This section describes the options available in the Diffuser Connections group in the Design Master HVAC Options dialog box.

Size diffuser runout to match diffuser neck size: Whether the runout to a diffuser is sized to match the diffuser neck size or based upon the airflow in the duct. The runout is defined as all of the ducts from the diffuser to the first branch.
• | Yes: The runouts ignore the sizing criteria and are sized to match the diffuser neck size. |
• | No: The runouts are sized using the sizing criteria like the other ducts in the system. |
In the example below, the ducts on the left side have been sized with this option set to No. The ducts on the right side have been sized with this option set to Yes. The ducts in red have been sized to match the neck size of the connected diffusers.

Default flex length (in): The maximum length of flex duct inserted during diffuser connection commands. If the diffuser connection length exceeds this distance, hard duct is inserted to make up the rest of the distance.
Once the diffuser connection is inserted, this value is no longer used. Changing this value will not change the length of flex duct of diffuser connections that were previously inserted. Moving the diffuser or modifying the duct layout can result in situations where the flex length exceeds this value.
Damper far from diffuser: Where balancing dampers are inserted in the duct system.
• | Yes: Balancing dampers are inserted as far from the diffuser as possible. They will be inserted at the start of the duct that begins the branch leading to the diffuser. |
• | No: Balancing dampers are inserted as close to the diffuser as possible. If there is flex duct leading to the diffuser, the balancing damper will be inserted just before the flex duct. Otherwise, they will be inserted just before the diffuser. |
Ceiling Connection: Fitting graphics: The graphics used when drawing ceiling diffuser connections in 2D.
• | Flex / Elbow: For connected flex ducts, flex duct is drawn connecting to the diffuser. For connected hard ducts, an elbow is drawn connecting to the diffuser. |
• | Elbow: An elbow is drawn connecting to the diffuser. |
• | Tee: An vertical tee is drawn connecting to the diffuser. |
Connection Graphics: Flex: The graphics used when drawing flexible connections to ductwork in 2D.
• | Single: The flex ductwork is drawn single-line, regardless of the size of the flex duct. The ducts in the diffuser connection are inserted with their Graphics field set to Single. |
• | Double: The flex ductwork is drawn double-line, regardless of the size of the flex duct. The ducts in the diffuser connection are inserted with their Graphics field set to Double. |
• | Single & double: The flex ductwork is drawn single-line and double-line, depending upon the width of the flex duct and the Maximum single line width option in the Ductwork options section. The ducts in the diffuser connection are inserted with their Graphics field set to Automatic. |
Connection Graphics: Hard: The graphics used when drawing hard connections to ductwork in 2D.
• | Single: The ductwork is drawn single-line, regardless of the size of the duct. The ducts in the diffuser connection are inserted with their Graphics field set to Single. |
• | Double: The ductwork is drawn double-line, regardless of the size of the duct. The ducts in the diffuser connection are inserted with their Graphics field set to Double. |
• | Single & double: The ductwork is drawn single-line and double-line, depending upon the width of the duct and the Maximum single line width option in the Ductwork options section. The ducts in the diffuser connection are inserted with their Graphics field set to Automatic. |
Supply, Return, Exhaust, Outside: Sets the default options for each section in the Change Connection Type command.
Ceiling Connection: Duct type: The material type used for the duct when connecting to a floor or ceiling diffuser.
• | Flexible: Flexible ducts are used to connect to the diffuser. The length of flexible duct is limited by the Default flex length option. If the connection is longer than that length, hard duct is used for part of the connection. |
• | Hard: Hard ducts are used to connect to the diffuser. |
Ceiling Connection: Lock duct shape: Whether ducts that are inserted as part of the diffuser connection have their shapes locked.
• | No: The duct shapes are not locked. The duct shape will be set when the duct is sized. |
• | Round: The duct shapes are locked as round. |
• | Rectangular: The duct shapes are locked as rectangular. |
• | Flat oval: The duct shapes are locked as flat oval. |
Sidewall Connection: Duct type: The material type used for the duct when connecting to a sidewall diffuser.
• | Flexible: Flexible ducts are used to connect to the diffuser. The length of flexible duct is limited by the Default flex length option. If the connection is longer than that length, hard duct is used for part of the connection. |
• | Hard: Hard ducts are used to connect to the diffuser. |
Insert balancing dampers: Whether a balancing damper is inserted in the duct connected to the diffuser.
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