An older home, a seven-foot basement, and ductwork inherited from three generations: that was where the real work lay
At At Sainte-Brigide-d'Iberville, the house welcoming us that morning had seen several heating systems come and go. A brick chimney still runs through the basement from end to end, a remnant of an earlier era. A cast-iron drainpipe runs down along the wall. The joist ceiling leaves barely seven feet beneath the beams, and slightly less beneath the ducts.
On the other side of the door, three metres from the work area, was a family room with hardwood flooring, a sofa, and children. The family was living in the house during the work. This detail changes the way you work just as much as the available height.
The mandate: replace an electric furnace with a GREE FLEXX R32 central system capable of heating and cooling the entire home, without redoing the ductwork, raising the ceiling, or requiring the family to leave the premises.
What we measured before ordering anything
Conversions in older homes almost always fail for the same reason: the equipment is chosen before the ductwork is understood. Our survey covered five points.
The actual clear height, not the advertised height
We systematically measure three heights: below the joists, below the existing ducts, and below the lowest point along the unit’s incoming path. In an older home, these three measurements differ, sometimes by several inches, and the lowest one determines everything.
The condition and size of the existing ductwork
The main trunk dated back to a previous conversion. It was usable, but with two caveats: connections added over the decades without a comprehensive review, and a return whose size was marginal for a system with sustained airflow.
The slab’s levelness
The original concrete slab had significant variations and a damp low spot. Placing a 90 kg unit directly on an uneven surface guarantees a twisted unit, panels that no longer close properly, and a condensate pan that does not drain on the correct side.
Older materials
In homes built before the 1980s, insulation and tapes installed on ducts should be inspected before any dismantling. We never assume what they are made of and adapt the removal method accordingly. This is a reflex every contractor should have, but too few apply it.
Electrical capacity
An existing electric furnace frees up amperage when it is removed, but the distribution between the new indoor unit, the auxiliary heating elements, and the outdoor unit must be recalculated, not carried over.
The selected unit: GREE FLEXX R32, indoor unit GUD60AH2/G-D(U)
The volume to be heated, the envelope of an older construction, and the number of existing connections led us to choose the 5-ton format.
| Feature | Data |
|---|---|
| Rated cooling capacity | 54,000 BTU/h |
| Rated heating capacity | 53,000 BTU/h |
| Heating modulation range | 35,000 to 60,000 BTU/h |
| HSPF2 | 10,5 — the best seasonal heating efficiency in the entire FLEXX R32 range |
| SEER2 | 18,5 |
| EER2 | 11,7 |
| COP | 3,4 |
| AHRI number | 217120762 |
| Certification | ENERGY STAR |
| Heating range | -30 °C to 24 °C |
| Factory R32 charge | 4.6 lb (162.3 oz) |
| Cabinet dimensions | 24 4/5 × 52 1/16 × 21 1/4 in (630 × 1320 × 540 mm) |
| Net weight | 199.5 lb (90.5 kg) |
The 10.5 CPSC2 deserves attention. It is the rating that reflects actual performance over a complete heating season, including October thaws and January nights. In an older home, where the envelope allows more heat to escape than a recent construction, it is the indicator with the greatest impact on the annual bill—more than cooling efficiency, despite the emphasis it usually receives in sales pitches.
The 35,000 to 60,000 BTU/h modulation range in heating also allows the unit to follow the home's actual needs instead of operating at full capacity or not at all, as the replaced electric furnace did.
The installation: three interventions that are not visible in a completed photo
The base: compensating for a slab that was never level
The unit does not rest on the concrete. We built a sheet-metal base, leveled it using calibrated shims at the support points, and then sealed it. This base serves three purposes:
- Leveling the unit, which is essential for proper drainage of the condensate pan.
- Raising it above the slab in a basement where water damage remains possible.
- Break between the concrete and the cabinet, which limits vibration transmission through the structure — an especially important point because an occupied room is located behind the partition.
In the site photo, the wooden shims are still visible beneath the base: they are used for adjustment before permanent fastening.
The plenum transition beneath low joists
This was the sheet-metal piece that took the most time. Only a few inches remained between the unit's supply outlet and the existing main trunk. The transition was custom-fabricated, adjusted on site, and then sealed with aluminum tape at all its joints.
An overly abrupt transition at the outlet of a unit creates turbulence, resulting in noise from the upstairs registers and a pressure loss that cannot be recovered later. We always favor the gentlest angle allowed by the available height, even if that means fabricating a one-off piece instead of assembling standard components.
