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Click here to see a descriptive illustration of a mini-duct, pressurized central air-conditioning system.
Dear Jim: My wife and kids have finally convinced me to invest in central air-conditioning. My contractor recommends a mini-duct, pressurized system instead of a standard ducted one. Are pressurized systems comfortable? - Gus H.
A: Pressurized central air-conditioning systems produce better comfort than most other cooling systems and they are extremely quiet indoors. The dense cool air blows from outlets high in the rooms, so the cool air does not puddle near the floor as with many standard-ducted systems.
These systems use the same super-efficient outdoor cooling compressor units as ducted systems, but the air delivery method is improved. The air blows out into the room from two-inch-diameter mini-ducts mounted in the ceiling or high on the walls. There are several mini-ducts per room.
The main blower unit is usually installed in the attic. The cool air follows a insulated main duct with the mini-ducts attached to it. Since mini-ducts are small, these systems are easy to install in an old home without an existing heating duct system. Pressurized systems are becoming the cooling method of choice in homes with warm radiant floor heating.
To move the cool air through the small ducts, the blower must pressurize the air much more than with a standard-ducted system. With the high pressure, a more effective coil design is used. This cooling coil design, coupled with the denser compressed air, results in improved dehumidification.
The final section of the mini-ducts, immediately before the small room outlets, is made with sound-deadening materials. This makes the system operate very quietly as the pressurized cool, dry air flows into the rooms.
Another comfort and efficiency advantage is the relatively high air velocity of the outlet air as compared to a standard-duct system. The high speed creates an aspiration effect at the outlets. This causes an instant mixing of the room air with the cooled air to eliminate chilly drafts.
These systems are ideal with hot water radiant heating, but they can use heat pumps and forced-air heating options. Even if you use radiant floor heat, installing a heat pump outside instead of just an air conditioner, allows you to use the efficient heat pump during milder weather periods. Some models allow you to add different types of heating modules.
With its high-pressure design, only one main air return grill, often in a hallway, is needed. The two-inch cool air outlets have a five-inch-diameter flange. When painted the same color as the room, they are barely noticeable. Natural wood, brass and other decorative finishes are also available. Rectangular ones are designed to fit in kitchen or bathroom cabinets.
Instant Download Update Bulletin No. 713 - buyer's guide of mini-duct pressurized central air-conditioning system manufacturers, model names, ranges of cooling capacities, main duct and room outlet sizes, many system/component illustrations, installation details, efficiency/cost-to-use chart, and a list of manufacturers of the most efficient compatible outdoor compressor units.
Dear Jim: I had new shingles installed on my roof several years ago. I just went up into the attic and I noticed nails sticking through the roof and some of the decking had broken off. Is this normal? - Kate J.
A: It is common for the nails to extend all the way through the roof sheathing (decking). This does not create a leakage problem because each row of nail heads is covered by the layer of shingles above it.
The sheathing should not be breaking loose and falling on the attic floor. This deterioration of the plywood may be an indication that moisture is getting in. If this is the case, you roofing warranty may cover the repairs.