Ducted HVAC

A ducted system heats or cools a whole house from one machine. Air is drawn out of the rooms through a return, passed over a filter and then over a heat exchanger or a cooling coil, and blown back through ducts to a vent in each room. One machine, one filter and one return serve everything, which makes it a single thing to maintain and filters the whole house at once - and also means a fault anywhere becomes a fault everywhere.

The ducts are where this system is won or lost. Twenty to thirty percent of the heated or cooled air is typically lost on the way, leaking into a roof space or crawl space instead of reaching a room, so sealing and insulating them matters as much as the machine's own rating and comes first. Sizing follows a heat-loss calculation on the actual building, not a figure per unit of floor area: a unit that is too large reaches temperature fast and stops before it has run long enough to pull moisture from the air, leaving rooms cool and clammy while occupants lower the thermostat at three to five percent more cooling cost per degree. Every room with a vent also needs a path for the air to get back out, or a shut door pushes that room up in pressure while the rest of the house is pulled down and makes up the difference through whatever gaps it has.

A leaking duct is a damp problem as well as an energy one: a return run through a humid roof space pulls that air in and spreads it through the house. Upkeep is a filter checked monthly through the busy season, the coil cleaned yearly, attention to the drain that carries off water condensed out of the air, and sealing of any duct running outside the heated part of the building - work a ductless system never creates. Running the fan all the time rather than only while the machine heats or cools puts back moisture just removed, so the automatic setting usually keeps a house drier. Installation and service are licensed trade work, and like any recirculating system it brings in no outside air, so a house tightened around it needs ventilation provided separately.