Wet ufh system

[RedSpottedSev]

Hello,

 

I started a project hastily and it has somewhat escalated. The information here has been amazing.

 

We have a 5 bed detached farmhouse (half/half previous extension, half solid 50cm stone walls, half insulated cavity). Very exposed to winds and rain.

 

We made the decision to put ufh downstairs and upstairs, but admittedly I really should have had a proper heat loss done and spent the extra on a heating engineer. Lack of knowledge and poor advice at the time... but here I am.

 

Build up is 70mm hardcore/blinding, DPM, 150mm concrete slab in mesh, 150mm PIR, 16mm ufh pipes at 150mm centres clipped to insulation with 75mm sand/cement dry screed to SR2.

 

Upstairs, removed old floorboards, leveled the joists, extra reinforced those that needed it, noggins etc... 5cm PIR between joists, soundproofing tape, routed floorboard for 16mm pipes at 150mm spacing. Primer, Perimeter 6mm expansion strip tape and then 1 to 3cm flow screed over the top to level, fill in boards.

 

Upstairs is 6 valves for 5 bedroom zones. The bathrooms are on electric ufh mats.

Downstairs is on 7 valves doing 4 zones.

I am likely going to add another 5 valves for 3 zones for an extension in the future.

All runs are below 100m, 16mm at 150 centres. My thought was this way I can reduce flows and wouldn't be left with a cold house (cant insulate internal or externals of the old part of the house).

 

The 3 manifolds have a manual mixing valve and each with its own pump.

Each manifold has a heatmeiser control that I am told connects to actuators that go on the valves. Then each room will have a thermostat that switches the actuators on and off when the rooms hit the set temperatures.

 

I had assumed that my current boiler/cylinder would have been enough to supply the system.

But my builder's plumber says that it is a very old boiler 10+ years and they would recommend an upgrade.

 

Finally to my question and thanks for reading so far:

My heatloss is around 15 to 18kw. I have ruled out ASHP due to only having access to cost/space and single phase electricity.

If I am going to upgrade my heating system, I would like to have weather comp option and hot water priority.

 

I have had lots of mixed messages and designs about this from different plumbers, with huge varying cost.

So here I am asking for option on what people have done with wet underfloor only set ups. Current recommendation has been a heat only system with a low loss header that supplies ufh and the cylinder...

 

In my head I was thinking a 4 pipe system boilder that has inbuilt domestic hotwater priority. 

Some kind of communication centre that means the heatmeisers can call for hotwater at a different temperature to the hot water cylinder.

Do I need a low loss header for the 3 manifolds to connect to and blend from?

 

Have I shot myself in the foot with the kit I already have (manual mixing valves and heatmeiser) to have weather comp? I am happy to invest time tweaking flow rates etc... to get a more stable heatoutput to stop the actuators constantly opening and closing.

 

Sorry if you think this is better suited to the the ufh forum

 

Thanks again

 

Edited Monday at 08:17 by RedSpottedSev

[JohnMo]

For me, I would reduce to the number of zones down to a minimum. Your issue is you will have a slow system response and you room temps could fluctuate quite a lot of you are bouncing of a thermostat.

 

Next choice of mixers, IVAR or electronic (ESBE etc) only. Or do you even need a mixer anywhere? Can your system boiler provide enough flow for all loops on its own? If not, heat only boiler and keep manifold mixer and pump. Then a single thermostat per manifold. Run an almost flat WC curve of about 35 to 40 degs.

 

Low loss header - no

 

Flow needed will drive system or heat only I suspect.

 

I would start by looking at the longer loop and all pipes to and from that loop and look at pressure drop. Once you have that, it will set pressure drop for system, then add all the flows you need together all loops). Now you have a pump duty point. You can now make a sensible choice of system or heat only.

 

Thermostats, implement in each room - but don't give all active control, use for analysis for system balancing. Don't install manifold actuators. Use a manifold wiring centre to just switch pump on or off if you keep the mixers. No mixers and balanced system still leave off you add later if you have a problem room that overheats.

[JohnMo]

Forgot to mention your current mixing valves are unlikely to work or work well with WC. They may require to run at circa 50 degs to have any authority of manifold temperature.

42 minutes ago, RedSpottedSev said:

Some kind of communication centre that means the heatmeisers can call for hotwater at a different temperature to the hot water cylinder.

A boiler suitable for X or W plan or 4 pipe will have suitable control for switching between the two duties (CH and DHW).

