Two questions relating to UFH manifolds

[Bancroft]

1. Can manifolds be fitted in the loft space of a single storey building, instead of on the ground floor?

 

Our loft is going to be within the warm envelope of the building.  I'm already looking at housing the MVHR and DHW in the loft area and I'm wondering whether mounting the UFH manifold. system there too is a good idea or not?

 

To my mind, the more 'plant stuff' I can shift out of the normal living space, the better.  As some houses have UFH on the first floor, I imagine pressure differentials shouldn't be an issue (but that's just a guess).

 

There's also a strong possibility that the pipes from the external ASHP into the manifold will be entering the house structure at ceiling level anyway so they're going to have to go from ceiling height to ground level at some point, so why can't the manifolds be at the high end of that drop?

 

If they are mounted in the loft, what are the potential down-sides of such an arrangement?

 

2. Can multiple sets of manifolds be run off the same ASHP?

 

We're building a 211 sq m single storey building so there's lots of floor space to cover.  One initial design I had done resulted in 18 different pipe circuits - although they did include laying dedicated circuits in the hallways, utility room and pantry which we could probably do without.

 

The maximum number of circuits on a single manifold system seems to be 12 and the likelihood is we will hit this and perhaps exceed it.  So, how easy is it to have two separate manifold sets in the system?

 

Having two sets might also help to reduce the number of pipe circuits/length of runs by having the manifold sets strategically placed apart, rather than trying to run everything back to a single point in a building that's 25m long.

[JohnMo]

7 minutes ago, Bancroft said:

We're building a 211 sq m single storey building so there's lots of floor space to cover.  One initial design I had done resulted in 18 different pipe circuits - although they did include laying dedicated circuits in the hallways, utility room and pantry which we could probably do without.

We are a similar size to you with 7 circuits. So there us plenty of room to reduce the number of loops. I wouldn't have dedicated loops on hall and certainly no loops in a pantry.

 

We have one loop per bedroom 3x, 2x in lounge, one loop ensuite, another loop does main bathroom, then does hall area near front door and then kitchen diner. I would simplify to a single manifold - post your design and get it reviewed?

 

Manifold can go anywhere, but you have a lot of pipes (36 at the moment) to bring down the walls, if upstairs, the pipes are likely to need insulation as the area will get very warm, also you will need a deep service void - I would find space central downstairs (airing cupboard) then run flow and return to manifold.

[Bancroft]

Thanks for that @JohnMo.  Plan attached below as recommended.

 

I think the design given to us was a lazy one and doesn't really look at the issue intelligently - hence a hefty dose of scepticism on my part.  150mm centres in an ICF house with thick slab foundations seems a little excessive...

 

I agree that pantry and hallway need to be deleted, and going to 200mm centres - or even 300mm - will massively reduce the pipework.  I just need to get the re-assurance that the wider centres will still achieve the aim with regards to heat output required.

 

If we are able to reduce to one manifold set then the lobby between bedrooms 2 and 3 would seem a logical place (centrally placed and cupboard space available) but I still like the idea of getting stuff like this out of the way, even if it does mean a bit of extra insulation.

[JohnMo]

I would 

Delete all dedicated hall loops, spread all pipes transitioning through halls out across floor.

 

Come down to one manifold only.

 

Do 200mm centres generally, but keep bathrooms at 150mm or below. Maybe even 250mm in bedrooms, but just do a single loop in each bedroom.

 

If you locate the manifold in utility, you wouldn't need a loop in there either, just spread pipes across the floor.

 

This is our floor, loose 300mm centres. Kitchen is generally 0.5 Deg cooler than lounge, bedrooms are a degree to 1.5 cooler than rest of house with doors closed. Open doors and the rooms even out over a hour or so.

 

[Bancroft]

Your example looks a lot more sparse than ours!

 

Couple of questions:

 

• I notice you haven't put any pipe under the gangway between kitchen units and island - does that not create a cold spot for people working in the kitchen?
• Also, in the bedrooms, you've not put pipe under the bed locations - does than not limit you for switching the room around or altering the layout?

I've been playing around and looking at loop sizes for 200mm spacing and managed to get down to 14 loops but I did this using a spreadsheet - how easy is loopcad to use and what other data do you need apart from room sizes/locations?

 

[JohnMo]

15 minutes ago, Bancroft said:

I notice you haven't put any pipe under the gangway between kitchen units and island - does that not create a cold spot for people working in the kitchen?

