Have a Residential system. One unit, dual zone forced air HVAC. 2 thermostats. Is this type of unit designed to run the heat downstairs, while running the AC upstairs at the same time? The house/unit is 2 yrs old. We have had multiple issues with the system from inside and outside fans running nonstop. AC not wanting to come on upstairs, Fan downstairs will run continuosly but doesn’t keep up to the temp of 71 that it is set for, Vice versa with the AC upstairs.

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  • There is no such thing as a dual zone system with a single air handler that can do heat in one zone and AC in another. Have you had someone out to look at your system? What do they say? – longneck Nov 9 at 0:06
  • Maybe I’m describing system incorrectly. 1 unit outside, 1 air handler in attic, 1 Thermostat 1st floor, 1 thermostat 2nd floor. We have had 3 different AC companies here. The one company is coming out for the 3rd time. They were originally called out for a loud thumping vibration noise when the system came on. Then all the other issues started happening. They aren’t sure what the issue is. He has ordered a fan motor. If I’m understanding u correctly, it cant work that way. – Darla Nov 9 at 1:14

No, that won't work

Residential single-air-handler zoning systems like yours are effectively small variable air volume (VAV) systems without any reheat functionality -- the air handler delivers a single temperature of air, while zone splitting is accomplished by using a damper to modulate airflow to the zone. Larger commercial systems have a heater in each zone that can turn on to allow for larger temperature splits between zones, but this is a bit of a waste of energy and also requires more control hardware, so it's not done in residential zoning systems.

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