User Guide
Zoning System Design Manual
70-2321—06 10
RETROFIT APPLICATIONS
For retrofit applications, first you have to ensure that the duct system is adequate for room/zone loads, and that the
existing HVAC system is properly sized to deliver heat/cool. After that, planning the zone system is very similar to
new construction.
Flex Duct
For retrofit applications in flex duct, use round ARD dampers. The round ARD is a galvanized steel single blade
damper with a low-leakage gasket, and comes in a range of sizes from 520 in. Up to 4 ARD dampers can be wired
in parallel to a zone as long as the transformer has sufficient VA. Use an SDCR isolation relay for zones with more
than 4 ARD dampers.
Thermostats
The existing thermostat can often be used for one zone, but as it might be difficult to run wires to the other zones,
RedLink wireless thermostats can be used.
Rigid Duct, Rectangular Sheet Metal Duct, Knockdown (KD) Duct
Using a retrofit round damper (RRD) significantly reduces labor—
it installs in a fraction of the time—and overall system installa-
tion cost. A retrofit damper slides into rigid round pipe for quick
installation.
The RRD dampers are available in 5, 6, 7, and 8-in. diameters.
Multiple RRD dampers may be wired in parallel.
M28119
Fig. 9. Installing retrofit round damper.