Calculating Heat Loss in Slab Construction

The heat loss for residential and small commercial buildings constructed on a concrete slab at or near grade level is computed on the basis of heat loss per foot of exposed edge.

For example, a concrete slab 20 ft x 25 ft would have an exposed edge of 90 ft (on a perimeter of the exposed edge of a concrete slab). The heat loss depends on the thickness of insulation along the exposed edge of the concrete slab and the outside design temperature range. This information can be obtained from ASHRAE publications.

To calculate a heat loss in Btu/hr, simply multiply the total length of the exposed edge by the heat loss in Btu/hr per lineal foot (lin ft).

Heat loss of a concrete slab = length of the exposed edge x heat loss per lineal foot

For example, a 90 ft exposed edge with 2-in-edge insulation at n outdoor design temperature of 35 degrees F can be calculated as follows:

90 lin ft x 45 Btu/hr/lin ft = 4,050 Btu/hr