Building regulations requirement for heating control in each room?

[Great_scot_selfbuild]

We're planning our UFH as a single zone, open loop for the downstairs with only one thermostat. I've been round this a lot elsewhere and on this forum, but just before going ahead, our ASHP installer has mentioned that building control tend to want to see temperature control in each room. I've read the Building Regs Part L and it does mention zones, and there's a brief mention of low heat demand homes, but I'm asking here to find out what the lived experience is in dealing with approved building inspectors on this topic. Ours is very particular, and hard to get hold of to discuss questions like this (which I will try).

 

In short - I'm wanting to know if anyone has actually encountered this issue, if they've had to argue the case, or if there's a simple way to phrase it to demonstrate it's compliant with the BR wording (screenclip of the BR section I've found on it).

 

 

Thanks

[jfb]

Madness! Do what you are planning to do.

 

(not based on any real knowledge of building regs on this but it was fine for us)

[JohnMo]

The 150m² multiple zones I covered with a thermostat in hall and another in ensuite controlling a towel radiator (direct electric). Use the thermostat to trip the ASHP off, if I have the fire on in winter and for summer cooling. The rest is  cover by 5.20b and 5.22a. High thermal mass buffering via thick screed floor and a thermostat in a room served by the heating circuit, in my case the hall.

 

But I have a temperature sensor in each room, most are not generally used except for monitoring temperature. They are useful to understand what is happening, how your system performs, system balancing etc.

Edited February 26 by JohnMo

[ProDave]

The regs are quite relaxed, >150m²  only requires 2 zones, so how about one thermostat upstairs and one downstairs?

 

BC are not going to spend the time to actually make sure they do what they think they do.

[SimonD]

Building Regs do tend to be open to interpretation, but what you can lean on and discuss with your BCO if it's a problem is that in accordance with industry practice and guidance (CIBSE Domestic Heating Design Guide) for any new build, a design temperature of 21C should be used throughout the building - because of higher insulation levels and we hope, better airtightness. In this sense, adjacent rooms can be considered as a single zone: 5.21.b 

 

[Russdl]

Alternatively.
 

