we are needing to clear 2.1litres which is 10.5second just to clear the standing water.

 

I shortened the pipework as much as I could too but it's still the case of hot on full flow for about 15seconds which is then wasting 3litres just to get warm water.

 

It is OK if washing up or needing hot water to clean things off but for hand washing it is a bit of a wait so often lots of soap and cold do - our boiler is however older, I won't change it just to wash my hands quicker in the sink so it's fine, never bothered me. Bathrooms are closer so water to those taps is about as fast as the boiler can spit it out.

 

I did contemplate plumbing to our kitchen sink in 10mm copper - I think it would have worked but without the facts and figures at the time of plumbing I went 15mm. 

[Nickfromwales]

On 01/04/2020 at 09:35, Russell griffiths said:

before I dismiss a manifold and start thinking about hot returns. 

Just to clarify;

The HRC is added to the manifold system, it doesn’t ‘replace’ it. I still would steer well clear of series plumbing with T-offs for each room and go with radial ( off manifolds ) for the best results.

 

FYI, you simply add a 3rd manifold which accepts the hot return pipe runs. That is required for when you need to isolate a hot supply to a particular outlet, as if you didn’t have that then the outlet would get back-fed from the other hot return outlet connections ( as they would still connected via the common HRC connection at / before the HRC pump so at full hot pressure ). 

Remember that if you go away from

manifolds then you have to increase the size of the hot water pipe work, significantly, at the start of the DHW pipe run to cope with multiple outlets drawling from the same common connection. 
 

Thread title says VS but it should read “hot return or not?”  

[Nickfromwales]

18 hours ago, Carrerahill said:

I did contemplate plumbing to our kitchen sink in 10mm copper - I think it would have worked but without the facts and figures at the time of plumbing I went 15mm. 

I now do the basins and kitchen / utility sinks in 10mm, routinely, but will do 15mm if they’re close enough to the hot water device not to need an HRC. That helps the flow rate so gets the slug of dead cold water out a little quicker when ‘unassisted’. 
As always, no 2 instances are exactly the same so you need to review and execute to suit your own dwelling. 10mm copper ( plastic coated ) is what I’m using, so you don’t have the issues of the copper contacting other dissimilar metals ( pozi webs etc ) and also you then get the fullest bore pipe internal available. 

[LA3222]

On 01/10/2020 at 07:40, Nickfromwales said:

I still would steer well clear of series plumbing with T-offs for each room and go with radial ( off manifolds ) for the best results.

 

FYI, you simply add a 3rd manifold which accepts the hot return pipe runs.

I'm dipping in and out of plumbing at the minute Nick and I had this thread at the back of my mind as your argument made me rethink the HRC situation and its probably something I will incorporate. Part of what put me off is not understanding how it is configured to a manifold setup - are you able to sketch out briefly the setup you describe above?

 

I'm struggling to envisage how I connect up two pipes (flow and return) to the outlet/tap. Do you run two pipes to it and tee them at the tap with a short piece going from the tee to the tap? Effectively giving you a loop with a bit sticking out of it. So you have the hot feed going to a manifold so you can feed each individually. Whats the best way to deal with joining up the return pipes before feeding back to the tank? Another manifold?

 

TIA

 

[Dan F]

On 25/11/2020 at 23:00, LA3222 said:

I'm struggling to envisage how I connect up two pipes (flow and return) to the outlet/tap. Do you run two pipes to it and tee them at the tap with a short piece going from the tee to the tap? Effectively giving you a loop with a bit sticking out of it. So you have the hot feed going to a manifold so you can feed each individually. Whats the best way to deal with joining up the return pipes before feeding back to the tank? Another manifold?

 

Did you work this out, what approach are you taking in the end?    Currently looking at this myself:

- Want to avoid a standard loop if possible, as we'd potentially need to start at 28mm to ensure enough flow for mutiple bathrooms + kitchen.

- The bathrooms aren't quite close enough to use "home run" approach for everything.   (although 10mm to these basins would improve things)

 

Plumber had suggested using satellite manifold for each of 3 bathrooms with HRC for each. Reading the posts here though, I'm realising that most of these outlets are quite close to the plant room and it will probably be simpler just to have direct 10/15mm pipe runs. (also no need to find somewhere to hide manifold in bathroom either)

 

The question then is what to do about the outlets (basins at least) on the other side of the house. I tihnk the options are:

1) Use "home run" for everything, and run dedicated HRC's for the 2 remote basins in question. (as seems to have been discussed above)

2) Mixed approach:
         - Everything close to plant room is piped direct to a manifold next to UVC (no HRC)

         - A satalite manifold(s) with HRC supplies all outlets in the 2 bathrooms on the other side of the house.  (22mm)

 

The second option seems to be most logical as a satiallte manifold would mean a single HRC back from manifold and not need for return connection under sinks (some of which are wall-mounted).

