Basic HVAC

April 14, 2021 | Updated: March 23, 2022
Author: Aaron Lee, BCIT

This readily accessible online introductory resource was developed for anyone who has interest in, or works with, HVAC controls and equipment. Designed for electrical and HVAC apprentices learning about the subject in school, you will find the descriptive text and original diagrams easy to navigate through, while the question bank will help students review the subject matter covered in each section.

Subject Areas
Trades, Electrical

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"Ventilator Fan Blowing" ( by PublicDomainArchive ( is licensed under a Pixabay Licence.

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Basic HVAC by Aaron Lee, BCIT is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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Reviews (1) Avg: 3.4 / 5

Claire Yan

Institution:University of British ColumbiaTitle/Position: Associate Professor of TeachingCreative Commons License

Q: The text covers all areas and ideas of the subject appropriately and provides an effective index and/or glossary

This book covers basic principles of heating, ventilation, refrigeration and air conditioning, in particular, various common heating and cooling equipment used in residential applications, such as electric heater, gas-fired furnace, hydronic heating and cooling systems, fans, and direct expansion cooling system, etc. It is at the introductory level for students in Trades and Apprenticeship programs.

The book has excellent accessibility features such as the audios in each section and the pop-out glossary. The H5P self-test questions in each section will be very useful for students to quickly evaluate their learning.

The book includes a good glossary; however, there are some errors or oversights. For example, the explanations for “overload” and “overload protection relays” are exactly the same.

Comprehensiveness Rating: 3 out of 5

Q: Content is accurate, error-free and unbiased

Some errors are found in the book, in particular, in mathematical expressions and diagrams. For example, the “=” sign is misused in several places, such as in sections 26, 32 and 34.

In section 26, the expressions to indicate the relations among fan speed, static pressure and fan power consumption, i.e., Fan Speed = Air Flow, Fan Speed = Static Pressure^2, and Fan Speed = Power consumed^3, are wrong and misleading. It’s recommended to change the “=” sign to “∝” (meaning proportional to), and write the three relations as follows to improve the accuracy and clarity:
Air flow ∝ Fan speed, Static pressure ∝ Fan speed^2 , Power consumed ∝ Fan speed^3

In sections 32 and 34, the expression “Temperature=Pressure/Volume” is misleading. The “=” sign shouldn’t be used here. From section 34, the author meant to use this expression to explain how temperature varies in an expansion valve due to the change of pressure and volume, in a much-simplified way. However, this expression appears to be very confusing and contradictory to the well-known ideal gas law, PV=mRT, that students may have learnt from thermodynamics or physics. In order to avoid the confusion and improve the clarify without going into theories in depth, it’s recommended to either delete the expression or change it into two expressions, i.e., Temperature ∝ Pressure, and Temperature ∝ 1/Volume, using the “∝” sign and provide an explanation in context.

Most diagrams are clear and serve the purpose. Some diagrams require more editing. For example, in section 24, the diagram of the axial fan does not show the correct direction of the air flow in relevant to the rotating shaft of the fan. This inaccuracy may cause confusion. None of the diagrams are numbered.

Some concepts are not accurately expressed. For example,

In section 32: “Temperature is the thermal energy contained by a material ……” This statement is incorrect because temperature and thermal energy are two related yet different concepts. It is suggested to change the word “is” to “represents” for clarity. In addition, the following sentences say “It is a representation of kinetic energy.” and “it takes energy to heat something, and a hot object will slowly cool by dissipating its kinetic energy to the outside environment.” In these sentences, “kinetic energy” may be easily misinterpreted by students as the kinetic energy of the hot object (from the macroscopic viewpoint), whereas the author might mean the kinetic energy of the molecules (from the microscopic viewpoint). These sentences should be revised to improve the accuracy and clarity.

In section 35, “As the refrigerant enters the expansion valve it is a high pressure, room temperature liquid ……”. As a general statement, this sentence is not accurate. The temperature of the liquid refrigerant entering the expansion valve depends on how and at what temperature the condenser is cooled. The refrigerant entering the expansion valve may not necessarily be at the room temperature. The author might need to provide more explanation or context to improve the clarity.

