Multi-zone heat pump, 3 zones: which FORESTAIR unit, and how far your lines can run
On lines alone, the FA-M27 is enough while your three lines total 60 m, with none over 30 m; beyond 60 m, you need the FA-M36 (80 m) or the FA-M42 (90 m). The heat you need in deep cold is decided next, at the on-site assessment. For two rooms, see our two-head systems.
Multi-zone, 3 zones: the 3 systems in the shop
On the FA-M27, FA-M36 and FA-M42, each with three wall heads.
Line budget for 3 heads: FA-M27, FA-M36 or FA-M42
Enter the planned total of your three refrigerant lines, then the longest one: the budget checks both limits on the chosen unit’s submittal, per line and in total.
Limits: FA-M27, FA-M36 and FA-M42 submittals (footer 112025), maximum length per line (“each”) and in total. The budget assumes one line per head: the submittals do not publish how many connections the unit has. Some pairs are impossible, a longest line under a third of the total, or equal to or above the total: the budget then picks another possible length. Elevation, 10 m at most, is not checked here; actual lengths are measured at the on-site assessment.
FA-M27 · 45 m in total, longest line 20 m
15 mof margin under the 60 m total
Within both FA-M27 submittal limits: per line and in total.
Three heads: the FA-M27’s cabinet, the per-line limit and SEER2
the FA-M27 has the dimensions of the outdoor unit of the E24 wall unit named 24,000 BTU/h
The FA-M27 submittal gives 978 × 803 × 421 mm, then a depth of 359 mm in its dimensions table. Both lines state 16-5/8 in, and 16-5/8 in is 422 mm (our calculation), so we use 421 mm. The E24 brochure publishes 978 × 803 × 421 mm for the outdoor unit of the E24 named 24,000 in its banner (23,000 BTU/h in its table). Net weights: 54 kg for the FA-M27, 47.5 kg for the E24.
FA-M27-D3TL/O submittal: Outdoor Unit Data and dimensions table; E24 series brochure, document 072025: outdoor unit.three lines at their maximum exactly fill the FA-M42’s total (our calculation)
On the FA-M42, the per-line limit comes before the total: three lines at their maximum land exactly on its 90 m. On the FA-M27 and FA-M36, the total can limit first.
FA-M27 to FA-M42 submittals: Refrigerant Piping Data; AirGreen calculation.the same SEER2 as the FA-M18, for 27,000 BTU/h of cooling instead of 18,000
Per their submittals, the FA-M27 (27,000 BTU/h of nominal cooling) publishes a SEER2 of 24.0, like the FA-M18 (18,000 BTU/h). The FA-M36 and FA-M42 publish 22.5 and 22.0. SEER2 counts the cooling delivered over a season per unit of electricity: at 24.0, the FA-M27 matches the smallest of the four.
FA-M18 to FA-M42 submittals: System Ratings.Multi-zone, 3 zones: FA-M27 or FA-M36
With three heads, the FA-M27 is at its maximum; the FA-M36 takes one more and longer lines in total. NEEP, which catalogues heat pumps built for the cold, also lists more heating capacity for its non-ducted combination: 26,000 BTU/h at −15 °C, against 19,800.
| Outdoor unit | FA-M27 | FA-M36 |
|---|---|---|
| Indoor units, at most | 3 | 4 |
| Nominal cooling (submittal) | 27,000 BTU/h | 35,000 BTU/h (named 36,000) |
| Nominal heating (submittal) | 28,000 BTU/h | 36,000 BTU/h |
| Heating capacity at −15 °C (NEEP) | 19,800 BTU/h | 26,000 BTU/h |
| Maximum at −25 °C (NEEP) | 14,000 BTU/h | 19,000 BTU/h |
| Outdoor unit, W × H × D | 978 × 803 × 421 mm (359 mm deep in the dimensions table) | 1,074 × 853 × 468 mm |
| Net weight | 54 kg | 66 kg |
| Outdoor sound level | 62 dB(A) | 65 dB(A) |
| Minimum circuit ampacity (MCA) · breaker at most | 18 A · 30 A | 22 A · 35 A |
| LogisVert, indicative amount | $2,688 | $3,288 |
Three heads, three lines: what we measure before the quote
- The longest of the three lines: 30 m at most, even on the FA-M42.
