A complete central system installed flat on one's stomach in a 42-inch crawl space
Some projects are difficult not because of the equipment, the load calculation, or the ductwork. The difficulty is the space. In Saint-Mathias-sur-Richelieu, on the east bank of the river between Chambly and Saint-Charles-sur-Richelieu, we replaced an aging central system with a GREE FLEXX R32 central heat pump in a crawl space with barely 42 inches of clearance beneath the joists. All of the home's mechanical systems are located there: the ventilation cabinet, the plenum, the round ductwork, the copper plumbing, the wiring, and now an R32 refrigerant circuit.
This text describes the project in detail because it raises questions that most articles about HVAC installation avoid: How do you bring a 61.5 kg cabinet through a hatch, where does the condensate go when there is no lower drain, and above all, how do you handle A2L refrigerant in a confined space that is the lowest point of the house?
Why Are There So Many Crawl Spaces in Saint-Mathias-sur-Richelieu?
The riverside villages along the Richelieu — Saint-Mathias-sur-Richelieu, Richelieu, Saint-Charles-sur-Richelieu, and part of Chambly — have a high proportion of homes built over crawl spaces rather than full-height basements. The nearby water table, the Richelieu River floodplain, and the age of the housing stock largely explain this choice. The Richelieu floods also left a lasting reflex among area homeowners: no habitable rooms below ground level.
What this means for us: in this part of Montérégie, a significant share of central heat pump projects takes place in a space where you work on your knees, with supplemental lighting, and where every positioning decision affects you for the next fifteen years. This is not a minor jobsite detail. It is the factor that determines the equipment choice.
The selected unit: GREE FLEXX R32, 2 tons
We selected the smallest configuration in the FLEXX lineup:
- Indoor unit (ventilation cabinet): GUD24AH2/G-D(U)
- Outdoor unit: GUD36W2/NhE-D(U)
- Certified AHRI matched-system number : 217120759
- Cooling capacity: 24,000 BTU/h nominal, modulating from 12,000 to 30,000 BTU/h
- Heating capacity: 23,000 BTU/h nominal, modulating from 12,000 to 30,000 BTU/h
- Efficiency: 18 SEER2, 10 HSPF2, 12.5 EER2, COP 3.6
- ENERGY STAR certified
- Heating range: down to -30 °C; cooling range: -15 °C to 54 °C
- R32 charge: 2.5 kg factory charge
- Power and control: 208-230 V, conventional 24 VAC thermostat, factory-installed Wi-Fi
- A2L leak-detection sensor included
- Warranty: 10 years standard, with 2 additional years upon registration
Two figures deserve emphasis. The COP of 3.6 and the 12.5 EER2 are the best in the entire FLEXX range: the smallest configuration is also the most efficient at the nominal operating point. A homeowner hesitating between 2 and 3 tons “to be safe” therefore loses efficiency while also paying more. That is the argument we made here, supported by the load calculation.
Why the smaller cabinet, specifically
The GUD24AH2/G-D(U) measures 18 1/8 x 43 1/2 x 21 1/4 inches (460 x 1105 x 540 mm) and weighs 61.5 kg net. The 3-ton cabinet is 21 1/4 inches wide and weighs 74 kg; the 4-ton cabinet is 24 4/5 inches wide and weighs 90.5 kg. In a 42-inch crawl space, this width difference determines whether the cabinet fits between two rim joists and whether service clearance is maintained in front of the electrical panel and the coil.
The FLEXX series is designed for horizontal (side-discharge) airflow, which allows the flat installation shown in our jobsite photos, with the cabinet set on metal supports that lift it off the plywood decking. This elevation is not cosmetic: in a crawl space in a floodplain, you should never place equipment directly on the floor.
An honest note about the data sheet
We read technical data sheets line by line, and the FLEXX sheet contains two errors that an installer should know about.
First, the refrigerant charge is listed under the heading “lb (oz)” with the values 2.5 (88.2) and 4.6 (162.3). These values are in kilograms, not pounds: 2.5 kg is indeed 88.2 oz. GREE Canada's documentation for the same equipment confirms the unit. A technician who weighed out 2.5 pounds of R32 would charge less than half the required amount.
Next, the advertised airflow of 3,176 cfm for a residential 2-ton unit is not realistic. The actual airflow of this cabinet is approximately 760 CFM at a nominal external static pressure of 125 Pa (0.5 in. w.c.). This second figure is the one that matters for duct-system design, and it directly guided our decisions on this installation.
