There are two main types of baseboard heaters: convection and hydronic. Although they look pretty much the same from the outside, there are some fundamental differences between the two. The convection process draws cool air into the bottom of the heater. The heater warms that air and then releases it into a room. Hydronic heaters, on the other hand, contain water or oil. The heating warms that liquid, which heats the air. “Most people prefer convection heaters, because they are cheaper,” says general contractor Alan Rickmint. “But hydronic heaters are more even, and the actual unit doesn’t get as hot.”