The return air grille and air path…

On all warm air installations there will be a large “return air grille” (sometimes called a register), which users are often puzzled about. It feels as though it is blowing cold air out when a hand is held close but in actual fact, it is sucking room air in and returning it to the boiler for re-heating. This can be demonstrated by holding a piece of paper close to the grill (a bank note can be convenient) and seeing it get sucked onto the grille if you want to check.

This return air grille will be located in a central area of the house of flat such as a hallway or landing, and there will be a large duct behind it leading directly to the warm air heater. 

The grille will be ‘non-closable’ (unlike the warm air outlet diffusers) and must never be blocked off or the heating will stop working. In addition, there needs to be a return air path from every room containing a heat outlet grille back to the communal space containing the return air register, as warm air blown into each room needs to be collected by the return air grille and returned to the boiler for re-heating. 

The open area of the return air grille and associated air duct is important, and will be defined in the boiler installation manual. The grille is easily identified as it will be far larger than any of the warm air outlet diffusers or registers, as well as being non-closable or adjustable.

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