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How much heat does the CSH6 + FXM4X system deliver in deep cold, with its heater kit?

The values on this page are the ones COMFORTMAKER publishes.

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COMFORTMAKER // Central systems

COMFORTMAKER central heat pumps: the CSH6 + FXM4X system, part by part

Two units and a heater kit: this page shows what each one publishes and adds them up. Nothing more.

The COMFORTMAKER central system brings together a CSH6 outdoor unit, an FXM4X fan coil and an electric heater kit, in six sizes from 2 to 5 tons. For each size, the page starts from the values the brand publishes for the combination it tested, and flags our own calculations.

Page updated November 5, 2026

This page answers

How much heat does the CSH6 + FXM4X system deliver in deep cold, with its heater kit?

AirGreen

Sold and installed by AirGreen.

We install in Montreal, Laval, Longueuil, the South Shore and the North Shore.

01 // The tool

The system in deep cold

Pick the size, the heater kit and the outdoor temperature. The tool takes the combination the brand tested for that size, adds the kit at 230 V and at 208 V, then shows both electrical supplies.

Size

Heater kit (kW at 230 V)

Outdoor temperature

AirGreen calculation: the kit’s printed output × 3,412 BTU/h per kW, rounded to the nearest ten, then added to the heat pump’s published value. Heat-pump values belong to the combination the brand tested for each outdoor unit. The fan coil sheet prints kW at 230 V and at 208 V, and amps at 208 V and at 230 V; it publishes no value at 240 V. The tool shows seven kits usable on single phase (the 24 and 30 kW kits are supplied three-phase, field convertible to single phase); from the 3600 cabinet, the sheet also approves a 9 kW kit (supplied single phase, convertible to three-phase) and a 15 kW three-phase kit, then, from the 4200 cabinet, an 18 kW three-phase kit. Value to be confirmed: last row of the sheet’s expanded table, read but not yet checked on the printed page. These values are those of the brand-tested combinations, not of the products of the same tonnage listed below.

51,150BTU/h

heat pump + kit at 230 V (AirGreen calculation) to confirm

Combination tested by the brand
CSH642 + FXM4X48 (cabinet 4800)CSH6 sheet, p. 15
Heat pump at −19.4 °C
17,030 BTU/h (COP not printed) to confirmlast row of the sheet’s expanded table; value as read, to be confirmed on the sheet
10 kW kit, printed output
10 kW at 230 V · 7.5 kW at 208 Vmodels EHK10AKN, EHK10AKB
Kit in BTU/h
34,120 BTU/h at 230 V · 25,590 BTU/h at 208 VAirGreen calculation: kW × 3,412, rounded to the nearest ten
Heat pump + kit
51,150 BTU/h at 230 V · 42,620 BTU/h at 208 VAirGreen calculation; includes the value to be confirmed above
Outdoor unit: MCA / max fuse
27.8 A / 40 Aone value printed for 208/230 V
Fan coil + kit: MCA / max fuse
53.8 A / 60 A at 208 V · 58.5 A / 60 A at 230 Vsingle circuit; minimum ampacity includes the motor of the largest fan coil used with the kit

Heat pump and kit together: 51,150 BTU/h at 230 V or 42,620 BTU/h at 208 V (AirGreen calculation, on a value still to be confirmed); what your home needs is measured on site.

CSH6 sheet (428 41 6400 02, April 25, 2019), expanded tables, pp. 7–13, and pp. 1 and 4; FXM4X sheet (496 41 5402 04, July 2, 2019), heater table.

The COMFORTMAKER shop

The COMFORTMAKER products on this page, right below

Price on quotation, after the on-site assessment.

COMFORTMAKER

02 // Did you know

Three details from COMFORTMAKER’s documents

One tested combination per outdoor unit

For each outdoor unit, one tested combination; for the CSH630 (2.5 tons), it is the FXM4X36.

CSH6 Product Specifications, 428 41 6400 02 (April 25, 2019), p. 15

10 kW at 230 V, 7.5 kW at 208 V

The fan coil’s spec sheet gives heater kit output at 230 V and at 208 V: a “10 kW” kit gives 7.5 kW at 208 V.

FXM4X Fan Coils Product Specifications, 496 41 5402 04 (July 2, 2019), heater kit table

61 m of refrigerant line

Published maximum refrigerant line length: 61 m; beyond 24.4 m equivalent or 6.1 m of vertical separation, the sheet applies its “long line” rules.

