Most forced-air heating systems include a supply register in each bedroom, but no return-air grille or other path to allow air to return to the furnace. Without a return-air path, bedrooms with closed doors can become pressurized. The result is room-to-room pressure imbalances, energy waste, and potential moisture problems in walls. Until now, there were three possible solutions to this problem:

• a return-air grille for every bedroom, ducted back to the furnace;
• a through-the-wall transfer grille to connect each bedroom with the adjacent hallway; or
• a crossover duct (also known as a jumper duct) to connect a ceiling grille in each bedroom with a ceiling grille in the hallway.

Tamarack Technologies has come up with a fourth solution: a transfer grille designed to be retrofit into the bottom of a bedroom door. Called the Perfect Balance In-Door Air Pressure Relief System, the grille is made of paintable ABS plastic.

The company says the grille works in both hollow-core and solid doors. To install it, you have to cut out a section of the bottom rail of the door, but the grille has a flange that slides over the door to strengthen the installation, and screws secure it on the bottom of the door where they won’t be seen.

According to Tamarack, the $29 grille provides up to 250 cfm of pressure relief at a pressure differential of 3 pascals.