I have a 1,560 square foot cathedral ceiling double wide mobile home.

using this vent calculator set at 300,

I need 5.2 sq ft x 144 = 748 sq inches

or 374 sq inches on each side?

It is my understanding that the intake and exhaust need to be balanced,

It is 374 total, so that is 187 intake and 187 exhaust, on each side.

CURRENT VENTING

There are currently 4 soffit intake vents on each side under the eaves.

Each one measure 9.5 x 24 = 228 x 4 = 912 intake

The exhaust are square vents, 4 on each side, 8 total.

I cannot measure them, see picture above, but I found replacement vents that look like mine.

Galvanized painted black - Overall dimensions: 15 1/2" width x 15 1/2" length x 4" height. 9" width x 9" length outlet with net 50 square inches of ventilation.

They are 50 sq inch x 4 = 200 exhaust.

that almost matches the 187.

But the intake soffits are much larger than the 187.

Could it be that the soffits allow much less air in?

228 x 4 = 912 intake

374 Needed (187 exhaust + 187 intake)

200 exhaust + 912 intake = 1,112

So this does not see like a balanced system?

PROPOSED NEW ROOF

Install 62 Ft of Ridge venting

60 foot long house x 12 = 1,080 sq inch ( assuming a 1.5 inch gap)

Would this 540 each side?

EDIT - Just looked up current building code for San Jose CA, where I live

and it is 150.

PROPOSED NEW VENTING ??? WHY NEEDED

& 6ea O Hagin vents, 3 each side, for In-Takes for proper attic ventilation

O’Hagin Tapered Low-Profile 72.0 sq. in NFVA

72 x 3 = 216, close to the 187.

But why would you need these when you already have more than enough soffit venting?