Another reason to call in the pros rather than head off to the DIY store is that
in order for a whole house fan to be as efficient as possible it has to be the right size for your home, which can be hard for an amateur to determine. An HVAC professional will be able to advise you and as the installation is fairly quick and easy it should only cost a few dollars more, which you should be able to recoup in energy savings many times over anyway.