I am renovated a house and now have a big l-shaped kitchen diner. I was going to put one big radiator under the window (RHS of picture below) but have changed my mind and think that having a slightly smaller rad under the window and another opposite might be better for a more even spread of heat. Dining room part is 4.5mx4.5m, kitchen is 3m x 3m.
I need 11,000 btus in total for the kitchen diner so will put a 8500 rad under the window and a circa 3000btu one opposite.
My thinking is that I only put a TRV on the large radiator. Why? Once the temperature gets up to the level set on the large rad it will shut it off – this is good as it is sort of out on a limb on the heating network – and the smaller rad will maintain the temperature.
But then again I could put a TRV on both of them and set the temp on the smaller rad to be slightly higher than the larger rad, so it doesn’t overheat the room but is the first to come on to maintain the temp if it drops rather than the large rad coming on which needs a lot more flow further away to work.
Confused!! Any ideas??

I can’t see any reason why you wouldn’t put TRVs on all the radiators (apart from a heat dump rad if you have one). I personally think you’re overthinking it.

Out of interest [presuming the dining room looks out onto the garden] why are you not replacing the ‘dining’ radiator with french windows/bifolds? That would then give you a great kitchen/living room. Is this for yourself or to sell on?

It’s for myself. The window is 1 storey up over the garden. We do plan one day to have patio doors out to a balcony looking out over the garden and woods but it’s going to cost a huge amount of money we won’t be able to afford for a long time (years!). I can just move the rads at a later date if we do that.

But then again I could put a TRV on both of them and set the temp on the smaller rad to be slightly higher than the larger rad, so it doesn’t overheat the room but is the first to come on to maintain the temp if it drops rather than the large rad coming on which needs a lot more flow further away to work.
Confused!! Any ideas??

Could you daisy chain them? TRV on the small radiator and the output from the small going to the input of the large?
Would make the large one slightly less powerful as its running on partially cooled water, but also makes it less costly, and reduces losses on the out/back pipe runs.

The window is 1 storey up over the garden

That seems a perfectly good reason 🙂

Could you daisy chain them?

Hmmmmm. I see what you are thinking. It wouldn’t be that easy as the pipework is nearly all there already.

I might be changing my mind again anyway, just checked the price of french doors. I might as well get a vertical rad for the side of the window and save up for french doors with a juliet balcony behind for the moment. Window is 6ft wide so could be a direct replacement with minimal building work required. Have them open inwards so we could enjoy having them open in the summer for the moment but then upgrade to a balcony in later years.

Back of house…..