Since 1978, Acutherm has been dedicated to creating
more comfortable, energy-efficient building environments.  

Therma-Fuser Systems have proven to be the
simple, reliable, and economical solution for
individual temperature control.

What is a Therma-Fuser™ Diffuser?

Each Therma-Fuser diffuser is an independent zone of VAV control with built-in room thermostats and modulating dampers for varying the air volume. The dampers are continuously adjusting to vary the volume of air flow (warm or cold) into the room, in response to room temperature. Unlike fixed opening diffusers, which dump cold air on occupants at low volumes, the variable air opening within all Therma-Fuser diffuser models creates high air velocity even at lower supply volumes. This maintains the Coanda effect where high velocity air hugs an adjacent surface, holding cold air up to the ceiling and prevents dumping.

View VAV Diffuser Products

View Associated Products

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    Acutherm Therma-Fuser Diffuser System

Therma-Fuser diffusion dampers, which are mechanically actuated by the thermostat/actuator, open and close to regulate air flow into the room in response to room temperature.  These thermostats are a more robust version of those used by the aerospace industry for jet engines.  When supply air is warm, the Therma-Fuser diffuser operates in the heating mode and the dampers open on a drop in room temperature. When the supply air is cold, the diffuser operates in the cooling mode and the dampers open on a rise in room temperature. Separate room temperature setpoints for heating and cooling are individually adjustable.


Each thermostat/actuator is a small brass cylinder containing petroleum-based wax. The wax expands when heated, driving a piston out. A spring retracts the piston when the wax cools and retracts. The movement of the piston either opens or closes the air dampers in a proportional manner.

Average room temperature is monitored by inducing a sample of air from the center of the room across the thermostat/actuator. Because this air sample is drawn directly from the air circulation pattern in the room, just before it mixes with air flowing into the room, it better represents average room temperature than air at a wall thermostat.

With Therma-Fuser diffusers, room temperature throughout the room can be held within 1 1/2ºF / 0.9˚C of the temperature selected. Temperature of the room is selected between 70º and 78º F / 21˚ and 25.5˚ C by adjusting the thermostat/actuator.

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