A sealed combustion furnace draws all combustion air directly from outside the home through a dedicated intake pipe rather than using indoor air, improving indoor air quality and efficiency. This design creates a fully isolated combustion chamber that prevents backdrafting and loss of conditioned air. Sealed combustion furnaces achieve AFUE ratings of 90 to 98 percent and are required in some building codes.
System Design and Operation
Two separate pipes penetrate the exterior wall: one draws outside air to the furnace while the other exhausts combustion gases. The induced draft fan maintains negative pressure within the sealed chamber. This configuration eliminates negative pressure effects in the home and prevents carbon monoxide risk from backdrafting. Typical installations use 2-inch and 3-inch PVC or metal pipes extending 12 to 24 inches above roofline.
Benefits and Installation
Sealed combustion furnaces do not consume heated indoor air, reducing energy loss by 1 to 2 percent compared to conventional systems. They work with high-efficiency condensing technology for optimal performance. Installation costs run 300 to 500 dollars higher than conventional furnaces due to additional ducting and piping. Modern building standards increasingly require sealed combustion in residential construction for safety and energy efficiency.