On Radiant-Floor Heating (2 letters)

Thank you for the January 2002 (EBN

Vol. 11, No. 1) article on radiant heating, which I enjoyed and wholeheartedly agree with. It is refreshing to see attention paid to mechanical systems instead of assuming an efficient envelope is enough to make a building efficient.

My experience designing and installing hydronic heating systems leads me to conclude that the article’s suggestions for zoning individual rooms and changing the heating system water temperature in response to outdoor temperature (outdoor reset) should be done in all radiant heating systems in all buildings, not just well-built buildings, as a way of avoiding overheating and underheating problems. I believe this practice should extend to all hydronic heating systems, radiant or not; otherwise, wasteful and uncomfortable overheating at certain times or in certain areas of the building is inevitable.

For scorched-air heating systems, I think the temperature of the air in the ducts should be changed in response to outdoor temperature, with a lower limit to prevent cool breezes coming from the ducts in mild weather. This is easiest to do with systems that use a hot water coil to heat the air, but difficult with other equipment. However, almost nobody does this, and almost nobody zones scorched-air systems. It is almost as if the whole energy-efficient building industry collectively makes believe one thermostat in one room can control comfort and energy use buildingwide. I think it is time for more people to pay attention to controlling indoor temperatures by methods other than the windowstat.

Henry Gifford

Gifford Fuel Saving Inc.

New York, New York

I very much enjoyed your thorough exposition and analysis of radiant-floor heating (EBN

Vol. 11, No. 1). I appreciated the skeptical, objective approach you took to an interesting, seemingly “green,” technology that in my opinion has been hyped (like ground-source heat pumps). I too have made the point about needing to lower thermostat settings to save energy with a radiant floor and have doubted that it happens. Some proponents of radiant-floor heating may be unaware of the need to lower space temps to achieve savings—so they don’t tell their clients. I also appreciated your analysis about possible heat losses into the ground (for on slab) and the possible incompatibility of radiant floors as solar thermal mass (since the heated floors do not absorb solar gain well).

An additional reason why radiant floors may not save energy is their incompatibility with night temperature setback. These floors have substantial thermal inertia and thus are likely to be operated in a way that keeps space temps more or less constant. Higher temperatures at night mean more nighttime heat loss, thus wasting energy. This is another argument showing that radiant floors are more about warm feet and comfort than about energy efficiency and environmental responsibility.

I also think that the claims radiant-floor people make about stratification in conventionally heated houses are overblown. I do not have more than a degree or two of delta T in my house between floor and 10-foot cathedral ceiling. Leaky houses (with conventional furnaces which blow hotter air) may have more stratification, but I think it would be extremely unusual to find 10, 20, or 30 degrees of temperature differential, as supposed by the exaggerated illustration accompanying the article.

Walter Simpson

SUNY Buffalo

Buffalo, New York