Bedroom radiator problem

[Bedroom radiator problem]

I have recently moved into a new house. We have a problem with the heating in a bedroom that sits above a garage. The garage is an integral part of the house with the bedroom above. The bedroom is very cold compared to the other bedrooms . The builder insists that the radiator in the room is the correct size for the room and I have checked this using an online calculator. However I don’t think the standard calculator takes into account the the fact that the bedroom sits above a very cold garage. Could anyone give me any advice on this ? Am I right in thinking that the calculation s flawed for this scenario ?
Thanks

 

[ShaunCorbs]

Is the floor insulated ?

 

[Deleted member 120897]

As per Shaun and is the roof-space insulated? Online calculators usually ask what is below, eg uninsulated floor, etc.

 

[Chuck]

Measure the flow and return temperature at the radiator when it is in use. Make sure that they are at least the values assumed in the sizing calculation. Compare with the values in the bedrooms that are okay.

 

[SimonG]

I'd be looking under the floor in the bedroom.