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One compressor for several rooms, or one per room?
Two bedrooms to heat and cool: a single multi-zone outdoor unit feeding two wall units, or two complete systems, each with its own outdoor unit. Both examples are FUJITSU AIRSTAGE XLTH units sold by AirGreen. Here is what changes on the outside of the house, in the electrical panel, in the piping and on the day an outdoor unit stops.
AQUILA XLTH · 2 zones · 18,000 BTU
AOUH18KWAH2 · AHRI 215447691 (wall units)
View the product page
2 × ORION XLTH · 9,000 BTU
ASUH09KZAS / AOUH09KZAH1 · AHRI 214888800
View the product pageWhat the electricity costs, in dollars, winter and summer
AirGreen estimate for the same 18,000 BTU/h zone in Montréal (two rooms of 9,000 BTU/h), at Hydro-Québec Rate D, taxes included. Both heat pumps are calculated exactly the same way, with the same method as on all our comparison pages; only their certified efficiencies change. Two identical 9,000 BTU wall units have the same HSPF2 region V as a single one: the calculation therefore uses the wall unit’s certificate for both rooms. Electric baseboards serve as the reference point.
How this amount is calculated
- Heat needed over the winter. A zone whose heat loss reaches 18,000 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 24-hour heating, all winter long. Heating degree-days (base 18 °C) and design temperature: Natural Resources Canada, HOT2000 climate data, Montréal Intl station. With fewer hours per day (“Heating” slider), the heat is reduced in the same proportion, for the heat pump and the baseboards alike: this is a simplification that does not account for recovery after a temperature setback.
- Electricity for heating. 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 expected when the heat pump is no longer enough. Electric baseboards: 1 kWh of electricity for 1 kWh of heat.
- Electricity for cooling. 18,000 BTU/h ÷ SEER2 × hours per day × 60 days ÷ 1,000: the method of Hydro-Québec’s air-conditioning calculator, with the SEER2 seasonal 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: this is a maximum, since a variable-speed unit slows down once the room is at the right temperature.
- Price. Hydro-Québec Rate D in effect April 1, 2026: 7.065 ¢ per kWh up to 40 kWh per day, 11.142 ¢ above that; the average price, 9.104 ¢, is the one Hydro-Québec’s calculators use. GST and QST included. The grid access charge, the same with or without a heat pump, is not counted.
AirGreen method v1.1, November 9, 2026. An estimate is used to compare units under the same conditions. Your actual bill depends on the house, insulation, settings and use; this amount is not a promise.
Add rooms, count the outdoor units
Choose the number of rooms to equip. On the left, the AQUILA range sold by AirGreen: a multi-zone outdoor unit whose size follows the number of rooms. On the right, one ORION XLTH per room. The outdoor units are real photos, scaled to their published dimensions.
Multi-zone
Separate wall units
What it changes, topic by topic, with no verdict
Filter by topic. Each row says what each layout involves in your home; nothing is ticked: the answer depends on your house.
A multi-zone system is certified by combination
A separate wall unit has one certificate: its indoor unit and its outdoor unit. The example multi-zone outdoor unit has three, depending on the type of indoor units connected. FUJITSU AIRSTAGE publishes them in submittal 18KWAH2.
SEER2, EER2 and HSPF2 region V published for each combination (submittal 18KWAH2, version 20250618A). The cost and the data sheet on this page follow the wall-unit certificate, 215447691. For comparison, each 9,000 BTU ORION XLTH: SEER2 33.1, EER2 18.8, HSPF2 V 10.7 (AHRI 214888800).
Below −15 °C: both rooms together, figure by figure
Both examples are XLTH, stated down to −26 °C, and NEEP measures them at the same temperatures. For the separate wall units, the capacity for both rooms is twice the certificate of one 9,000 BTU wall unit: two identical certificates, added together and labelled as such. Nothing is calculated between two temperatures.
What FUJITSU AIRSTAGE states about the two layouts
Based on the multi-zone unit’s submittal and the ORION XLTH wall unit’s data sheet.
Multi-zone: compact cassettes, medium static pressure ducted units, multi-position air handlers, slim ducted units and wall units, according to the submittal.
