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Airflow Limits - 700 Series

Each zone, after performing a duct measurement, will give you the option to set airflow limits. These airflow limits are used to increase comfort primarily by limiting the system airflow and capacity to what the zone or zones can handle. With a traditional zoning system, it was all or none and a bypass was often required to dump excess air.

To access airflow limits from the zone 1 Smart Thermostat, click the menu icon in the bottom left of the screen. Click on settings and select zoning. Airflow limits are at the bottom of the zoning setting screen. If you have more than two zones, zone 3- 6 are on the next page and can be accessed by clicking on “More” in the bottom right.

Your choices for airflow are:

• Unlimited,
• High
• Med-High
• Medium
• Med-Low
• Low

A setting of unlimited is not going to work in the vast majority of systems. Unlimited will allow the system to stage all the way up and send ALL airflow to that zone. There is a time and a place for it, but it will be rare.

The CFM values listed in the settings are based on the results of the equipment detected and the duct measurement.

Any airflow limit setting that is below the system’s minimum cooling airflow capacity will be indicated by a flashing asterisk (*). This flashing asterisk is telling you that in a case where only that zone is calling it will either require assistance from another zone in the form of demand or in some cases, overconditioning, or from the assistance of a bypass if one is installed. If neither option is available, the system will not come on until another zone has enough demand to provide the difference.

Dampers are positioned according to the following rules.

• Any zone demand greater than 0.5°F will drive damper to full open position.
• Largest demand of all zones will always be full open as long as there is demand.
• Other zones with demand are positioned based on distance from full open to closed which is -.25°F.
• Zones with a demand beyond -.25°F are closed and considered satisfied. 

A zone may allow overconditioning if needed and allowed. See Overconditioning for more information.

Some of the (-)P20**B models have higher minimum airflows than the A models.  For instance, the (-)P2036B and (-)P2048B have a much higher heating minimum airflow than the A models. The (-)P2060B has a higher cooling minimum airflow.  If these airflows are causing grief, you can reach out to your distributor and see if the Zone 1 thermostat can be updated to revision 26 or later.  In this revision, the system recognizes the system is zoned, and that it is a B model and it will lower the airflow in the instances listed above.

Airflow Limits - 800 Series