CSH6 Product Specifications, 428 41 6400 02 (April 25, 2019), pp. 5 and 6

03 // The comparison

Compared with the SoftSound® 36,000 wall unit

Same capacity, two ways to heat: here is what the tested CSH636 + FXM4X48 combination and the SoftSound® DLCSRA 36,000 wall unit publish. Sound is not compared, because the two documents do not measure it the same way.

ValueCSH636 + FXM4X48 (tested combination)SoftSound® DLCSRA 36,000
Heating at 8.3 °C35,000 BTU/h (COP 4.16)36,000 BTU/h (COP 3.44)
Heating at −8.3 °C20,800 BTU/h (COP 2.86)21,000 BTU/h (COP 2.60)
SEER1618.0
Outdoor unit weight (basis)107.5 kg operating65 kg net
Outdoor unit: MCA / max fuse21.6 A / 35 A25 A / 35 A
Published maximum refrigerant line length61 m50 m
Air deliveryThrough ductwork1,350 mm wall head

At the two temperatures both documents publish, the wall unit lists slightly more heat. The central system, for its part, holds an electric heater kit in its fan coil, on its own supply.

CSH6 Product Specifications, 428 41 6400 02 (April 25, 2019), pp. 1, 6 and 15; COMFORTMAKER Residential and Light Commercial Ductless Systems Catalog, 328-42-0499-00 (May 2018), pp. 20 to 24

04 // Published figures

The six tested combinations, as published

Value2 ton2.5 ton3 ton3.5 ton4 ton5 ton
Outdoor unitCSH624CSH630CSH636CSH642CSH648CSH660
Tested fan coilFXM4X24FXM4X36FXM4X48FXM4X48FXM4X60FXM4X60
Cooling at 35 °C23,000 BTU/h29,200 BTU/h35,000 BTU/h40,500 BTU/h48,000 BTU/h55,000 BTU/h
SEER / EER16 / 1316 / 1316 / 1316 / 1316 / 1316 / 13
Heating at 8.3 °C (COP)22,800 BTU/h (3.90)28,600 BTU/h (3.72)35,000 BTU/h (4.16)41,000 BTU/h (3.94)46,500 BTU/h (3.84)55,000 BTU/h (3.82)
Heating at −8.3 °C (COP)14,200 BTU/h (2.60)17,400 BTU/h (2.56)20,800 BTU/h (2.86)25,400 BTU/h (2.82)29,600 BTU/h (2.74)33,600 BTU/h (2.82)
HSPF (no region printed)8.59.08.58.59.08.5
Outdoor unit: MCA / max fuse15.5 / 25 A19.9 / 30 A21.6 / 35 A27.8 / 40 A31.8 / 45 A33.9 / 50 A
Tool kits approved (kW at 230 V)5, 8, 10, 155, 8, 10, 15, 205, 8, 10, 15, 20, 24, 305, 8, 10, 15, 20, 24, 305, 8, 10, 15, 20, 24, 305, 8, 10, 15, 20, 24, 30

Values of the combination the brand tested for each outdoor unit. Per the note on p. 15 of the CSH6 sheet, ratings are net: they include fan heat, but not supplemental electric heat. MCA: minimum circuit ampacity; max fuse: the largest fuse or breaker allowed (printed as MOCP or max fuse depending on the document).

CSH6 Product Specifications, 428 41 6400 02 (April 25, 2019), pp. 1, 4 and 15; FXM4X Fan Coils Product Specifications, 496 41 5402 04 (July 2, 2019), heater applicability table

05 // Good to know

Good to know before the on-site assessment

Three components, two power supplies

Outside, the CSH6. It heats and cools, from 2 to 5 tons. Inside, the FXM4X fan coil. It pushes air through your ductwork; its thermostatic expansion valve (TXV) is factory installed. In the fan coil, the EHK kit. Installed on site, it gives 5 to 30 kW depending on the cabinet. The outdoor unit has its own supply; the fan coil and its kit have theirs.

In deep cold, two sources of heat

The last published row of the CSH6 heating table is −19.4 °C (row read, to be confirmed); the brand publishes no minimum temperature. Per the note on p. 15, its ratings are net: they count fan heat, not supplemental electric heat. That heat comes from the fan coil’s kit, and the tool adds it separately. Defrost is controlled by time and temperature.

