Where to put plumby bits?

[G and J]

My history is mostly with gravity systems, apart from a couple of small and simple gas combi based ones. Perhaps that’s why when we designed our new house I automatically drew the cylinder in a cupboard in our bedroom which gave short hot water runs, and the UFH manifold under the stairs, to minimise the flow and return from the ASHP half way down the garden. I’ll call that plan A.

 

 

I’m a tight sod, so I want the MCS grant thingy. So I opened comms with a local MCS plumber and he said lots of the right things, so I gained confidence in him.

 

Now that we are getting down to the nitty gritty he’s advising me to put the UVC in the garage, next to the water softener, along with the water pump and other gubbins. His rationale is noise from water being drawn from an unvented system is not something one wants in one’s bedroom; plus the water softener has a nice and convenient drain already hopefully making his life easier and thus my costs lower; plus it means future servicing is better as the engineer doesn’t have to traipse through the house.

 

Sounds plausible. But it does mean longer flow and returns from the heat pump, about 10m longer, and another extra 10m back to the under stairs where I’d assumed I put my UFH manifolds. He assures me as long as the system is designed well then the extra flow and returns lengths won’t matter, and could be run in less expensive internal pipe work rather than more external u/g insulated piping. I’ll call this plan B.

 

 

So, is it a good idea to move me gubbins to the garage and accept longer f&r runs? Or is there another downside I've not spotted?

 

If I do do plan B should I move the UFH manifolds to be with the cylinder? In my normally highly imaginative manner I’ll call that plan C.

 

 

Opinions gratefully received.

[Nickfromwales]

GIA is important in a “compact” dwelling, so I say to go with your plumbers advice. 
 

If someone said I’m going to put your UVC in the bedroom cupboard they’d be sent packing on the spot. 💩👎. Garage for plant, bedroom cupboard for spare trollies 🩲 😉🫡

[Nickfromwales]

Are you having a new slab etc or running off / adding to existing?

 

If all new then run ducts in the insulation of the floor and pipe your hot runs that way (as the crow flies) and you’ll not be waiting very long at all to get hot water out of the furthest outlets.

 

If you’re brave, just put 15mm hep into 25mm flexi conduit and set that in first as last, just needs you to babysit (protect) the ends until 2nd fix so the pipe doesn’t get damaged. Can be pulled out and changed if the worst comes to the worst, but better off with 30mm ducts minimum if you’re going to pull these in afterwards. 

[G and J]

  On 13/04/2025 at 15:11, Nickfromwales said:

GIA is important in a “compact” dwelling, so I say to go with your plumbers advice. 
 

If someone said I’m going to put your UVC in the bedroom cupboard they’d be sent packing on the spot. 💩👎. Garage for plant, bedroom cupboard for spare trollies 🩲 😉🫡

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Sadly I don’t know what GIA is, though I’ve a sinking feeling that I’m being dumb again. 
 

But (@Nickfromwales) given your response then the cylinder is def going in the garage.  
 

Shall I put the manifold there too?

[Tony L]

Gross Internal Area.  Even I know that one, & I know nothing.

[JohnMo]

  On 13/04/2025 at 19:55, Tony L said:

Gross Internal Area.  Even I know that one, & I know nothing.

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I didn't, hadn't come across it.

 

An alternative to the garage, is an insulated shed near the house between ASHP and house. It maybe better than an uninsulated garage, it may allow much shorter pipe runs, the cylinder could live there, and be closer to heat pump. The expansion for cylinder and heating could be in there as well.

 

Or form an insulated space in the garage. 

 

We have an insulated shed between heat pump and house, expansion vessel, heat meter etc are in there. Shed insulated on floor, roof and walls, all pipes are covered in 25mm insulation. We also have our well treatment filters in there also. No issues even down to -9.degs.

 

A couple of things to consider with long runs between cylinder and heat pump. 

1. Cylinder temperature, are you using a temperature sensor connected to heat pump, and signal strength?

2. Or a thermostat. Think about wiring runs.

 

Other thing is the three port valve location that will determine where pipes have to run

 

 

[G and J]

I am hoping that our internals won’t be too gross, but that relies on J.  I do engineering.  J does aesthetics. 
 

  On 13/04/2025 at 20:42, JohnMo said:

Or form an insulated space in the garage. 

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I'm planning a state of the art auto-climatic plant enclosure facility in the eco friendly vehicle storage zone.  In other words a small insulated cupboard to house MVHR and cylinder plus gubbins in the unheated garage.  
 

  On 13/04/2025 at 20:42, JohnMo said:

 

A couple of things to consider with long runs between cylinder and heat pump. 

1. Cylinder temperature, are you using a temperature sensor connected to heat pump, and signal strength?

2. Or a thermostat. Think about wiring runs.

 

Other thing is the three port valve location that will determine where pipes have to run

 

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To 1 and 2 I simply don’t know. I’m chasing the MCS plumber dude for details and costs.  I think the valves (be it a 3 port valve or two 2 port valves, which is my preference). 
 

We could have designed in space for a quasi external cylinder but sadly that moment has passed us by.  

