do a search on home ventilation and you will find alot of companies that sell variour ventilator and will have this info.. i went to either Home depot or lowes and took some advertising papers from the racks.. in the area of the power vents.. think they had some on the stationary vents for the soffit.. i recently changed out my soffit vents. about 8 in. by
16 in. alum. vents that were nailed to the bottom of the soffit... none in the front of house.... the 16 were placed around the sides and back of the 30 by 60 brick house on concrete slab.. built in 1972 by a home builder... about 15 yrs. ago i build a garage/workshop in the back yard about 15 by 20 ft. and there is soffit on both sides(two) non in the front or back.. i got four soffit vents on each side of the building....