Replacing an existing wall-mounted system: what can be reused, and what can never be reused
A replacement is not a new installation with one fewer unit to purchase. It is a project with its own pitfalls, most of which are found in what the customer thinks has already been paid for: the refrigerant lines in the wall, the electrical circuit at the panel, and the pad beneath the old outdoor unit. In Saint-Zotique, the house already had a wall-mounted system that served only part of the rooms. The project involved removing it completely and switching to five zones on a single outdoor unit.
Saint-Zotique: old cottages turned into homes
Saint-Zotique occupies the north shore of Lake Saint-François, at the western end of the Vaudreuil-Soulanges RCM, along Highway 20. The municipality is known for its municipal beach and, above all, its network of navigable canals serving narrow, deep waterfront lots.
A large part of this housing stock shares the same history: vacation residences built for summer use, expanded, insulated in stages, and eventually occupied year-round. This progression has very concrete implications for an HVAC project, which we revisit in the second part.
Five zones, one possible model
Five indoor units require the GWHD(42)ND6MO, the only unit in the FreeMatch R32 range that can connect to five heads—the full range limit is covered in our Sainte-Martine article.
Installed distribution: 12,000 + 9,000 + 9,000 + 9,000 + 9,000 = 48,000 BTU/h, or 114% of the nominal cooling capacity. The main living area, facing the water and featuring extensive glazing, receives the 12,000 BTU head; the four other rooms, which are similar in size, receive identical 9,000 BTU heads. Four identical capacities mean a single filter reference, consistent performance from room to room, and no oversized unit in a small bedroom.
Outdoor unit data:
- 42,000 BTU/h nominal cooling capacity (modulation from 8,870 to 44,300), 44,300 BTU/h heating capacity (modulation from 8,870 to 54,590)
- SEER2 21, HSPF2 10, EER2 12, COP 3.9, ENERGY STAR certified
- MCA 30 A / MOCP 45 A on a single dedicated circuit
- R32, 2,700 g factory charge, 50 m precharge, maximum 100 m, 25 m elevation difference, 20 g/m additional charge
- AHRI 214931590 (non-ducted), 214931596 and 214931600 for the ducted and mixed variants
- Heating range -30 °C to 24 °C, G10 inverter, intelligent defrost, A2L detector included
Five lines measured: 7 + 11 + 14 + 16 + 21 m, for a total of 69 m developed length, therefore 380 g of R32 weighed out beyond the factory charge.
Existing refrigerant lines cannot be reused
This is the item every cheap quote leaves out, and it is the decision that determines the new compressor's service life.
Contamination. A line that has been used contains a film of compressor oil, brazing residues, sometimes moisture, and, if the old compressor failed, acids. All of this migrates to the new compressor. A manufacturer generally accepts reuse only under strict, documented flushing conditions, and the unit's instructions govern. Our practice, when replacing a system, is to install new lines.
Diameters. The FreeMatch range requires 1/4 in. liquid and 3/8 in. gas lines per head. An older high-capacity single-zone system often had a 1/2 in. gas line. Reusing that line for a 9,000 BTU/h head creates a cross-section that is too large for the fluid velocity, compromising oil return to the compressor. Oversizing a diameter is not a safety margin; it is a defect, as we detailed in our Verchères article.
Number. A home going from one or two zones to five does not have the required routing in any case. Four new runs must be created, which puts the whole question of reuse into its proper perspective.
What can actually be reused
- Existing wall penetration, often, provided the location of the old head is also suitable for the new one. The enclosures have neither the same dimensions nor the same mounting plate, and the offset generally means repairing the finish beside the unit.
- The outdoor base, if it is level, not sunken, and at the right height for snow and defrost drainage.
- The disconnect, if it is in good condition and adequately rated.
The real hidden cost: the electrical circuit
This is the point we put in writing before signing any project of this type. An older single-zone system often needed only a modest dedicated circuit. The GWHD(42)ND6MO requires a circuit sized based on an MCA of 30 A, protected at a maximum of 45 A.
In other words, going from one zone to five is not a matter of multiplying indoor units: it is a change in electrical category. The existing circuit must be inspected, and often rewired, by an electrical contractor, along with the corresponding panel load calculation. In a converted vacation home, this calculation can bring surprises because the electrical service has rarely kept pace with successive additions. The division of responsibilities between the HVAC contractor and the electrician is detailed in our Saint-Clet article.
