The following was saved from the old guide4home website just in case anyone was looking for it. With the help of the archive.org website.
High Velocity Models and the Duct System Explained
Central air conditioners using ductwork normally utilize the ducts in existing air handling systems that have already been built into the house, such as a forced air furnace.
They tend to be split systems with the evaporator coil and air handler inside the building and the compressor and condensing unit outside. These are connected by refrigerant tubing and the ductwork circulates the cool air around the building or house. The indoor unit is usually installed in the attic or another small and out-of-the-way space. Many modern central air conditioners are small enough to fit into any number of small spaces, such as closets.
Central air conditioners using a duct system can easily be installed into houses that already use a ducted furnace for heating. This is because the ductwork is already in place and the air conditioner simply uses the existing ducts to circulate the cool air.
Houses that are heated with baseboard heating, radiant heat or steam radiators may not have any existing ductwork. In cases like this ducts would have to be installed along with the central air conditioner making it a very difficult, expensive and in some cases an impossible, job. A more practical solution would be to opt for a ductless or mini-split air conditioner.
The ductless air conditioner system uses tiny refrigerant lines that go through a small three inch hole in the wall which connect the outside condenser unit to the inside air handling unit. These refrigerant lines circulate refrigerant into the house from the outside unit to the indoor air handling units where it used to cool the air. The cooled air is then released into the building while the refrigerant carries the excess heat back to the outside unit for disposal. These systems do require good drainage otherwise condensate may stain concrete and other building materials.
Another option would also be the flexible tubing ductwork known as high-velocity or ‘mini-duct’ air conditioners. These tubes are the pliant equivalent of the more conventional metal ductwork normally used but which only take up about one tenth of the space.
They perform the same functions as the metal ductwork the difference being that they can weave behind walls, ceilings and floors without causing any damage to building materials. It is a far cheaper and less intrusive installation and means central air conditioners can be installed in just about any building, old or new.