The air pressure differential switches work from 20 to 200 Pa.

They can work in conjunction with the Merlin CT1200s, Merlin 1500GD or Merlin 2000GD panel.

Fitting the air pressure differential switch across the intake and extract side of the fan will the Merlin panel to monitor when the fan is operational. Once the fan seen to be operational the gas solenoid valve can be opened. 

*Please note prices quoted exclude carriage and VAT