Understanding ufh, flow rates and mixer

[Chuci24]

Bought a house where the previous owner had done a lot of work back in 2023. Along with the rear and side fill ground extension, One of the things was fitting a 2 zone ufh downstairs and removing the rads. 1st floor and loft still only have rads. He's also put a wb 8000 35kw life boiler, kingspan 300l cylinder, heatmiser ufh4, nest gen 3 and heatlink (for the radiator and hot water control)


With the cold approaching, I've recently turned on the ufh for the last few days. I've never had it before but have read that it should be left on constantly with only a degree or two set back. Currently both zones are set to 20.5 when not in use and 22 for when in use. I think the neostats v2 have a 1 degree differential which I've not touched.

What I'm not sure about is the flow rates and mixer temp. Boiler rad temp is set to 65. However the ufh mixer seems to be set to 55 which reading online seems quite high. Ive verified it by leaving it on and looking at the dial above the valve. Also the manifold flow tubes seem to vary. 2 of them are at 5l/m. Again that seems quite high based on what I've read online

I don't have any diagrams or installation details so have no idea how long the pipes are. I also don't know if it's screed or suspended timber below. Based on the level 3 survey it indicates the extension is solid floor but the living room (the other ufh zone is suspended timber) Should I assume it was set correctly or should I be messing about with it.

Lastly, it's a 1909 property with solid walls except for the rear ground extention. Even at 22 degrees it doesn't feel toasty which I assumed it would. Today for example it managed to reach the set temps in both zones just fine after an hour or so but the has used about 30kwh of gas based on my octopus mini (excluded the 32 mins of radiator heating and the 1hr of cylinder heating). Total gas use today was 42. Its been about 11 degrees outside.

Pics attached if it helps. Any advice would be greatly appreciated.

 

[Madrab]

Should I assume it was set correctly or should I be messing about with it.

Difficult one without anything to show the design of the system, or at least a description from the owner who installed it. Also looking @ loop 3 (from the left), even with the actuator open there doesn't seem to be any flow? I'd also have caps on the 1st port in/out - just in case.

If the system isn't running or heating properly then you will need to re-commission.

Starting point of flow rates - they wouldn't normally exceed ~ 2L/Min

Mixing Temps - this will be governed by required output per m2 (heat loss calcs) coupled with flow - also consider what floor covering is being used.
If it is traditional concrete and screed or suspended floor voids insulated and biscuit screed then yes, the thermal mass would need to be maintained at a stable constant temp. If it is an overlay or suspended floor/spreader plates then that works more like radiators and wouldn't need to be kept warm. Each type would be run and controlled differently. In a mixed setup then that would need 2 different setups.

 

[Chuci24]

Difficult one without anything to show the design of the system, or at least a description from the owner who installed it. Also looking @ loop 3 (from the left), even with the actuator open there doesn't seem to be any flow? I'd also have caps on the 1st port in/out - just in case.

If the system isn't running or heating properly then you will need to re-commission.

Starting point of flow rates - they wouldn't normally exceed ~ 2L/Min

Mixing Temps - this will be governed by required output per m2 (heat loss calcs) coupled with flow - also consider what floor covering is being used.
If it is traditional concrete and screed or suspended floor voids insulated and biscuit screed then yes, the thermal mass would need to be maintained at a stable constant temp. If it is an overlay or suspended floor/spreader plates then that works more like radiators and wouldn't need to be kept warm. Each type would be run and controlled differently. In a mixed setup then that would need 2 different setups.

Thank you for your reply!

So the system is heating correctly, not too sure about maintaining though as ive no idea how much gas usage they take up. Eg over last couple of days here in London it's been anywhere between 9-15 degrees, I'm averaging about 32/33kwh of gas usage based on it being at 22 from 6am till 10:30pm and 20.5 overnight.

Is there such a thing as a ufh service like a boiler service and is it worth commissioning one. Like you've mentioned, it's hard to tell anything without diagrams or what was installed.

 

[endecotp]

No installer’s name on a label somewhere? (I see the label on the cylinder is blank.)

 

[Johntheo5]

Thank you for your reply!

So the system is heating correctly, not too sure about maintaining though as ive no idea how much gas usage they take up. Eg over last couple of days here in London it's been anywhere between 9-15 degrees, I'm averaging about 32/33kwh of gas usage based on it being at 22 from 6am till 10:30pm and 20.5 overnight.

Is there such a thing as a ufh service like a boiler service and is it worth commissioning one. Like you've mentioned, it's hard to tell anything without diagrams or what was installed.

You can do a fair bit of investigating yourself. Try and obtain a digital pipe temperature sensor, these can be got very cheaply but I don't have a link just now. A typical loop flowrate is the loop length/40, so, initially, suggest setting the flowrates at 2.5LPM (100/40), set the mixing valve to say 40C, typically, you might then get a dT of 8C, (difference between the loop flow and return, 40C/32C. The loop output is then the flowrate in (LPM x 60 x dT)/860 kW, above = 2.5*60*8/860, 1.4kW. IF so, you're 6 loops were/are emitting a total of, 6*1.4, 8.4kW while on.

 

[Madrab]

Is there such a thing as a ufh service like a boiler service and is it worth commissioning one

The system could certainly be re-commissioned but as suggested, depending on your level of handiness you could do some tweaking with the system as is, or if very confident, reset the system back to standard settings and start from scratch.

 

[Chuci24]

No installer’s name on a label somewhere? (I see the label on the cylinder is blank.)

Unfortunately not!