High Velocity AC in Brooklyn & NYC
Central Air for Brownstones, Without Gutting the Walls
Brooklyn brownstones weren’t built for conventional ductwork. The floor plates are too narrow, the plaster walls too thick, and the floor joists run the wrong direction. High-velocity small-duct systems thread 2-inch flexible ducts through existing cavities, delivering true central air without tearing out rooms.
The Brownstone Problem
Why Conventional Ductwork Fails in Prewar Buildings
A typical Brooklyn brownstone row house is 18 to 20 feet wide. The floor-to-ceiling height is often 10 feet or more on the parlor floor. Conventional rectangular ductwork, 8 inches by 10 inches or larger, needs to fit inside finished ceilings or walls, and there’s simply no room. The original builders packed every inch of framing with plaster, brick, and structural timber.
Prewar apartment buildings face the same constraint from a different angle: thick plaster walls with horsehair backing, radiator chases that bisect the usable wall cavities, and floors that can’t be opened without significant restoration cost. A gut renovation to add conventional ductwork easily runs $150,000 to $250,000 for a full-floor apartment.
High-velocity systems use 2-inch insulated flexible mini-ducts. They thread through stud bays, around radiator chases, and through existing closet walls. The air handlers can be mounted in closets, attic spaces, or mechanical rooms. The result is genuine central air conditioning without opening walls or ceilings.
Brooklyn Brownstones
Typical brownstone row houses from Carroll Gardens to Park Slope to Bed-Stuy. The 2-inch supply tubing runs through the existing stud bays between floors. Supply outlets are small round vents, nearly invisible in high ceilings. One air handler per floor, typically located in the front bedroom closet or rear utility space.
Prewar Apartment Buildings
For prewar co-ops and rental buildings, high-velocity systems can serve individual apartments where thru-wall units aren’t suitable, large floor-through units, penthouse apartments, or buildings with structural constraints that prevent sleeve installation. Units mount in kitchen ceilings or closet spaces.
Local Law 97 Compliance
Buildings over 25,000 square feet face NYC Local Law 97 greenhouse gas emission caps beginning in 2024. High-efficiency high-velocity systems help buildings meet 2024 to 2029 targets and avoid fines of $268 per metric ton of excess CO2 equivalent. Aerosys systems with high SEER ratings are a strong LL97 compliance tool.
How much capacity does your space need?
Free, instant, and built on the same physics a Manual J uses. It measures the surfaces actually gaining heat rather than multiplying square footage, which is what makes it work in an apartment.
Estimate your load
This works the way a Manual J does: it measures the actual surfaces losing and gaining heat rather than multiplying square footage by a rule of thumb. That matters most in apartments, where shared walls carry almost no load.
IECC climate zone
Enter a ZIP to set design temperatures
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Zone 1 is hottest, 8 coldest. New York City is Zone 4A, which the NYC Energy Code requires for all city projects. Heating varies enormously by climate; cooling much less, because outdoor cooling design temperatures sit within a narrow band nationwide.
This is an estimate to start the conversation. It follows the structure of an ACCA Manual J, using real U-values, design temperatures and infiltration rates, but it assumes a roughly square footprint and average window sizes and does not do per-window orientation or a measured blower-door test. A stamped Manual J is a different thing. Airflow and outlet counts follow published Unico and SpacePak design practice. We supply equipment and handle delivery; your contractor installs it.
Authorized Dealer
Unico and SpacePak Systems
Unico and SpacePak build the high-velocity small-duct systems we supply, the industry standard for retrofit central air in prewar residential buildings. Air handlers run from 1.5 to 5 tons, matched with 2-inch insulated mini-ducts and round supply outlets that blend into plaster ceilings. Six to seven outlets per ton is the usual layout, at roughly 250 CFM per ton.
We size Aerosys systems based on your building’s square footage, ceiling height, window exposure, and existing mechanical infrastructure. The right sizing matters more in high-velocity than in conventional systems, an oversized unit causes humidity problems; an undersized unit runs constantly without reaching setpoint. We get it right before ordering. Read our Aerosys TTWC Condenser Guide for full specs and model comparisons.
Sizing a High-Velocity System for a Brownstone?
We need your building’s square footage, floor count, ceiling height, and window orientation to design the right system. Submit the details below and we’ll respond with a system recommendation and preliminary sizing within one business day.