Recovery and disposal of the old system
The old refrigerant is recovered, never vented into the atmosphere, using equipment designed for that purpose and by a certified technician. The outdoor unit and heads then go to a metal-recycling facility. The customer can, and should, ask for these two steps to appear on the invoice rather than being bundled into a flat-rate fee.
Repair or replace: the honest answer
An existing six- to eight-year-old wall-mounted system that loses a capacitor, an outdoor fan motor, or an expansion-valve coil can be repaired, and repaired for a fraction of the cost of replacement. The parts that fail first are almost never the compressor, as we documented in our Saint-Louis-de-Gonzague article.
Replacement is justified when one of these conditions applies:
- We are adding zones anyway. That is the case here: four additional rooms to serve, so an outdoor unit that does not have the necessary ports anyway.
- The compressor has failed, contaminating the system and bringing the repair cost close to the cost of replacement.
- Parts are no longer available through the local distribution network.
- The refrigerant is no longer supported, a situation experienced by owners of R22 systems.
The envelope before the equipment: why a converted cottage misleads load calculations
A load dominated by infiltration, not floor area
In a house built all at once according to current practices, the heating load is calculated mainly from the surface areas: walls, ceiling, windows, and their insulation values. In a vacation home converted in stages, that is no longer true. The dominant factor is often air infiltration: junctions between the original building and additions, a crawl space accidentally ventilated, an interrupted air barrier, windows replaced at different times, and summer patio doors left in place.
The consequence is direct and unpopular: a heat pump cannot compensate for an air leak. It heats the air that remains in the house; it can do nothing about the air escaping through the joints. A five-zone system installed in a leaky envelope will produce disappointing results in January, and the customer will blame the equipment for the failure.
There is an important nuance: in air conditioning, infiltration also brings in outdoor humidity, which loads the evaporator with latent heat. A waterfront home in July, with a leaky envelope, therefore requires more dehumidification than its floor area would suggest.
The order of the work
What we recommend, in this order, and what we applied here:
- Identify leakage points before sizing the system. A thorough inspection of junctions, the crawl space, and the perimeter of openings takes a few hours and changes the calculations.
- Correct the air leakage and insulation at the most cost-effective points — additions’ junctions, thresholds, and floor perimeter — before installation whenever the budget allows.
- Then size the system based on the envelope as it will be, and put the calculations in writing. The complete reasoning on sizing a building envelope during construction work appears in our Dundee article.
- Keep the electric baseboard heaters for at least one full season, set 2 to 3 °C below the thermostat settings, while you observe their actual performance.
A contractor who agrees to size five zones without asking a single question about the envelope of a converted home is selling a unit, not a solution.
Mistakes to avoid
- Reuse existing refrigerant lines to save one line item on the quote.
- Assume that the old system's electrical circuit will be sufficient for a five-head unit.
- Vent the old refrigerant into the atmosphere.
- Reuse a sunken outdoor base simply because it is already in place.
- Rely on five heads to correct a leaky building envelope.
- Remove the baseboard heaters in the first year.
- Have the additional charge estimated rather than weighed: 19 m beyond the precharge amounts to 380 g.
Rebates, warranty, and maintenance
The unit is ENERGY STAR certified and eligible for local rebates. For an electrically heated home, the programs to verify are Hydro-Québec's LogisVert and Rénoclimat; Chauffez vert applies to replacing fossil-fuel heating and does not apply here. For a conversion project like this one, it is worth checking whether envelope work and the unit can be included in the same application: criteria change and are confirmed when the application is opened. The declared AHRI number must match the configuration actually installed.
The warranty is 10 years, extended to 12 years upon registration with the distributor and proof of installation. For a replacement, we keep the recovery documentation for the old refrigerant and the commissioning sheet for each component on file.
For maintenance, five zones mean five filters, five drain pans, and five drains, a topic covered in our Sainte-Martine article.
Our coverage
At AirGreen, we design, install, replace, and maintain HVAC systems — wall-mounted heat pumps, multi-zone systems, air conditioners, and central systems — in Montreal, Laval, Longueuil, on the North Shore, and throughout the South Shore, including Saint-Zotique, Les Coteaux, Rivière-Beaudette, and all of Vaudreuil-Soulanges. For a replacement, we price new and reused components separately so that quotes can be compared on an equal basis.