 

Look at Viessmann, Atag, Intergas boilers. Size about 20 to 24kW.

 

If you are doing a new cylinder, buy a heat pump cylinder (3m² coil) so you get decent condensing and or rapid reheat when doing DHW.

[RedSpottedSev]

Thank you,

 

My understanding is that the current system boiler cant provide enough flow. So I am looking at a new boiler and will upgrade cylinder as we need 250L vs the 170L currently.

 

My priority is avoiding constant on/off yoyo switching of each room and making sure they stay as constant comfortable temperature as outside temperatures fluctuate. Efficiency gains would be a bonus.

 

I was sold the manifolds with pump and mixer initially before I had done any research (and hadn't planned upstairs ufh and getting rid of all radiators) so I have some of the kit ie pump, mixer, manifold, heatmeiser control and thermostats.

 

So, talking about the ideal set up (which I may have to do in stages and accept some wastage of things already ordered), I can swap out the fixed/manual mixing valve on the manifolds to ESBE. I haven't come across IVAR but will read about them.

Each manifold will then have ESBE/grundfos upm3 auto as a pump station and a hestmeiser.

 

Manifold 1 - main downstairs (can reduce to 2 zones)

Manifold 2 - kitchen and extension (high heat loss - glass sliders etc.. reduce to 3 zones)

Manifold 3 - upstairs (single zone but option to shut off guest room when not in use)

 

So... can I have a set up where if and when properly balanced, the heatmeiser and actuators close/open rooms that might not be in use, and the rooms in use will just have thermostats for info only, with the esbe running weather comp?

 

How do you decide where the call for heat comes from for each manifold? (Coldest room and then adjust other flow rates down?)

Also do I need extra wiring pulling up alongside the 5 core (heatmeiser) for the ESBE valves?

 

Which boiler and control unit is likely going to offer the easiest communication/connection set up to the heatmeisers and esbe?

 

Thanks again, I appreciate I have a lot to learn yet..

 

[JohnMo]

Not sure you really save anything by not heating rooms, the unheated rooms just suck in the heat from other rooms, so net energy input really doesn't change.

 

Would really try to move to a single zone per manifold, the loops in that manifold get balanced to get room temps you want. Having room sensors in each room allows you run all loops or none just by switching pump. So example, room 1 is targeting 20 and rooms 2,3 and 4 targets 20.5. if any room drops below there target all loops come online and later all go off. But better still balance the whole lot to run WC. If suitably balanced all should be ok.

 

Issue I found was if you are shutting down loops you can run into the situation where only one zone is calling for heat and the boiler goes into meltdown, short cycling and all the gain just get burnt with excess gas consumption.

 

Share your current boiler and mixer model/make?

[marshian]

On 27/10/2025 at 16:47, JohnMo said:

Not sure you really save anything by not heating rooms, the unheated rooms just suck in the heat from other rooms, so net energy input really doesn't change.

 

Just to add to @JohnMo's comments - Covered very well below with a bit of the maths

 

 

On 27/10/2025 at 16:47, JohnMo said:

Issue I found was if you are shutting down loops you can run into the situation where only one zone is calling for heat and the boiler goes into meltdown, short cycling and all the gain just get burnt with excess gas consumption.

 

Hell yes - Been there done that - "Smart TRV's" that can call for heat from the boiler even if only one room needs it will result in massive energy wastage as the boiler fires up and then potentially short cycles until demand increases

 

[RedSpottedSev]

Thank you @marshian and @JohnMo. I have been doing some more reading and your posts in the ufh section. That video is maths heavy, but I am working through things back to front. In that I am doing my heat loss, then using the formulas from heat geek and urban plumbers to calculate what flow I would need and use that as a starting point for each loop (work in progress).

 

Old boiler is Worcester 430/i unknown age but on last service it was not looking good. I think at least 12 years old.

New boiler: will go in loft with new cylinder (heat pump coil) to be both decided on compatability of current ufh kit i have (specifically the heatmeisers and how to get weather comp working)

 

I will be doing my best to run each manifold as a single zone, only using actuators on the loops as on/off or very high/ low set back temperatures.

 

The manifolds and it's pump (Grundfos upm3 auto)/mixer is from Thermrite. X2 will be downstairs in garage, supplying the downstairs area. One upstairs for bedrooms.

 

I am assuming if I was to do the above, I would still need to change my mixer valves to ESBE electronic valves for proper weather compensation? Do they work with the heatmeisers?