There is a single pipe, between wall units and island not on drawing but on photo, floor temp is low - you don't notice it unless really cold outside, talking -9 for a day or 2. Then you only notice it, but only with feet at the kickboards. We have 100mm concrete screed, so the temperature spread is pretty wide away from the pipes.

 

16 minutes ago, Bancroft said:

• Also, in the bedrooms, you've not put pipe under the bed locations - does than not limit you for switching the room around or altering the layout?

 

Very unlikely the rooms will get moved about as whole is there for the views, which disappear with the bed on a different wall or dining are at the other side of the room.

 

18 minutes ago, Bancroft said:

how easy is loopcad to use

I found it ok. You basically build the house in the software, so you need U values, window sizes etc. Its good for balancing floor outputs, I got mine to within a few Watts for each room, so system balance is good out the box.  I found later wife had very different ideas to floor covering for bedrooms than me, as a result bedroom output is a little low than planned, but works ok. Nice wool carpet insulation.

[Bancroft]

18 hours ago, JohnMo said:

I found later wife had very different ideas to floor covering for bedrooms than me

I'm sure 99.9% of builds would be easier without the spousal input!

[JohnMo]

7 minutes ago, Bancroft said:

I'm sure 99.9% of builds would be easier without the spousal input!

But would life be worth living afterwards, "I would of or I wouldn't of" being mentioned many times, comes to mind

[Bancroft]

On 25/11/2025 at 12:06, JohnMo said:

his is our floor, loose 300mm centres.

200mm seems to be the 'go to' spacing for ufh - can you explain:

 

why you went for 300mm?

does that result in any 'heat striping' across the floor?

what impact does it have on the SCOP of your heat pump (I understand higher target temperatures that 300mm would require would heavily impact the SCOP)?

[JohnMo]

19 minutes ago, Bancroft said:

200mm seems to be the 'go to' spacing for ufh - can you explain:

 

why you went for 300mm?

does that result in any 'heat striping' across the floor?

what impact does it have on the SCOP of your heat pump (I understand higher target temperatures that 300mm would require would heavily impact the SCOP)?

I was happy to minimise pipe in floor and designed in loopcad. The insulation values at the time didn't get down to my levels, and even then at -9 had a design flow temp of 35 deg. Actually the highest flow temp I need doing WC is about 32.

 

Just installed a new smaller heat pump, as previous one didn't modulate well at all (it's being reused for hot tub). The last few days the CoP has been (in order they appeared)

Average 4.5 day temp CoP 5.11

Average 6.8 day temp CoP 5.68,

Average 5.6 day temp CoP 5.8.

 

Still fine tuning WC curve, so performance is improving. Even with 4 poor running days, my weekly SCoP is 4.56. in a weeks time, I expect that to closer to 5+ even with more snow on the way for NE Scotland.

 

Heat striping - pipes are 100mm down and by the time the heat gets to the surface you cannot feel any difference in temperature.

 

It also works acceptably well in cooling.

 

 

[Bancroft]

23 hours ago, JohnMo said:

I was happy to minimise pipe in floor and designed in loopcad. The insulation values at the time didn't get down to my levels, and even then at -9 had a design flow temp of 35 deg. Actually the highest flow temp I need doing WC is about 32.

 

Just installed a new smaller heat pump, as previous one didn't modulate well at all (it's being reused for hot tub). The last few days the CoP has been (in order they appeared)

Average 4.5 day temp CoP 5.11

Average 6.8 day temp CoP 5.68,

Average 5.6 day temp CoP 5.8.

 

Still fine tuning WC curve, so performance is improving. Even with 4 poor running days, my weekly SCoP is 4.56. in a weeks time, I expect that to closer to 5+ even with more snow on the way for NE Scotland.

 

Heat striping - pipes are 100mm down and by the time the heat gets to the surface you cannot feel any difference in temperature.

 

It also works acceptably well in cooling.

Thanks for that - still struggling to get my head around how best to achieve a sensible ufh set up.

 

You mention your previous heat pump didn't modulate well - was that because it was not being 'stretched' in terms of required output because of the efficiency of your build?  I presume it's as important to have a heat pump that is not too big as it is to have one not too small but guidance on getting the Goldilocks size seems lacking.

[JohnMo]

30 minutes ago, Bancroft said:

You mention your previous heat pump didn't modulate well - was that because it was not being 'stretched' in terms of required output because of the efficiency of your build? 

Mainly because it was a 10kW unit software limited and badged to 6kW, so generally min output was close to 4kW. 

