12 Questions to Ask Before You Buy an Inverter System

Before buying an inverter system, ask how the size was calculated, what the unit's minimum and maximum capacity are, how much heat it delivers at low temperatures, how loud it is, what thermostat and controls it requires, which installation and commissioning steps will be performed, and what the warranty, parts and support cover.

An inverter system is a variable-speed air conditioner or heat pump, and the answers to these twelve questions separate a thorough installer from a fast one. Both will arrive in a clean truck. Only one will bring a load calculation.

The questions below are grouped by topic, each with why it matters and what a good answer sounds like. Our inverter buying guide covers prices, brands and financing; this article is the list you bring to the kitchen table.

What should you ask before buying an inverter system?

The questions to ask before buying an inverter system cover six areas: sizing and the load calculation, modulation range and ratings, cold-weather heating performance, installation and commissioning, controls, and warranty and parts. The table lists all twelve questions with why each matters and what a good answer sounds like.

ENERGY STAR sets the expectation early: the contractor should spend significant time inspecting your current system and home to assess your needs. A quote delivered from the driveway is a guess with a letterhead.

What should you ask about sizing and the load calculation?

Ask how the system size was calculated, whether a room-by-room ACCA Manual J load calculation was performed on your home, and how the equipment was then selected against that load. A good answer includes a written load report based on your insulation, windows, orientation and ducts rather than square footage.

An ENERGY STAR bid checklist tells homeowners that the contractor should calculate your home's heating and cooling loads using ACCA Manual J or equivalent, and ACCA's Manual S is its guide for selecting and sizing residential heating and cooling equipment once the load is known. ENERGY STAR also warns that oversized equipment may cycle too frequently, resulting in less comfort and a shortened lifespan.

Square footage is to a load calculation what shoe size is to a suit fitting. Related, occasionally helpful, and nobody should cut fabric from it. For a closer look at the sizing question itself, see our article on what size inverter AC unit you need.

What should you ask about modulation range and ratings?

Ask for the inverter unit's minimum and maximum capacity at your local conditions and the AHRI reference number for the exact indoor and outdoor combination being quoted. The minimum capacity shows how well the system can run steadily on mild days, and the reference number confirms the ratings apply to that matched pair.

The maximum capacity gets the attention because it keeps the house cool in August. The minimum capacity does the quieter work in May, when the load is small and a unit that cannot turn down far enough starts cycling like the equipment it replaced. Ask for both numbers from the manufacturer's performance data, not from memory.

For ratings, AHRI advises that the easiest way to verify that the system is properly matched is to ask your installer for an AHRI Reference Number or an AHRI Certificate of Certified Product Performance, and that when improperly matched, the efficiency and longevity of these systems are significantly compromised. A SEER2 figure quoted without a matched reference number is a rating looking for a system.

What should you ask about heating performance in cold weather?

Ask how much heating capacity the heat pump delivers at your area's design low temperature, what its efficiency is at 5°F, and what backup heat will cover the gap below that point. A good answer compares the stated capacity with your home's calculated heat loss and names the backup source and its settings.

ENERGY STAR's Most Efficient criteria give a useful yardstick: cold climate heat pumps must show a COP at 5°F of at least 1.75 and heating capacity at 5°F of at least 70% of the capacity at 47°F. NEEP's cold climate specification was designed to identify heat pumps best suited to heat efficiently in cold climates, IECC climate zone 4 and higher.

The catch is that a heat pump's nameplate capacity is measured on a pleasant day. Your coldest night did not agree to those conditions.

What should you ask about installation and commissioning?

Ask whether the installer will test static pressure and duct leakage, measure and adjust refrigerant charge and airflow at startup, and leave written records of those readings. Commissioning is the set of startup measurements that confirms the installed system performs as designed, and it should appear in the written proposal.

The ENERGY STAR bid checklist suggests asking whether the contractor will test to determine the maximum system size that can be installed with your existing ductwork, confirm proper levels of refrigerant and airflow across the coil, and leave documentation including Manual J calculations, the AHRI certificate and records of measurements. The same checklist notes that more than half of new systems in U.S. homes do not perform to their rated efficiency as a result of improper installation.

That distinction is where fast installers and thorough installers part ways. Anyone can make a system turn on. Commissioning proves it is doing what the spec sheet promised. Refrigerant work also requires credentials: technicians who service equipment that could release refrigerants must be certified. Our article on finding an installer for your equipment covers how to locate one.

What should you ask about controls, warranty and parts?

Ask which thermostat or control the inverter system needs to modulate fully, what the written warranty covers for parts and labor, whether registration is required, and who will supply model-specific parts after installation. Good answers name the control in the quote, show the warranty terms and identify a parts source.

Some inverter systems modulate best with the manufacturer's own communicating control, and a third-party thermostat can reduce them to fewer stages. A smart thermostat is a Wi-Fi enabled device that automatically adjusts heating and cooling settings, which is convenient, but convenience and full modulation are separate features. Ask which one you are getting.

For warranty terms, the FTC advises that parts or repairs not listed as covered should be assumed not covered, and suggests asking whether you pay for labor and whether a registration card is required for warranty service. AC Direct sells inverter systems and heat pump units and ships them nationally, while the labor warranty comes from the installer you hire, so get both in writing before anyone unboxes anything.

Which answers should make you keep shopping?

Keep shopping if an installer sizes the system by square footage, cannot state the unit's minimum capacity or low-temperature heating output, will not provide an AHRI reference number, skips duct and refrigerant measurements, or cannot explain the warranty terms. Each of those answers signals that the installation will be quicker than it should be.

Here's the short version of a weak quote: "It's the same size as the old one." Maybe the old one was right. Maybe it spent fifteen summers being wrong in a very consistent way. The phrase "we've always done it this way" is not a measurement either. For the regret side of this checklist, our article on HVAC buying mistakes walks through what those shortcuts cost.

Frequently Asked Questions

What questions should I ask an HVAC contractor before installation?

Ask how the system was sized and whether a Manual J load calculation was done, the AHRI reference number for the matched equipment, whether duct leakage and static pressure will be tested, how refrigerant charge and airflow will be verified, and what the equipment warranty and installer labor warranty cover in writing.

How do I know if an HVAC quote is properly sized?

A properly sized HVAC quote is based on a written room-by-room Manual J load calculation that accounts for insulation, windows, orientation and ductwork. Ask for a copy. A size chosen by square footage or by matching the old unit has not been verified against your home's actual heating and cooling loads.

What is an AHRI reference number?

An AHRI reference number identifies a specific indoor and outdoor unit combination whose performance ratings have been certified by the Air-Conditioning, Heating and Refrigeration Institute. The number confirms that the quoted efficiency ratings apply to the matched pair being installed. It can be checked in the AHRI Directory.

What does commissioning an HVAC system mean?

Commissioning an HVAC system means taking measurements at startup to confirm the installed system performs as designed. Typical steps include verifying refrigerant charge, measuring airflow and static pressure, checking duct leakage, and confirming controls operate correctly. The readings should be recorded and given to the homeowner.

Does an inverter heat pump need a special thermostat?

Many inverter heat pumps modulate fully only with the manufacturer's communicating thermostat or control. A standard or third-party thermostat may limit the system to fewer operating stages. Check the installation manual or ask the installer which control the quoted system requires and whether it is included in the price.

What should an HVAC warranty cover?

An HVAC warranty should state the parts coverage term, including the compressor and control boards, whether labor is covered, and any registration or installation requirements. Installer labor warranties are separate from manufacturer parts warranties. Get both in writing before work begins, and keep the receipt, model numbers and installation records.