Central Heat Pump ADD-ON ARCOAIRE H4H5S ION | 3.5 Tons - 42,000 BTU (Coil EVD4X 17.5 in.) - R410A

An outdoor unit that works all winter, placed accordingly

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's electric elements are only used as backup. The Central Heat Pump ADD-ON ARCOAIRE H4H5S ION | 3.5 Tons - 42,000 BTU (Coil EVD4X 17.5 in.) - R410A pairs the H4H5S42AKAAA outdoor unit with the EVD4X42M17A coil.

A central air conditioner spends the winter switched off. A heat pump works outside in cold weather, under snow and freezing rain. The location of the outdoor unit therefore becomes a major decision in the project, just like the choice of size. This page explains how we choose it.

What happens outside while the house is heating

In heating mode, the outdoor unit captures the heat contained in the outdoor air, even cold air, and the R-410A carries it to the coil on the furnace. The outdoor unit's coil then becomes colder than the surrounding air, and the air's moisture settles on it as frost. To clear it, the heat pump runs short defrost cycles: a plume of white vapour rises from the unit, and you may hear a brief whoosh when the reversing valve changes position. Both are normal.

In summer, the role reverses: the unit rejects outside the heat removed from the house. In both seasons, it needs open air around it to run normally.

Above the snow, away from ice

A unit set on the ground can end up buried after a storm, or blocked by snow sliding off the roof or pushed aside when clearing the driveway. We install it on a stand that keeps it above the usual snow line on your property, taking into account the snowbanks that clearing creates every winter.

The stand also deals with water. During defrost, the water draining from the unit must be able to get away. On a raised unit, it falls to the ground and runs off; on a unit at ground level, it can freeze under the equipment and form a block of ice that interferes with its operation. We also avoid placing the unit above a walkway or stairs, where that water would freeze in the path.

Roof drip and wind

Water falling from a roof without a gutter, or from an overflowing gutter, freezes in layers on the unit and can damage the fins or the fan. We place the unit outside the roof's drip line, or plan protection when the location leaves no other option.

Wind matters too: a corner of the house exposed to prevailing winds collects snow and blows it onto the unit. A sheltered but not enclosed location is preferable. The unit must keep the clearance specified by the manufacturer all around it, with no hedge, fence or shed blocking the airflow.

Neighbours, windows and municipal rules

A heat pump that runs in winter also runs at night. We avoid placing it under a bedroom window, yours or your neighbour's, or near outdoor sitting areas. The municipalities and boroughs of Montreal, Laval and Longueuil often regulate the location of outdoor equipment: setbacks from property lines, front-yard restrictions, a visual screen in some cases. We check these rules for your address before setting the location.

The 3.5-ton size and the ION series

The 3.5-ton size often serves a large house on two levels, a two-storey home with a finished basement or an extended semi-detached house on the North Shore. These examples are only a guide: insulation, windows and airtightness change the load, which we establish with a room-by-room load calculation. Because the furnace's electric elements cover the coldest days, the heat pump is sized on cooling, which avoids the short cycles of an oversized unit.

The H4H5S42AKAAA unit is part of Arcoaire's ION series. For this size, the same EVD4X42M17A coil goes with several series of outdoor units; the ratings of each pairing are confirmed before the quote.

System ratings

The pairing of the H4H5S42AKAAA outdoor unit and the EVD4X42M17A 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.

We give them to you in writing with the quote. No rating is shown on this page, since there is no certificate for this exact pairing.

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.

Installation on the existing furnace

The coil sits on the furnace's air outlet, and a compatible thermostat decides when the heat pump heats alone and when the electric furnace takes over. We check the condition of the furnace, the airflow of its blower and the duct sizes before the quote. The outdoor unit goes on a stand, above the snow line, on a dedicated circuit.

Inside: the 17.5 in. coil and the heat pump thermostat

In the basement, the EVD4X42M17A coil sits between the furnace's air outlet and the plenum. Its 17.5 in. format must match the width of the furnace cabinet; when needed, a sheet-metal transition joins them. The coil has its own condensate drain: in summer, it removes humidity from the air in the house, and that water drains to the floor drain or a condensate pump.

The heat pump thermostat decides when the heat pump is enough and when backup is needed. In cool weather, the heat pump works alone; when the cold deepens, the thermostat brings in the furnace's electric elements as auxiliary heat, and in deep cold, they take over. The auxiliary heat threshold is set at commissioning, according to the heat loss of the house and your comfort. The heat pump's air is less hot than the air from the electric elements, and its cycles are longer: this is normal.

The line set route

The refrigerant line set connects the outdoor unit to the coil. It passes through the wall via an opening that we seal against air and water, then runs to the furnace by the most direct and tidy route possible. The suction line is insulated along its entire length to prevent condensation in summer and losses in winter. Outside, a line cover protects the line set from sun and impacts when the location calls for it.

The joints are brazed under nitrogen, then the line set undergoes a pressure test and a vacuum before the refrigerant charge.

Electrical: dedicated circuit and disconnect

The outdoor unit is fed by a dedicated circuit from the electrical panel. An outdoor disconnect, installed within sight of the unit, lets it be de-energized for maintenance. Before the quote, we check that the panel has the required space and capacity, taking into account the electric furnace that stays connected for backup; if a modification is needed, the quote spells it out. A control cable also connects the outdoor unit to the furnace and the thermostat.

Maintenance

Replace the system filter according to its format, keep the outdoor unit clear of snow and leaves, and plan annual HVAC maintenance of the coil, condensate drain and electrical connections. In winter, white vapour during defrost is normal.

After a storm, clear the snow around and on top of the unit by hand or with a broom, without an ice pick or metal shovel that could damage the fins. Do not cover the unit for the winter: it must be able to run at all times.

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 | 3.5 Tons - 42,000 BTU (Coil EVD4X 17.5 in.) - R410A. We assess the home room by room and confirm the right size and your grant eligibility before signing.

Available while supplies last.

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