Heat Pump Vs. Heat Engine: Which Heating Technology Reigns?

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By Debarghya Roy

Heat pumps and heat engines are two of the most common methods for transferring energy in a system. Both devices use thermal (heat) energy as their input, but they operate in different ways/

In this blog post, we take a look at how Heat Engines and Heat Pumps differ and explore what makes each device unique so that you can gain an appreciation of their individual advantages.

Key Takeaways

  • Heat pumps transfer thermal energy from a colder area to a hotter one using principles of thermodynamics and electrical power.
  • Heat pump systems are more efficient compared to conventional heating devices, potentially saving up to 50% on energy bills with no emissions into the environment.
  • Heat engines convert thermal energy into other forms of energy such as mechanical work but require fuel inputs when working at maximum capacity/ efficiency.
  • Pros and cons should be carefully considered before deciding between a heat engine or heat pump system for your home’s air conditioning needs.

What Is A Heat Pump?

A heat pump is an energy-efficient device that uses mechanical/electrical energy to transfer thermal energy from a colder area to a hotter one.

Heat Pump Vs Heat Engine

Definition Of Heat Pump

A heat pump is a device that transfers thermal energy from one place to another, typically a colder location to a warmer location. 

How Does Heat Pump Work?

Heat pumps use various principles of thermodynamics including Carnot’s Law which states that the amount of thermal energy transferred increases when the temperature difference between two reservoirs becomes larger.

This process works by extracting thermal energy from an initially cooler environment and transferring it to the desired warm area, usually through external work (action or application of an external force).

In order for this transfer of heat energy to be efficient, both hot and cold reservoirs must exist at different temperatures with one known as the “cold reservoir” outputting small amounts of heat into its environment.

While the “hot reservoir” takes in enough input so as not to reduce its total internal energy but instead creates more overall mechanical power.

Functions Of Heat Pump

Heat pumps use energy (usually electricity) to transfer heat from one place to another. Heat is transferred from a colder environment (like the outside air) into a warmer environment (like the indoor space). 

This process is conducted in three phases: compression, expansion, and condensation.

In compression phase, liquid refrigerant is drawn into a compressor where it is compressed into high-pressure gas. This increases its temperature.

In the expansion phase, the high-pressure gas passes through an expansion valve which cools and reduces the pressure of the gas, thus reducing its temperature as well.

In condensation phase, this cool gas then passes through the outdoor coil where heat from inside air is absorbed by the cooler outdoor coil. At this point, the gas turns back into liquid due to its drop in temperature as it absorbs heat from outside.

The liquid refrigerant then enters back into the interior evaporator coil and transfers energy to indoor air by releasing latent hot air trapped in the refrigerant liquid turning it back into cold gas state once again. 

The cycle starts all over again helping maintain desired room temperatures at all times whenever necessary using minimal inputs of energy.

Pros And Cons Of Using Heat Pumps

It is crucial for heat pump owners to weigh the pros and cons of heat pump systems before making a purchase or deciding to switch. 

Here’s a comparison of the pros and cons in a table format for easy reference:

Heat pumps are cheaper to run compared to combustion-based systems, resulting in long-term savings on energy bills.Heat pumps may be less effective in colder temperatures, which could necessitate the use of alternative heating methods.
Heat pumps are safer than combustion-based systems, reducing the risk of accidents and damage to your home.Initial installation costs for heat pumps can be higher than for traditional heating systems.
Heat pumps are environmentally friendly, as they emit fewer greenhouse gases compared to combustion-based systems.Heat pumps may require more frequent maintenance to ensure optimal performance and efficiency.
Heat pumps can be used for both cooling and heating applications, making them versatile and useful throughout the year.Heat pump systems may be more complex than traditional heating systems, potentially leading to more expensive repairs if problems arise.

What Is A Heat Engine?

A heat engine is a device that converts thermal energy, such as body heat or waste heat, into other forms of energy, such as mechanical work.

Definition Of A Heat Engine

A heat pump is a device that transfers thermal energy from one body to another. Heat pumps are used for space heating, air conditioning, and in refrigerators.

How Does Heat Engines Work?

Heat engines work by moving heat from either a cold reservoir or the environment into a hot reservoir such as your living room during winter. 

This process is achieved through a cycle of compression and expansion stages where mechanical power input is required to produce thermal output at a given temperature.

Unlike standard engines which convert chemical energy directly into mechanical energy, heat pumps use electric current as an input source in order to transfer and manipulate heat between reservoirs via the laws of thermodynamics.

Making them much more efficient than conventional combustion-based engines or turbines that require fuel inputs.

Functions Of Heat Engine

Heat pumps move thermal energy from one source to another, helping maintain desired temperatures in a designated area. 

They transfer heat by reversing the flow of a refrigerant from liquid back to vapor form between two reservoirs at different temperatures. 

The process is repeated according to the law of thermodynamics and the second law of thermodynamics, alternating between heating and cooling through evaporation, condensation compressing, and expansion depending on its purpose.

The primary use for Heat pumps is for air-conditioning, along with providing comfort cooling during hot summer months they can also be automated systems that provide both heating and cooling throughout winter months. 

