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Central heat pump or multi-zone: it all starts with your ducts
A house heated by a forced-air furnace does not have the same options as a house heated by baseboards. A central system carries air to every room through the ducts, from a single indoor unit. A multi-zone system puts a unit in each room you choose, all connected to one outdoor unit. To make the comparison concrete, this guide takes two 36,000 BTU systems from the same family, each with its own AHRI certificate.
CENTAURI XLTH R32 · 36,000 BTU
AMUH36KUAS / AOUH36KUAH1 · AHRI 217895717
See the product page
AQUILA XLTH R32 · 36,000 BTU
AOUH36KWAH4 + wall units · AHRI 215735282
See the product pageWhat the electricity costs, in dollars, winter and summer
AirGreen estimate for the same 36,000 BTU/h (3-ton) house in Montréal, on Hydro-Québec Rate D, taxes included. Both examples are calculated exactly the same way, with the same method as on all our comparison pages; only their certified efficiencies change. The certificates give 36,000 BTU/h of cooling at 35 °C for the central system and 35,200 for the multi-zone (four wall units): the calculation uses their common nominal size, 36,000 BTU/h. Electric baseboards serve as the reference.
How this amount is calculated
- Heat to supply over the winter. A house whose heat loss reaches 36,000 BTU/h ( kW) at −23.1 °C, the Montréal design temperature: kW × 24 h × 4,167 degree-days ÷ (18 − (−23.1)) = kWh of heat for round-the-clock heating, all winter. Heating degree-days (18 °C base) and design temperature: Natural Resources Canada, HOT2000 climate data, Montréal Intl station. With fewer hours a day (“Heating” slider), the heat is reduced in the same proportion, for the heat pump as for the baseboards: this simplification ignores the recovery after a temperature setback.
- Heating electricity. Heat pump: heat × 3.412 ÷ HSPF2 Region V, the AHRI certificate value published by NEEP. Region V is the coldest in the standard, and its calculation includes the electric backup heat expected when the heat pump is no longer enough. Electric baseboards: 1 kWh of electricity for 1 kWh of heat.
- Cooling electricity. 36,000 BTU/h ÷ SEER2 × hours a day × 60 days ÷ 1,000: the method of Hydro-Québec’s air-conditioning calculator, with the seasonal SEER2 efficiency from the AHRI certificate. The number of hours is a scenario, adjustable above from 1 to 24 h. At 24 h, the calculation assumes rated capacity all day long: that is a ceiling, since a variable-speed unit slows down once the room reaches its set temperature.
- Price. Hydro-Québec Rate D in effect April 1, 2026: 7.065¢ per kWh up to 40 kWh a day, 11.142¢ beyond; the average price, 9.104¢, is the one Hydro-Québec’s calculators use. GST and QST included. Grid access charges, the same with or without a heat pump, are not counted.
AirGreen method v1.1, November 9, 2026. An estimate is a way to compare units under the same conditions. The actual bill depends on the house, its insulation, the settings and how it is used; this amount is not a promise.
Ducts that light up, or units that appear room by room
Switch between the two systems. With a central system, a unit in the basement pushes air through the duct network to every connected room. With a multi-zone, tap the rooms you want to equip: each one gets an indoor unit, connected by its own piping to the same outdoor unit.
Illustrated cross-section: the house, the ducts and the piping are a diagram. The units are the real photos of the two FUJITSU AIRSTAGE examples, at the same scale as each other: AMUH36KUAS air handler (21 × 48 in), AOUH36KUAH1 and AOUH36KWAH4 outdoor units (37 × 39 5/16 in each), ASUH12KPAS wall unit (32 13/16 × 10 5/8 in). Four-indoor-unit limit and piping lengths: Aquila brochure FG2057B, rev. 8/2025.
Four questions about your house
Answer with your own house in mind: each answer shows what changes for the central system and for the multi-zone. Nothing is ranked, and the estimator’s visit is what confirms what your ducts allow.
What living with each one is like
A central system and a multi-zone can heat the same house; they just don’t move through it the same way. The table describes the two examples, based on their documents.
| For the homeowner | Central (example) | Multi-zone (example) |
|---|---|---|
| In the rooms | Grilles in the floor, wall or ceiling | An indoor unit in each room served, up to 4 |
| In the basement | The AMUH36KUAS air handler on the duct network | Nothing, unless you choose a ducted unit |
| Temperature setting | One thermostat for all connected rooms | One control per indoor unit |
| The filter | Just one, at the air handler’s return | One in each indoor unit |
| Rooms without a unit | Every room connected to the ducts gets the air | Existing heating, or air moving through the doorways |
| The electrical panelPer the manufacturer | Outdoor unit: breaker max. 35 A (MCA 33.9 A) | Outdoor unit: 35 A breaker (MCA 34.8 A), a single circuit for all 4 rooms |
NRCan advises changing or cleaning the air filter every 3 months, and notes that an all-electric air-source heat pump usually requires a 200 A electrical service, and that a panel upgrade may be needed (“Heating and Cooling With a Heat Pump”, modified December 24, 2025).
Below −15 °C: the two examples, at the same temperatures
NEEP measures both examples at the same temperatures, down to −26.1 °C (−15 °F). Between −15 °C and −26.1 °C nothing is published: the table shows the two values that frame each temperature.