[Nickfromwales]

  On 13/04/2025 at 21:07, G and J said:

 

I am hoping that our internals won’t be too gross

 

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Pmsl. 
 

GIA needs preserving as I was quite concerned that you might suffer beyond all hope without an attic to stuff all your unwanted useless crap into, eg until the ceilings below began to sag…..like our old attic, lol.

[G and J]

No chance of that. In our house now anything stationary for more the 27 hours is photographed and listed on gumtree and faceache and if it doesn’t sell in four hours it’s bagged up for the next tip run.   We are on a mission to dump the excess stuff. 
 

The latest debate is loft hatch size.  J is suggesting that maybe we make it nearly as big as an A4 sheet….   :-0 

[JohnMo]

  On 13/04/2025 at 21:39, G and J said:

latest debate is loft hatch size

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Big is best, with a ladder built in. All our Christmas stuff goes up there - it makes killing yourself, a little less likely.

[G and J]

  On 13/04/2025 at 21:42, JohnMo said:

Big is best, with a ladder built in. All our Christmas stuff goes up there - it makes killing yourself, a little less likely.

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Space for Xmas deccies already reserved in the garage.  Besides, I’d miss the repetitive amusement of hitting my head as I climb the loft ladder to squeeze through the slightly too small hatch I hurriedly built 34 years ago. 

[Iceverge]

Attic hatches should be limited in size to prevent anyone less agile and slim than a circus trapeze artist from entering. 

 

Amazingly Christmas decorations survive pretty well in a cupboard. Who would have thought it. If a single box kept out of the loft tips your house over the edge from austere bliss to hoarders bordello then you really have been living in the absolute limit. 

 

I would put the UVC into the utility room. Thermally vastly superior and central to all your taps. The only one that really matters by the way is the kitchen tap. Consider 10mm Hep to this if you can live with about 6l/min of hot water. You'll be rewarded by super speedy water delivery.  Displacing something else out to the garage would be preferable in my view.

 

Is there somehow preventing you having your ASHP right outside the utility? Absolutely minimising runs of piping outside the unheated envelope. 

 

Alternatively if there space you could put your UVC under the stairs. 

 

 

 

[saveasteading]

  On 13/04/2025 at 21:39, G and J said:

loft hatch size.

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Big. Mine was enough with a normal ladder, but the fold down one takes more space, and some stuff is now stuck up there forever.

Just 100mm too small and it becomes awkward.

[G and J]

  On 13/04/2025 at 23:17, saveasteading said:

Big. Mine was enough with a normal ladder, but the fold down one takes more space, and some stuff is now stuck up there forever.

Just 100mm too small and it becomes awkward.

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That’s exactly what I did here.  Built a loft hatch that felt just right then installed the pull down loft ladder.  I imagine my bald spot has many little scars as a result.

[G and J]

  On 13/04/2025 at 23:13, Iceverge said:

Is there somehow preventing you having your ASHP right outside the utility? Absolutely minimising runs of piping outside the unheated envelope. 

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Types.  The 1m from the boundary rule, plus, the alleyway is 1,030mm wide so an ASHP wouldn’t work very well down there.  
 

  On 13/04/2025 at 23:13, Iceverge said:

Alternatively if there space you could put your UVC under the stairs. 

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It’s hard to be precise but I think that would require a UVC less than 1.2m in height assuming a 550mm width.  A quick web search tells me that would limit the capacity too much. I agree though it would be ideal.

 

  On 13/04/2025 at 23:13, Iceverge said:

I would put the UVC into the utility room. Thermally vastly superior and central to all your taps. The only one that really matters by the way is the kitchen tap. Consider 10mm Hep to this if you can live with about 6l/min of hot water. You'll be rewarded by super speedy water delivery.  Displacing something else out to the garage would be preferable in my view.

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Interesting ideas. I’d planned on 10mm HEP2O to each hot tap anyway, and I've just measured, (like you do at 06:00 in the mornings), our current kitchen taps delivers 7litres per minute so that’s looking good.

I value the space in the utility above that in the garage, but it’s worth taking a mo to think about that.  I’m thinking (guessing) that the cost difference will be two to three hundred quid in terms of more piping plus a larger insulated cupboard, and the garage dies have the convenient servicing thing.  But how often do these things need attention?

 

[Nickfromwales]

  On 14/04/2025 at 05:03, G and J said:

It’s hard to be precise but I think that would require a UVC less than 1.2m in height assuming a 550mm width.  A quick web search tells me that would limit the capacity too much. I agree though it would be ideal.

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No room for a horizontal UVC under the stairs? I’m doing one for someone else on another new build, where we’ve tried to stuff the M&E into every nook and cranny to preserve useable storage / spaces for living. 

[Nickfromwales]

  On 13/04/2025 at 23:13, Iceverge said:

I would put the UVC into the utility room. Thermally vastly superior and central to all your taps.

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Yup. 100%. 
 

A tall, slimline HP UVC would fit in there a doddle.

Waaaaay better option tbh. 

[JohnMo]

  On 13/04/2025 at 23:13, Iceverge said:

would put the UVC into the utility room.

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That would get my vote also, would also consider putting MVHR in there as well. 210L slimline is only 400mm diameter.

