Installation of a GREE UNIX R32 48,000 BTU central heat pump in Richelieu, Rouville RCM

Four tons suspended from a wall: the four things that change when you increase capacity, and the one almost no one checks

There is a persistent belief that moving from a three-ton central heat pump to a four-ton model simply means checking another line on an order form, paying a little more, and installing a slightly larger unit in the same place.

The Richelieu project illustrates why this is not the case. Between the single-fan chassis and the two-fan chassis in the GREE UNIX R32 range, four parameters change simultaneously — and one of them causes complete installations to fail every year.

Richelieu: generous homes, but not generous side clearance

Richelieu, in the Rouville RCM, occupies the banks of the Richelieu River south of the Chambly Basin. The municipality has experienced sustained residential development, and its housing stock is, on average, larger and newer than that of the agricultural villages in inland Montérégie.

Larger homes mean higher heating and cooling loads, and therefore greater capacities. Unfortunately, they do not mean more generous side clearances: on this property, the available space between the brick wall and the adjacent structure remained narrow, with a basement window in the immediate vicinity.

It was this combination — large capacity, limited space — that dictated all the technical decisions.

The two-fan chassis

The selected outdoor unit is the GUD60W2/NhE-D(U), recognizable by its two fans stacked behind a full-height grille. It measures 900 x 1260 x 340 mm and is clearly different from the single-fan chassis used for the lower capacities: taller, less deep, and above all much heavier.

Two 1/6 HP fans rather than one allow a significantly greater volume of air to be moved without spinning a single propeller at high speed. The announced sound pressure level remains at 62 dB(A) despite a capacity doubled compared with the smaller configurations in the range.

Change number one — electrical service: from 30 A to 45 A

The single-fan chassis requires an MCA of 27.7 A and maximum protection of 30 A. The two-fan chassis rises to MCA 39.9 A and MOP 45 A.

In practice:

• The dedicated circuit for the outdoor unit increases from 30 A to 45 A, with the corresponding conductor size.
• The indoor unit adds its own circuit, at MCA 7.1 A / MOP 15 A.
• The outdoor disconnect must be rated accordingly.

On a 200 A panel in a newer home, the addition usually goes in without difficulty. On a 100 A panel in a 1970s home already equipped with an electric water heater, range, and dryer, it is not a given. The electrical load calculation is done before ordering the equipment, never on the morning of installation.

We systematically refuse to “see how it goes on site.” A project that goes off track because the panel is short two spaces turns a one-day job into a three-week file, with an electrician to find and sometimes an application to change the electrical service with Hydro-Québec.

Change number two — airflow, and the existing-ductwork trap

Here is the parameter that causes the most retrofit installations to fail, and the one mentioned least often in quotes.

1,200 CFM at 125 Pa

The GUD48AH2/G-D(U) indoor unit moves 2,040 m³/h, or 1,200 CFM, at a nominal external static pressure of 125 Pa (0.5 in. water column).

These two figures go together and should not be read separately. The stated airflow is what the unit delivers if the duct system does not impose more than 125 Pa of resistance. Beyond that, airflow drops.

However, a residential duct system originally designed for a three-ton furnace was not sized to move 1,200 CFM without creating resistance. The ducts, elbows, drops, return grilles: each component adds pressure loss, and that loss increases with the square of the velocity. Increasing airflow by 20% in an unchanged system can increase resistance by 40% or more.

What happens when the ductwork can't keep up

The system works. That's the problem: it works poorly, and no one understands why.

• In cooling mode: insufficient airflow through the coil, evaporation temperature too low, indoor coil icing, then shutdown. Between episodes, the house is cooled but remains humid.
• In heating mode: excessively high air-discharge temperature across the coil, safety shutoffs, short cycling.
• In both cases: a blower that has to work harder consumes more energy, makes more noise, and actual performance deviates from the TRÉS2 shown on the specification sheet.

The customer concludes that the unit is faulty. The unit is not at fault.

How we verify it

Before the quote, not afterward:

1. Measuring the static pressure of the existing system while operating, supply and return.
2. Surveying the duct sections and identifying restrictions — undersized returns, tight elbows, plenums improvised during a previous renovation.
3. Calculating the airflow actually available at the measured pressure.
4. Costing the corrections, if any: enlarging the return, replacing a drop, rebuilding a plenum.

These corrections appear in the quote as a separate line item. A quote for a four-ton system on a three-ton duct network that mentions no duct modifications is an incomplete quote — this is the first thing to check when two prices differ significantly.

Change number three — refrigerant charge and the A2L rule

The single-fan chassis contains 2.9 kg of R32. The dual-fan chassis contains 4.6 kg, nearly 60% more.

R32 is classified as A2L: mildly flammable. For this refrigerant class, the maximum permissible charge in a system depends in particular on the volume of the room housing the indoor section. The reasoning is simple: in the event of a complete leak, the concentration reached in the room must not exceed a threshold, and that concentration depends directly on the ratio between the charge and the available volume.

