No air ducts? How to add air conditioning to your old house

What's the best way to add air conditioning to a house with a hot-water heating system and no air ducts?

Houses with forced-air heating systems are natural candidates for air-conditioning because ductwork is already in place. Add a condensing unit outside and an evaporator inside the air handler and you're in business. Cool air is distributed around the house in the same ducts used for heat.

Homeowners with hyronic heating systems aren't so lucky. If you want central AC, you have to install a complete system, not only the condenser and evaporator but also a means of distributing cool air to where it's needed.

The rub is that conventional ducts take up a lot of room, and squeezing them into an old house can mean sacrificing a lot of period charm.

There are two other options--high-velocity systems that use small, flexible ducts to distribute cold air, and ductless mini-split systems that, as the name suggests, don't use any ducts at all.

High-velocity ducts go into little spaces

High-velocity AC makes cold air in the same way as a conventional system. What's different is the distribution. The flexible ducts are as small as 2 inches in diameter, making installation much less disruptive.

Chilled air is forced into a main supply trunk under high pressure. The smaller distribution ducts supply individual rooms at rates of up to 1,200 cubic feet per minute.

Manufacturers claim these systems do a much better job of mixing air than conventional systems working at lower pressures, which results in even temperatures and no stratification. Baffles inside the ducts reduce noise and air outlets may be as small as 5 inches in diameter, much smaller than conventional air registers.

You need to find an installer familiar with these systems, and costs are likely to be somewhat higher. But you won't have to tear out walls and ceilings or live with ugly duct chases to stay cool.

Two companies that make these sysems are SpacePak (www.spacepak.com) and Unico System Inc. (www.unicosystems.com).

Mini-splits skip ducts completely

Another option is the ductless mini-split, pioneered by Mitsubishi in Japan. An outdoor condenser supplies coolant to one or more air handlers in individual rooms. Unlike conventional AC, there is no central distribution system.

The small lines that carry the refrigerant need only a small opening in the wall. The air handlers are certainly larger and more obtrusive than a standard air register, but not as bulky as a window air conditioner.

A single condenser can supply enough coolant for a half-dozen air handlers inside. That makes these systems extremely flexible, and because there are no air ducts to route around the house, installation is fairly simple.

Mitsubishi, which produced its first ductless AC system in 1968, sells it under the Mr. Slim tradename. You can read more about it at www.mitsubishicomfort.com.

Our forbears suffered through the heat and humidity of summer because they had no alternatives. Now we can enjoy the charms of the same old houses, only a lot more comfortably.

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