The refrigerant line along the joists
The insulated piping, visibly running up along the cabinet, is secured at regular intervals, with no stress points and the bend radius respected at every change in direction. The insulation is continuous, with no interruption at the attachment points — a common defect that causes localized condensation in summer, followed by moisture marks on the joists that the owner will attribute to a roof leak.
The diameters comply with the manufacturer's specification for this format: 3/8 in. for the liquid line, 3/4 in. for the gas line. The system accommodates up to 98.4 ft (30 m) of piping and 49.2 ft (15 m) of elevation difference between the units, with a precharge covering 24.6 ft (7.5 m) and an additional charge calculated at 0.22 oz per foot beyond that.
Working in an occupied home
The family stayed on site during the two days of work. Our method under these conditions:
- Work area demarcation and protection of the threshold leading to the finished room.
- Source extraction when cutting sheet metal, rather than sweeping afterward.
- Planned and announced power outage, limited to time periods agreed upon with the occupants.
- Restoring the heating by the end of the first day, even partially, rather than leaving the house cold overnight.
- Complete removal of debris and the old equipment at the end of the work, without leaving material behind a wall or under a staircase.
This last point seems obvious. It is not: during our HVAC maintenance visits, we regularly find sections of old ductwork or pieces of equipment abandoned by the previous installer in a crawl space.
What an older home requires beyond a recent construction
External static pressure, the indicator almost no one measures
A central system is designed to operate within a specified static-pressure range. In an old system modified through successive additions, this pressure frequently exceeds the permissible value without anything making it noticeable by ear.
The consequences are tangible: reduced airflow, temperature differences between rooms, a fan that consumes more power, and actual seasonal efficiency far below the rated efficiency. The unit lists 18.5 TRÉS2 on its specification sheet but delivers significantly less in the home.
We measure static pressure during commissioning and record the value. When it falls outside the range, the correction involves the return air, the filter, or reworking a connection—never increasing the fan speed, which masks the symptom and amplifies the noise.
Five key practices for a conversion in an older home
- Measure before making promises. Clear height, duct dimensions, slab levelness, electrical capacity. An estimate prepared without an on-site survey is an estimate that will be revised during the work.
- Address the return air first. It is almost always the weak link in an old system, and it is the first thing to correct.
- Always level the unit. A level cabinet drains properly, closes properly, and lasts longer.
- Do not inherit the previous sizing. The capacity of the old electric furnace is not a design specification; it is an inheritance.
- Have old materials inspected before dismantling any original ductwork or insulation.
Financial assistance programs in 2026
This type of conversion may provide access to Hydro-Québec's LogisVert program, whose assistance for central air-to-air systems is calculated per 1,000 BTU/h increment, as well as the Rénoclimat program, which can be combined with it for the home's energy assessment component.
The conditions to be met:
- Existing residence in Quebec served by Hydro-Québec.
- ENERGY STAR certified appliance — the FLEXX R32 range is fully certified.
- AHRI number corresponding to the exact installed match, here 217120762.
- Contractor holding an RBQ licence and registered with the program.
- Application submitted within the prescribed period after invoicing.
An older home offers an indirect advantage here: a Rénoclimat energy assessment often reveals insulation and air-sealing improvements that, when completed at the same time as the conversion, improve the new system's efficiency and may open the door to additional financial assistance. We systematically discuss these options with the homeowner when preparing the quote. Finally, note that the Chauffez vert program does not apply here, as it is intended for replacing oil- and propane-fired systems.
Recommended maintenance
- Filter: quarterly inspection and replacement based on the observed buildup.
- Condensate pan and drain: annual flushing and inspection of the base's level.
- A2L leak sensor: functional test at every visit.
- Outdoor coil: annual cleaning and winter snow removal.
- Static pressure: new measurement after any added connection or change in filter type.
- Electrical connection tightening: annual inspection, particularly on auxiliary heating circuits.
Our service areas
Sainte-Brigide-d'Iberville is part of the kind of rural Montérégie community where homes are older, properties are spacious, and winters are unforgiving. We work there just as we do in Saint-Césaire, Farnham, Iberville, Saint-Alexandre, Ange-Gardien, and throughout Haut-Richelieu.
At AirGreen, we design, install, and maintain HVAC systems in Montréal, Laval, Longueuil, the North Shore, the South Shore, and throughout Montérégie. A well-chosen central heat pump cannot compensate for a poorly assessed duct network: that is why every electric furnace replacement project begins with us with a complete assessment of the home and ends with measurements recorded during commissioning.