Thank you Ook, Eric, trader4 & Jim R for the replies. Looks like most
of the replies aren't favorable towards the powered vent, so I'll
probably stay away from that.

One thing I forgot to mention is that there's no air-conditioning in the
house, so the attic staying hot is a major discomfort to the wife &
infant in the living area, which is why I am trying to address the
problem. I did install a window unit, but in some areas of the house
where there are larger, connected, open spaces, I am not sure what to
do. I'm considering a split-type a/c in the future.

Anyway, back to the attic ventilation:

Would any of you recommend installing a whole-house fan? Keep in mind
that I'm in New Hampshire and July & August are probably the months that
get really hot.

And if yes to the whole house fan, is a powered vent required on the
roof? I was under the impression that eaves+ridge vent would be enough.

Again, the fan itself is not too expensive, but the installation & labor
makes me think twice. As an example, the fans can be $200-$400, but
the installation estimates are between $1000 (without powered vent for
the roof) & $1800 (with powered vent).

--
Himanshu