20.2 Installing Split & Package Heat Pumps

20.2 Installing Split & Package Heat Pumps

The next Trade Area C cluster is installing split and package heat pumps: cycles, condensers (outdoor coils), air handlers, refrigerant piping, insulation, thermostats, heat strips, condensate, overflow protection, and fire stats. Everything in 20.1 still applies — nitrogen purge, evacuation, 307 drains, 301.15 wind, Class B 25 tons / 500,000 Btu. This section is the reversible cycle and the electric heat that must not steal the job from the compressor.

Quick Answer: A heat pump moves heat both ways. The reversing valve decides which coil is the condenser. Size on cooling (FBC Energy R403.7.1.2.1, 1.15 cap). Supplementary electric heat is locked out except for the R403.1.3 conditions (cannot meet setpoint, defrost, compressor or thermostat failure). Install an outdoor thermostat, firestats on the strips, both-line insulation, and the same 307 condensate/overflow stack as a cooling coil.

The heat-pump cycle — reversing valve and coils

A heat pump is not “an air conditioner with strips.” It is a vapor-compression machine with a four-way reversing valve in the discharge line. In cooling, the outdoor coil is the condenser and the indoor coil is the evaporator — identical to Section 20.1. In heating, the valve reverses the flow: the indoor coil is the condenser (it rejects heat to the room) and the outdoor coil is the evaporator (it absorbs heat from outdoor air, even at 40°F). Refrigerating effect still happens; it just happens outdoors.

Most U.S. split heat pumps energize the reversing valve on the thermostat O terminal in cooling. Some brands (commonly Rheem/Ruud family) energize B in heating. Installing a cool-only thermostat, or landing O when the outdoor unit wants B, leaves the valve in the wrong position all season. Package heat pumps use the same valve inside the cabinet; you still have to land O/B correctly on the low-voltage strip.

Outdoor unit / condenser on a heat-pump drawing is the outdoor heat exchanger. Give it the listing’s airflow clearances in both modes. Recirculated discharge that hurt cooling in 20.1 also starves heating capacity and drives frost. Air handlers are the indoor coil plus blower, often with a heat-strip kit in the leaving-air section. Package heat pumps put that stack in one rooftop or pad cabinet, still with supply/return ducts, still with 301.15 wind anchorage, still with a drain pan.

Defrost. When the outdoor coil is the evaporator, moisture freezes on it. Time-temperature defrost runs a clock plus an outdoor coil sensor; demand defrost looks at coil temperature versus outdoor air or at pressure/delta-T and defrosts only when needed. During defrost the reversing valve shifts toward cooling, the outdoor fan often stops so the hot gas can melt the ice, and the indoor coil briefly gets cold — which is why auxiliary heat strips are usually brought on during defrost to temper the supply air. That strip operation during defrost is allowed by R403.1.3. Running strips whenever the owner bumps the setpoint 2°F on a 65°F Tampa afternoon is not.

Piping, insulation, charge — both legs matter

Field piping on a split heat pump is still a liquid line and a vapor line, still nitrogen-purged, still nitrogen pressure-tested, still evacuated, still charged to the nameplate. Oil return still cares about suction velocity — and in heating the “suction” is at the outdoor coil, so vertical outdoor risers and long equivalent lengths still belong on the manufacturer’s table.

Insulation differs from cool-only. In cooling the large vapor line is cold (must be insulated so it does not sweat and so attic heat does not steal refrigerating effect). In heating that same large line carries hot gas to the indoor coil (must be insulated so the heat you just paid to pump is not dumped into a 130°F attic, and so someone does not grab a 180°F pipe). The small line also sees reversed roles. Insulate both line-set legs on a heat pump unless the listing says otherwise, UV-jacket the outdoor run, and keep the insulation dry and continuous through the wall sleeve. Cool-only “suction only” insulation is the usual wrong answer on a heat-pump item.

TXVs on heat pumps are often bi-flow or paired with a check valve so metering works in both directions. A cooling-only piston left in a heat-pump indoor coil is a heating-capacity complaint waiting for the first cold front.

Thermostats, outdoor thermostats, heat strips, fire stats

FBC Energy R403.1.1 still wants a thermostat per system. It must be a heat-pump thermostat: O/B reversing output, Y compressor, G fan, W/W2 or E for electric heat, and usually an emergency-heat switch that runs strips and locks out the compressor. A cooling-only subbase that jumps W whenever Y is on will fight the reversing valve and the energy code at the same time.

