Ducted vs ductless heat pumps

The difference is where the indoor coil sits and how the air gets to the rooms. NRCan describes the two:^{[Source 1]}

• Ducted: "The indoor coil of the heat pump is located in a duct. Air is heated or cooled by passing over the coil, before being distributed via the ductwork to different locations in the home."
• Ductless: "The indoor coil of the heat pump is located in an indoor unit. These indoor units are generally located on the floor or wall of an occupied space, and heat or cool the air in that space directly."

Ductless systems come as a mini-split (one indoor unit on one outdoor unit) or a multi-split (several indoor units on one outdoor unit).^{[Source 1]} There are also ducted mini-split air handlers, small ducted units that serve a few rooms through short duct runs; they sit between the two categories.

Side-by-side

	Ducted	Ductless
Indoor equipment	Air handler or furnace with a coil, usually in a basement, attic, closet or garage	Wall, floor or ceiling units in each zone
Air delivery	Supply and return ducts	Directly into the room
Duct losses	Present, especially with ducts outside the conditioned space	None for the ductless units themselves
Zones	Usually one per system unless zoning dampers are added	Each indoor unit is its own zone
Typical fit	Homes that already have good ducts	Homes without ducts, additions, rooms that run hot or cold
Filter care	Central filter, checked monthly	Filters in each indoor unit, cleaned often

Duct losses

DOE says "duct losses can account for more than 30% of energy consumption for space conditioning, especially if ducts are in an unconditioned space like an attic."^{[Source 2]} That is the main efficiency case for ductless in homes where ducts would run through unconditioned space, and the main reason to seal and insulate ducts when keeping a ducted system.

Efficiency ratings

DOE gives these ranges: "Ducted heat pumps typically achieve efficiency ratings between 15.2 to 25 SEER2, while ductless minisplits can achieve ratings between 15.2 and 35 SEER2."^{[Source 2]} Programs set separate thresholds for ducted and non-ducted products. NEEP's Version 4.0 specification, for example, requires HSPF2 of 8.5 for non-ducted systems and 7.7 for ducted.^{[Source 5]} Compare products within the same category.

Ductless installation facts

From DOE's mini-split page:^{[Source 2]}

• "Many models support up to four indoor air-handling units connected to one outdoor unit."
• "The outdoor unit can be located up to 50 feet away from the indoor evaporator." Actual limits are model-specific: Mitsubishi's MUZ-FS15 and FS18, for example, allow up to 100 feet of piping.^{[Source 6]} See Line set.
• The wall penetration for the line set and wiring is "only a three-inch hole."
• Indoor wall units are "about seven inches deep."

Who tends to use which

• Existing ducts in good condition: a ducted heat pump can replace a furnace and air conditioner on the same ducts. NRCan notes that "heat pumps generally operate at higher airflows than furnace systems," so "some modifications may be needed to your ductwork to avoid added noise and fan energy use."^{[Source 1]} See Static pressure.
• No ducts: DOE notes that in climate zones 5 to 7, about 32% of homes lack ductwork.^{[Source 3]} For these homes, ductless avoids adding new ducts.
• Mixed: some homes use a ducted system for the main floors and a ductless unit for an addition, a finished basement or a room over a garage.

Living with each

• Ducted systems heat and cool every room the ducts reach from one thermostat. Comfort depends on how well the ducts are designed and balanced (Manual D).
• Ductless systems control each room separately, but rooms without an indoor unit rely on air moving through open doors. Filters in each indoor unit need frequent cleaning; one Mitsubishi operation manual recommends cleaning air filters "every 2 weeks."^{[Source 4]} See Heat pump filters and maintenance.

Both types use the same outdoor technology and both go through Heat pump defrost cycles in winter.