How to Gracefully Add Air Conditioning to a Vintage Brooklyn Townhouse

Figuring out where to squeeze central air conditioning in a century-old brownstone or townhouse can be perplexing even for the most seasoned renovators, especially when the original walls are remaining intact.

Single unit central air conditioning systems have basically become obsolete in Brooklyn townhouse renovations, replaced by so-called mini-split systems that separate the condensing unit and the interior air handler. Split systems are more energy efficient, quieter, and the air handler can be hidden in closets or ceilings with minimal ductwork.

“Central air is hard because brownstones don’t have an expandable wall,” said Vincent Croce of Cool Tech HVAC Corp. “The brownstones that we do, we’re putting in Mitsubishi — either ducted or wall-mounted — units. They’re expensive but they do the job.”

Many homeowners use split systems for both heating and cooling, Croce said. The new Mitsubishi hyper-heating system works well even in sub-zero temperatures, he said.

In addition to a split system, architect Brent Buck of Buck Projects recommends hydronic trench heaters or in-floor radiant heating systems near large walls of glass.

While installing visible air handlers on outside walls is typically the cheapest option, a good architect can cleverly design a mini-split system to be as unobtrusive as possible. Usually in such an approach the ductwork rises through the core of the house cached in areas such as closets and bathrooms. Air handlers are hidden, existing architectural details are not disturbed, and ugly and awkward soffits are minimized or nonexistent.

In gut renovations, Buck adjusts layouts to accommodate ductwork. Interior units are typically located above closets, in cellars, or above bathroom ceilings.

“For non-gut renovations we utilize the cock loft or other existing conditions for ductwork,” Buck said. “At times, we drop ceilings in an entire hallway or bathroom to accommodate the interior air handlers.”

Exterior compressors are placed mainly on steel dunnage on the roof, Buck said.

“We try and avoid installing them in rear yards or on the backs of buildings,” he said.

Architect Alexandra Barker of Barker Freeman Design Office typically recommends one or two air handlers per floor, concealed within 12-inch ceiling drops above bathrooms, or in hallways or closets, she said. Wall registers and grilles come in a variety of price points and styles, including linear slot diffusers – the most expensive and least obtrusive option.

“A variation on this system that is a little less expensive is an exposed mini split, where the air handler is mounted on a wall and is visible in the room,” Barker said. “These two approaches can be combined. For example, you could use exposed air handlers in an open plan basement, which is a bit of a lower cost, and concealed ones on all the other floors.”

Costs to add air conditioning to a home vary considerably. Some of the many variables affecting cost are whether the system is added as part of a larger renovation, if an architect is involved, whether structural supports need to be added to the roof, if a crane is required to hoist the system onto the roof, and construction and finishing needed to hide the system.

Expect a mini-split system for a three-story Brooklyn row house to start at about $30,000 to $40,000. Barker puts it at $13,000 to $15,000 per floor. Buck said $50,000 to $100,000 is typical for a four-story brownstone, depending on the number of zones and units and the types of controls.

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