R32 in a confined space: the real challenge of this installation
R32 is an A2L-class refrigerant, meaning it is mildly flammable. In an ordinary installation—a cabinet in a finished 1,200-cubic-foot basement—the issue is resolved quickly. In a crawl space, three factors combine and warrant serious analysis:
- The volume is small. The floor area may be large, but the 42-inch height drastically reduces the available volume for diluting a potential leak.
- R32 is denser than air. In the event of a leak, it sinks. The crawl space is the lowest point in the house—exactly where it would accumulate.
- Natural ventilation is nonexistent or nearly so. A sealed crawl space, as it should be in Quebec's climate, has no spontaneous air exchange.
This is where the 2.5 kg charge of the 2-ton configuration becomes a technical advantage, not merely an economic one: the smallest charge in the range reduces the minimum area required by the dilution calculation. We verified the actual space volume before ordering, not afterward.
The factory-supplied A2L leak-detection sensor is integrated into the cabinet and controls the indoor fan: if a leak is detected, the blower starts and circulates air from the duct system, preventing localized accumulation. We confirmed its location, power supply, and operation during commissioning, and explained to the customer what activation would mean if it ever occurred—a fan starting on its own, without a thermostat call, is not a malfunction but a signal.
Getting 61.5 kg through a hatch
The part nobody photographs. The cabinet arrives packaged at a gross weight of 65.5 kg, in a 525 x 1175 x 660 mm box. The crawl-space access hatch in a waterfront home is rarely more than 24 inches wide.
Our method for this type of installation:
- Measure the entire route before ordering: access hatch width, clear height above it, tilt angle, and any copper piping or drains crossing the path.
- Unpack outside the crawl space and lower the bare cabinet, with the straps in place, using two technicians.
- Prepare the supports before lowering the unit, so the cabinet is never temporarily set on plywood or plumbing.
- Plan the exit route. This is the question we ask the customer out loud: in twelve years, someone will have to bring this unit back out through the same opening. If the answer involves dismantling a plenum or cutting ducts, we reposition the unit while there is still time.
Drainage: a condensate pump, because gravity is not available
In a basement, there is almost always a floor drain lower than the coil. In a crawl space, the coil is already at the lowest point in the house. There is no gravity-drainage route.
We therefore installed a dedicated condensate pump, separately powered, which lifts the condensate to the sanitary drainage system. The complete sequence around this pump:
- A compliant PVC trap at the pan outlet, sized according to the negative pressure in the cabinet—a coil under suction without an adequate trap simply will not drain, and the pan will overflow.
- Two cleanout plugs installed on either side of the trap, visible in our photos, to allow annual flushing without dismantling the piping.
- A continuous slope toward the pump, checked with a level along the entire run.
- A high-level safety switch wired to the low-voltage control.
The detail that costs the most when neglected
This safety switch is the point we do not compromise on. A condensate pump will eventually fail—because of the motor, float, or clogged tubing. Without a switch, the system keeps running, the pan overflows, and the water falls onto the floor decking of a crawl space, meaning directly onto the insulation and floor structure. With the switch, the unit shuts down, the customer calls, and we replace one pump.
We have seen water-damage claims arise from exactly this omission, including cases where a condensate pipe was simply directed into a water-heater pan. Condensate from a central heat pump is produced for several months of the year and amounts to liters per day: it is not an insignificant trickle of water.
The existing ductwork: what we keep and what we correct
The house already had a galvanized round-duct network with a supply plenum, and the outlets had been handwritten by the original installer—“L.R.,” “DEN.” These markings, often mocked, saved us time locating the outlets.
The YORK electronic air cleaner retained
The system included a YORK electronic air cleaner mounted on the return plenum. The commercial reflex would be to replace it. We kept it, for a measured rather than sentimental reason: after inspection, the cell and power supply were working, and the client maintained the equipment.
But an electronic air cleaner imposes a pressure drop, and a dirty cell can impose a considerable one. With a budget of 125 Pa (0.5 in. water column) of external static pressure for 760 CFM, the return-air path through an air cleaner and a duct network in an unheated space can consume the entire available budget. We therefore measured the network's actual static pressure, on both the return and supply sides, before and after replacing the equipment. This measurement also guided the choice of filter media—a filter that was too restrictive would have canceled the equipment's modulation and caused coil icing in cooling mode.
A message for any homeowner comparing quotes: a contractor who has never taken a differential pressure gauge out of their truck does not know what their equipment will actually deliver in your home.
