HVAC System Replacement

Intro to How a Residential HVAC Zoning System Works

What is a zoned system? 

A standard residential HVAC system has a single thermostat and a single area or “zone”. In other words, if all the heated or conditioned air is evenly distributed (as it should be), the entire house will be within a degree or two of the set temperature. A zoned system provides one or more additional zones with their own thermostats, providing greater temperature control throughout the house. A zoned system isn’t the same as having a unique system for each area of the house, but zone systems, in most cases are the most cost effective way to provide a level of temperature control throughout a residence.

How Does a zoned system work?

Despite how cool (or warm!) the idea of zoning is, the concept is actually relatively simple. Zone dampers are installed in the supply ducts that service the various zones. Thermostats placed in those zones work in conjunction with the main system to control heated or cool air delivery into those zones.

This chart demonstrates an example of how the zone system would deliver the temperatures requested at the thermostat. For this example let’s assume the outside temperature is 85 and we just adjusted the thermostats to its current position.

Unit Mode: Cooling

Thermostat SettingCurrent 

Room Temperature

Damper Position
Zone 1 (Living Room)7268Closed
Zone 2 (Bedroom 1)6875Open
Zone 3 (Bedroom 2)7572Closed


As you can see from the table above two of the zones, the living room and bedroom two, are already cooler than the desired temperature. Because all zones are below the outside temperature the unit will operate in cooling mode. One of the zones is warmer than what the thermostat is calling for and will need to be cooled. In this scenario the cool air supplied by the system is delivered primarily to bedroom one. The dampers to the other two rooms are closed, which will allow those temperatures to rise naturally based on the outside temperature of 85. Once the thermostat’s requests in each room are satisfied, the zone dampers will open and close automatically to maintain the desired temperatures. 

What are the benefits of zoning?

One of the primary benefits of zoning is managing warm and cold spots in a house, especially where the sun or other variable conditions make it unrealistic to use manual dampers to deliver even temperatures throughout the house. Another benefit, of course is the control to set different temperatures throughout a house to accommodate individual preferences. 

What applications would not be a good fit for a zoned system?

A zoned system would not be a good fit where large temperature differences are required. An example might be a wine cellar. Because you would want a constant temperature well below the average temperature in the home a zone system would struggle to provide the consistency that you would want. Zoned systems work best when temperature variation is minimal. Additionally, a zoned system is limited to operating either above or below the outside temperature, not both. You would need multiple systems to satisfy zones calling for both temperatures above and below the outside temperature.