Destratification

When a gymnasium, manufacturing building or other building is heated in winter, warm air rises towards the roof. The air settles into layers of different temperatures with the warmest air at the highest point. This condition is called stratification. Destratification is the process of mixing the air with ceiling fans to evenly distribute heat. Destratifying room air brings heat down to floor level where it is needed to keep people comfortable. Mixing the air also reduces ceiling temperatures, which in turn reduces energy losses through the roof and saves money.

Destratification can be done with paddle or ducted ceiling fans. Paddle fans work well in most applications, mixing the air throughout the room. Ducted ceiling fans blow warm air through a flexible duct to a spot at floor level. The ducted fans can supply heat to specific locations such as work stations. Both types of fans are rated in square feet of floor space covered.

A rule of thumb states that you can expect the temperature of air to rise 1/2° for every foot above the thermostat level (5 feet). For example, if the thermostat is set at 68°, the temperature 10 feet above the thermostat will be 73° (68° + (1/2 x 10)).

Typical energy savings expected with destratification is about 0.5% of the total heating costs per foot of distance between the ceiling and the thermostat. In areas with a high rate of exhausted air, this savings may be 0.1% per foot above the thermostat level.

For example, a gymnasium has a 25 foot high ceiling and a thermostat mounted at 5 feet. The thermostat is set at 68°. Since the ceiling level is 20 feet above the thermostat, expected savings would be .5% for every foot above the thermostat, or a total of 10%.


The following table summarizes the energy savings expected with destratification. This table supports the savings of .5% per foot above the thermostat, but also indicates that savings will vary depending on the indoor set point temperature. These savings are listed as a percent of the total annual heating costs.

Thermostat Setting
Savings per 10 feet of ceiling height above the thermostat level
68°
5%
60°
6%
50°
7%