Diagram #9A: Forced Air Furnace having a replacement air supply duct together with an exhaust fan controlled by a designated ventilation switch and/or an interval timer.

 

ADDED: 1. Replacement Air Damper, power close recommended, (HAC-0x10-OPC) to control fresh air inlet.  2. Ventilation Switch supplies Controlled and Regular 120Vac power (3-Wires) to the furnace area. 3. Relay Adaptor with Interval Timer (TMADP-1102-TPX) functions as a control centre.

 

OPERATION: 1.Furnace fires with thermostat signal. 2.Ventilation Switch turns on Ventilation Fan, opens Replacement Air Damper and turns on Furnace Fan simultaneously without interfering with the AC. 3. Interval Timer can be set for minimum or multiple consecutive settings of 15 minutes to simultaneously turn on Ventilation Fan open Replacement Air Damper and turn on the Furnace Fan. 4. Optional switch (i.e. toggle switch, timer, de-humidistat) allows full control of Replacement Air Damper to open as required provided it is a PC type.