 

As each of the 3 manifolds have it's own pump on different flows, do I need to do anything special? Can I get a boiler that deals with this set up without special kit? Im confused about LLH/kimbo/closed coupled Tee...

 

Right now I want to make sure I've pulled up all cables needed from each manifold as we are due to start plastering. Currently have 6mm and 2.5mm going up to loft for boiler and cylinder, and 5core from each manifold to future boiler position. Do I need more for ESBE? Do I need temperature monitors on each inflow for the manifolds?

 

Thanks again for the help and education!

 

PS the upstairs orange coloured rooms will be guest rooms which I wanted to zone off, but from what I gather it is better to continue to keep warm even when not being used?!

 

 

 

Edited 6 hours ago by RedSpottedSev

[marshian]

16 minutes ago, RedSpottedSev said:

Thank you @marshian and @JohnMo. I have been doing some more reading and your posts in the ufh section. That video is maths heavy, but I am working through things back to front. In that I am doing my heat loss, then using the formulas from heat geek and urban plumbers to calculate what flow I would need and use that as a starting point for each loop (work in progress).

 

 

It seems that way initially but like most things but you do get you head around it eventually

 

16 minutes ago, RedSpottedSev said:

PS the upstairs orange coloured rooms will be guest rooms which I wanted to zone off, but from what I gather it is better to continue to keep warm even when not being used?!

 

Unheated rooms will steal heat from wherever they can - let me help with an example

 

My house (stupid T shape) has front bedroom above front hallway both having 3 external walls and with the added bonus of north facing - being a  "lets not be wasteful with energy sort of chap" (Mrs Alien says "tight b'stard") I didn't heat the front hall for most of the time just bringing it up to temp for the few hours we might use it (arriving and leaving). The Rad in the bedroom above had to have much higher flow rates as well as a higher set point than the other bedrooms (one because of the 3 external walls and two because some of the heat was being stolen by the hall below)

 

Now you might say but heat rises and yes it does but a better statement is that heat always moves to cold and it doesn't care if down is a direction it can move in.

 

So now I heat the front hall to 17 deg - it's cooler than the rest of the house but it does have an internal door to separate it - as a result the bedroom above needs a lower flow rate to the rad because the difference between the two rooms is much narrower

 

So by all means run rooms at lower temps but consider the impact on rooms above or below is all I would say - if you size rads or UFH for low flow temps to provide the heat needed based on a heat loss calculation you could find that the room won't reach target temp if it's having it's heat stolen by a room above or below or even beside it.

 

[RedSpottedSev]

Thank you

@JohnMo can you point me to a resource on how to do this properly:

 

"I would start by looking at the longer loop and all pipes to and from that loop and look at pressure drop. Once you have that, it will set pressure drop for system, then add all the flows you need together all loops). Now you have a pump duty point. You can now make a sensible choice of system or heat only."

 

Do you mean I calculate the distance from boiler to manifold 28/22mm and then add the longest loop which I think is 98m at 16mm. Somehow calculate the pressure drop? Then find the overall flow I would need through each zone based on my heat loss and heat output from each floor?

 

One more thing I cant get my head around...on DHW priority, when cylinder calls for heat, boiler diverts to dhwp, then do the pumps on each manifold keep circulating water around each manifold....but what happens if the mixing valve opens to draw heat and dhwp is running.

- do the manifolds not fight each other trying to draw from each other? Then do i need a directional flow control

- or heatmeisers are smart enough to turn the pump off when cylinder calls for heat?

- I know you said no to Low loss header, but this was why I thought it would let the pumps on each manifold to circulate at their leisure without fighting

 

Thanks again,

 

[marshian]

24 minutes ago, RedSpottedSev said:

One more thing I cant get my head around...on DHW priority, when cylinder calls for heat, boiler diverts to dhwp, then do the pumps on each manifold keep circulating water around each manifold....but what happens if the mixing valve opens to draw heat and dhwp is running.

- do the manifolds not fight each other trying to draw from each other? Then do i need a directional flow control

- or heatmeisers are smart enough to turn the pump off when cylinder calls for heat?

- I know you said no to Low loss header, but this was why I thought it would let the pumps on each manifold to circulate at their leisure without fighting

 

Thanks again,

 

 

In a DHWP set up the flow to rads or UFH stop - the heat source re-charges the HW cyl and then the system reverts to heating

 

House doesn't or shouldn't lose much temperature in the time it takes to do HW unless it's a massive tank