Buy some cheap/dummy thermostats, stick them all over the place and bin them when your house is signed off 😃
~~~

Our place is a bit smaller than yours and we only have one thermostat downstairs. Nothing was mentioned. 

[DownSouth]

We have 200sqm total, zone 1 ground floor, zone 2 on the first floor, a controller / temp probe in the hallway on each floor. 
We’ve switched them to 19, from 21 degrees and it’s comfortably warm to work in. It might need to go back up when we are eventually just sitting around 😊 but while we’re still working away inside it’s nice and warm.

We parted company with our original ASHP heating system designer because they refused to do 2 zones, wanted trv in every room and wouldn’t factor MVHR into their calculations. BC were happy with the two zones so that’s what we’ve got.

[SimonD]

44 minutes ago, DownSouth said:

ASHP heating system designer because they refused to do 2 zones, wanted trv in every room and wouldn’t factor MVHR into their calculations

 

Numpties.....

[Great_scot_selfbuild]

9 hours ago, DownSouth said:

We have 200sqm total, zone 1 ground floor, zone 2 on the first floor, a controller / temp probe in the hallway on each floor. 
We’ve switched them to 19, from 21 degrees and it’s comfortably warm to work in. It might need to go back up when we are eventually just sitting around 😊 but while we’re still working away inside it’s nice and warm.

We parted company with our original ASHP heating system designer because they refused to do 2 zones, wanted trv in every room and wouldn’t factor MVHR into their calculations. BC were happy with the two zones so that’s what we’ve got.

Great to hear - thank you.

 

Our ASHP installer is complying with the MCS requirements (which doesn't allow MVHR to be taken into account, and only goes down to 35deg flow temp), however, he knows exactly what we want and, importantly, he has done exactly the same in his own house, so there's making sure it can achieve the MCS sign-off, but able to modulate down low enough to run efficiently as very low flow temp. They even audited his house as luck would have it and it still met the requirements for the BUS grant, so after being initially frustrated at the MCS / BUS restrictions, I'm happy I've found an installer who understands how to comply with it whilst delivering what we want.

[Great_scot_selfbuild]

Well I have been pleasantly surprised by the UFH supplier - they understood my request to increase the spacing between the supply / return pipes, replace the utilities area and have re-done the design. Where they're still bunched close, I'll insulate so that there is an exposed pipe every 150mm. Here's the revised drawing for those who will be interested.

 

UFH-FHW CAD Drawing Rev 2.PDF

[Nickfromwales]

1 hour ago, Great_scot_selfbuild said:

Well I have been pleasantly surprised by the UFH supplier - they understood my request to increase the spacing between the supply / return pipes, replace the utilities area and have re-done the design. Where they're still bunched close, I'll insulate so that there is an exposed pipe every 150mm. Here's the revised drawing for those who will be interested.

 

UFH-FHW CAD Drawing Rev 2.PDF 2.99 MB · 3 downloads

I doubt you'll be able to use that much insulation with a screed. You'll be removing a lot of volume of screed and by the look of where you pinch points are, you'll likely just have to leave them uninsulated. It won't matter one little tiny bit btw, so my advice is to step away from micro-managing this to death and accept that the flow temps will simply be so low you won't even know the UFH is on .

 

If you have any pre(mis)conception of having hot sections of floor where the pipes group together, then you're going to be proven pleasantly wrong, as it just doesn't.

 

Losing such large volumes of screed at very localised areas, especially at entrances to rooms etc, will be a bad idea and is something I actively avoid, so the way the pipes are bunched up are a bit daft and not how I'd lay it out. Living room should be fed from the utility and the pipes for those two loops taken under the partition stud wall, as that deletes 4 pipes from the first lot of congestion. Yes, people "frown" on pipes going under partitions, but the reality is zero ill effect as you're stuck to this project like velcro and can mitigate against any misadventure.

 

Entrance hall needs to be completely reconfigured, that's just silly. Pipes can then be spaced equidistantly in the double doorway leading into the kitchen / open plan room.

 

Close, but no cigar I'm afriad.

[SimonD]

On 03/03/2026 at 07:37, Great_scot_selfbuild said:

which doesn't allow MVHR to be taken into account, and only goes down to 35deg flow temp

 

What are they talking about? Of course MVHR is taken into account in the designs and you can use whatever flow temperature you want as long as you can demonstrate in the design that the system provides the heat to heat the house properly. With MVHR you use the calculation methodology from SAP where the efficiency of the system is taken into account to calculate ventilation heat loss. This is really important because often ventilation losses make up more than the fabric losses. Where do these people come from?

 

BTW I know this because I'm MCS Certified for design and installation of ASHP.

[SimonD]

2 hours ago, Great_scot_selfbuild said:

Well I have been pleasantly surprised by the UFH supplier - they understood my request to increase the spacing between the supply / return pipes, replace the utilities area and have re-done the design. Where they're still bunched close, I'll insulate so that there is an exposed pipe every 150mm. Here's the revised drawing for those who will be interested.

 

UFH-FHW CAD Drawing Rev 2.PDF 2.99 MB · 5 downloads

 

And yet the pipes are all still at 150mm and no variation between rooms.

 

29 minutes ago, Nickfromwales said:

accept that the flow temps will simply be so low you won't even know the UFH is on

 

Whilst we have seen the design we don't know the heat losses the design is supposed to cater for. If this is a properly insulated house with low losses and in particular low down losses, the 150mm spacing is frankly silly, It'll end up overheating the house and then the installer will start telling them they need a 1000l buffer or something to prevent the heat pump from cycling when all the actuators start closing down and it all unravels from there. Instead they could do a proper job of UFH design. 

 

But show us the design numbers and I'll be open to correction! 😉 

[Nickfromwales]

36 minutes ago, SimonD said:

 

And yet the pipes are all still at 150mm and no variation between rooms.

 

 

