Cold room - replace radiator?

[Merrow]

We're sorting out a nursery in the house and it is the coldest room. Currently 13 degrees while the living room is 16.5. There's some things we're doing to address this - there's single glazing in one window that we're replacing with double glazing, and single glazing in the room below that we're replacing. However, some of it is just the nature of the room in that it's basically in a slightly annexed bit of the house so is under the roof and has 2 and a bit external walls. There's a standard single panel radiator that I feel does a pretty poor job of heating up the place, is replacing this going to be the best course of action? We currently have a plug in radiator that we use to heat the room when we are using it.

I'd put insulated lining paper up - it's really effective on outer walls. Any room with two external walls is going to be chillier though.

As for the radiator, is it big enough? Is it heating up properly?

I've never heard of insulating lining paper, thanks! I'll look into that now.

As for the radiator, it's heating up fine it's just that the heat doesn't really feel like it's warming the room if that makes sense. It's a decent size, but it's never a room that feels toasty with just it on.

Check the loft insulation above the room. You might be losing all your heat through there.

There's no loft above - it's a sloped ceiling so the roof tiles are literally right above it. It really does have everything working against it in terms of keeping it warm! Apart from the fact it is a very small room.

We had a bathroom that was the coldest room in the house as it sticks out and has 3 external walls. We had insulated panels put in and replastered. Insulation put in the roof and a new radiator put in. It's the warmest room in the house now.

The radiators in all the rooms had sludged up completely - replaced them with double radiators. They are more efficient now so they looked smaller than the 30 year old ones we replaced. So much better and warmer.

There's various online calculators for radiator size you can use to see if the setup you've got is right for the space, have you looked in the loft to check that there's enough insulation too? One of our bedrooms is much colder (doesn't get the sun, and has two exposed external walls) but there was also barely any insulation above so we have been able to improve temps a bit by increasing that.

Some radiator websites have BTU calculators where you can input some info about your room size and how many external walls, and it will give you an idea of how much heat output you need in a radiator / what size radiator. It might be that you need a larger radiator.

If it seems to be the correct size/output for the room, you might need to balance the radiators in the house, which involves turning some up or down (at the other valve that is not the thermostatic valve) in order to divert more hot water to that radiator. Sometimes the hot water system makes a loop that bypasses the cooler radiator, if that makes sense.

If there is anything you can do to increase the insulation, that should help, as well. If you can bear to lose a few inches from the room size, you could add an extra layer of insulated plasterboard to all the cold walls and ceiling, spaced off the existing walls with 1x2 timber strips, for example. Then taped & jointed (plaster the joins), add skirting boards, then paint/decorate.

Heavy curtains can help. Rugs/carpet can help. Fabric wall hangings (like a quilt hung on the wall) can help.

Sounds dramatic but I would consider taking the ceiling down, putting insulation in and reboarding / plastering. There is not much point insulating the walls if the heat is just going straight up and out through the roof.

We put insulated plasterboard in DS’s room and it made a big difference. As others have said you could also look to see if anything can be done with the roof.

We have since moved house and DS is 16 and never has his radiator on his room. His early years must have made him hardy! He will be one of the competitive under heaters on MN in a few years time ha ha ha

Can you drop the level of the ceiling, fill it with rockwool then board it with insulation backed plasterboard.
I think most of the heat you are losing is thru the roof, then walls/window.

Thanks everyone! Some really helpful ideas. Looks like insulation is the way forward.