Duct design is the art of matching duct size to how much heating and cooling each room needs AND the size of the HVAC. It also provides accountability for the installing contractor.

In new construction these are a very good idea, that is the best time to do this right. In retrofits not every job needs one, it's mainly for when major changes are being made or the duct system is being replaced. That said, a duct design should be offered for every job.

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