New roof, ridge vent and whole house fan ?? Help!
Powered attic exhaust fans sound like it would be an sure way to keep your attic from becoming an oven in the summer. But unless your attic is completely draft free and sealed from the living space below running an attic fan will increase your electric bill and increase the cooling load on your HVAC (cooling).
When the attic fan runs it is pulling air from the house while make-up air is being drawn in from the outside through any gaps (door thresholds, window frames, etc.) your conditioned cooled air is being pulled into the attic and exhausted out the vent.
A ridge vent when properly sized, allows an easy route for the hot attic air to escape;the vent is at the highest point in the attic.
The make-up air being drawn in is through the soffit vents (openings).
If the roofers have calculated how many roof vents you need accurately than there is no need for the energy consuming powered fan. A quick way of finding the number of attic vents is for every 300 square feet of attic floor space there should be 1 square foot of vent opening*.
*Audel HVAC Fundamentals, Volume 1.