Separate: one ORION XLTH wall unit per room.
Multi-zone: exactly 2 indoor units; up to 130% connected capacity, from 14,000 to 24,000 BTU in total.
Separate: 9,000 BTU per room, one system per room.
Multi-zone: built in, according to the submittal.
Separate: built-in base pan heater, according to the ORION XLTH data sheet.
Multi-zone: depends on the indoor units chosen; check their data sheets.
Separate: backlit remote included and built-in Wi-Fi, according to the data sheet.
Multi-zone: current limit function, according to the submittal.
Separate: not indicated in the data sheet.
Multi-zone: depends on the indoor units.
Separate: economy mode, energy saving, powerful mode, minimum heat, automatic defrost and restart, according to the data sheet.
Outdoors: one unit, or two
The choice plays out mostly outdoors. FUJITSU AIRSTAGE publishes the sound pressure of each outdoor unit; with separate wall units, there is one per room.
How to read these figures. dB(A) measures a noise level as the ear perceives it: the lower the number, the quieter the unit. Two units running at the same time do not add up like two numbers: the combined level is calculated on a logarithmic scale, and depends on their position.
Why this is not a ranking. A single value is published per unit and per mode; the location, nearby walls and the season change what you hear.
Outdoor units
Published sound pressure, cooling and heating
ORION XLTH wall units, indoors
Published sound pressure by speed, cooling (data sheet FG8153D); the multi-zone system’s wall units have their own values
Measurements published by the manufacturer for each unit. Read them as reference points, not as a ranking.
One large unit, or two smaller ones
The multi-zone unit is taller and heavier than a wall unit’s outdoor unit, but there is only one. The line sets, however, all run back to it.
Outdoor units, height at the same scale
Perspective photos from AirGreen product pages, at the same height scale: 884 mm for the multi-zone unit, 632 mm for the wall unit’s (dimensions published by the manufacturer). The visible width includes the depth of the unit.
| Installation | AQUILA XLTH 2-zone | 2 × ORION XLTH 9,000 BTU |
|---|---|---|
| Outdoor units on the house front | 1 | 2 |
| Outdoor unit W × H × D, weight | 32 5/16 × 34 13/16 × 12 3/8 in, 117 lb | 31 7/16 × 24 7/8 × 11 7/16 in, 86 lb each |
| Maximum piping length, per indoor unit | 82 ft | 82 ft |
| Maximum piping length, total | 164 ft for both indoor units | Not applicable: each wall unit has its own limit |
| Precharged length, for both rooms | 98 ft in total | 98 ft (49 ft per wall unit) |
| Maximum height difference, outdoor unit – indoor unit | 49 ft | 66 ft |
| Maximum height difference between indoor units | 33 ft | Not applicable: independent systems |
| Liquid – gas diameters | 1/4 – 3/8 in, two pairs | 1/4 – 3/8 in, one pair per wall unit |
| Electrical protectionPer the manufacturer | Max. 20 A breaker (MCA 19.9 A), one circuit | 15 A breaker per wall unit, two circuits |
| Stated heating / cooling range | −26 to 24 °C / −10 to 50 °C | −26 to 24 °C / −10 to 50 °C |
Sources: FUJITSU AIRSTAGE submittal 18KWAH2 (version 20250618A) for the multi-zone system (dimensions published as height × width × depth: 884 × 820 × 315 mm; minimum piping 33 ft in total and 16 ft per unit); ORION XLTH data sheet FG8153D (rev. 4/2025) for the 9,000 BTU wall unit.
What people ask us about multi-zone systems
Does each room keep its own temperature?
In both cases, each room has its own indoor unit and its own control. The difference is behind the wall: a shared outdoor unit, or one per room. The modes allowed from one room to another are checked in the manual of the model proposed.
What happens if the outdoor unit stops?
With a multi-zone system, all connected rooms depend on the same outdoor unit. With separate wall units, only the room served by the stopped unit is affected.
Can a room be added later?
The example unit accepts exactly two indoor units. For a third room, another outdoor unit is needed: either a model with more zones, or one more separate wall unit.