Whilst we have seen the design we don't know the heat losses the design is supposed to cater for. If this is a properly insulated house with low losses and in particular low down losses, the 150mm spacing is frankly silly, It'll end up overheating the house and then the installer will start telling them they need a 1000l buffer or something to prevent the heat pump from cycling when all the actuators start closing down and it all unravels from there. Instead they could do a proper job of UFH design. 

 

But show us the design numbers and I'll be open to correction! 😉 

It won’t end up overheating if they turn the flow temp to a couple of degrees over the room stat set point. Can’t happen.

 

I’ve been around enough of these types of projects to know this isn’t an issue, just lots of people like the complex math behind it all and then still just come up with the same conclusion. 
 

This really isn’t rocket science at all tbh, any any seasoned (and directly experienced) M&E consultant or ‘heating engineer’ (not the ones on their mothers side) should be able to just look at this holistically and call it.

 

If it’s going to be an MCS certified job then it’ll just be about ticks going into boxes, and then the system fettled afterwards to perform to suit the dwelling based on real life experience in the actual address, and the occupants feeding back to the installer after a full 12 months of occupancy.

 

Tick boxes don’t take the occupants own quirks or preferences into account, imho these are the most important factor but often get overlooked.   

[SimonD]

26 minutes ago, Nickfromwales said:

It won’t end up overheating if they turn the flow temp to a couple of degrees over the room stat set point. Can’t happen.

 

I’ve been around enough of these types of projects to know this isn’t an issue, just lots of people like the complex math behind it all and then still just come up with the same conclusion. 
 

This really isn’t rocket science at all tbh, any any seasoned (and directly experienced) M&E consultant or ‘heating engineer’ (not the ones on their mothers side) should be able to just look at this holistically and call it.

 

If it’s going to be an MCS certified job then it’ll just be about ticks going into boxes, and then the system fettled afterwards to perform to suit the dwelling based on real life experience in the actual address, and the occupants feeding back to the installer after a full 12 months of occupancy.

 

Tick boxes don’t take the occupants own quirks or preferences into account, imho these are the most important factor but often get overlooked.   

 

It's not about complex maths. None of the maths involved is complex. It's actually pretty straightforward and it's not about box ticking here. It's just about good old transfer of heat. If you've got a low energy build, lets say 30W/m2 at design outdoor temp, your mean water temp in a screed floor is going to be about 29C, now consider what that needs to be when you're at the average outdoor temp of 7C in England. The mean water temp requirement is then below the required floor temperature to even produce heat into the space because there's then no MW-AT difference and it'll probably below the minimum flow temp of the heat pump. You then have to rely on controls to switch flow on and off, which we all know is not the way to be running a heat pump.

 

TBH finger in the wind look at it and call it, is exactly why we're in the situation we're in here in the UK, because very few heating engineers and possibly M&E Consultants are up to basic design and so many systems are shite and inefficient when they don't need to be. Just a bit of maths and thought is all that's needed at the early stage.

Edited 10 hours ago by SimonD

[Nickfromwales]

40 minutes ago, SimonD said:

 

It's not about complex maths. None of the maths involved is complex. It's actually pretty straightforward and it's not about box ticking here. It's just about good old transfer of heat. If you've got a low energy build, lets say 30W/m2 at design outdoor temp, your mean water temp in a screed floor is going to be about 29C, now consider what that needs to be when you're at the average outdoor temp of 7C in England. The mean water temp requirement is then below the required floor temperature to even produce heat into the space because there's then no MW-AT difference and it'll probably below the minimum flow temp of the heat pump. You then have to rely on controls to switch flow on and off, which we all know is not the way to be running a heat pump.

 

TBH finger in the wind look at it and call it, is exactly why we're in the situation we're in here in the UK, because very few heating engineers and possibly M&E Consultants are up to basic design and so many systems are shite and inefficient when they don't need to be. Just a bit of maths and thought is all that's needed at the early stage.

For the majority, perhaps, as they're heavily bound by commercial worries; not many clients will pony up money for any kind of review / discussions / etc, so a rubber stamp is lifted and struck down onto the paper and barely any of these are available to gather evidence or 12 month seasonal feedback from (so we don't know what the masses are doing).

 

Last couple I've done have been not much more than a finger in the air (a finger connected to a body and a brain that's been heating homes for over 30 years) and one we dialled into recently is at a SCOP of mid 5's.

 

44 minutes ago, SimonD said:

now consider what that needs to be when you're at the average outdoor temp of 7C in England

In a truly well insulated, well air tightened, MVHR featured build with excellent fenestration etc, then the outdoor temp has just so little to do with the interior temps it's barely worth considering. The main effect is the heat pump changing how it runs to suit the temp of the air it is extracting heat energy from.

 

I've been in these properties over xmas with plasterers screaming at me to turn off the heating as the indoor temps are mid 20's and the plaster is going off too fast. Then I go show them the UFH pipes sticking out of the floor, zero manifold, and say to them "the heating isn't on mate". Then they ask how TF is the house so hot. I say it's from body heat, work lights, and solar gain.

 

Completely agree that poor performing individuals are the cause of the problem, so, as said, choose a good consultant to guide you through the varying offerings out there, or get installers with very good reptations and proof of it, or fly solo and roll the dice.

 

