All that advice and no mention of existing attic ventilation??? What gos in must go out. Translated means that unless you have far more square inches of attic vents than normal,a ceiling installed fan will perform poorly. You might even create health hazzards if the attic has insufficent exhust vents. The fan creates a high postive pressure in the attic and negative pressure inside living area. Air leaking back into living area will be heavly contaminated with dust,insulation particals and possibly worse. The conventional method of overcoming this is large movable shutters in one or more gables. Your origional plan of mounting fan in gable completly eleminates issues of pushing dirty attic air into living area.

Hi Jacko, Sounds like you have your work cut out for you. To help you out on your questions: 1) Having your cold air supply vents by the windows will help and it is recommended, but vents can be put in other locations. However you have 10' ceilings so I would recommend vents by the windows . It is an old house, and you may have historic rules on modifying the looks of your home, so will you be allowed to fur your ceiling down a liitle which could help for new ducts, electrical, cable, and comunication wiring.( if you have to have it. 2)Centered based vents need to have a register that is designed for that special throw of air. 3) Your basement will need return and supply air in it. As far as how many, you will need a load calc done to tell that, it will tell what each room wil need for your new ac system.I have attached a link for you to look at below. 4) Whole house fans are logical for air circulation during mild temperature days. But I don't recommend them for indoor air quality. The attic fan can help remove heat from your attic, but it can shorten the life of yor roof shingles. 5) Values of homes are different due to the area you live in. DC is high, so talk with your realtors around that area. A general rule of thumb is half te investment of your system.lol Here is a link that might be useful: ACCA AND ASHRAE CERTIFIED HVAC LOAD CALCULATIONS

An attic fan, as the name implies, is designed to cool the attic. Their primary advantage is keeping the attic cooler thereby extending the life of the shingles and they do keep the house itself a little cooler. They do need to be sized and positioned correctly for maximum effectiveness and depending on the size and configuration of your attic, you may need more than one fan. There are some that say they are a waste of money because they create only localized cooling (air takes the path of least resistance) and/or if the attic is vented properly, no additional cooling is necessary. A whole house fan works best in climates or seasons where there are warm days and cool nights. They are placed in a central location (on the second floor if applicable). Basically you open the windows and flip on the fan, which pulls cool air in and pushes hot air into the attic. Again they need to be sized correctly and your attic needs to be vented properly to give the air some place to go. They can eliminate the need for air conditioning, which is why your utility is giving a rebate. Since you are moving a lot of air, they can be noisy.

There are other styles of whole house fans. Walls, Windows, homes without attics.