Going Where No HVAC Has Gone Before

Need to cool off an old house? Consider a mini-duct system.

March 31, 2004

 

This cutaway shows the module, trunk lines and individual tubes to each room.

Photos courtesy of Unico System

As a professional remodeling contractor, how would you solve the following situation? Your clients own a historic, 19th-century home with a coffered-ceiling dining room, four-piece crown moldings throughout the rest of the house, and lath and plaster walls as smooth as butter. They are sick and tired of living with noisy, hissing

radiators and want them replaced with something “new, efficient and quiet.” On top of that, they want whole-house air conditioning. No cheap window units here.

They know your reputation for being innovative and solution-oriented, and they want you to give them the heating and cooling system they deserve.

You can:

  • run like hell and pretend you never met them;
  • politely educate them on the wonderful benefits of dropped ceilings, boxed-out duct runs and new, improved interior trim (“that original stained crown was looking a little dated anyway”);
  • or install one of several innovative systems on the market designed just for this type of problem.

“The high-velocity, flexible mini-duct system is the answer to preserving the architectural integrity of a home,” says Earl Strauther, brand manager with Unico Inc., which makes just such a system.

Mini-duct systems are not new, just unknown to many professionals and consumers. The Unico System (www.unicosystem.com) and SpacePak (http://www.spacepak.com) have been around for decades, while newer products such as AirLink (www.heatlink.com) expand on the tried-and-true technology.

Trunk and insulated tubing in a whole-house renovation

What is a mini-duct system? More important, what can it do for remodelers? Essentially, a typical mini-duct system uses a small heating/cooling coil module that installs easily in an attic, a basement or a crawl space. (Some manufacturers also have units that convert easily to a vertical discharge if a closet is your only possible location.) The typical module distributes cooled or heated high-velocity air through flexible, pre-insulated tubing ranging from 2 1/2 to 4 inches in diameter, depending on the manufacturer.

Complete cooling and heating ducts can be run through the house without major disturbance to existing finished surfaces. No need to drop the ceiling to accommodate large, rigid ducts. No more tearing into walls and trim to run metal piping from room to room. Installers simply thread the tubing between wall studs and floor joists to provide each room with its own air supply. This is truly an advantage in historical renovations.

Although the tubing is flexible, the insulating jacket is generally stiff enough to prevent kinking. And the air in the tubing loses little heating/cooling thanks to high-efficiency insulating wrapping, such as AirLink’s new 2-inch, pre-insulated jacket, which has an R-value of 8-plus.

The tubes can be terminated at the ceiling or walls. Most manufacturers use a round “outlet” approximately the size of a CD-ROM with a 2-inch hole in the middle. Unico recently came out with an 8x1/2-inch slotted outlet that can be used in a cabinet toe kick or in a short baseboard application. The outlets can be painted or stained and in some cases come in several pre-painted colors.

As the high-velocity airstream enters the room, it gently mixes with the existing air to create a uniform, balanced temperature, virtually eliminating hot and cold spots.

“The system works on the principle of aspiration instead of diffusion,” Strauther explains. “By moving the airstream faster through the room, the air feels cooler to the body, the system runs and cycles less, and you get a better cooling temperature at a higher setting.”

What to watch out for

Your installer needs to be experienced and familiar with the system. Just because someone is good with conventional HVAC systems doesn’t mean he or she will get this right. Ask your local heating/cooling equipment supplier to recommend a qualified trade contractor for this type of work.

A standard outlet about the size of a compact disc

Your local supply house or even the manufacturer generally will custom-design the system. Just send the project plans and heat calculations, and the supply house or manufacturer will work directly with you and your installer.

Most mini-duct manufacturers can modify their systems to work with any existing power source, including electric, hot water, radiant floor, baseboard, radiators and steam. Whatever the existing system, have it checked out thoroughly. Just because the old boiler runs doesn’t mean it’s safe. Seals can dry up, and controls can go bad, creating gas leaks and carbon monoxide.

If the mini-duct system will be used for cooling, run a drainage pipe from the heating/cooling module to a suitable location such as a basement floor drain or the outdoors. Again, this requires thoughtful design of every aspect of the system.

Terry Richards of Johnstone Supply in Colorado Springs, Colo., warns of additional potential problems. “The correct length of the tubes is critical to keep proper static pressure and balance of the system and to reduce noise while maintaining efficiency,” he says. “Also, make sure you have the right number of outlets for each room as well as the proper main trunk size.”

Unico and SpacePak both use a trunk design that carries the conditioned air from the module. If the trunk is too small, the rooms in the house will not receive enough air, and the system will be unbalanced. If the trunk is too large, obnoxious whistling might come from the outlets.

AirLink uses a distribution box instead of the conventional trunk. “Our distribution box pressurizes the air,” explains Richard Carroll, AirLink product manager, “sending equal pressure to all of the outlets, which in turn self-balances the system, saving time and money.”

 


 

Another Cooling Solution

 

Much different from a window unit, this product can be installed almost anywhere.

Photo courtesy of SlimDuct

Have you heard of ductless split-room air-conditioning systems? They have existed for more than 30 years, selling mainly in Japan at first and then gaining popularity in East Asia and Southern Europe in the late 1980s. They have been in the United States only since 1998.

These are not window units but actual evaporator units that install within the house on interior or exterior walls. The units connect to each other and to a condenser that uses an oversize heat exchanger and a quiet, slow-moving fan. For retrofits, the condenser can be installed outside or in an interior, isolated compartment and wrapped with a sound blanket for added sound containment. The line set that carries the coolant from the outside condenser to the wall-mounted unit can be covered with trunking from SlimDuct (www.slimduct.com).

With this type of cooling unit, you don’t have to cut a large hole in a wall or give up a window to a box hanging out of the house. Instead, you drill a simple hole through the exterior wall and connect the line set directly into the back of the unit. As the air passes through the heat exchanger, more heat and moisture are removed from the ambient air.

“When you don’t have space or access for a mini-duct system or you just want to spot-cool one area, the ductless split-room unit is a simple and inexpensive way to go,” says Terry Richards of Johnstone Supply.

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