The warm air outlet grilles:

Most users are very aware of the warm air outlet grilles in each room. These are the reason most people like their warm air systems as they do the same job as a large ugly radiator but without taking up the wall space.

These outlet grilles are generally called “diffusers” as they have vanes to split and direct the outlet air around the room, and often have adjustable vanes to turn it on or off too. They are sometimes called “registers” but there is little consistency in the terminology. In my view a register is a non-adjustable grille while a diffuser is adjustable, but not everyone agrees with me.

The diffusers themselves on older systems can get very tatty and worn with age, and new diffusers can still be obtained from Johnson and Starley Ltd, or from a number of third-party suppliers. A brief google for “warm air outlet diffusers” turns up a number of suppliers, the first (today) being https://warmairgrilles.co.uk/. I’ve no connection with this firm but their website appears professional and to-the-point. 

The diffusers have adjustable balancing vanes built into them so the heating system can be ‘balanced’, meaning adjusted so rooms which heat up too much can be turned down and rooms heating more slowly, made to warm more quickly by adjusting the vanes. 

Diffusers also have a lever on one side allowing the grill to be closed, in order to turn off the heating in rooms not being used. 

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