Shared Knowledge

"Zone Forced Air - Lennox Harmony III Zone Control Board"

17 Jan 2022

Summary: The Lennox Harmony III has a few marginally beneficial features over the more popular Honeywell Zone Control Board but is less well known by heating, ventilation, and air conditioning (HVAC) service technicians and is harder to configure without multiple technician visits.


Background: Bought a house with zoned forced air heating and cooling. Previous home for 25 years, had zoned baseboard hot water and 3 separate air conditioning (AC) systems for forced air air conditioning.  All AC units were single stage.  "New" home has 4 zones. Zone 1, 2 & 3: main floor, room over garage and limited second floor. Zone one has a Lennox natural gas furnace and blower in the attic and a 2-stage 3.5ton Lennox AC compressor. Zone 3: downstairs. the lower level or finished walkout basement uses a Lennox heat pump.

Zone 1, 2 and 3: As stated above, zones 1, 2 and 3 have a Lennox gas furnace, air handler and a Lennox AC compressor. I also consists of 3 thermostats or one for each zone, the Harmony III control board and Honeywell zone control valves in flex ducts off the air handler. All thermostats, 3, go to the Harmony control board which then command the furnace, AC unit and all Honeywell zone control valves. Note here, that thermostats do not directly control either the furnace or AC compressor. They all go to the Harmony III control board which then is connected to the AC unit and the gas furnace in the attic-based blower unit.