HSV does not have gas lines running through it, which means that you WILL have electric heat and air.
Most houses in HSV use regular heat pumps where heat is exchanged with the outside air. Integrated backup resistance heat kicks in when the thermostat is set up higher than the heat pump can draw from the outside air.
Lakefront houses in HSV have the option of having geothermal heat pumps at a reasonable price because the pipes for heat exchange can be run under the water.
For non-lakefront houses, geothermal heat pumps are probably not worth the cost of drilling the holes for it through the rock laying just below the surface of the ground in HSV.
Update: During the big ice storm of 2000, the compressor fan outside the house became completely encased in ice in December. We did not know at the time because it is tucked away on the far side of the house out of sight. Finally, when the golf courses opened again in that latter part of January, someone driving by on the cart path on that side of the house saw our compressor and called us. It took hours to dig all the ice off. The fan blade was completely encased in about 10" of ice.
When we got our electric bill for December, it was over $500!! The one for January wasn't much better. For all the time the outside unit was iced over, the heat pump could not work and we were heating the house with the resistance strips.
We had a partial enclosure put over the unit so that in the future, ice from the room could not fall down into the unit.
We opted for having our heat and a/c units in the attic instead of under the house. We felt having air outlets in the floor put too many restrictions on the placement of furniture.
If you do decide to have your air units under the house, specify that the outlets must be sealed when the duct work is put in. Otherwise, during construction all sorts of dirt, debris, bugs, etc., will fall through the floor vents into the ducts, and your a/c will be blowing out sawdust and dirt for a long time to come. (It's almost impossible to clean out 100%.)
Of course, dirt, debris and bugs will continue to get into the floor vents after you have moved in, and then when the air turns on, the stuff will be blown all over your house, but there is not much you can do about that if you go with floor outlets.
Our a/c subs were going to have a single air return for the whole house, which is not an entirely unreasonable plan for a one-story house. However, when we simply asked how bedrooms with doors closed at night would get air circulation, Craft answered by getting the subs to put additional air returns in each bedroom. At Judy's house, the builder (Jim Buss) put a return in the master bedroom in addition to the main return.
I have since read that another reason to put a return in a bedroom is that if you do not have one and have the door closed at night and the air comes on, the door will rattle.
Update: In 2009 and ten years of use, after a couple of years of problems with the HVAC, it was replaced with a new unit of a larger capacity which was also more energy efficient. Kay's sister had to replace her HVAC unit after about 5 years.