R403.1.3 Heat pump supplementary heat (Mandatory). Heat pumps with supplementary electric-resistance heaters shall have controls that limit supplemental heat to only those times when:

1. The vapor-compression cycle cannot provide the heating energy to satisfy the thermostat setting,
2. The heat pump is in defrost,
3. The vapor-compression cycle malfunctions, or
4. The thermostat malfunctions.

The field device that enforces a lot of that logic is the outdoor thermostat (ODT) in series with the strip contactor: above the setpoint (often in the 35–40°F neighborhood on older lockouts, or as the control sequence requires), the strips cannot energize on a simple call for heat. Emergency heat on the thermostat is the manual exception for a failed compressor — it is not an all-winter operating mode in Orlando. R403.7.2 (prescriptive): electric resistance shall not be the primary heating system in Climate Zone 2 (most of Florida). Zone 1A still does not get a free 10 kW furnace as the only heat on a new or full-replacement system if a heat pump can do the job under the energy path in force.

Fire stats on this outline are the electric-heat high-limit stack: an automatic-reset primary limit in the airstream and a manual-reset or fusible-link secondary that opens if the blower dies and the strips glow. They are safety controls, not operating thermostats. Package and split heat pumps with strips both need them. A jumper across a limit “until the part comes in” is how attics burn. Listed clearances to combustibles (304.9) still apply to the strip section.

Heat-strip math. 1 kW = 3,413 Btu/h. A 5 kW kit is about 17,065 Btu/h; an 8 kW kit is about 27,300 Btu/h; a 10 kW kit is about 34,130 Btu/h. Those kW sit inside the air handler; they do not raise the cooling tons for the Class B cap, but a package gas heat module of 600,000 Btu on a 20-ton RTU is still over Class B’s 500,000 Btu heating limit even though 20 tons of cooling looks legal.

Sizing, condensate, package heat pumps

R403.7.1.2.1 Heat pumps. Size on the cooling requirements of R403.7.1.1. Total cooling capacity shall not be more than 1.15 times the design cooling load even if the design heating load is 1.15 times greater than the design cooling load. Do not upsize a Miami house to 5 tons because a salesperson wants “extra heat.” Use expanded heating data at the winter outdoor design to see how many Btu the compressor actually makes, then let strips (locked out per R403.1.3) cover the gap. Climate Zone 2 winter design is mild compared with cooling; the 1.15 cooling cap is usually the binding constraint.

Condensate and overflow do not go away because the machine also heats. The indoor coil still sweats in cooling, still sits over finished space in a Florida attic, and still needs 307.2.1 disposal, 307.2.1.1 no direct sanitary tap, 3/4-inch pipe, 1/8 in./ft slope, and 307.2.3 auxiliary protection. Package heat-pump drain pans on a roof curb over occupied space are the same rule. During heating the indoor coil is hot and dry; the pan still has to work next July.

Package heat pumps are the same reversing-valve cycle in one cabinet. You set a curb or pad, flash the roof, anchor for 301.15 wind, connect ducts, land a heat-pump thermostat, set the ODT, verify firestats, and pipe condensate. There is no field line set to insulate, but there is still a defrost board and still a strip kit. A 25-ton package heat pump is the Class B ceiling; 25 tons is 300,000 Btu/h cooling.

Florida HVAC scenario

A certified Class B firm in Orange County (Climate Zone 2A) replaces a failed 3-ton cool-only split with a 3-ton heat pump. Manual J cooling total is 32,000 Btu/h; heating is 18,000 Btu/h. The salesperson wants a 4-ton because “heat pumps are weak.” R403.7.1.2.1 forbids using the heating load to blow past 1.15 × 32,000 = 36,800 Btu/h of cooling — a 4-ton AHRI nominal is about 48,000 Btu/h and fails the cap. The 3-ton match’s expanded heating data at the winter design covers most of 18,000 Btu/h; a 5 kW strip (~17,000 Btu/h) is supplemental only, locked out by the ODT and R403.1.3. The attic coil still gets a secondary pan. Both line-set legs get insulation. The reversing valve is landed on O for that brand. Class B is legal. If the same drawings had shown a 30-ton package heat pump on the office next door, Class B stops at the bid table; the reversing-valve theory still shows up on the exam.

Traps: (1) Sizing heat pumps on heating in Florida. (2) Insulating only the vapor line. (3) Cool-only thermostat on a heat pump. (4) Strips as primary heat in Zone 2. (5) Skipping firestats because “it’s only 5 kW.”