Heat loss

Heat loss is the rate at which heat leaves a room or whole property through walls, floors, roofs, windows, doors, thermal bridges, ventilation and air leakage. In heat pump design, heat loss is calculated room by room so the heating system and emitters can be sized to replace that lost heat at the chosen indoor and outdoor design temperatures. It is not the same as heat load, annual energy use, an EPC rating, a heat loss report, a running-cost forecast or proof that every survey assumption is correct.