Sealing and insulating ductwork in an unheated space
A crawl space is not heated. Every unsealed foot of ductwork loses conditioned air there, and every uninsulated duct generates condensation there in summer. We redid the joints with aluminum tape and mastic at critical points, checked the continuity of the insulation, and resealed the polyethylene vapor barrier where the refrigerant lines had torn it. A vapor barrier left open in a coastal crawl space leads to moisture, condensation on the ducts, and eventually mold on the subfloor.
The integrated electric auxiliary heater: what the client calls “the electric furnace”
The house is fully electric. There is no fuel-burning appliance to take over below the balance point, so an integrated electric auxiliary heater was required in the air-handler cabinet.
This resistance coil plays three distinct roles, which are worth separating:
- The deep-cold supplement, below the home's balance point.
- Tempering during defrost. When the outdoor unit reverses its cycle to defrost, the air blown indoors cools down. Without auxiliary heat, you feel a draft of cold air from the vents. This is the main source of complaints after converting to a central heat pump, and it is avoidable.
- Backup heat in the event of a heat pump failure.
Two installation precautions. First, adding an electric heat kit changes the cabinet's MCA and MOP: the values on the datasheet (4.7 A MCA and 15 A MOCP for the indoor unit alone) no longer apply, and the circuit must be recalculated and protected accordingly. Second, the auxiliary heat must be interlocked so it cannot operate while the heat pump is sufficient. Poorly sequenced auxiliary heat that engages with every call for heat turns a heat pump with a COP of 3.6 into a very expensive electric baseboard heater. The FLEXX is controlled with a conventional 24 VAC thermostat, which makes this configuration simple—provided someone actually sets it up that way.
On the outdoor side, the GUD36W2/NhE-D(U) unit requires an MCA of 27.7 A and an MOCP of 30 A. In an older lakeside home with a 100 A service entrance, this circuit together with the electric auxiliary heat warrants a panel load calculation before signing, not on the day of installation.
Brazing and safety in a confined space
Brazing copper in a crawl space surrounded by plywood, fiberglass insulation, and polyethylene requires particular discipline:
- Nitrogen purging during brazing, to prevent copper oxide scale from forming inside the pipes—the contaminant that eventually ends up in the expansion valve and compressor.
- Heat shields and removal of combustible insulation within the work area.
- Post-brazing monitoring before leaving the space, with a fire extinguisher within reach.
- Maximum prefabrication outside the confined space, to reduce the number of joints made on site.
- Nitrogen pressure test, followed by evacuation with a micron gauge and a standing vacuum test, before opening the valves.
The refrigerant line for this project remained under the 7.5 m (24.6 ft) precharge length, so no refrigerant had to be added. Beyond that, add 0.32 oz/ft (30 g/m) for this unit size, weighed on a scale and recorded on the unit label. The maximum permitted length is 30 m (98.4 ft), with a maximum elevation difference of 15 m between the two units.
What this Saint-Mathias-sur-Richelieu project changes for your project
The mistakes we see most often in crawl spaces
- Choosing the capacity before measuring the space. The 4-ton cabinet will not fit everywhere, and, more importantly, it cannot be removed everywhere.
- Installing the unit directly on the subfloor, without supports, in a space exposed to ground moisture.
- Failing to install the condensate pump's safety switch.
- Ignoring the A2L volume calculation because “it's just a crawl space.”
- Keeping a filter or purifier without measuring the static pressure it places on the new blower.
- Failing to reseal the vapor barrier after the lines and wiring have been routed through.
- Leaving the electric backup heat free to operate, which wipes out the advertised savings on the very first winter bill.
Rebates, certification, and warranty
The installed system combination bears AHRI number 217120759 and is ENERGY STAR certified. These are the two elements that financial assistance programs verify. Eligibility criteria, amounts, and the programs themselves change from year to year: we systematically confirm the eligibility of the exact model and exact configuration before the contract is signed, rather than announcing an amount that will not hold up.
As for the warranty, the FLEXX line is covered for 10 years as standard, with 2 additional years when the product is registered and proof of installation is provided. We complete this registration for our customers; it's the kind of formality worth two years of coverage that too many installers let slide.
Where we work
At AirGreen, we carry out this type of HVAC installation in Saint-Mathias-sur-Richelieu, Chambly, Richelieu, Marieville, Otterburn Park, Mont-Saint-Hilaire, and throughout the South Shore, as well as in Montreal, Laval, Longueuil, and on the North Shore. Crawl-space, low-attic, and restricted mechanical-space projects represent a significant share of our work, and we approach them with systematic preliminary measurements—because in these spaces, a decision made by guesswork comes at a cost throughout the system's entire service life.
If your project looks like this one, the first question to ask us is not the unit's price: it's how many inches of clearance you have beneath your joists.