Comparing single-stage, dual-stage, and variable speed heat pumps – which one to choose

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Compare single-stage vs. dual-stage vs. variable speed heat pumps, or good vs. better vs. best in electric heating and cooling, and find out which type provides maximum comfort, efficiency, savings, and long lasting operation - and why.

The main difference between these heat pumps is the type of a compressor they use. When comparing them side by side, both efficiency ratings should be checked; SEER as the cooling efficiency and HSPF as the heating efficiency. The first one have values usually from 13 and up (some over 20) while HSPF ranges from 7 up… higher better. And the efficiency is affected by the type of  a compressor.

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First, we had single-stage heat pumps when the unit was either ON, at the full power and no matter the weather conditions, or OFF. 

Then, we got two-stage heat pumps where the unit runs either with the 100% (during colder weather), with the reduced power (great for milder weather) or is OFF. 

And the most advanced heat pumps are with the variable speed so the equipment can operate at many more stages between the full power and OFF position.


Single stage heat pumps utilize single-stage compressors that have two functions; either OFF or ON – when working at the maximum power, 100%. This is the simplest type which is also the most affordable (lowest unit cost and the installation) – ideal for budget-oriented families, such as this Lennox Merit.

As they were present on the market for so many years, they are considered reliable with a good track record. The main disadvantage is when it works at the full power even if it is not needed, for example in milder weather.

Due to the only ON/OFF option, these heat pumps usually have shorter cycle, which unfortunately doesn’t provide great humidity control as it doesn’t have time to establish a steady air flow.

Better and more expensive models are heat pumps equipped with two-stage compressors and these can operate at the full power (100%) or at lower level (60-70%), while the efficiency is up to 40% higher.

This advantage over the single-stage models allows them to run at the full blast during cold weather or with the reduced power during milder days. It works more often and it consumes less energy than the single-stage unit as it doesn’t have to work as hard to adjust to temperature swings.

This type also brings better dehumidification due to its ability to vary the airflow by using the electronically commutated fan motor (ECM).

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The best and most expensive are models with the variable speed making the heat pump operate at different levels. Based on the home cooling and heating needs, the variable speed heat pumps can incrementally adjust its power providing better temperature control and more consistent temperature.

As it runs the longest at a lower capacity it will create a constant air flow resulting in better humidity control, better distribution of the warm or cold air, and while the air passes more through the filters, the air quality is greater over other two types. The SEER rating is over 20 on these machines and good examples are Trane XV20i and Carrier Infinity 20.

Advantages of single stage heat pumps

  • Simple
  • Affordable
  • Cheaper to install and replace

Disadvantages of single stage heat pumps

  • When it is ON, it operates only at full power no matter the weather conditions
  • Short run times
  • Poor humidity control
  • More energy use
  • Least efficient

Advantages of two-stage and variable

  • Longer run times means better air distribution and less hot and cold spots
  • Better temperature and humidity control
  • Better air quality
  • Responds better to actual indoor and outdoor conditions
  • Saves on energy as it can adjust the power relative to the outside temperature
  • Lower noise level

Disdvantages of two-stage and variable

  • Higher unit and installation costs
  • Complicate to fix
  • Higher price


The single-stage heat pumps are the most affordable, or cheapest of all three – that is why these are recommended for budget-oriented families. The two-stage unit can cost from a few hundred to over a thousand dollars more, while the variable cost the most, reaching a few thousand dollars more than the cheapest ones.

Most of the homeowner will base their decision on the price, efficiency, noise level and fancy features, before buying a heat pump. And without any knowledge and analysis a single-stage system could be the first choice, as it cost less - but also provide less.

Now, as most of us homeowners are very cautious about the energy spending and high energy bills, so it is worth considering variable speed heat pumps due to all the benefits they bring. If this type is too pricey, then two-stage unit should be taken into consideration. These, more advanced models cost more upfront but cost less to operate. And it allows your contractor or heat pump dealer to size the unit more precisely.

The ability of the heat pumps to operate with the variable speed compressor provides great operating cost benefits to the homeowners as it works more efficiently, consumes less energy as working with less stress and provides greater comfort.


Use the links provided to compare features and specs; Trane vs.  Carrier vs. Bryant vs. Lennox vs. Amana vs. American Standard vs. Goodman.