wrote:

Tom The Great wrote:

wrote:

... I am told it is a bad thing to install a gable vent when you have a
ridge vent.

No.

I talked to a contractor, and found I did anything other than improve
the natural circ, I would have to block the ridge vents.

No.

A lot of people claim this to be true, but I wonder if anyone has any
real data...

Page 23.9 of the 1993 ASHRAE HOF says

Greatest flow per unit area of openings is obtained when inlet and
outlet areas are equal; Equations (17) and (18)

Q = 14.8Asqrt(HdT) cfm, with A in ft^2 (18)

are based on this equality. Increasing the outlet area over inlet area,
or vice versa, increases airflow but not in proportion to the added area.
When openings are unequal, use the smaller area in the equations and
add the increase, as determined from Figure 5.

Figure 5 says 15% more air flows when one opening is 50% larger than the
other, 27% more flows with a 2:1 ratio, 34% more flows with a 3:1 ratio,
and 37% more flows with a 6:1 ratio.

So it's like this: more vent area makes more airflow, with dimininishing
returns for unequal areas...

Nick