Negative home air flow causes sick house syndrome

You must let air into your house. Recovery, make-up and combustion air control increases comfort and effectiveness, and reduces improper air infiltration.

Here is an easy solution for inadequate combustion air.

One way to target that air is to use an insulated flex duct to connect the outside air to the cold air return of the furnace. The duct connects the unit to a screened, fresh air inlet mounted outside the home. When the furnace blower operates, the air control damper opens, automatically drawing outside air into the furnace. The air is filtered, heated or cooled, then circulated through the home’s duct system. As a result, a slight pressure builds up in the home, keeping untreated air from seeping in around windows and doors.

These types of units are designed to supply combustion air to fuel-burning appliances that have inadequate combustible air sources, like dyers and heaters. They also replace air used by fans in bathrooms and kitchens.

By connecting to a duct which, in turn, connects to a screened, fresh air inlet mounted on the home’s exterior, the air used is not house air you have conditioned. As the colder, heavier outside air enters the duct, the unit acts as a check valve or cold air trap, automatically diffusing auxiliary combustion air into the area around the appliance.


  • Supplies fresh make-up air to the home.
  • Comfortable by reducing uncontrolled air filtration and cold winter drafts.
  • Helps reduce in-house stale air problems created by today’s tightly constructed homes.
  • Improves appliance efficiency by providing proper air for combustion.
  • Reduces drafts caused by negative pressure.