Downstairs towel rail to feed off CH or UFH?

[Ruggers]

I'm going to fit wet UFH downstairs to a new build and radiators upstairs. Most of these rooms will be zoned in the house. Because the downstairs bathroom is small, 2.35m x 1.85m, I'm not sure it will provide plenty of heat even with 150mm pipe centres. I'd like to fit a towel rail to the wall so wondering which system it's best taken from, the UFH or the radiator system.

Not keen on electric as it's expensive to run.

Taking from the UFH if possible would means it's running cooler but can be linked to the same zone on the manifold. If it comes off the upstairs rad system, I'd have to fit a TRV and it would come on and off whenever an upstairs zone calls for heat.

 

[flameport]

Take it direct from the flow/return of the boiler, so it can be used whenever the boiler is on.

It can then be used at any time including in the summer to dry towels etc.

 

[MeldrewsMate]

As above, though you can take the tappings from the primary supplies to the UFH manifold, either before or after its zone valve. If before, the rad will come on as @flameport says, if after it will come on when any UFH zone calls for heat. In all cases fit a TRV; its mandatory for Building Regs and easy to turn down or off - you won't get much heat out of a towel rad if you take supplies from the UFH manifold, even for a small room. At ΔT of 20°C (UFH at 45 so rad average temp = 40°C, room = 20°C)

 

[Ruggers]

If I do what @flameport suggests, would the towel rail would heat every time the boiler operates to heat the water cylinder, despite my CH being turned off during the summer? The plan is to have 2no. 2 port valves, one for downstairs UFH zoned system, and another for the upstairs radiator system which will feed each radiator from an upstairs manifold with actuators zoned. The radiators will be over sized to have a lower delta T closer to the UFH temps.

Why do building regs require a TRV on the towel rail, i thought it was essential or at least good practise to have one radiator in a system always open to allow expansion & somewhere do dissipate the heat after the boiler shuts off while the pump is still operating?

 

[flameport]

would the towel rail would heat every time the boiler operates to heat the water cylinder, despite my CH being turned off during the summer?

Yes, unless you turn the towel rail off at the valve / TRV on it.