In addition heat pumps offer humidity control while not adding extra moisture or raising refrigerant levels as some additional models do.

Some other examples where Heat Pumps can be used include:

  • Swimming pools heated through underwater pipes
  • Geothermal systems
  • Underfloor heating systems circulate warm air around spaces using a sealed unit system based upon an increase in temperature being delivered as needed
  • Commercial chillers for industrial equipment such as computer room environments or supermarkets etc.

Pros And Cons: Heat Pumps Vs. Heat Engines

When evaluating the best heating option for your home, understanding the pros and cons of heat pumps and heat engines can be essential. 

Let’s analyze the advantages and disadvantages of both systems through the following table:

Heat PumpsHeat Engines
ProsHigh energy efficiency, transferring up to 3 times more heat energy than the electrical energy consumed.Can provide both heating and cooling, making them versatile for different climates.Environmentally friendly, as they use renewable energy sources (air, ground, or water).Lower operating costs compared to traditional heating systems, potentially saving up to 50% on energy bills.Long lifespan of around 15-20 years with proper maintenance.Heat engines have a wide range of applications, including power generation, transportation, and industrial processes.Can achieve high-power output, making them suitable for heavy-duty applications.Uses waste heat efficiently, as the heat engine’s efficiency increases with the temperature difference between the heat source and sink.Some heat engines, like the Peltier device, have no moving parts, which results in a longer service lifetime.
ConsInstallation costs can be higher compared to traditional heating systems, especially for ground-source heat pumps.Requires a backup heating source for extremely cold temperatures.Performance can be reduced in areas with fluctuating or extreme temperatures.Regular maintenance is necessary to ensure efficiency and prolong lifespan.Heat engines have a lower efficiency compared to heat pumps, as their efficiency relies on the ratio between the work output and heat input.Some heat engines, like the Peltier device, require a large amount of electrical power, making them less cost-effective.Produces greenhouse gas emissions if powered by fossil fuels, contributing to environmental concerns.

Comparing Heat Pumps And Heat Engines

Heat pumps and heat engines function differently from each other, and they must be evaluated in terms of energy efficiency, cost-effectiveness, heat transfer efficiency and thermal efficiency.

Differences: Heat Pumps Vs. Heat Engines

The following table outlines the major differences between these two systems:

Heat PumpsHeat Engines
Uses work to transfer heat from a colder area to a warmer areaWork-producing devices that convert heat into mechanical energy
Operates based on the same principles as a refrigerator, but can reverse its function to heat an interior spaceCannot heat an interior space; primarily used in engines for vehicles and power generation
Provides both heating and cooling capabilitiesDoes not have the ability to cool spaces or provide temperature control
Typically more energy-efficient and eco-friendly for heating and cooling purposesLess energy-efficient and may produce more greenhouse gas emissions, depending on the fuel source
Can be costlier upfront, but offers long-term savings due to lower energy consumptionMay have a lower initial cost, but ongoing fuel costs and maintenance requirements can add up over time

Energy Efficiency

Heat pumps are far more energy efficient than heat engines. Heat pump efficiency is measured in terms of Coefficient of Performance (COP), which is a number that indicates the ratio of usable heat output from a given input.

The COP for any heat pump is always greater than 1, meaning it outputs more thermal energy than what was put into it.

This makes them ideal for cooling and heating applications since they use little to no additional energy to reach desired temperatures.

On the other hand, an average heat engine has COP lower than 1. This means it consumes more energy than the actual amount converted to useful work  resulting in significantly higher costs and environmental pollution.

To ensure maximum efficiency when deciding between two types of machines like these, look at their respective COPs carefully.

If one device’s Cops exceeds another by a certain significant margin then you can be sure that the former would be better suited to your requirements.


Heat pumps are a great money-saving alternative to traditional heating and cooling systems. 

The efficiency of the pump itself is beneficial since it requires less energy input than a heat engine, making them more economically attractive.

This means that owners can save up to 60% on their yearly energy costs when compared with other systems such as heat engines.

When properly maintained, a heat pump will last for many years meaning that owners not only save money on initial purchase and installation of a unit but also its long-term operation costs over time compared to a heat engine.


What is the difference between a heat pump and a heat engine?

The main difference between a heat pump and a heat engine is that both are capable of transferring energy through heating or cooling.

A heat pump moves energy from one place to another without using combustion while a heat engine does use combustion in order to generate power.

How much energy efficiency can I expect from my system by using either a Heat Pump or Heat Engine?

Although the amount of energy efficiency varies depending on your individual system and needs, typically Heat Pumps offer significantly more efficiency as compared to traditional Heat Engines due to their ability to move energy with little effort needed for operation.

What type of environment does each type work best in? 

The automotive industry widely uses Heat Engines due their ability to produce high levels of power in short-term intervals.

  • However suitable environments for their use are limited mostly to over areas containing open spaces large enough to cause safety hazards of thermostats (housing etc.) 
  • Set a proper distance away from ignition sources present (ie vehicles driving recreational sites).


The comparison of heat pumps and heat engines has revealed the advantages and disadvantages which make them attractive for different applications. Heat pumps can be more energy efficient than traditional furnaces, yet they are limited to low temperatures.

Heat Pump