Installation decides the result
Two identical heat pumps can perform very differently depending on how they went in. Field studies have long found that installation faults, especially charge and airflow, cost a meaningful share of a system’s rated efficiency.
Bluffline Memphis Heat Pumps works through the checks below on every installation and leaves the readings with you in writing.
The checklist at a glance
| Stage | Check | Good result |
|---|---|---|
| Before | Load calculation | Size matched to the house |
| Before | Static pressure on the ducts | Near the blower’s design, about 0.5 |
| Install | Brazing under flowing nitrogen | Clean joints, no internal scale |
| Install | Pressure test | Holds with no drop |
| Install | Evacuation | Below 500 microns and holding |
| Start-up | Charge by weight | Maker’s charge plus line set adjustment |
| Start-up | Subcooling or superheat | Within the maker’s target |
| Start-up | Airflow and static | Within the maker’s range |
| Start-up | Defrost and backup heat | Tested and working |
| Start-up | Thermostat | Configured as a heat pump with lockouts set |
| After | Paperwork | Readings, model numbers, settings in writing |
Before the install
Sizing
The heat pump should be sized from a room-by-room load calculation for Shelby County’s 95-degree summer and 20-degree winter, not copied from the old nameplate. The sizing guide covers the method.
Matched equipment
The outdoor unit and the indoor coil or air handler should be a listed, matched pair, so the system’s SEER2 and HSPF2 ratings actually apply. The model numbers belong on the estimate.
The ducts
A static pressure reading on the existing ducts shows whether they can carry the new system’s air. If not, the duct work goes on the estimate. The crawl space ductwork guide explains the fixes.
During the install
Brazing under nitrogen
When copper is brazed, the inside of the pipe oxidizes and flakes unless dry nitrogen flows through it. Those flakes travel through the system and can clog metering devices and damage the compressor.
Pressure test
After brazing, the line set and coils are pressurized with dry nitrogen and watched for any drop. A drop means a leak, found and fixed before refrigerant goes in.
Evacuation
A vacuum pump pulls air and moisture out of the lines until a micron gauge reads below 500 microns. Then the pump is isolated and the reading watched. If it rises quickly, there is a leak or moisture still in the system.
At start-up
Charge
New heat pumps come with refrigerant for a standard line set length. Longer line sets need more, added by weight with a scale. Then the charge is checked against the maker’s target:
- Subcooling for systems with a thermostatic or electronic expansion valve.
- Superheat for fixed-orifice systems.
Charge checks in cooling mode are most reliable in warm weather; in winter, weighing in the charge is the main method, with a check later if needed.
Airflow and static pressure
The blower is set for the system’s size, usually about 350 to 400 cubic feet per minute per ton, and static pressure is measured with the system running. The temperature drop across the indoor coil in cooling, or rise in heating, gives a second check.
Defrost
A forced defrost cycle confirms the reversing valve shifts, the outdoor fan stops, the coil clears and the backup heat covers the cycle. The defrost guide explains what normal looks like.
Backup heat
Each stage of the strips, or the gas furnace on dual fuel, is called and confirmed. On dual fuel, the changeover between heat pump and furnace is tested.
Thermostat
The thermostat is configured as a heat pump, the outdoor sensor checked against a thermometer, the strip lockout or dual fuel switchover set with you, and the fan and dehumidify settings chosen. The thermostat setup guide walks through each.
Condensate and safety
The condensate drain is tested with water. On attic units, the float switch on the secondary pan is tripped to confirm it shuts the system off.
The inspection is not the commissioning
Your town’s mechanical inspection checks code items: the permit, the disconnect, the pad, clearances, the condensate disposal and the electrical connections. It doesn’t measure charge, airflow or vacuum. Those are the installer’s job, which is why the readings matter.
Where to find the permit
Memphis, Germantown and unincorporated Shelby County permits go through the joint Office of Construction Code Enforcement; Bartlett and Collierville run their own offices. The service areas page lists the office for each town.
What goes wrong when steps are skipped
Each step exists because skipping it causes a known problem:
| Skipped step | What can follow |
|---|---|
| Load calculation | Oversizing, short cycles, a clammy house |
| Nitrogen while brazing | Oxide flakes clogging the metering device or harming the compressor |
| Pressure test | A slow leak that shows up months later as weak cooling |
| Deep vacuum | Moisture in the system, acids, compressor damage |
| Charge by weight and check | Over- or undercharge, lost efficiency, compressor stress |
| Airflow and static | Noise, a frozen coil, lost capacity, poor humidity control |
| Defrost test | Ice that never clears on winter mornings |
| Backup heat test | A cold house when the strips or furnace are needed |
| Thermostat setup | Strips running on mild days, a high winter bill |
A sample start-up sheet
A completed sheet for a 3-ton heat pump might read like this. The numbers show the format; your system’s targets come from the maker’s data, and a reading outside the target is a reason to adjust before anyone leaves, not a note for later.
| Item | Reading |
|---|---|
| Pressure test | Held with no drop |
| Final vacuum | 380 microns, held |
| Refrigerant added for line length | Weighed in per the maker’s chart |
| Subcooling | Within the maker’s target range |
| Total external static | 0.48 inches of water column |
| Temperature drop across the coil | About 18 degrees |
| Defrost | Forced and cleared; backup heat on |
| Strip lockout | 32 degrees |
Readings in a Memphis season
Some checks depend on the weather. A charge check by subcooling is most reliable on a warm day in cooling mode. A system installed in January is charged by weight, and a cooling check on the first warm day confirms it.
Defrost can be forced in any weather. The start-up sheet should note which checks were done in which mode, so a later visit knows what to confirm.
What to keep
At the end you should have:
- Model and serial numbers for both halves.
- The load calculation result.
- Pressure test and vacuum readings.
- Charge added and the subcooling or superheat reading.
- Static pressure before and after any duct work.
- Thermostat settings: lockout or switchover, recovery, fan.
- The permit and inspection result.
Keep them with the warranty registration. They make future service faster and answer rebate questions. The TVA rebate guide explains how the participating contractor submits the rebate.
Questions to ask before you sign
Whoever installs your system, ask:
- Will you run a load calculation, and will I see the result?
- Will you braze under nitrogen and pull a vacuum below 500 microns?
- How will you set the charge?
- Will you measure static pressure before and after?
- Will I get the start-up readings in writing?
The replacement page covers what a replacement includes, the cost page lists the typical ranges, and the Memphis buying guide puts the decision in order.