Why does the page add two certificates together?
Because two 9,000 BTU rooms need two wall units. Each ORION XLTH has the same certificate (214888800); the capacity of both together is the sum of the two, and the page says so every time. Seasonal efficiencies, on the other hand, do not add up: two identical wall units have the same HSPF2 as a single one.
Does the multi-zone system heat as well in extreme cold?
Both examples are stated down to −26 °C. At −26.1 °C, NEEP certifies a maximum of 12,060 BTU/h for the multi-zone system, and 11,400 BTU/h for each 9,000 BTU wall unit, or 22,800 BTU/h for both.
Is more space needed outdoors for two units?
Two locations are needed instead of one, each with its own clearances. The multi-zone unit is taller (884 mm versus 632 mm) and heavier (117 lb versus 86 lb), but on its own.
All AHRI and NEEP values for both examples
| Certified value | AQUILA XLTH 2-zone (system) | ORION XLTH 9,000 BTU (one wall unit) |
|---|---|---|
| Cooling | ||
| Rated capacity at 35 °C | 18,000 BTU/h | 9,000 BTU/h |
| SEER2 | 22 | 33.1 |
| EER2 | 13.5 | 18.8 |
| Heating, same conditions | ||
| HSPF2 region IV / V | 11 / 9.3 | 13.3 / 10.7 |
| 8.3 °C: min. / rated / max.BTU/h, system versus one wall unit | 6,800 / 22,000 / 25,000 | 3,500 / 12,000 / 23,000 |
| 8.3 °C: COP min. / rated / max. | 4.53 / 4.39 / 4.39 | 5.13 / 5.33 / 3.08 |
| −8.3 °C: min. / rated / max.BTU/h, system versus one wall unit | 4,700 / 14,800 / 22,800 | 2,200 / 7,500 / 17,500 |
| −8.3 °C: COP min. / rated / max. | 3.28 / 3.24 / 2.58 | 3.39 / 3.60 / 2.49 |
| −15 °C: min. / rated / max.BTU/h, system versus one wall unit | 3,900 / 22,000 / 22,000 | 1,900 / 15,400 / 15,400 |
| −15 °C: COP min. / rated / max. | 2.79 / 2.18 / 2.18 | 3.09 / 2.26 / 2.26 |
| Coldest point — system versus one wall unit, not highlighted | ||
| Test temperature | −26.1 °C (−15 °F) | −26.1 °C (−15 °F) |
| Capacity min. / max. | 2,500 / 12,060 BTU/h | 1,370 / 11,400 BTU/h |
| COP min. / max. | 1.83 / 2.02 | 2.23 / 1.70 |
| Listings and refrigerant | ||
| ENERGY STAR / cold climate (NEEP) | Yes / Yes | Yes / Yes |
| AHRI certificate · NEEP listing | 215447691 · 455168 | 214888800 · 392123 |
| RefrigerantGWP per IPCC (AR4); ASHRAE 34 class | R-32 · GWP 675 · A2L | R-32 · GWP 675 · A2L |
higher marks the highest value of the same measurement, under the same conditions. It is not a recommendation. Capacities are never highlighted here: the left column is a two-room system, the right column a single wall unit.
AirGreen offers both.
One compressor or several: bring the number of rooms, where they are in the house, the possible locations outdoors and the free space in your electrical panel, and talk it over with our team.
Where each figure comes from
Data verified on November 9, 2026. Performance: AHRI certificates and the NEEP database. Dimensions, sound, piping and features: per the manufacturer. When a source contradicts the AHRI certificate, the certificate prevails. This guide explains two layouts using examples; it does not rank any unit. Other models have other values.
Trademarks. FUJITSU AIRSTAGE, AQUILA, ORION XLTH and AIRSTAGE are trademarks of their respective owners. Logos are used only to identify the products shown. AirGreen is a retailer of the brand; this page is not produced, sponsored or endorsed by the manufacturer. FUJITSU AIRSTAGE systems are also sold under the GENERAL AIRSTAGE name.
Photos: AirGreen and manufacturer, for identification purposes.
Does a figure look wrong to you? Write to us: every reported figure is checked again.