Radiant heat in the ceiling is very comfortable. It works solely on radiant heat coming from the surface to people without heating the air directly. Radiant heats surfaces throughout the room and in the process heats the air next to the surfaces. One noticeable difference is when legs are under desks an tables, there is no radiant under that shield. However, when in the lounge chair or on the floor it is comfortable.
In former days, hot water tubing was covered in lath and plaster. The latest was to lay electric heater strips on the drywall before insulating. Some of the electric heaters were less safe than others. You would want to know which one your had to be sure.
The efficiency of your ceiling radiant heat depends upon the amount of insulation above it which should be R-22 or better. You don't want some of the heat warming the attic.
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