Marginal heating with radiant panels
We recently had a gas fired hydronic system installed, using panel radiators. One of the rooms seems a bit marginal on heat input; it takes a long time to warm up, and will only just hold a temperature of 70F on a cold day, which means about 35F where we live. Obviously, this translates to 35 deg temperature difference, inside to outside.
The system installer is suggesting replacing the radiator in that room with a larger unit, giving about 25% more heat output. Since heat loss is roughly proportional to temperature difference, am I right in thinking that the present 35 deg difference would go up to 35 x 1.25 = 43.75, for a final temperature of 78.75?
This would be more than sufficient for our needs, but I'd like to be sure that the proposed 25% increase is going to be enough.
Thanks in advance.