Central Heat Pump ADD-ON ARCOAIRE R4H5S Economy | 3.5 Tons - 42,000 BTU (Coil EVD4X 17.5 in.) - R410A

Keep what works in the house and add what is missing

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 R4H5S Economy | 3.5 Tons - 42,000 BTU (Coil EVD4X 17.5 in.) - R410A pairs the R4H5S42AKAAA outdoor unit with the EVD4X42M17A coil.

The ADD-ON starts from a simple observation: in many homes, the electric furnace and the ducts still have good years ahead of them. It would be a shame to replace them only to get air conditioning and more efficient heating. This pairing adds a central heat pump to the existing system and leaves in place everything that is still in good condition.

What you keep

• The electric furnace, whose heating elements become the backup for the coldest days.
• The duct system, the supply registers and the return air grilles.
• The filter rack and the filter format you already know.
• Accessories connected to the furnace, such as a humidifier, in most cases; we check their position relative to the coil.
• The thermostat location, even though the device itself changes.

What the installation adds

• The R4H5S42AKAAA outdoor unit, on a stand above the snow line.
• The EVD4X42M17A coil, a 17.5 in. format, placed on the furnace's air outlet.
• An insulated refrigerant line set between the outdoor unit and the coil.
• A condensate drain to the floor drain or a pump.
• A dedicated circuit and an outdoor disconnect.
• A heat pump thermostat that controls the heat pump and brings in the furnace's electric elements as auxiliary heat.

If an old central air conditioner already had its coil and line set, we assess what can be kept. The coil itself is replaced, since it must now work in heating as well as cooling.

The furnace: what we check before proposing an ADD-ON

An ADD-ON is only worthwhile if the furnace that goes with it is reliable. During the visit, we examine:

• the age and general condition of the furnace, along with its maintenance history;
• the width of the cabinet, to match it to the 17.5 in. coil;
• the blower: type of motor, speeds available and ability to deliver the airflow the coil requires;
• the clearance above the furnace, since the coil fits between the air outlet and the plenum;
• the condition of the heating elements and their connections, and the compatibility of the furnace control with a heat pump thermostat that manages auxiliary heat.

When an ADD-ON is not the right choice

We sometimes advise against this type of installation. A furnace at the end of its life, a blower unable to deliver the required airflow or a duct system too small for air conditioning turn a simple addition into a series of compromises. In those cases, a central heat pump paired with a new air handler, which replaces the furnace, is often the most sensible long-term solution.

If the furnace shows signs of advanced wear, such as heating elements that keep failing, electrical connections that have overheated or a tired blower, it is better to settle that question before adding anything to it. We would rather tell you during the visit than install a new coil on equipment that will need replacing shortly after.

The Economy series

The name Economy designates the series of the R4H5S42AKAAA unit in the Arcoaire lineup. The EVD4X42M17A coil is the same as in the other series of this size; it is the outdoor unit that changes. In an ADD-ON, the furnace's electric elements handle the coldest days: the heat pump concentrates on summer cooling and on heating in the shoulder seasons, and the choice of series becomes a matter of priorities.

The series name does not tell the whole story, though. What counts are the ratings of the pairing, and we confirm them before the quote.

System ratings

The pairing of the R4H5S42AKAAA 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.

This page therefore shows no efficiency rating. The confirmed ratings, provided in writing, let you compare this series with the other options of the same size on a concrete basis.

The 3.5-ton size

This size often suits a family home of good size: a two-storey house with a finished basement in Laval, a split-level on the South Shore, an extended bungalow. These examples are only a guide, since insulation, windows and airtightness change the load. Because the furnace's electric elements cover the deep cold, we size the heat pump on the cooling load, established by a room-by-room load calculation: an oversized unit cools in short cycles and dries the air poorly.

Winter and summer, day to day

In mild and cool weather, the heat pump heats alone. When the cold deepens and it can no longer keep up, the thermostat brings in the furnace's electric elements as auxiliary heat; in deep cold, they carry the heating. The point at which the backup comes in is set according to the heat loss of the house and your preferences; we set it at commissioning. The air delivered by the heat pump is less hot than the air from the electric elements and the cycles are longer: this is normal. During defrost cycles, a plume of vapour comes out of the outdoor unit, and the furnace's elements may come on briefly to keep the supply air comfortable.

In summer, the same unit cools the whole house through the existing ducts. The coil removes humidity from the air, and the water goes to the condensate drain. If the upper floor stays warmer than the main floor, we look at register balancing and return air during the visit.

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.

On site, the order of work stays the same: installation of the coil and drain, installation of the stand and outdoor unit away from roof drip, routing of the line set, electrical connection, then commissioning with a nitrogen pressure test, vacuum, and adjustment of the R-410A charge, the airflow and the thermostat's auxiliary heat setting.

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.

The filter stays where it was, at the furnace inlet. It now also protects the coil: a clogged filter reduces the airflow and the capacity of the system, summer and winter. The electric furnace keeps its usual maintenance, centred on the blower, the heating elements and their connections.

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 R4H5S Economy | 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.