Duct size for addition

[Jeff H]

Hi all, I'm new around here and have a question.
I'm currently battling with the shallow-end-of-the-gene-pool employees of the building dept about heating and cooling of my proposed addition.

Here is the issue. The addition is 225sf approx 20x11 single story and the building dept says that I have to show the heating and cooling requirements. Now I don't care about being super accurate, but I do have to meet code

The plan reviewers comments were:min natural ventilation = 4% of floor area; and mech.ventilation capable of . 35 air exchanbges per hour shall be provided in all adjoining rooms.

Now my TLAR logic says that 2 4x10 registers supplied by 6" round should be plenty. But I'm not sure

My question is how do I calculate this and how do I show it on the plans

I should have been a mech engineer instead of structural[:I]

[Hube]

Jeff; There are many variables that can enter in to a calculation that will be mathematically true, but a simple calculation, disregarding the present system layout, duct size, static pressure, equivalent length calculation, Delta T, Temperature differentials,etc etc, would be; A 6" round will handle approx 100 cfm, which is sufficient to SUPPLY an area of 160- 180 sq ft of floor space (assuming normal ceiling heigth, and adequate insulation)....Return air must be sized for 100 % of the supply. Note ; your .35 a/c (air change) has nothing to do with this calculation. Hube