Q. The heat and humidity are killers this year. I need a central air conditioner that is quiet and controls the humidity level. How effective and efficient are miniduct and high-velocity systems?
A. Actually, high-velocity and miniduct are just different names for the same type of superefficient and comfortable central air-conditioning systems. These systems are very quiet, distribute the cool air evenly throughout the house and dehumidify very effectively.
Advantages: Although these systems are becoming popular in new homes for heating and cooling, they are most often installed in homes for central air conditioning. Because the flexible miniducts are easy to install with little remodeling, they are particularly popular in houses with hot water heat and no ductwork.
The design concept of using insulated miniducts (2 inches in inside diameter) makes more sense than running large, noisy sheet-metal ducts throughout a home. Most older sheet-metal ducts are leaky, and much of the cooled or heated air is lost before it gets to the rooms.
With a mini-duct system, air blows out tiny 2-inch openings in the ceiling or high on the walls. The outlets are barely noticeable when painted the same color as the room. For a decorative look, natural wood ones are available. With the outlets properly located, there are no drafts.
The key to the high efficiency and excellent dehumidification is the higher-pressure blower (often mounted in the attic) used with the miniducts. The higher pressure compresses the air and allows it to be in contact with the cooling coils longer. This drops its temperature to remove more humidity.
The high-pressure, dry, cool air (heated air in the winter) exits the tiny room outlets at a high velocity. This, coupled with the sudden pressure drop, creates an aspiration effect that mixes all the air in the room. With even temperatures and low humidity, you can set the air-conditioning thermostat higher for big savings.
Quiet: When you hear the words "high-velocity and pressure," you would think that these systems are noisy. Actually, you can barely hear them running, and there is no air-flow sound at the tiny outlets. Most systems have a short sound-attenuation duct section immediately before each air outlet.
In two-story houses, the miniducts are run down from the attic through corners of closets or inside walls to the first floor. In a single-story house, the entire system is located in the attic with outlets in the ceiling below.
Mini-duct systems use ordinary outdoor air-conditioning compressor units. A unit with a single-speed scroll compressor is ideal.
Q. I have older vinyl windows that have held up well. One of them is near the flue from my fireplace, and the frame is badly discolored. Is there any good way to paint the frame beige again?
A. Vinyl window frames are not meant to be painted, because the color goes completely through the material; however, there are paints that will adhere to the frames. Take one of the sashes to a paint store for advice.
The soot that has impregnated the vinyl may cause some painting problems. You might try lightly sanding the discolored frame surface first to get down to the original color. Just a clear satin finish over this may work.
XWrite for Update Bulletin No. 432, a buyer's guide of mini-duct, high-velocity air-conditioning systems listing sizes, features, installation details and a list of the most-efficient outdoor compressor units. Downloads are available at www.dulley.com, or send $3 and a business-size SASE to James Dulley, c/o The Vindicator, 6906 Royalgreen Drive, Cincinnati, Ohio 45244.