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Manual J Calculations

Posted on August 31st, 2022. Last updated on November 9th, 2023.

Q: Can Design Master HVAC perform Manual J calculations?

A: While Design Master does not perform Manual J calculations specifically, its calculation basis is as precise or more precise than those provided in Manual J.

Manual J is a standard intended for use by residential HVAC contractors. It is essentially composed of two parts: a simplified set of HVAC load calculations, and ventilation rates for various room types.

Load Calculation Basis

Our load calculations use the CLTD method as described in the 1997 ASHRAE Handbook, Fundamentals. ASHRAE changed its calculation method to RTS in the 2001 Fundamentals, but the CLTD method is still considered valid.

The CLTD method can be expected to provide values that are at least as precise as Manual J.

Ventilation Rates

You can modify the room types in your project to match the ventilation rates provided in Manual J using the Room Project Schedule command.

For each room type used in the project, set the appropriate values in the Ventilation (OSA) section of the dialog box.

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