- The FA-M27’s circuit: its submittal calls for wiring that can carry at least 18 A (MCA), under a breaker of 30 A at most.
FORESTAIR multi-zone, 3 zones: common questions
My heads are on different floors: how much elevation is allowed?
The FA-M27, FA-M36 and FA-M42 submittals publish a maximum refrigerant pipe elevation of 10 m. They do not say whether the outdoor unit may sit above or below the heads, nor the height allowed between two heads. We measure those heights at the on-site assessment.
One of my three lines would be 35 m: is that possible?
Not per the FA-M27, FA-M36 and FA-M42 submittals: their 30 m per-line limit applies even when the total leaves room. The answer lies in where the outdoor unit goes, which we choose at the on-site assessment.
Is the FA-M27 enough for three rooms?
Its submittal allows up to three indoor units. For heating capacity, NEEP lists 19,800 BTU/h at −15 °C for its non-ducted combination, without naming any heads. We assess it on site, room by room; one of the rooms can also go to an E24 wall heat pump, with its own outdoor unit.
Can a fourth head be added later?
Not on the FA-M27: its submittal allows three indoor units at most. The FA-M36 allows four heads and the FA-M42 five heads; no submittal covers adding one after installation, so we discuss it at the visit.
How much LogisVert assistance for a 3-zone FORESTAIR system?
FA-M27: $2,688; FA-M36: $3,288; FA-M42: $3,720, indicative amount each, from our product pages. Where $2,688 comes from for the FA-M27: 22,400 BTU/h listed on NEEP at −8.3 °C, multiplied by the LogisVert guide v1.10 rate, $120 per 1,000 BTU/h at −8 °C for an ENERGY STAR “cold climate” heat pump. Being on NEEP does not make a heat pump eligible: the guide relies on ENERGY STAR. Only Hydro-Québec confirms the assistance granted.
Before the visit: your floors and the outdoor unit’s wall
- Note the floors of your three rooms: 10 m of elevation at most between the outdoor unit and the heads, per the submittals.
- Photograph the wall planned for the outdoor unit and the route to each room: that is where the longest of the three lines is decided.
Hydro-Québec never solicits by phone or door to door for the LogisVert Efficient Homes Program.
Sources
- FORESTAIR, submittal data FA-M18-D2TL/O, “Multizone Series Condensing Unit”, footer 112025, © FORESTAIR 2025. PDF
- FORESTAIR, submittal data FA-M27-D3TL/O, “Multizone Series Condensing Unit”, footer 112025, © FORESTAIR 2025. PDF
- FORESTAIR, submittal data FA-M36-D4TL/O, “Multizone Series Condensing Unit”, footer 112025, © FORESTAIR 2025. PDF
- FORESTAIR, submittal data FA-M42-D5TL/O, “Multizone Series Condensing Unit”, footer 112025, © FORESTAIR 2025. PDF
- FORESTAIR, E24 series brochure, document 072025 (2025): performance, outdoor unit, refrigeration system. PDF
- NEEP, Cold Climate Air Source Heat Pump List, records 508676 to 508678, read November 5, 2026. ashp.neep.org
- ENERGY STAR, heat pump registry, Canadian market (dataset w7cv-9xjt), records 4529623 and 4529625, read November 5, 2026. data.energystar.gov
- Hydro-Québec, LogisVert Efficient Homes Program, participant’s guide, version 1.10 (September 15, 2026). Indicative amounts: those on our product pages. hydroquebec.com
- Government of Québec, “Noise measurement”, updated June 16, 2022. quebec.ca
Page updated November 11, 2026.