Expansion provision for Hep2O?

[Alan Ambrose]

The instructions say:

 

 

A 10 metre run of 15mm pipe on a hot water circuit (ΔT = 55°C) will expand by approximately 72mm.

Expansion must be accommodated with:

• Directional changes in pipework routing (natural offsets)
• Expansion loops where long straight runs cannot be avoided
• Proper use of fixed points (anchor brackets) and guide brackets to direct expansion into loops

 

How do peeps handle that in practice?

[Russell griffiths]

You don’t. 
there is absolutely no reason to be heating your water to that temp, so expansion is not a thing to worry about. 

[G and J]

Our max temp difference will be 35°C (ambient background temp min to max hot water temp).

 

Long runs are bad news for hot water so to be avoided anyway.  (Most of our sinks/basins are served by 10mm hep to get hot water PDQ, which is working well though it does mean the flow rate isn’t torrential).

 

In practice I’ve only one straight section over a metre long and that’s to the garage through a 4.5m duct with bends either end.  
 

Do you really need long straight sections?

[Nickfromwales]

6 hours ago, Alan Ambrose said:

The instructions say:

 

 

 

A 10 metre run of 15mm pipe on a hot water circuit (ΔT = 55°C) will expand by approximately 72mm.

Expansion must be accommodated with:

• Directional changes in pipework routing (natural offsets)
• Expansion loops where long straight runs cannot be avoided
• Proper use of fixed points (anchor brackets) and guide brackets to direct expansion into loops

 

How do peeps handle that in practice?

It’s not a real world problem, and I have been putting Hep2o into very large projects since 2010, and beyond; never a single groan, creak, or complaint. The only instances of failure I have ever heard of are from JG Speedfit, where idiots have not used the plastic cir-clips and the fittings have simply unscrewed themselves. Not a good design, but most merchants sell bucketloads of the JG fittings each day (but stare blankly at you when you ask for cir-clips).

 

#tickingtimebombsaplenty

 

My comment regarding real world doesn't mean the pipe does not expand, “ye cannae change the laws of physics, Jim”, it means that in real life you won’t have a house that does not require the pipe run to turn left / right and go uppy / downy and more. Ergo, the issue is self-resolving; you will not have any arrow straight, fixed point A to fixed point B runs without a single turn, (in all likelihood / reality, and my continued direct experience(s).

 

Note: I do not directly fix the distribution pipework any more, instead I insulate the pipes with EPS lagging (minimum 9mm wall) and then I band to that relatively loosely; this is so the pipe is free to creep inside the insulation without the ‘grabbing’ that comes from clipping to it directly. Also means 100% of the pipe run is insulated vs stopping and starting at each clip. 
 

I consider the ‘here and now’, but also the not getting of “that phone call”, eg the one where I get informed that the pipes are making noises (behind the paint, plaster, plasterboard, insulation etc); by then they all live there too, so adding in the upheaval of having to fix things after the house becomes occupied = feck that!

Belt & braces people!!!

 

Furthermore, I almost always fit an accumulator on the cold mains and this will accept any unwanted additional ‘peak’ expansion too, should such a thing ever occur. The UVC control group does not feature an NRV btw, so all of the hot network can ‘see’ straight to the accumulator.

 

Re the 55°, temps are only that high on runs to the kitchen sink / utility sink (55°C is my go to, to cut / emulsify grease etc effectively) with everything else being <50°C; baths MUST be capped at 46°C so you’ll either need these off a TMV, or to have thermostatic bath taps / fillers which can be commissioned to go no higher. I almost always go TMV as it kills more than 2 birds; reasons to follow. 
 

As an aside, 46°C bathwater is too bloody hot for me by a mile, as I’m not a fan of steamed plums.

 

Anyhoo…..

 

I am currently in the middle of plumbing a sizeable dwelling that I have “designed” for, with 1x full family bathroom, 1x full master ensuite, 1x teen shower room, 1x guest ensuite shower room, a cloak WC, kitchen, and utility.
 

*Full means bath + shower. 

 

All this is being plumbed in 15mm Hep2o with the longest run being about 18/19m, bar the cloak WC which is in 10mm as it’s next door to the wet plant room. That longest run is to the teen shower room which is at the opposite side of the house to the ‘wet plant’ room; originally this teen shower room didn’t feature in the house design, and everything ‘wet’ was on the side of the house that was local to the ‘wet’ plant room.
 