Content Accuracy Rating: 3 out of 5

Q: Content is up-to-date, but not in a way that will quickly make the text obsolete within a short period of time. The text is written and/or arranged in such a way that necessary updates will be relatively easy and straightforward to implement

The basic principles of HVAC do not change over time; thus, the content of the book will not be obsolete quickly. The book consists of four parts; all of the parts can be easily rearranged and updated with new information.

Relevance Rating: 4 out of 5

Q: The text is written in lucid, accessible prose, and provides adequate context for any jargon/technical terminology used

The text is written in plain language. Most parts of the text are clear and easy to understand with some descriptions require more editing to improve the clarity. It is expected that students with little knowledge in HVAC can easily understand the text.

Clarity Rating: 3 out of 5

Q: The text is internally consistent in terms of terminology and framework

The text is consistent in terms of its structure, general descriptions and terminologies.

Consistency Rating: 4 out of 5

Q: The text is easily and readily divisible into smaller reading sections that can be assigned at different points within the course (i.e., enormous blocks of text without subheadings should be avoided). The text should not be overly self-referential, and should be easily reorganized and realigned with various subunits of a course without presenting much disruption to the reader.

The book consists of four separate yet interconnected parts: electrical terms, heating, ventilation and mechanical cooling. Each part may be used independently without presenting much disruption to the readers. The book can be easily reorganized.

Modularity Rating: 4 out of 5

Q: The topics in the text are presented in a logical, clear fashion

The book is written in a logical, clear fashion and covers a list of rudimentary topics commonly seen in an entry-level HVAC textbook. The book can be easily reorganized and modified.

Organization Rating: 4 out of 5

Q: The text is free of significant interface issues, including navigation problems, distortion of images/charts, and any other display features that may distract or confuse the reader

Most parts of the book display very well without any significant issues. However, there are occasionally display issues and inconsistency between the web and PDF versions. For example,

In section 1 (page 6 of the PDF version), “To calculate the power of any particular component in a circuit, multiply the voltage drop across it by the current running through it.” The words “drop across it” seem to be a display issue rather than a typo.

In section 23 (web version), “Sometimes called the air-handler unitno post”. The words “no post” seem to be a display issue on the web version rather than a typo, as the printed PDF version has the correct display.

Interface Rating: 3 out of 5

Q: The text contains no grammatical errors

The book contains grammatical and spelling errors and requires more editing. For example,

In Part I of the web version (or line 2 on page 3 of the PDF version), “… power the equipment which …” “power” should be “powers”.

In section 1 of the web version (or on page 6 of the PDF version), “also know as voltage.” should be “also known as voltage.”

“Current” in Glossary, “When one coulomb of charge moves past one point in once second,” “in once second” should be “in one second”.

“Anticipator resistor” in Glossary, “the temperature-sensitive bi metallic strip inside the thermostat.” “bi metallic” should be bimetallic.

In section 3 of the web version (or on page 12 of the PDF version), “Fuses come in two categories: Fast-acting fuses (Type P)”. “Fast-acting” should not be capitalized.

In section 29 of the web version (or on page 71 of the PDF version), “Often used in association with rooftop water coolers to rapidly release thermal energy collected in the building.” is not a full sentence.

In section 31 of the web version (or line 4 on page 76 of the PDF version), “because with out a temperature gradient,” “with out” should be “without”.

Grammar Rating: 2 out of 5

Q: The text is not culturally insensitive or offensive in any way. It should make use of examples that are inclusive of a variety of races, ethnicities, and backgrounds

The book is written in plain, technical language. No insensitive or offensive language were found at all.

A great feature of the book is its audiobook in each section and the pop-out glossary, which make the book accessible.

Cultural Relevance Rating: 4 out of 5

Q: Are there any other comments you would like to make about this book, for example, its appropriateness in a Canadian context or specific updates you think need to be made?

The book is at an appropriate level and may be used as a starting point for an introductory HVAC course in Trades programs. It may also be used by students as a supplementary reading material. This is the first version of the book containing spelling and grammatical errors and some ambiguous descriptions. It is highly recommended that more editing be done to fix errors in future versions for clarity.