HR91's, towel radiators and Evohome

[stevewills66]

Hi

I've just got 11 HR91 radiator controllers to finish my Evohome setup. This will leave me with 2 x towel radiators in bathrooms that can't be controlled by HR91. Should I use the Evohome controller as the main room thermostat downstairs and assume that the heating in the other rooms will keep the towel radiators 'ticking over' as and when heat is demanded from other rooms? Or is there a better way to ensure that the bathrooms are kept warm?

[Richard]

Personally, I don't design heating systems with towel radiators for any kind of space heating. If a bathroom needs heat, this is done with a radiator or UFH in the same room. As the name suggests, 'Towel Radiators' are for heating towels not the actual rooms they are in (they are usually too small to do this anyway, especially when covered with a towel).

Leaving the towel radiators with a manual valve means you can turn them on and off and they will come on whenever there is a heating demand in another HR91/HR92 zone. They can come on when there is a hot water demand too, if you use the evohome installation guide page 46 diagram. I've not had anyone complain where this has been the case.

[stevewills66]

Thanks

I should have said keep the towels warm, not the bathrooms, I know the towel radiators are not good room heaters. It's just if that is ok to leave them on, and then have them in the loop when an HR91 is active.

Excuse my ignorance, I have seen a few posts regarding 'page 46', in that case, what setup is used in the BD91, as it's currently setup as CH demand to control the boiler/valve. Should I lock open and electrically isolate the CH valve as has been suggested and use the HR91's to control the flow to each rad, plus the couple of open towel rails? In which case do I need a second BD91 for CH demand? If not, what should I set the BD91 to control or leave it as CH?

Many thanks

Steve

[Richard]

Sorry Steve missed this...

Page 46 is exactly that... The diagram schematic on page 46 of the evohome installation guide. This schematic is the way you should install the evohome system for best efficiency over a longer term operation, and uses a BDR91 or OpenTherm Bridge at the boiler (this is the only thing that switches the boiler on and off, no orange wires off the zone valve anymore) and a BDR91 opening and closing the hot water motorised zone valve (orange and grey wires are redundant and made safe).

No motorised zone valve on the heating, with exception of an OpenTherm system when you would use 'X Plan' which means a NO (normally open) zone valve goes on the heating to create PDHW (but this is powered by the hot water motorised zone valve).

More on PDHW here - https://theintergasshop.co.uk/content/1 ... -be-banned

[Rupes]

I have an HR91 on a radiator in a hallway and I basically use this to drive all the towel rails along with any other radiators without smart trvs. It is programmed with a high target temperature for a couple of hours in the mornings and evenings when towels might need warming/drying.

The towel rails also come on whenever any of the other smart TRVs is calling for heat.

It works well for me and means I can also heat the towel rails in the warmer months.

It’s a bit of a fudge but it works and with no special plumbing required.