In modern airtight buildings, how is combustion air typically supplied to fuel-burning appliances?

In modern airtight buildings, the correct method for supplying combustion air to fuel-burning appliances is through ducting of outside air. This approach is essential because many contemporary structures are designed to be energy-efficient and minimize air leakage to maintain temperature control. The airtight nature of these buildings can restrict the amount of fresh air that can enter naturally, which can pose a risk for appliances that require a certain level of combustion air for safe and efficient operation.

By utilizing ducting to bring in outside air specifically for combustion, these systems ensure that appliances like furnaces and water heaters receive the necessary amount of air without negatively impacting the overall air quality of the living space. This method also helps to prevent the backdrafting of exhaust gases, which can occur if appliances rely on interior air for combustion, potentially leading to unsafe conditions.

In contrast, methods like natural drafts or ventilation from interior spaces may not provide a consistent or adequate supply of fresh air due to the controlled environment of airtight buildings. Sealed ventilation units also address ventilation needs but do not supply combustion air directly in the way that ducting of outside air does. Thus, the ducting of outside air is the most effective and reliable solution in these modern constructions.