I have a slightly undersized radiator in my living room. The calculation says 6315 btus and my rad is 6019 btus. It was a replacement radiator, the same size as the previous one (so pipes were in the right place). There is a gas fire in the room as well. Should this undersizing cause a problem. To move up to a p+ rad would make the radiator about 30% oversized. Thoughts please.