Q. My hvac sub tells me that hot water radiant heat is "more efficient" than traditional forced hot air. Is this true?

A.Larry Drake responds: When applied to home heating systems, the term "efficiency" most often refers to the actual energy used, as reflected in the monthly utility bill. One of the main arguments for the reduction in utility costs of radiant heat over a convected air system is that occupants will feel comfortable at a lower air temperature with radiant heat. Unfortunately, scientific studies don’t always support this. Various studies have put the energy consumption of radiant heat at anywhere between 52% less to 10% more than conventional air systems. Nevertheless, there is a substantial body of circumstantial evidence from contractors in the field, who often hear reports from radiant customers on how much more comfortable they are at lower thermostat settings. Unofficial side-by-side comparison testing within the radiant heat industry has also demonstrated utility savings.

Exact energy-efficiency numbers are elusive because of the tremendous number of variables involved. Two houses can be built side by side with everything exactly alike except for the heating system. A comparison can then be made through the heating season demonstrating the energy efficiency of one heating system versus the other. But the results, while interesting and informative, cannot then be applied generally to all installations (which is unfortunately too often done).

I advise radiant heating contractors to tell customers that radiant heating systems can provide energy savings up to 30% over conventional hot air systems in most cases. Houses with high ceilings, large windows, poor insulation, high air infiltration, or a combination of these factors are more likely to have greater energy savings.

Larry Drake, of Hyram, Utah, is executive director of the Radiant Panel Association.