Heating Commercial Buildings

Combustion heating systems are often used in commercial buildings. Though less common, but on the rise, is the use of in-floor heating systems in large commercial facilities.

Furnaces and Boilers

This chart shows the relationship between boiler return water temperature and efficiency for condensing boilers.

Common commercial heating systems include furnaces and boilers. Furnaces provide heating with warm air and boilers provide heating with warm water.

Furnaces and boilers can be categorized as either condensing or non-condensing. In Wisconsin, most new furnaces are the condensing type and have a combustion efficiency of over 92%. Non-condensing furnaces have a combustion efficiency of around 80%. Some condensing furnaces also have variable speed fan motors. The motor speed varies depending on heating needs. This reduces energy use and adds to comfort.

It is relatively easy to switch from a non-condensing to condensing furnace. Combustion air and flue gas venting is added along with a line routing condensate (water) to a drain. Changing to a condensing boiler is not as easy. Just replacing a non-condensing boiler with a condensing boiler does not usually provide energy efficient operation.

Condensing boilers only provide the expected comfort and energy savings if the temperature of the water returning to the boiler is between 60°F and 125°F. To maintain this temperature range, the pumps, piping and radiators for the heating system need to be designed and installed properly.

Condensing furnace. Return air is on the lower right. The white PVC pipes are for combustion air in and flue gases out. The smaller white pipes are for draining the cooling coil and the flue gas conde


Wall-mounted condensing boiler. The white PVC pipes are for combustion air in and flue gas out.

In-floor Heating

In-floor heating creates a warm floor that radiates heat. The radiant effect allows the room air temperature to be set lower than normal. Radiant floor temperatures are generally 78° to 85°F. Condensing boilers are a great match for radiant floors because they provide heated water at lower temperatures. Conventional (non-condensing) boilers deliver hot water at 180°F and return it at 140°F.

Low temperature heat can be located below sub floors, in concrete and other floor applications. Low temperature radiant wall panels are common in Europe, less common in the U.S.

For radiant heat to work properly, building walls need to be well insulated and have low infiltration. Older, leaky buildings are not a good match unless they are weatherized first.

Designers and installers can use this technical resource: https://www.caleffi.com/usa/en-us/technical-magazine.