A duct network, or piping for each room
The units of both examples, at the same scale
Heights and widths published by FUJITSU AIRSTAGE. Grid: 12 in. Both outdoor units have the same published dimensions.
| Installation | Central (example) | Multi-zone (example) |
|---|---|---|
| Maximum piping length | 246 ft | 230 ft total82 ft maximum per indoor unit |
| Precharged length | 98 ft | 164 ft |
| Maximum height difference | 98 ft | 49 ftto the farthest indoor unit; 33 ft between two indoor units |
| Outdoor unit W × H × D, weight | 37 × 39 5/16 × 12 5/8 in, 159 lb | 37 × 39 5/16 × 12 5/8 in, 154 lb |
| Indoor unit, weight | Air handler 21 × 48 × 21 in, 137 lb | Wall unit ASUH12KPAS 32 13/16 × 10 5/8 × 8 3/4 in, 21 lb |
| Outdoor unit electrical protectionPer the manufacturer | Breaker max. 35 A (MCA 33.9 A) | 35 A breaker (MCA 34.8 A) |
| Stated heating / cooling range | −26 to 24 °C / −21 to 50 °C | −26 to 24 °C / −10 to 50 °C |
| Number of indoor units | 1 | 2 to 4connectable capacity: 25,000 to 46,000 BTU/h |
Sources: FUJITSU AIRSTAGE, submittal sheet 36KUAH1M (version 20260123A) for the central system; Aquila multi-zone brochure FG2057B (rev. 8/2025) for the AOUH36KWAH4 and the ASUH12KPAS wall unit.
Before you choose
Are my current ducts suitable for a heat pump?
Often, but not always: their size, their condition and the airflow the heat pump needs are checked on site, during the estimator’s visit.
Can I keep my baseboards with a multi-zone?
Yes. Rooms without an indoor unit stay heated by their baseboards, and the baseboards in equipped rooms can stay in place as backup.
And a ducted unit in a house without ducts?
It is a middle path: a hidden unit and short ducts for a few neighbouring rooms. The manufacturer of the example lists ducted units among its R-32 multi-zone indoor units, depending on the outdoor unit.
Why compare two FUJITSU AIRSTAGE systems?
To isolate the question of the type of installation: same manufacturer, same XLTH family, same 36,000 BTU nominal capacity, and each with its own AHRI certificate. Other brands have other values; the page ranks neither type.
Does the multi-zone heat as well in extreme cold?
Per NEEP, at −15 °C the central example reaches 41,000 BTU/h and the multi-zone 36,400 BTU/h; at −26.1 °C, 32,000 and 22,140 BTU/h. These values belong to these two combinations; another model will have its own.
Are they eligible for rebates?
NEEP lists both combinations as ENERGY STAR and cold climate. Eligibility depends on the official list in effect on the purchase date and on the combination installed; this page promises no amount.
The AHRI and NEEP values of both examples
| Certified value | CENTAURI XLTH (central) | AQUILA XLTH (multi-zone) |
|---|---|---|
| Cooling | ||
| Rated capacity at 35 °C | 36,000 BTU/h | 35,200 BTU/h |
| SEER2 | 18.3 | 22.0 |
| EER2 | 11.4 | 13.0 |
| Heating, same conditions | ||
| HSPF2 Region IV / V | 10.2 / 8.2 | 10.0 / 8.0 |
| 8.3 °C: min. / rated / max.BTU/h | 9,200 / 38,000 / 43,000 | 12,000 / 36,400 / 42,000 |
| 8.3 °C: COP at min., rated, max. | 3.80 / 3.89 / 3.28 | 5.41 / 4.30 / 4.04 |
| −8.3 °C: min. / rated / max.BTU/h | 8,300 / 25,200 / 41,600 | 8,300 / 24,400 / 38,000 |
| −8.3 °C: COP at min., rated, max. | 3.86 / 2.90 / 2.25 | 4.19 / 3.33 / 2.28 |
| −15 °C: min. / rated / max.BTU/h | 7,900 / 41,000 / 41,000 | 6,800 / 36,400 / 36,400 |
| −15 °C: COP at min., rated, max. | 3.86 / 1.98 / 1.98 | 3.62 / 1.90 / 1.90 |
| −26.1 °C: capacity min. / max.BTU/h | 6,000 / 32,000 | 4,300 / 22,140 |
| −26.1 °C: COP at min. and max. | 2.93 / 1.82 | 2.52 / 1.66 |
| Listings and refrigerant | ||
| ENERGY STAR / cold climate (NEEP) | Yes / Yes | Yes / Yes |
| AHRI certificate · NEEP record | 217895717 · 306746 | 215735282 · 385699 |
| RefrigerantGWP per the IPCC (AR4); ASHRAE 34 class | R-32 · GWP 675 · A2L | R-32 · GWP 675 · A2L |
higher marks the higher value of a given measure, under the same conditions. It is not a recommendation. Capacities and COPs at each test point are not highlighted: which one is higher changes from point to point. The multi-zone is certified with wall units (“Multizone All Non-Ducted” per NEEP).
Central or multi-zone: both examples are on the AirGreen website.
With or without ducts, we start from your house: bring your current heating type, the condition of your ducts if you have any, the rooms to heat and cool, and your electrical service.
Where each figure comes from
Data checked on November 9, 2026. This guide explains two types of systems; it designates no type and no brand. The models cited serve as examples, sold by AirGreen. Performance: AHRI certificates and the NEEP database. Dimensions, piping and ranges: per the manufacturer. When a source contradicts the AHRI certificate, the certificate prevails.
Trademarks. FUJITSU AIRSTAGE, CENTAURI and AQUILA are trademarks of their respective owners. Logos are used only to identify the products shown. AirGreen is a dealer for the brand; this page is not produced, sponsored or endorsed by the manufacturer. The FUJITSU AIRSTAGE system is also sold under the name GENERAL AIRSTAGE.
Photos: AirGreen and the manufacturer, for identification.
Does a figure look wrong to you? Write to us: every reported figure is checked again.