Mini-ducts provide alternative

Q We are considering installing a heat pump or central air conditioner. We currently have radiant heating. I have heard mini-duct systems are very comfortable and quiet. How do they work?

A: Mini-duct systems are also called pressurized or high-velocity systems. They are ideal for installation in an existing home without central ducts or in a new house instead of installing a standard central duct system.

Although they are often used for air conditioning, they are also equally effective for wintertime heating. The heating source can be an efficient standard heat pump, geothermal heat pump, electric furnace, etc. Because mini-duct systems are often installed in homes with radiant heating, hot-water coils can be added to also provide supplemental forced air heat.

Mini-duct systems use small ducts (2 or 3 inches in diameter) instead of large metal ducts. The ducts are highly insulated and covered with foil. The complete insulated duct is small enough to run through an existing wall or ceiling made with stud framing.

Instead of the main blower in a utility room or basement, it is usually located in the attic. A large main insulated trunk duct is run through the attic. The many small insulated 2-inch ducts run from this long trunk duct to the individual rooms. You may choose to heat or cool just several rooms, or perhaps an addition, with the mini-duct system.

In order to get enough air flow through the small ducts, the blower operates at a higher pressure than a blower using standard large ducts. This is a distinct advantage when cooling in humid climates. With the high pressure, the heating/cooling coils can be dense and three times deeper than standard coils. This dramatically improves the dehumidification.

Instead of floor registers, the heated or cooled air blows out from 2-inch diameter outlets in or near the room ceiling. There are several outlets per room. The air flows out at a high velocity, but it is very quiet. Its velocity creates an aspiration effect that mixes the heated or cooled air with the room air for more even (floor-to-ceiling) temperatures.

The 2-inch ducts have a 5-inch diameter flange. They can be painted to match the wall color or are available in brass and natural wood. For outlets in bathrooms or kitchens, long, narrow, rectangular ones fit above or below cabinets.

With the high pressure (and suction) of the mini-duct system blower, often only one return air duct is required. This can be in a hallway where sound will not be annoying when your family is sleeping. Special sound-muffling sections can also be added near the end of the ducts.

Send inquiries to James Dulley, The Post and Courier, 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit www.dulley.com.