User Guide

Zoning System Design Manual

5 70-2321—06

DUCTS AND DAMPERS

Size the Ductwork

In New Construction: ductwork is sized as usual for the size of the home; trunks are sized for the

amount of air going to the zone.

Ductwork should be designed normally, typically .10 or .08 in. w.c./100 ft.

Proper duct design of a zoned system will:

• Maintain proper airflow through the HVAC unit when only one zone is open.

• And maintain proper airflow to all zones when all are open.

In Retrofit Applications: zones are somewhat limited by how the ducts were originally constructed, but

any home can be zoned provided there is access to the ductwork. See page 10 for zoning information

specific to retrofit applications.

Select Dampers

Use ZD dampers for rectangular ducts. Use ARD or RRD

dampers for round ducts in residential systems up to

2000 CFM.

For systems over 2000 CFM or commercial systems,

see page 11.

Install the Dampers

A supply air damper should not be placed closer than 6

ft. to a diffuser. The damper should also be at least 3 ft.

away from the plenum. (Less than 6 ft. between damper

and diffuser could create objectionable air noise in the

conditioned space and 3 ft. of duct off the plenum will

reduce turbulence.) These minimums are recommen-

dations for optimal performance; however, each instal-

lation presents its own challenges, so each installation

will vary. For instance, in some installations the damper

may need to be mounted directly on the plenum.

Allow for Access

Dampers should be installed in a location that can be

accessed for service. If a damper needs to be "buried,"

place a decorative register over it to provide access.

Balancing Dampers

Balancing dampers should be included in the duct work, because a zoned home needs to be balanced

just as a non-zoned home does.