Cast iron and steel radiators - efficient? Where to buy from?

[mardinor]

Unless you have an automatic bypass fitted this is not recommended and may invalidate the boiler warranty depending on manufacturer.

Thanks for the warning. Yes, bypass fitted.

 

[Stevers]

Unless you have an automatic bypass fitted.

We had TRVs on all but one radiator from new, those TRVs have now been replaced with smart TRVs. The radiator without one is in our shower room and has a towel rail over it. That means that the room is always comfortable, has dry towels, and any overheating warms the rest of the house which will mean the other rads won't be working so hard - a bit like having an efficient Aga in the house, but only when you need it. Something I hadn't realised immediately on upgrading from dumb TRVs, was that the shower room radiator would only be 'on' if at least one of the smart TRVs was calling for heat.

Smart TRVs call for heat via the controller, and I wonder if in that case a bypass radiator is still necessary. There's definitely no warranty remaining on my Baxi Solo 2 from 1997 to worry about!

 

[fernicarry]

Smart TRVs call for heat via the controller

Boiler may still short-cycle or otherwise be unhappy if the output of the radiator calling for heat is less than the minimum the boiler can modulate down to.

All the radiators here are on individual room stats controlling actuators instead of TRV's, but the heat comes from a thermal store so it can go as low as necessary. The circulating pumps also modulate according to the pressure drop.

Being a good Scot the idea of turning the heating down to almost nothing appeals...

 

[a twig]

Does the house actually heat with that flow temperature? Mine certainly wouldnt during the winter. The important thing for efficiency is the return temperature at the boiler, ideally we want this at around 55deg and if the system is designed correctly for a 20 degree temperature drop across each radiator then the boiler should be near full efficiency with the flow at 75deg. Depending on the boiler if its fitted with an opentherm controller(eg Nest) this will take into account the external temperature and adjust the flow temperature accordingly.

Just a slight nitpick, it’s the max return temp that should be 55’C for a condensing boiler to do its condensing properly. Lower than this on the return is fine and often more efficient.

The section on condensing boilers in this article explains it well