06 // Warranty

Warranty published by COMFORTMAKER

  • CSH6 outdoor unit: 5-year No Hassle Replacement limited warranty; 5-year parts limited warranty, including compressor and coil; with timely registration, an additional 5-year parts limited warranty, including compressor and coil. The sheet adds: applies to original purchaser/homeowner, some limitations may apply.
  • FXM4X fan coil: 5-year No Hassle Replacement limited warranty; 5-year parts limited warranty; with timely registration, an additional 5-year parts limited warranty. For owner occupied, residential applications only.
  • COMFORTMAKER does not cover labour.

Each sheet refers to the warranty certificate for complete details.

CSH6 Product Specifications, 428 41 6400 02 (April 25, 2019), p. 1; FXM4X Fan Coils Product Specifications, 496 41 5402 04 (July 2, 2019), p. 1

AirGreen // COMFORTMAKER

What COMFORTMAKER publishes, what AirGreen does

COMFORTMAKER

What COMFORTMAKER publishes

  • The units and their spec sheetsThe values shown here are the ones the brand publishes; our calculations carry the label “AirGreen calculation”. The −19.4 °C value is marked “to confirm”.
  • The parts warrantyAs printed in its documents, with its conditions.
AirGreen

What AirGreen does

  • Sold and installed by AirGreen.Montreal, Laval, Longueuil, the South Shore and the North Shore.
  • The on-site assessmentThe series and the size are chosen in your home.
  • One clear quotationThe unit, the install and the accessories you choose, on one document.

07 // Questions

The questions we get

Does the system heat on Montreal’s coldest days?

The brand publishes no minimum temperature for the CSH6, and its heating tables stop at −19.4 °C (row read, to be confirmed). According to Environment and Climate Change Canada’s 1981–2010 climate normals (station MONTREAL/PIERRE ELLIOTT TRUDEAU INTL A), January averages −9.7 °C with a mean daily minimum of −14.0 °C; the minimum drops below −20 °C on 14.3 days a year and below −30 °C on 0.27 days a year. What your home needs is measured during the on-site assessment.

Which combinations did the brand test?

One per outdoor unit: CSH624 with FXM4X24, CSH630 with FXM4X36, CSH636 and CSH642 with FXM4X48, CSH648 and CSH660 with FXM4X60 (CSH6 sheet, p. 15). The values on this page belong to those combinations, and to them only.

What efficiency does the brand publish for these systems?

SEER 16 and EER 13 for all six tested combinations; HSPF 8.5 or 9.0 depending on size, with no climate region printed. The sheet is dated April 25, 2019: these are SEER, EER and HSPF ratings under the test methods of the time.

Which wall control goes with the system?

The CSH6 sheet names the Observer® wall control (TSTAT0201CW). With it, operation is communicating and self-configuring, and diagnostics are shown as text. The CSH6 also has a factory-installed outdoor temperature sensor.

Is the FXM4X fan coil a furnace?

The brand calls it a fan coil: it moves the air and holds the EHK electric heater kit. On our site it is listed under the name people search for, the FXM4X electric furnace, with a tool that shows which kit goes in which cabinet.

What warranty does COMFORTMAKER give on a central heat pump?

For each unit, the sheet publishes a 5-year No Hassle Replacement limited warranty, a 5-year parts limited warranty and an additional 5 years on parts with timely registration; on the CSH6, compressor and coil are included. Each sheet’s wording applies: original purchaser/homeowner for the CSH6, owner occupied residential applications for the FXM4X. COMFORTMAKER does not cover labour.

Sources checked November 5, 2026

  • CSH6 Product Specifications, 428 41 6400 02, April 25, 2019, pp. 1, 4 to 6, 7 to 13 and 15: shareddocs.com
  • FXM4X Fan Coils Product Specifications, 496 41 5402 04, July 2, 2019, p. 1 and heater kit tables: shareddocs.com
  • Residential and Light Commercial Ductless Systems Catalog, COMFORTMAKER, 328-42-0499-00, May 2018, pp. 20 to 24 (SoftSound® DLCSRA 36,000): shareddocs.com
  • Canadian Climate Normals 1981–2010, Environment and Climate Change Canada, station MONTREAL/PIERRE ELLIOTT TRUDEAU INTL A (7025250), read November 5, 2026: climate.weather.gc.ca

AirGreen calculations (kW conversions, sums, percentage shares) are made on the published values and labelled as such.

AirGreen // Air conditioning and heating

The system is sized in your home

We look at the house, the ductwork and the panel, then propose the combination and the heater kit.

Book my free estimate514-316-2973
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Page updated November 5, 2026