A power vented gas water heater tolerates greater negative pressures, up to -15 pascals. Armed with a manometer, you can compare the air pressure near these devices with the pressure outside. If pressure conditions pose a risk, make adjustments before the home owner complains. Better yet select sealed-combustion equipment that doesn't require indoor air for venting. Measure and balance air flow for each room with a closeable door.
Balance flows with dampers at the takeoff end of each branch duct.
However, to solve the duct leakage problem, heating contractors must put extra time into system design and air sealing. The key is a duct tester, such as the Duct Blaster. It allows workers to check their work, learn where leaks occur and evaluate the most effective sealing methods. A duct tester also helps sell customers on the extra costs of duct sealing. Some heating contractors have enough interest in stopping duct leakage to justify the expense.