 

[JohnMo]

6 hours ago, Bancroft said:

presume it's as important to have a heat pump that is not too big as it is to have one not too small but fuidance on getting the Goldilocks size seems lacking

Work out your heat loss at your design outside temp, then get a heat pump that will modulate to half that or less. Then it should just tick away all day. If you have a secondary heat source like a wood stove, it will cut any peaks in demand, so size it tight to the calculation heat load or even slightly smaller. But then you need to consider DHW, I just do immersion then heat pump sizing doesn't matter.

 

Closer pipe spacing decrease flow rate for a given heat demand, but only by a little, but generally not by as much as people make out when your house is already a low heat demand.

Edited 19 hours ago by Nickfromwales

[Nickfromwales]

23 hours ago, JohnMo said:

Average 5.6 day temp CoP 5.8

We aimed for an SCOP 6 at Leicester, always a big "ask", but for a system sold to Joe public we're happy with mid 5's, very happy actually.

 

Your near 6 is pretty much unheard of, excellent result, so I assume an SCOP of mid 5's at yours, also?

 

Are you still "dialling this in" as it were?

[JohnMo]

8 minutes ago, Nickfromwales said:

assume an SCOP of mid 5's at yours

Hoping - well happy for NE Scotland.

 

8 minutes ago, Nickfromwales said:

Are you still "dialling this in" as it were?

Yep, need a couple of nice cold days to finish, got a couple coming later this week 

[SimonD]

36 minutes ago, Nickfromwales said:

Your near 6 is pretty much unheard of, excellent result,

 

Dont't want to blow my own trumpet, but I was a bit dissappointed when mine dropped from SCOP of 6.2 to 6.1. This is for the whole winter so far since October and it's a system on radiators 😉: 

[JohnMo]

15 minutes ago, SimonD said:

 

Dont't want to blow my own trumpet, but I was a bit dissappointed when mine dropped from SCOP of 6.2 to 6.1. This is for the whole winter so far since October and it's a system on radiators 😉: 

Energy counter 1 is showing 1.88 / 0.3 that is a CoP of 6.26, but it's reported as 6.8? Or is it showing an average over a time period and reporting that as the CoP?

[SimonD]

31 minutes ago, JohnMo said:

Energy counter 1 is showing 1.88 / 0.3 that is a CoP of 6.26, but it's reported as 6.8? Or is it showing an average over a time period and reporting that as the CoP?

The electric power only goes to 1 decimal place and is rounded up, for whatever reason, so at 6.8 actual electricity input is  0.276kW. Likewise in this screen grab showing cop of 7.2, actual input is 0.28kW, so the display is a little annoying. I'm wondering whether to get the open energy monitor kit installed before next winter. 

[MikeSharp01]

5 hours ago, JohnMo said:

Work out your heat loss at your design outside temp, then get a heat pump that will modulate to half that or less.

Ours is 1.2kW at -3, half that is 600W is there such a Heat pump? - I think your latest goes down to 1kW, ours only goes down to 1.8kW. We are still a long way from COP of 6 although today I was playing again and I managed a short run at 5.

[SimonD]

5 minutes ago, MikeSharp01 said:

ours only goes down to 1.8kW

 

At what temperature? These figures are often quoted at 10C so below that may be a lot less. My own heat pump is a 6.5kW unit (at -5) and has a quoted minimum output of 2.4ish. I regularly see a very comfortable 1.2kW output. So best to test it out to see what it can do.

 

You still need to give your unit and house more time.

[Nickfromwales]

1 hour ago, SimonD said:

 

Dont't want to blow my own trumpet, but I was a bit dissappointed when mine dropped from SCOP of 6.2 to 6.1. This is for the whole winter so far since October and it's a system on radiators 😉: 

 

 

Bastard.

 

 

 

 

 

 

 

 

 

[marshian]

2 hours ago, SimonD said:

 

Dont't want to blow my own trumpet, but I was a bit dissappointed when mine dropped from SCOP of 6.2 to 6.1. This is for the whole winter so far since October and it's a system on radiators 😉: 

 

Outstanding........................ Bravo

[SimonD]

12 hours ago, Nickfromwales said:

 

 

Bastard.

 

 

 

 

 

 

 

 

 

 

Let the battles of SCOP begin, eah. And it's not even pure open loop, but actually has some room influence in the way of TRVs due to large solar gains! Shock horror 😁

[Nickfromwales]

10 minutes ago, SimonD said:

large solar gains

Get the family to safety, immediately!!!!!