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Cooling · Small-Duct High-VelocityHigh-Velocity AC Installation
High-velocity AC installation adds central air conditioning to a house with no ductwork by feeding each room through 2-inch flexible tubes threaded inside walls, floors and closets, so the plaster stays intact. It suits radiator-heated and century homes where you want a whole floor cooled with nothing on the walls. It costs more than ductless mini-splits and needs an attic, closet or basement space for the air handler.
A small-duct high-velocity system has four parts: a conventional outdoor condenser or heat pump, a compact air handler, an insulated main trunk about 20 cm across, and a set of 2-inch insulated supply tubes branching from it. Each tube ends at a small round outlet in a ceiling, floor or wall. Air leaves the outlet in a narrow, fast stream and stirs the room air as it goes, which evens the temperature from floor to ceiling. One central return grille, usually in a hallway ceiling, brings the air back.
It was designed for the houses found across lower Hamilton, Old Oakville, downtown Burlington and west Toronto: pre-war brick with hot-water radiators, lath-and-plaster walls and no cavity big enough for sheet-metal duct. The tubes bend around joists and drop through closets and wall cavities, so the second floor is typically fed from the attic and the main floor from the basement ceiling. The radiators stay as the heating system. Finished surfaces are opened only for the outlets and the return.
Compared with ductless mini-splits, high velocity wins on appearance and coverage: every room on a floor gets an outlet, nothing hangs on a wall, and one thermostat runs it. Ductless wins on cost, efficiency and room-by-room control, and on heating, since a cold-climate head also heats while most high-velocity systems here are cooling-only additions to a boiler. A single-zone ductless system is $4,000–$7,000 installed; high velocity is a larger project quoted after a walkthrough. Air conditioning without ductwork compares every route, including ductless mini-splits.
Noise is a design outcome, not a property of the equipment. Each ton of cooling needs a minimum number of outlets, and each tube needs a minimum length with a sound-attenuating section before the outlet; too few outlets or tubes cut short, and the system hisses. In an attic the air handler sits on vibration isolation with a secondary drain pan and float switch beneath it, and the trunk and tubes are buried in insulation. An attic with no hatch, no headroom or vermiculite insulation, which can contain asbestos and has to be dealt with by an abatement contractor first, changes the plan.
High velocity is worth pricing when
- The house is heated by radiators or in-floor hot water and has no ducts at all
- Original plaster, trim or heritage details rule out bulkheads and wall-mounted heads
- You want every room on a floor cooled from one thermostat
- There is an accessible attic or an open basement ceiling to carry the main trunk
- You plan to stay long enough to justify a larger project than ductless
How it works
A room-by-room cooling load sets the outlet count. Then we look for the paths: stacked closets, attic access, the basement ceiling, and a spot for the outdoor unit that respects the side-yard clearances on a narrow lot.
The air handler and trunk go in first, then each tube is pulled to its room and the outlet is drilled in a ceiling corner or along a wall, out of the seating area so the airstream is not aimed at anyone. The condenser, line set and electrical circuit follow.
Airflow and static pressure are measured, each outlet is checked, and the system is run in a quiet house so any outlet that hisses is corrected before the job is closed. Arrange a walkthrough to find out whether your house has the routes.
Common questions
Is high-velocity air conditioning noisy?
A correctly designed system makes a soft rush of air at each outlet, comparable to a conventional register. The loud ones were built short on outlets or with tubes cut too short, which pushes air speed and noise up. Ask any installer how many outlets the design has per ton of cooling and how long the shortest tube is.
Can a high-velocity system heat as well?
It can. The air handler can take a hot-water coil fed from the boiler, or the outdoor unit can be a heat pump. In a radiator house the radiators usually remain the main heat because they are quiet and even, with the high-velocity side handling cooling and perhaps spring and fall heating. Both options can be priced in the same quote.
Will the installation damage my plaster?
The planned openings in finished surfaces are the outlet holes, a few centimetres across, and the return grille. Tubes travel through the attic, the basement and closet corners. Now and then a route needs a small access hole that is patched afterward, and those are counted on the walkthrough so you know the number before agreeing to anything.
High velocity or ductless for a century home?
Choose ductless if you mainly need two or three rooms cooled, want heating from the same equipment or want the lower price. Choose high velocity if you want the whole floor cooled evenly and will not accept wall-mounted heads. A third route, a ducted mini-split in the attic, covers a few bedrooms through hidden ceiling grilles.
Does high velocity dehumidify well?
Yes. Small-duct systems move less air across a colder coil than conventional central air, so they remove more moisture for each hour they run. In a brick house near Lake Ontario, where July discomfort is as much humidity as heat, that drier air lets many people set the thermostat a degree or two higher.