Enter the air exchanges per hour, the total volume of the room, and the change in temperature to determine the ventilation heat loss.

Ventilation Heat Loss Formula

The following equation is used to calculate the .

Q = .33 * n * V * ΔT

  • Where Q is the ventilation heat loss (W)
  • n is the air exchanges per hour
  • V is the volume of the room (m^3)
  • ΔT is the change in temperature (C)

To calculate the ventilation heat loss, multiply the air exchanges per hour by the volume to get the volume per hour. Next, multiply the result by .33, and finally, multiply that result by the change in temperature.

What is Ventilation Heat Loss?


Ventilation heat loss is the loss of heated air from a building. It is caused by infiltration of outdoor air and exfiltration or release of interior air due to differences in pressure.

Ventilation heat loss is an important element in the energy balance of the building envelope, particularly in the design stage where mechanical heating and cooling loads are considered.

Note that ventilation heat loss is different from infiltration. Infiltration is the amount of outside air that enters a building by means other than the HVAC system (e.g., through cracks, doors, etc.). Ventilation heat loss is usually expressed as Btus per hour and infiltration is usually expressed as cubic feet per minute (cfm).

What Does Ventilation Heat Loss Mean?

In an un-air-conditioned building, ventilation heat loss accounts for a large portion of the total heat loss. A common rule of thumb is that ventilation heat loss is about 50% of total heat loss, but this assumes that there is no mechanical heating/cooling system in operation, which is rarely the case. In many cases, mechanical heating/cooling systems use more energy than is saved by their prevention of ventilation heat losses.

In other words, it takes more energy to run the HVAC equipment than is saved by preventing ventilation heat losses. The result is that total heat losses increase with increasing use of HVAC equipment: An un-air-conditioned house might have a total annual heat loss rate as low as 10 BTU/ft2*°F (5 W/m2*K).