[Nickfromwales]

  On 14/04/2025 at 07:58, JohnMo said:

That would get my vote also, would also consider putting MVHR in there as well. 210L slimline is only 400mm diameter.

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510mm for a 250L.
 

@G and J, you would still be able to dress a larder unit around it for cosmetics and not know it’s there; plinth should still go on too, with this sitting on the deck, or raise it on a masonry platform if not.

 

@JohnMo, Which HP cylinder did you see at 400mm / 210L for a HP? 

[JohnMo]

  On 14/04/2025 at 08:14, Nickfromwales said:

Which HP cylinder did you see at 400mm / 210L for a H

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Sorry just double checked it is 475mm - ideal HP cylinder

[G and J]

  On 14/04/2025 at 07:58, JohnMo said:

That would get my vote also, would also consider putting MVHR in there as well. 210L slimline is only 400mm diameter.

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I went for the garage for the MVHR as I couldn’t work out where sensibly to put the intake and exhaust vents if I put the MVHR in the utility room. 
 

The utility room window looks out on a 1m wide alleyway which is a bit pongy with next door’s drains/ gas boiler output.  So not great putting an intake there. 
 

likewise the other side, so the MVHR in the garage looks to tick lots of boxes:  Easily accessible for filter cleaning; Intake 3m from exhaust; Intake upwind of exhaust etc. 

[G and J]

So, the new plan is Plan D :

 

 

The ASHP flow and return twin insulated underground pipes surface behind the fridge, thence to travel in normal pipes either to the understairs or to the utility room, depending on....

 

Choice D1 : Normal Heat Pump UVC (250l?), and separate gubbins.  Water pump under stairs with 2 port valves and maybe expansion vessel.

 

Choice D2 : All in one unit which I think means all but the UFH manifolds are in the utility room.  I like the look of the all in one type units - which appear to need few other gubbins, but would give a smaller cylinder (typically 190l).

 

Are there any obvious factors that would make D1 or D2 clearly better?

 

 

[JohnMo]

  12 hours ago, G and J said:

Choice D1 : Normal Heat Pump UVC (250l?), and separate gubbins.  Water pump under stairs with 2 port valves and maybe expansion vessel.

 

Choice D2 : All in one unit which I think means all but the UFH manifolds are in the utility room.  I like the look of the all in one type units - which appear to need few other gubbins, but would give a smaller cylinder (typically 190l).

 

Are there any obvious factors that would make D1 or D2 clearly better?

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Why do you need a pump?

Why 2 port valves, you just a 3 port diverter! You definitely need an expansion vessel X2 one for DHW cylinder and the other for the heating system. 

 

All in one cylinder (assume you mean pre-plumbed) full of sh*te you shouldn't need. Would be my opinion.

 

Reality is you need a 3 port valve and some isolation valves. If you do need an additional pump due to pipe length (distance from ASHP) you will just add a fixed speed pump on the return line after cylinder and UFH tee together.

[Nickfromwales]

I’ve just done a Panasonic monoblock with its own integral pump, so no need for another pump other than the one on the manifold.

Some will say to have a pumpless and blending-valveless manifold and fire that off the ASHP pump, with ASHP flow temp as your UFH flow temp which is a little less user friendly an option, imho, but doable.

 

Pre plumbed cylinders will have all the generic stuff on there for a standard S or Y plan arrangement. Plug and play, but a more cumbersome lump in one place; has a much bigger diameter for both physical size and also access / service / maintenance etc so not sympathetic with it hiding in a utility cupboard. . Cost goes up too, and not sure about slimline options there either(?).

 

Don’t have the ASHP pipe rise out of the slab until they are in the plant space!!!! Terrible idea to bring them out early, so go kneel on some pencils until you’ve removed that silly thought from your mind 👉

 

I use 2 port valves as they’re easier to swap out and you lose one service not both if it snuffs it. 3-ports (diverter valve not mid-position) I only now use if it’s a thermal store with DHW priority as the wiring is standardised and I like these to be generic.

 

Most heat pumps service a 2x 2-port setup out of the box.

[G and J]

  11 hours ago, JohnMo said:

Why do you need a pump?

Why 2 port valves, you just a 3 port diverter! You definitely need an expansion vessel X2 one for DHW cylinder and the other for the heating system. 

 

All in one cylinder (assume you mean pre-plumbed) full of sh*te you shouldn't need. Would be my opinion.

 

Reality is you need a 3 port valve and some isolation valves. If you do need an additional pump due to pipe length (distance from ASHP) you will just add a fixed speed pump on the return line after cylinder and UFH tee together.

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The all in one thingy is the next step beyond preplumbed, if I’ve understood correctly.  It’s this kind of thing:

https://bpcventilation.com/products/aquarea-all-in-one-water-to-air-heat-pump?variant=53736366866758

 

If I don’t go for the all in one type unit then there’s a choice re pre plumbed vs naked.   I would naturally err towards naked but some of the pre plumbed ones do look ridiculously neat!  My assumption would be I’d save money and a bit more choice on placement with naked, and our utility room is not going to be terribly spacious.