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Just How Efficient Are Variable Speed Inverter Heat Pumps and Air Conditioners?

April 4, 2024

With rising electricity costs, homeowners and businesses are looking for ways to reduce electricity consumption. As a result, making the jump to Inverter HVAC systems is becoming an increasingly popular option. The average home uses ~50% of its energy on heating & cooling. For many homes, heating & cooling represents even more than 50% of energy costs. Reducing the energy used to heat or cool a home is an obvious starting point in efforts to reduce overall energy costs.

We are commonly asked this question by customers: “How much will X system save me on electricity?

Answering this question precisely requires calculations that are made over time, and the same calculations would need to have been made before installing a new system, which is rarely the case. Simply comparing electric bills before and after new HVAC equipment is rarely an accurate way to calculate efficiency savings because there are factors this approach doesn’t consider, such as inevitable changes in weather. However, we have adequate information to make safe assumptions in estimating the efficiency savings of various equipment based on efficiency ratings and types of equipment. 

Image of Mitsubishi Mini Split Inverter

Understanding Key Terminology 

First, we must understand the various terminology and approaches used to assign efficiency ratings to HVAC equipment. There are 3 primary and widely used rating systems for heat pumps and air conditioners:


SEER stands for Seasonal Energy Efficiency Ratio or “Rating.” This is the ratio of the cooling output of an air conditioner or heat pump over a typical cooling season, divided by the energy it uses in Watt-Hours. The higher the rating, the more efficient the heat pump or AC is in cooling.

Heating Seasonal Performance Factor (HSPF): 

This is a heating efficiency rating for heat pumps. The higher the rating, the more efficient the heat pump is in heating.


An air conditioner’s efficiency is measured by the energy efficiency ratio (EER). The EER is the ratio of the cooling capacity (in British thermal units [Btu] per hour) to the power input (in watts). The higher the EER rating, the more efficient the air conditioner.

Within the industry, SEER and SSER2 are most commonly used in conversation. It is safe to assume that a heat pump with a higher SEER/SEER2 rating also has a comparably higher HSPF and EER rating.  

SEER/ SSER2, HSPF and EER are all mathematical ratings, and the increased efficiency % of a higher-rated system can be calculated. For example, comparing a system rated at 18 SEER2 to a system rated at 14 SEER2 can be done as follows:

18 / 14 = 1.2857.  

This means an 18 SEER2 system is 28.57% more efficient than a 14 SEER2 system.  

Variable speed inverter systems create a challenge in comparing and calculating efficiency.  Here’s why: Variable speed inverter systems are designed to operate at capacities much lower than 100% when the demand for heating or cooling within a building can be satisfied at a lower capacity. Most variable speed inverters can operate as low as 25% capacity, only “ramping up” as needed.  

A system designed to maintain 72F indoors, when the temperature is 92F outdoors, will not need 100% cooling capacity when it’s only 82F outdoors. Although we know that variable speed inverter systems will operate at speeds less than 100% capacity a significant amount of the time, when they are tested to assign efficiency ratings, they are tested at 100% capacity.  This means that the actual performance of a variable speed inverter system will virtually always be significantly higher than its efficiency rating.

In 2023, we tested a variable-speed inverter heat pump system in our training lab at Ward PH&A. The system was rated 18.6 SEER2 but performed at 31.4 SEER2 because during the time we tested the system, it was running at less than 100% capacity. In this test, the system performed 68.8% more efficiently than its rating!

Brad Waldrop, GM of Ward PH&A adds “We encourage customers to ask themselves ‘Would I rather spend $2,500 more today on higher efficiency equipment that will save $ and keep my family more comfortable, or pay the electricity company $4,500 more over the next 12 years and be less comfortable in my home?’ 

The answer to this question is obvious for many homeowners, which is why ~85% of the systems we design and install at Ward PH&A are variable-speed inverter systems. With increased energy costs, investing in efficiency is becoming much more common.

A Few Commonly Asked Questions

How do Variable Speed Inverter Heat Pumps and Air Conditioners improve energy efficiency?

Variable Speed Inverter Heat Pumps and Air Conditioners adjust their compressor speed and power consumption based on real-time cooling or heating demands. This ensures that the system operates at optimal levels, reducing energy wastage associated with frequent cycling on and off. By continuously matching output to the required load, these systems maintain consistent indoor comfort while consuming less electricity, leading to significant energy savings over time.

What are the benefits of investing in Variable Speed Inverter technology for heating and cooling needs?

Variable Speed Inverter technology offers several advantages, including enhanced energy efficiency, precise temperature control, quieter operation, lower humidity in cooling, and extended system lifespan. By modulating compressor speed and capacity, these systems can adapt to varying indoor conditions more efficiently than traditional single-speed or 2-stage units. This results in reduced energy consumption, lower utility bills, improved comfort levels, and minimized wear and tear on components, making it a cost-effective and environmentally friendly choice for residential and commercial applications.

How does the variable speed feature of Inverter Heat Pumps and Air Conditioners impact indoor comfort?

The variable speed capability of Inverter Heat Pumps and Air Conditioners allows them to maintain a more consistent indoor temperature compared to conventional systems. By adjusting compressor speed and airflow to match the exact cooling or heating requirements of the space, these units prevent temperature fluctuations and eliminate the “on/off” cycling typical of single-speed units. This results in a more even distribution of conditioned air, reduced humidity levels, and improved comfort throughout the living or working environment. Variable speed inverter systems also decrease humidity levels in cooling by creating longer run cycles which remove more humidity. Lower humidity significantly increases comfort, even at higher indoor temperatures.  

Are Variable Speed Inverter Heat Pumps and Air Conditioners suitable for all climates?

Yes, Variable Speed Inverter Heat Pumps and Air Conditioners are designed to perform efficiently in a wide range of climates. Unlike traditional systems that may struggle to maintain consistent comfort in extreme temperatures, inverter technology allows these units to modulate their output capacity to meet the specific demands of the environment. Whether it’s extremely hot or cold outside, the variable speed functionality enables these systems to adjust operation accordingly, ensuring reliable performance and energy savings year-round.

About The Author

Ward Plumbing, Heating & Air

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