My house has an extension attached to it which is always colder than the main house, i’ve added as much insulation as i can in the roof space but its still cold. Currently has single convector radiators in the bedroom and bathroom which i want to replace.

So.. should i replace with P+ radiators, or double convectors? I was going to go for P+ ones but double convector is only about £15 more. Is it best to go as big as possible? They will have TRV’s on so the rooms wont overheat.

Do the rada in your extension get warm at all ?

Is your boiler up to the number of rads ?

Have you had te system balanced ? Its possible they just tacked the extension on the end of the system with wreckless abandon ?

I just stuck doubles an trvs in all my rooms at about half the size on the wall as my old singles with a new boiler and with the lot on low its warmest my house has ever been , made a crazy difference

Yeah they all get hot (as hot as the rest of the radiators) but even when they are hot the rooms still take a long time to warm up.

Think i will get double convectors as i can then put a slightly lower radiator in the bedroom which i can easily tuck curtains behind, and i think the bathroom needs one as the tiled walls / floor probably suck a lot of the warmth up

much insulation as i can in the roof space

What about the walls and glazing?
Is the room north or south facing?
How big are the windows?

Double glazed uints (fairly modern), cavity wall but no insulation as far as i know. Dont fancy adding cavity wall insulation though as heard in damp conditions it can be a problem, and the room is exposed to a lot of wet lakes weather. Doesnt get much sun either.

got by size.. what looks good to your eye? 600 high is standard look on the manufacturer sites for heat values. I use Purmo they have a decent finish and i ve never had issues with any i ve fitted ( probably 500+)

double panel double convectors are BIG they take up a lot of room on the brackets they stand something like 13/15 cm out into the room but by jove they kick out some heat

i dont give a sausage for can your boiler take it… it makes water hot.. and it will do it all day long.

possibly the issue may be the size of the pipework in the extension, possibly 10mil and plastic which will take longer to heat a rad if the rest of the property is on 15/22mm..

rads are big and white you should notice the heat when you enter a room not the rad..