Bottom line is that each instance is completely unique, with the clients needing to be part of the equation (often just ignored), and the process needs to be far more holistic than it is; insulation, MVHR, airtightness, fenestration etc all play huge parts in arriving at a successful system design, and the way it then functions to suit the occupants, not just the basics that MCS asks for. The typical approach from most is very rudimentary at best.

[DownSouth]

We dumped our first MCS Certified ASHP designer - they refused to factor in MVHR ‘in case it failed’ as the BUS apparently required a single heat source calculation. So finding someone who is certified but also understands the reality of ASHP + MVHR and won’t oversize the heat pump because of the ASHP only calculation is key.

[Nickfromwales]

31 minutes ago, DownSouth said:

We dumped our first MCS Certified ASHP designer - they refused to factor in MVHR ‘in case it failed’ as the BUS apparently required a single heat source calculation. So finding someone who is certified but also understands the reality of ASHP + MVHR and won’t oversize the heat pump because of the ASHP only calculation is key.

MCS means that most who GAF are hands-tied by the forms they have to fill out and that they then have to take ownership of.

[SimonD]

3 hours ago, Nickfromwales said:

Last couple I've done have been not much more than a finger in the air (a finger connected to a body and a brain that's been heating homes for over 30 years) and one we dialled into recently is at a SCOP of mid 5's.

 

So this is very much where we diverge Nick. I wouldn't let anyone near my house if they told me they'd design my system with their fingers in the air because they had so much experience. That's partly why I do what I do now.

 

Now, everyone develops experience and knowledge so of course you get to know approximately what size pipes carry what loads etc. but you still have to back that up with the numbers. It's like a seasoned SE will know a lintel will take the load but they provide the calcs to confirm it under those specific circumstances. Every heating engineer needs to do the same. And the problem with rules of thumb is that over the years they diverge from reality through Chinese whispers and become useless and wrong - that's partly why people put in 30kW boilers into new builds when they don't need anything more than 6kW.

 

 

[Nickfromwales]

3 hours ago, SimonD said:

 

So this is very much where we diverge Nick. I wouldn't let anyone near my house if they told me they'd design my system with their fingers in the air because they had so much experience. That's partly why I do what I do now.

 

Now, everyone develops experience and knowledge so of course you get to know approximately what size pipes carry what loads etc. but you still have to back that up with the numbers. It's like a seasoned SE will know a lintel will take the load but they provide the calcs to confirm it under those specific circumstances. Every heating engineer needs to do the same. And the problem with rules of thumb is that over the years they diverge from reality through Chinese whispers and become useless and wrong - that's partly why people put in 30kW boilers into new builds when they don't need anything more than 6kW.

 

 

Typing in my spare time, so to add that all these finger in the air designs are then backed up accordingly, after I submit what I want installed, and they (chosen commission agents or manufacturers) come back with green lights all the way, hence the SCOP of mid 5’s I mention above.

 

You don’t actually need the numbers as the physics basically overrule in every case, x amount of heat loss requires the same to maintain 21°, so the heat pump will push that out as required. It shall take no more.

 

As long as you’ve not oversized then pipe centres are pretty much as you please, I’ve done 100mm cc and @JohnMo has his sending postcards to each other, one with a buffer and his without, both performing extremely well / efficiently etc. 

 

[Great_scot_selfbuild]

7 hours ago, SimonD said:

None of the maths involved is complex.

@SimonD I'm interested in doing my own calculations on this. Whilst I head off and do some searching, can you help me expedite this by directing me to any resources / reference material that takes me through the process specific to sizing UFH to a room / heat loss etc? It sounds like this should be a lot easier than trying to dig out my thermodynamics notes from 20+yrs ago (I hope... never was my favourite, but now I'm more motivated 🤣).

 

 

 

8 hours ago, SimonD said:

And yet the pipes are all still at 150mm and no variation between rooms.

In an earlier post which evolve into a focus on the UFH layout / sizing I had actually asked about this - I was wanting to understand if I should be looking to tailor the UFH pipe spacing and design to each room, which largely received the response "it'll all end up at the same temperature, so don't bother" (I'm heavily para-phrasing). However, I do like to learn a new aspect of engineering and although I have no available time, I'll happily sacrifice some of my sleep to work this through myself. Would be grateful for a steer... (btw I did look up Rob Berridge and in the YouTube interview he mentioned that he provided training material but I can't find it; I've reached out to him, but no response yet). 

 

 

8 hours ago, SimonD said:

But show us the design numbers and I'll be open to correction! 😉 

I'm still waiting myself.

 

 

8 hours ago, SimonD said:

 

What are they talking about? Of course MVHR is taken into account in the designs and you can use whatever flow temperature you want as long as you can demonstrate in the design that the system provides the heat to heat the house properly. With MVHR you use the calculation methodology from SAP where the efficiency of the system is taken into account to calculate ventilation heat loss. This is really important because often ventilation losses make up more than the fabric losses. Where do these people come from?

 

BTW I know this because I'm MCS Certified for design and installation of ASHP.

This sums up so many of my frustrations. How are the general public (i.e. me) meant to know enough to challenge the information we're provided. I've surprised myself at how much I've spotted, been brave enough to question and then, disappointingly actually, found out I'm right and something needs to be changed or corrected! (from architect designs, timber frame structural elements, roofing construction and roof light installation). Micro rant over. Thanks for this - I will be re-visiting the ASHP / heat loss calcs (though I know it's 'just numbers plugged into a software tool' - hence my interest in learning the calcs).