I suggested adding this teen shower room mid-build, to keep the kids ablutions ‘that side of the house’, but also to mitigate excessive wear and tear on the (to be very nicely presented) family or guest bathrooms; reduced cleaning / extended longevity etc etc and reduced noise at the bed 1 side of the landing so mum and dad can have some peace. I’d kill for that tbh, ours is like the O.K. Corale all bloody day and night.   

 

All basins, the teen shower, and the kitchen sink will be on the hot return circuit; controls methodology is currently being pondered over, but no 2 projects / client(s) remit are the same so these always differ.
 

For this project the lions share of the hot outlets will be fed via a TMV at 46°C^*, usually only 22mm but in this instance I will beef that TMV up to 28mm and take off it both of the bath hots and 4 shower hots, to cap the distribution temps in those pipes and reduce latent losses (albeit these will be quite insignificant in real life as this all happens within the heated envelope) and to stop excessively high water from leaving the UVC to then be lost as wasted energy. 

 

In a nutshell, no hot water leaves the UVC without going via thermostatic control.

 

^*Not being able to scald yourself anywhere in the home is also something that should be considered; especially with young kids or elderly / infirm etc. Most hotel showers would see me in the burns unit if I flicked the controls the wrong way…..

 

The kitchen and utility sinks are the only exceptions here typically, but that’s on the proviso that I’ll be including another TMV (15mm) to cap that at 55°C. This allows us to max out the stored temps in the UVC when PV is covering hot water production via the immersion on timed bursts; late morning and another early > late afternoon etc (in line with generation info gleaned from the inverter / app to say “when’s best to do so”). Differs job to job obvs, and also very relevant if you're using timed chunks of off peak electricity > immersion; immersion would be set to max out the stored heat energy at say 75°C then, to increase the storage and utilisation of the cheap energy, hence you defo need the 55°C TMV so extremely (eg scalding) hot water can never arrive at ANY outlet, ever.

 

Some will argue that the cheap or free electricity should go into the heat pump and that should provide DHW, but I argue back that you cannot expect a heat pump in summer to be jumping back and forth from cooling to full blast hottest possible temp for DHW for 15/30/60 mins, and then screeching to a halt thereafter to go back to cooling. Yo-yo’ing back and forth like this cannot possibly be good for these things, imho, adding unnecessary wear and tear to the heat pump (when you can just dump this straight into a 99% efficient immersion heater and let the heat pump lay down, or sleep). IMO, if you give your heat pump an easy life it’ll live longer, and given the choice between immersion or heat pump, I know which one I’d rather have to replace.

 

Some digression, but best to give some additional info, as is ‘the way’ here. 

 

Bonjour. 

[JohnMo]

29 minutes ago, Nickfromwales said:

ome will argue that the cheap or free electricity should go into the heat pump and that should provide DHW, but I argue back that you cannot expect a heat pump in summer to be jumping back and forth from cooling to full blast hottest possible temp for DHW for 15/30/60 mins, and then screeching to a halt thereafter to go back to cooling. Yo-yo’ing back and forth like this cannot possibly be good for these things, imho, adding unnecessary wear and tear to the heat pump (when you can just dump this straight into a 99% efficient immersion heater and let the heat pump lay down, or sleep). IMO, if you give your heat pump an easy life it’ll live longer, and given the choice between immersion or heat pump, I know which one I’d rather have to replace.

Or just time DHW to coincide with peak PV production, heat to normal temperature via immersion thermostat. Leave heat pump to do heating or cooling and immersion to do DHW or if DHW production not needed export, just export or charge battery - maybe both.

[Nickfromwales]

1 hour ago, JohnMo said:

Or just time DHW to coincide with peak PV production, heat to normal temperature via immersion thermostat. Leave heat pump to do heating or cooling and immersion to do DHW or if DHW production not needed export, just export or charge battery - maybe both.

My point entirely, as above, you need to choose a time based on your own statistical information from your own inverter app either way, but it’s just a pointless exercise to get your heat pump slaving away when you won’t use all the excess up anyways. 
 

Plus if cooling then I’d not want the heat pump being pulled in all different directions. Any homes with fan coils and no buffer would see these shutting down during DHW production too.

 

Juice > immersion = dead simple, and with a decent PV array you’ll still end up exporting anyways so why end up with a tired heat pump at all?

 

ASHP’s take time to get up to temp too, so this situation isn’t as efficient as it first sounds either, whereas the immersion is a whiff under 100% efficiency.

