Pressure Control
If a furnace is operating at a fixed temperature, pressure will change with mass flow of flue gases and fuel input rate. As high temperature gases are discharged at a level higher than the inflow air, negative pressure arises. This will cause ambient air to leak into the furnace, lowering the temperature and more energy is required to heat the extra air. In furnaces where volatile gases are present, a slightly negative pressure is required to eliminate the risk of hazardous gases leaking out (U.S. Department of Energy, 2005).