The Heat Pump Installation Process, Step by Step

The heat pump installation process runs in a fixed order: load calculation, equipment selection, duct evaluation, outdoor unit placement, refrigerant piping, pressure testing, evacuation and charging, electrical and controls, commissioning, then inspection and handoff. For a ducted system on usable ducts, the on-site work usually takes one to three days. Each step depends on the one before it.

The Seattle Heat Pump Company plans and manages ducted heat pump installations across Seattle and King County, and the work is carried out by licensed and insured contractors. This guide walks through each step in order, explains why skipping or rushing one shows up later, and ends with the commissioning checklist worth asking about on any quote.

Before installation day

Load calculation to equipment selection

Everything starts with the house. A room-by-room Manual J calculation finds the heating load at Seattle’s 24°F design temperature and the cooling load at 83°F. Manual S then picks a specific model whose published capacity at those conditions meets the load without oversizing, as Seattle’s energy code requires. The size is an output of this step, not something copied from the old furnace. The sizing guide explains the calculation.

Equipment selection to duct evaluation

The chosen equipment sets the airflow the ducts must carry. A heat pump delivers air at a lower temperature than a gas furnace, so it moves more air to deliver the same heat. A static pressure test with the blower running shows whether the existing return and supply ducts can carry that airflow. If they cannot, the scope adds duct work, or the equipment choice changes. The order matters: choosing equipment and only then discovering that the ducts cannot feed it is how comfort complaints start. See heat pumps with existing ductwork.

Electrical, siting and permits

The panel and service are checked against the heat pump and any backup heat strips, which decides whether a new circuit is enough or an upgrade is needed; the electrical panel guide covers that. The outdoor unit location is chosen for airflow, service clearance, a short line set route and Seattle’s noise limits, which put a side-yard unit through a noise review. Then the permits are filed: refrigeration, electrical, and furnace or mechanical when the indoor equipment changes. The Seattle permit guide lists each one.

Installation day, step by step

1. Removal and refrigerant recovery

Any old outdoor unit has its refrigerant recovered into a cylinder before it is disconnected; venting it is illegal. An old furnace or air handler being replaced comes out. In older houses, the Puget Sound Clean Air Agency requires an asbestos survey before renovation, and old duct wrap or furnace insulation is where that usually matters.

2. Unit placement to mounting

The outdoor unit goes on a level pad or a wall bracket. The mount keeps the unit stable and off wet ground, lets defrost water drain away from the base, and isolates vibration so the unit does not hum through the house or the ground. Sea-Tac averages about 6.3 inches of snow a year, so in the city a modest riser is usually enough; higher, colder sites can call for more.

3. Indoor equipment and ducts

The indoor coil goes on top of the existing furnace, or a new electric air handler replaces the furnace. Duct changes from the evaluation happen now: a new return, a resized transition, sealed joints. A new filter rack goes in where the old one was inadequate.

4. Refrigerant piping to pressure testing

The refrigerant line set runs between the units, either new copper or a reused set that the manufacturer permits and that is the right size. Brazed joints are made with nitrogen flowing through the pipe, which keeps oxide scale from forming inside the copper where it would later circulate through the system. The finished line set is then pressurized with nitrogen and held to find leaks before any refrigerant is at stake.

5. Evacuation and charging

A vacuum pump pulls the system down to a deep vacuum, measured with a micron gauge, which boils off moisture and removes air. The vacuum is then isolated and watched: if the reading climbs, something is leaking or still wet. Only after it holds is the factory refrigerant charge released. The charge is then adjusted for the line set length using the manufacturer’s method. Since January 1, 2026, new equipment in Washington uses refrigerants such as R-454B, with handling rules of their own; the refrigerant guide covers them.

6. Electrical connections to controls

A dedicated circuit and an outdoor disconnect power the outdoor unit. An electric air handler gets its own circuit, larger if it holds backup heat strips. Low-voltage control wiring connects the thermostat, the indoor equipment and the outdoor unit, including the outdoor temperature reading the controls need for backup heat lockouts.

7. Condensate

In cooling mode, the indoor coil pulls water out of the air. A drain line with a trap carries it to a floor drain, a pump or outside, and an overflow switch or secondary pan protects against a blocked drain. Water damage from a clogged condensate line is one of the most avoidable problems in a heat pump installation.

Commissioning: the checklist

Commissioning is the step that confirms the installed system matches the design. It is also the step most easily skipped, because a system can run without it.

Airflow setup to commissioning

Airflow comes first because everything else depends on it. The blower speed is set for the equipment and the ducts, then static pressure and the temperature change across the coil are measured to confirm the air handler is moving roughly what the design called for. Refrigerant charge readings are only meaningful once airflow is right, which is why airflow is set before charge is verified.

The full checklist

• Airflow: blower setting, external static pressure, temperature split across the coil
• Charge: verified by the manufacturer’s method, with pressures and line temperatures recorded
• Heating and cooling: each mode run and recorded, including supply and return air temperatures
• Defrost: the defrost cycle forced or observed, with the outdoor coil clearing as it should
• Backup heat lockout: supplemental heat kept off above 40°F and the lockout set at 35°F or lower, as Seattle’s energy code requires at final inspection
• Condensate: water poured into the pan to confirm the drain flows and the overflow switch works
• Thermostat handoff: system type, staging, lockouts and recovery configured for a heat pump, then explained to you

The backup heat settings guide explains the thermostat side in detail.

Inspection and handoff

Commissioning to performance verification

Commissioning records become the system’s baseline. The final inspection checks the installation against the permits and the code, including that lockout setting. The walkthrough with you covers what normal looks like: warm rather than hot supply air, long gentle run times on a variable-speed system, and defrost cycles with a cloud of steam from the outdoor unit in damp weather near freezing. Knowing that keeps a normal defrost from looking like a failure. Over the first weeks, rooms that run warm or cool can be balanced with dampers if the design included them.

The recorded numbers also help any technician later, because a change from the baseline points to what has shifted. The maintenance guide covers the owner’s side of keeping the system near that baseline.

How long each part takes

Before work starts, the assessment, the design, permits and equipment availability set the lead time. On site, a straightforward ducted installation on usable ducts usually takes one to three days. Duct rework, a panel or service upgrade, or an oil tank decommissioning on a conversion adds time, and inspections follow the permit schedule.

To understand what each component does, see how a ducted heat pump works. To check that a quote includes these steps, use the quote comparison guide. For the full service, see ducted heat pump installation.