 

So,   

[JohnMo]

Plus those using something like a heat geek cylinder, could be spending a couple hours heating via the heat pump.

 

I was finding a reported CoP of 3 to 4 over a few years, but reality is I haven't seen a noticeable change in electric consumption or export amounts since moving to immersion only DHW. So really ASHP is not as efficient as it cracked up to be.

[Alan Ambrose]

Well that all v interesting, thanks.

 

I guess my longest straight runs are about 6m, so maybe 15-20mm expansion at a delta T of say 25C.

 

So, it sounds like expansion is a thing to think about but mostly taken care of by pipe geometry and a little care with installation i.e. allowing it to expand and shrink and generally move about a bit without a problem.

 

Could trip you up though if you were not bearing it in mind.

 

[G and J]

So how long does an average heat pump last then?

 

Whilst it’s a bit of string question in many ways there must be norms.   Modern condensing gas boilers seem to have a useful life of about 9 years, so is there an equivalent for heat pumps?

 

Or are they trigger’s broom?

[G and J]

So they last forever then.  Fab. 

[dpmiller]

how long does a domestic fridge last for, it's the same basic tech.

[Nickfromwales]

On 28/09/2026 at 22:01, G and J said:

So how long does an average heat pump last then?

 

Whilst it’s a bit of string question in many ways there must be norms.   Modern condensing gas boilers seem to have a useful life of about 9 years, so is there an equivalent for heat pumps?

 

Or are they trigger’s broom?

I thought my digressions were bad lol. 
 

All depends on use and how you’ve set it all up / where it lives etc. If fitted in a typical UK home, brick and block, draughty, full of rads that will be on flat out to keep the place ‘almost warm’, and lots of high temp DHW runs, then I’d say you’d be lucky to see 10 years out of it. 
 

In your house, can’t recall if you have PV or not, it’ll live a nice ‘low temp life’ and prob last 15 years minimum. Subject to routine and preventative maintenance obvs, but in a nutshell if it moves it’ll break one day, so pumps = head and fan = handle, Trigger. 

[Nickfromwales]

9 hours ago, G and J said:

So they last forever then.  Fab. 

I was having a glum morning, dealing with insurance pricks, again, but that cheered me right up. PMSL.  

[marshian]

On 27/09/2026 at 14:25, Nickfromwales said:

Re the 55°, temps are only that high on runs to the kitchen sink / utility sink (55°C is my go to, to cut / emulsify grease etc effectively) with everything else being <50°C; baths MUST be capped at 46°C so you’ll either need these off a TMV, or to have thermostatic bath taps / fillers which can be commissioned to go no higher. I almost always go TMV as it kills more than 2 birds; reasons to follow. 
 

As an aside, 46°C bathwater is too bloody hot for me by a mile, as I’m not a fan of steamed plums.

 

Anyhoo…..

 

Hmm that's interesting.....

 

With my 115 Litre old tank I'd have to heat the water to 60 deg C (was my legionaires cycle once a week) for it to stand a chance of a long soak in a bath that makes Mrs Alien happy (That would be initial fill and a couple of top ups) which would pretty much mean I got just enough warm water left for a shower.

 

With my new 180 Litre tank I'm doing it to 55 Deg for her bath night (I'm just doing it earlier to allow for a longer heat soak) and she had her normal bath with top ups and I had a shower and then we both had showers the following day and still didn't run out of HW

 

Rest of the week we heat to 45-48 Deg C

 

I'm thinking I might drop it to 50 Deg for bath night and maybe move to a once a month "60 deg sanitisation cycle" - temp isn't going to be much different to daily target and it uses a fair chunk of energy to get the tank up to 55 compared to 48

 

[G and J]

6 hours ago, Nickfromwales said:

I was having a glum morning, dealing with insurance pricks, again, but that cheered me right up. PMSL.  

Happy to oblige.  
 

To be fair I’ve a big history of making people laugh, especially on the build.  Shame it’s usually either at me or me work lol

 

6 hours ago, Nickfromwales said:

In your house, can’t recall if you have PV or not, it’ll live a nice ‘low temp life’ and prob last 15 years minimum. Subject to routine and preventative maintenance obvs, but in a nutshell if it moves it’ll break one day, so pumps = head and fan = handle, Trigger

So I’ll be nudging into my ninth decade, and therefore one replacement = 30 years so that’ll see us both into our android staffed in orbit care facility.   Like Wall-E but with fewer cocktails and more meds.