A jobsite enclosed and heated for winter concreting will be warmer than its surroundings, naturally, so there will be a constrant outflow of heat. To maintain a temperature level, this outflow munst be replaced. Let's examine a simple method of calculating heat losses. Our example will apply to reinforced polyethylene enclosure material; with slight alterations, this calculation technique can be used for other enclosure materials. For the example, compute heat losses and heating costs for a 16 story building of reinforced concrete construction. The first floor is 12 feet in height; upper floors are 10 feet; dimensions are 60 feet by 140 feet. Assume the outside average temperature is 0 degrees F during the entire construction period. The required minimum inside temperature is 50 degrees F. Assume that the construction schedule is one floor per week and that each floor requires protection for four weeks. The upper enclosure on the ground will be 14 feet high and will extend 2 feet 8 and one-half inches beyond all building walls. Assume that 20 foot wide tarpaulins will be used for enclosure walls and that panels will be used for the enclosure roof. Hence, 5,900 square feet of wall area; 9,500 square feet of ceiling area; and 590 lineal feet of wall crack area. The temperature differences are 50 degrees on the ground, 55 degrees 5 feet above ground, 65 degrees at ceiling, with the average wall temperature difference of 60 degrees. Therefore the heat losses would be: at ceiling level 722,000 btu per hour; for walls 354,000 btu; for floors 85,400 btu; for cracks 87,400 btu; the total heat then required 1,561,000 btu per hour. Natural gas rates are often expressed in therms (a therm is 100,000 btu). If the gas is being sold for 8 cents a therm; the cost per hour would be 1 dollar and 25 cents.