[LA3222]

@Dan F I have the kernels of a plan at the back of my mind.

 

Going to have manifold for everything located in my plant room. This is in one corner of my house (14.5m wide) so not ideal for runs but such is life.

 

All the big stuff will be in 15mm Hep2O and the smaller stuff in 10mm Hep2O.

 

Only things I will put on a HRC are the basins. All the other hots go to things like baths, showers, sinks where waiting 30s for hot to come through isn't an issue.

 

The 4 basin hots will have a flow and return manifold. So as IUI the each of the 4 loops will have a tee coming off it at the outlet. So the hot in the loops get circulated and there will be a small dead leg at the appliance outlet.

 

[JFDIY]

I'm going to feed my bathroom toilet with 15mm pipe and a TMV set to about 30c. If you pause for a moment before washing your hands the cold slug of water is in the toilet cistern and not wasted.

 

Got this arrangement in my current bathroom and it works well.

 

Also going to pipe washing machine and dishwasher in same way, with TMV set to 35-40c to reduce run times on appliances, cheaper way of heating water and it will purge the kitchen tap pipe run when in use

[ProDave]

9 minutes ago, JFDIY said:

Also going to pipe washing machine and dishwasher in same way, with TMV set to 35-40c to reduce run times on appliances, cheaper way of heating water and it will purge the kitchen tap pipe run when in use

I have not seen a WM that takes a hot feed for a very long time, and never seen a DW that does.  They are all cold fill only.

 

A common theme here is people putting the HW tank in the "plant room"  I nearly fell into that mistake, but then relocated the HW tank to an airing cupboard formed in the forned of the spare bedroom to put the HW tank central to all points of use.

[JFDIY]

12 minutes ago, ProDave said:

I have not seen a WM that takes a hot feed for a very long time, and never seen a DW that does.  They are all cold fill only.

 

Agreed, but they should all cope with a 30c or so inlet temp on the cold feed as that is a hot summers day.

 

Beyond that better check manufacturers spec on allowable inlet temp.

 

Think the reason hot fill disappeared was creative accounting in the eco ratings as you're only heating the water being directly used by the appliance. But they're ignoring the cost differential between heating sources (gas Vs elec in my case)

[mvincentd]

1 hour ago, JFDIY said:

the cold slug of water is in the toilet cistern and not wasted.

?....if your cistern is already 'charged' won't that slug just effectively go to overflow?

[ProDave]

1 hour ago, JFDIY said:

 

Agreed, but they should all cope with a 30c or so inlet temp on the cold feed as that is a hot summers day.

 

 

So you are going to feed slightly warm water into the cold feed as a pre heat?

 

I can see that saving some energy when it wants to heat the water, but when it's just rinsing and expecting cold water, you are then just wasting your warm water?

[JFDIY]

5 hours ago, mvincentd said:

?....if your cistern is already 'charged' won't that slug just effectively go to overflow?

 

The hot water pipe goes to the tap, but also has a T close by, this feeds a thermostatic mixer, the output from the mixer (30c) goes to the toilet.

 

When you flush the toilet, it fills with tempered water and purges the hot pipe to the tap. 

 

Agreed, if you don't use the toilet then you still have a bit of a wait. But my current bathroom needs to clear about 3litres before the hot comes through which takes around 30secs or more.  with the set-up as above its about 5 secs, and the water isn't wasted.

[Dan F]

11 hours ago, LA3222 said:

The 4 basin hots will have a flow and return manifold. So as IUI the each of the 4 loops will have a tee coming off it at the outlet. So the hot in the loops get circulated and there will be a small dead leg at the appliance outlet.

 

OK, so 4 seperate loops to each of the 4 basins and back?  This makes sense, just trying to justify (to myself) if/why this approach is better than:

i) A single 10/15mm loop picking up all remote basins.

ii) A satellite manifold(s) on the same side of the house as the remote basins.

 

These are my thoughts, interested to know if there are any other pros/cons though:

-  A satalite manifold serving whole bathroom(s) would likely require 22mm+ which means more heat losses without any obvious advantages. 

-  A loop picking up 3-4 remote basins wouldn't give you centralized independant isolation.  15mm may be needed instead of 10mm.  You'll be keeping more water warm during recirculation, but not much more if all in 10mm (vs 15mm)

 

The other challenge though is if there is enough space in the plant room. If we go with everything radial, we'd have:

- 15 hot

- 3 hot recirculation

- 18 cold

- 4 cold unsoftened

 

 

 

[Gone West]

13 hours ago, JFDIY said:

When you flush the toilet, it fills with tempered water and purges the hot pipe to the tap.

Nice idea, also will prevent condensation forming on the outside of the cistern.