What this means in the field:

• An indoor section in an open basement generally poses no difficulty.
• The same indoor section in a small, enclosed mechanical room may require measures such as a louvered door, a connection to a larger volume, ventilation, or relocating the unit.
• The factory-installed refrigerant leak detector on the system’s indoor sections is part of the safety system. It must be connected and checked during commissioning, not merely present in the box.

This assessment is made when choosing the location for the indoor section. A contractor who installs a 4.6 kg load in a mechanical shed without asking the question has not done their job.

Change number four—the weight, outside and inside

109.5 kg on a wall bracket

The outdoor unit weighs 241.4 lb (109.5 kg) net, compared with 187.4 lb (85 kg) for the single-fan chassis. That is nearly 25 kg more, suspended cantilevered from a wall.

The bracket visible in the photo is made of galvanized steel, with a diagonal brace on each arm. The triangulation is not decorative: it converts a bending force into tensile and compressive forces, which the structure handles far better. Without a brace, the entire moment is transferred to the upper anchors in tension.

The anchors are installed in the foundation concrete, using suitable hardware, never in a mortar joint or non-load-bearing cladding. The blue vibration-isolating pads, visible between the unit’s feet and the bracket arms, are compressed without being crushed.

90.5 kg to bring down to the basement

The indoor section measures 630 x 1320 x 540 mm and weighs 199.5 lb (90.5 kg) net, and nearly 218 lb in its packaging.

This is not a minor logistical detail. A cabinet of this size must pass through a basement door, a winding staircase, and sometimes a hatch. We record these dimensions during the technical visit—clear door width, ceiling height above the staircase, landing radius. Sometimes the answer is to remove a door, and more rarely, to choose a different unit configuration.

No one likes finding out at 9 a.m. on installation day that the unit will not fit through.

Installation in a narrow clearance

The elevated installation on wall brackets addressed several constraints at once: preserving ground-level passage, clearing the basement window, moving the base out of the snow-accumulation zone, and allowing the manufacturer’s clearances to be maintained on the rear and side faces—which a unit of this size installed on the ground in a narrow passage would not have allowed.

The trade-off, which we address systematically: access for HVAC maintenance. A 109.5 kg unit mounted high must remain reachable from a stable ladder, both for annual heat-exchanger cleaning and for taking pressure readings. The selected height is always a compromise between winter clearance and maintenance feasibility.

The installed combination

Efficiency, rebates, and the right order for checking

TRÉS2 of 19.0: why this is the most efficient configuration in the range

This combination has the highest TRÉS2 of the four UNIX R32 configurations with a ventilation cabinet: 19.0, compared with 18.0 for the lower capacities and 18.5 for the largest.

The explanation lies in the pairing. The GUD60W2 outdoor unit is the same for the 48,000 and 60,000 BTU configurations. Paired with the 48,000-BTU indoor section, it operates below its maximum much of the time, in the portion of its range where performance is best. Paired with the 60,000-BTU section, it is worked harder, and seasonal efficiency drops to 18.5.

This is reasoning that applies to any sizing decision: the performance shown on a data sheet belongs to a combination, not to an appliance. Two systems built around the same compressor can display different figures.

LogisVert

Hydro-Québec's LogisVert program calculates the rebate for an air-source heat pump based on the heating capacity at -8 °C, according to a scale of approximately $120 per 1,000 BTU/h, with a ceiling of around $6,700, and provides enhanced amounts when the installation replaces oil or propane heating.

For a capacity of 48,000 BTU/h, the program cap becomes a real factor: beyond a certain level, additional capacity no longer increases the assistance. This obviously does not justify undersizing a system — but it is worth knowing before comparing two quotes for systems with different capacities.

Conditions: be a residential property owner and a Hydro-Québec customer, have the work performed by a contractor holding an RBQ licence, and install an approved, ENERGY STAR certified system bearing an AHRI number corresponding to the combination actually installed. Since the rates change periodically, we validate the amount applicable to the project before including it in a quote.

The order in which we check things

For a four-ton project, our sequence does not vary:

1. Home load calculation — this is what determines the capacity, not the floor area.
2. Static pressure measurement and assessment of the ductwork for the targeted airflow.
3. Electrical load calculation and verification of availability at the electrical panel.
4. Assessment of the room intended for the indoor section, including its volume relative to the refrigerant charge.
5. Verification of passage dimensions to bring the unit to its destination.
6. Selection of the outdoor unit location, clearances, anchoring, defrost water drainage, and maintenance access.
7. Validation of the AHRI combination and the applicable rebate amount.

A quote prepared without steps 2, 3, and 4 is not a quote: it is an equipment price estimate.

Our coverage

At AirGreen, we install and service central heat pumps, wall-mounted heat pumps, and central air-conditioning systems in Richelieu, Chambly, Marieville, Saint-Mathias-sur-Richelieu, and throughout the Rouville RCM, as well as in Longueuil, Boucherville, Saint-Hyacinthe, and Châteauguay. We also serve Montréal, Laval, the North Shore, and the South Shore.

If you are considering a capacity of four tons or more, ask to see the static pressure measurement and the electrical load calculation. We provide them systematically, including when the conclusion requires us to add corrections to the quote.