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HVAC glossary
Diffuser / air terminal
A diffuser is an air terminal at the end of a duct through which air is supplied to or extracted from a room.
A diffuser (also called an air terminal or ventilation valve) is the visible part of the ventilation system in the ceiling or wall. Although it looks like a small detail, it determines whether there will be draughts and noise in the room.
The key points:
- Type – supply and extract diffusers differ; a supply diffuser must distribute air so that it does not blow directly at people.
- Size and flow – an undersized diffuser with a high flow whistles; selection is based on the design airflow in m³/h.
- Location – supply air is usually introduced into living rooms and bedrooms, extract air is taken from the kitchen, bathroom and WC.
- Adjustment – many diffusers have an adjustable opening or a damper in front of them; they are used to balance the system.
Important: turning a diffuser on your own unbalances the whole system – other rooms may get less air. If you notice draughts or noise, contact us instead. Our team balances an installed Mitsubishi Electric Lossnay system and records the settings during commissioning.