Central Heat Pump ADD-ON ARCOAIRE H4H5S ION | 3 Tons - 36,000 BTU (Coil EVD4X 17.5 in.) - R410A

Choosing three tons for the right reasons: the load calculation comes first

The ADD-ON system adds a heat pump to an existing electric furnace: a coil is installed on the furnace and the outdoor unit heats and cools through the same ducts. The furnace is only used as backup, through its electric elements. The Central Heat Pump ADD-ON ARCOAIRE H4H5S ION | 3 Tons - 36,000 BTU (Coil EVD4X 17.5 in.) - R410A pairs the H4H5S36AKAAA outdoor unit, from the ION series, with the EVD4X36M17A coil.

A large house does not automatically call for a large heat pump. In an ADD-ON system, the size is chosen according to a precise logic, and the load calculation is what says whether 3 tons is the right choice for yours. This page explains that logic, then what the installation includes.

Two loads to calculate, not one

Every house has two distinct needs: the heat to supply in winter to make up for its losses, and the heat to remove in summer to stay cool. In Quebec, the first is almost always larger than the second. A heat pump sized to cover the deep cold on its own would therefore be too big for summer.

The ADD-ON system resolves this dilemma: since the furnace's electric elements cover the coldest nights, the heat pump is sized first on cooling, while checking that it carries a good share of the heating the rest of the year. The result is a unit that is right for summer, and a house that stays warm in winter.

What we measure, room by room

The load calculation is not based on floor area alone. During the visit, we record for each room the exterior walls and their insulation, the attic or roof above, the size and orientation of the windows, the overall airtightness of the house and how the rooms are used: an open kitchen, an office full of equipment or a glassed-in sunroom do not behave like a north-facing bedroom. The basement, partly below ground, is counted separately.

This survey gives two results: the size of the heat pump, and the airflow each room must receive. The second is then used to check the ducts and to balance the dampers at commissioning.

Why an oversized unit hurts comfort

An oversized unit reaches the setpoint in a few minutes, shuts off, then starts again. These short cycles do not give the coil time to remove humidity: the house is cool, but clammy. They also create differences between the rooms near the thermostat and the others, and they wear the components more. In an ADD-ON system, an oversized unit causes another difficulty: it asks the furnace blower for more air than it can deliver.

When three tons is the right choice

The 3-ton size suits roomy homes whose cooling load justifies it: a large cottage, a bungalow with a large finished basement, an open-plan house with many south- or west-facing windows. If the house already has a central air conditioner of this size that cooled it well, that is a useful clue; if it cooled in fits and starts, that is one too. A recent, well-insulated house, even a large one, is sometimes fine with the next size down.

Summer: cool, dry air

In cooling mode, the cold coil removes heat and humidity from the air; the condensed water flows through a drain to a floor drain or a pump. Summer is when the right size shows the most: a properly sized unit runs in long, steady cycles, keeps humidity low and spreads cool air all the way to the rooms far from the furnace. In an open-plan house, large windows exposed to the afternoon sun call for well-placed supplies; we check their position and the return air during the visit.

What the size changes for winter

A heat pump moves heat instead of producing it. In winter, its refrigerant, R-410A, captures heat from the outdoor air and delivers it to the coil; in summer, a reversing valve flips the cycle. The colder it gets, the less heat it captures, while the house loses more. The point where the two cross determines when the furnace's elements must take over: a properly sized heat pump pushes that moment fairly deep into winter, without being too big for summer.

The thermostat manages this handover: it brings in the furnace's electric elements as auxiliary heat when the heat pump is no longer enough, and leaves them off the rest of the time. During defrost, they may heat for a few minutes so that the air from the grilles stays warm. This pairing does not carry the cold-climate designation; the furnace's elements cover the coldest nights.

The furnace and the ducts must keep up

We check the condition of the furnace, the airflow of its blower and the duct sizes before the quote. A 3-ton coil requires substantial airflow: the furnace must be able to deliver it, and the ducts, especially the returns, must be able to carry it. The 17.5 in. coil is set on the furnace's air outlet; if it does not line up with it, we fabricate a sealed transition. If duct adjustments are needed, they appear in the quote.

System ratings

The pairing of the H4H5S36AKAAA outdoor unit and the EVD4X36M17A coil is not listed with SEER2 ratings in the AHRI certification directory. We confirm the ratings of the complete system before the quote; they also determine grant eligibility. This page therefore publishes no rating figure.

LogisVert

This pairing does not carry an amount on Hydro-Québec's LogisVert list of October 19, 2026. If the grant matters for your project, we will point you to an eligible pairing of comparable size. Our page on the grant for efficient heat pumps summarizes the program's conditions.

Installation by AirGreen

The work and commissioning

• Coil: set on the furnace's air outlet, connected to the plenum, condensate drain to a floor drain or a pump; relocation of a humidifier mounted on the plenum if applicable.
• Outdoor unit: on a bracket or a pad, above the snow line, away from roof drips, dryer vents and bedroom windows.
• Refrigerant line: insulated copper, brazing, pressure test and vacuum before the valves are opened.
• Electrical: dedicated circuit, outdoor disconnect, check of the panel, which already carries the electric furnace's elements, and control wiring.
• Thermostat: a model that manages the heat pump and electric auxiliary heat, since a furnace-only thermostat cannot control a heat pump.
• Commissioning: refrigerant charge, airflow according to the load calculation, defrost, the furnace's elements coming in and balancing of the dampers.

Maintenance and warranty

The furnace filter now works all year: check it every month and replace it according to its format. Keep the outdoor unit clear of snow and leaves, without covering it in winter. Plan annual HVAC maintenance of the coil, the condensate drain and the electrical connections, in addition to a check of the electric furnace and its elements. In winter, white vapour during defrost is normal.

Warranty: 10 years on the compressor, 10 years on parts and 6 years on labor.

AirGreen, for the life of the installation

A family business active for more than fifteen years in Montreal, Laval, Longueuil, the North Shore and the South Shore, we hold RBQ licences for ventilation, refrigeration and electrical work and carry $5,000,000 in liability insurance. The in-home assessment is free, the quote is in writing, and our financing options let you choose the right unit rather than the cheapest one.

Request your free estimate for the Central Heat Pump ADD-ON ARCOAIRE H4H5S ION | 3 Tons - 36,000 BTU (Coil EVD4X 17.5 in.) - R410A. We do the load calculation room by room and confirm the right size and your grant eligibility before signing.

Available while supplies last.