Energy Efficiency Definitions (An Eco-Tech Cheat Sheet)

Abbreviations, anagrams, and technical jargon can make the world of energy efficient design look like a puddle of alphabet soup.  But fear not – in plain language, here’s a glossary of some commonly-heard terms (and what they mean to you).

Active Solar Energy

Energy from the sun that is utilized through electronic or mechanical equipment (such as solar panels).

Carbon Emissions

A benchmark for the environmental impact of a product or energy source, since carbon emissions like carbon dioxide (CO2) emissions are a principal contributor to global warming.  Fossil fuels such as coal and petroleum have a high carbon content, thus releasing greenhouse gasses like CO2 when burned.

Carbon Footprint

A reference to the impact of activities on the environment, as related to carbon emissions.

Carbon Neutral

The concept of reducing carbon emissions to achieve a net carbon footprint of zero.  Organizations may do this by pursuing more environmentally friendly practices, and/or by purchasing “carbon offsets” that support the reduction of carbon emissions (for example, funding for a reforestation project).

Compact Fluorescent Lights (CFLs)

Bulb-style lighting source that uses electrical current to provide illumination from mercury vapor.  CFLs are much more energy efficient than traditional incandescent bulbs, but their mercury content makes disposal of the bulbs an issue.

Embodied Energy

The total energy content of a product, considering not just its direct manufacture, but also factors like the acquisition of raw materials and transportation of the finished product.

Energy Star

A rating system developed by the Environmental Protection Agency to highlight energy efficient appliances and household products, as well as larger systems like homes.  (view our Energy Star Ratings article)

Geothermal Heat

Literally, heat from the earth.  Because temperatures below ground level remain a constant 50-60 degrees F, a system that circulates air or water from below ground can be used for either geothermal heating in cold weather or cooling during the hot months.


Inaccurately portraying a product or service as environmentally friendly.  As public awareness of environmental issues has increased, unfortunately so has manufacturers’ tendency to use “green-ness” as a selling point (that may not tell the whole story).

Kilowatt Hour (kWh)

The standard measurement unit of electrical energy for utility companies.  One kilowatt hour is the energy of 1,000 watts over a period of one hour.

Low-Emissivity (Low-E) Windows

Windows designed to transmit minimal heat, in order to maintain a building’s energy efficiency.  Glass is typically coated with a microscopic layer of metal or metal oxide, and can be customized to allow visible light while blocking thermal transfer such as solar heat.

LED Lights (Light Emitting Diodes)

Solid-state, electrically-illuminated semiconductors.  They are extremely energy efficient since they convert nearly all energy into visible light, as opposed to wasting energy in the form of heat.  LEDs are approximately 50% more efficient than fluorescent bulbs, and they are also extremely durable.

LEED (Leadership in Energy & Environmental Design)

A system of certifications developed by the U.S. Green Building Council to evaluate a structure’s environmental footprint.  Based on points awarded in a range of categories such as site selection and choice of materials, a project can earn a LEED rating of Platinum (the highest level offered), Gold, Silver, or “certified”.

Life Cycle

The entire process of a product’s manufacture, usage, and disposal.  Considering energy use over a product’s entire life cycle generally provides a more accurate gauge of environmental impact than focusing on just one aspect (for example, an item that requires little energy to produce but needs frequent replacement may not actually be considered energy efficient).

Passive Solar Energy

Energy from the sun that is utilized without the assistance of any mechanical equipment (e.g., a home with windows positioned where they will allow sunlight to heat the home).

Photovoltaics (PV)

Materials that create voltage when exposed to light energy.  Solar panels use photovoltaics such as silicon crystals to create an electrical current from sunlight.

Power Grid or Electrical Grid

General term for the network of power generating facilities, substations, and transformers that provide electricity to consumers in a given area.  Hence, a stand-alone home which is not connected to a municipal power supply is said to be “off the grid”.

Renewable Energy

Energy from a source that can be replenished as quickly as it is consumed.


In construction, the standard measurement of resistance to heat transfer (commonly seen in items like insulation or thermal windows).  Higher R-values indicate better insulation (more resistance to heat transfer).

SEER / EER Score (Air Conditioners)

The “Energy Efficiency Ratio”, a measure of an air-conditioner‘s energy efficiency.  Literally a measurement of how much cooling is provided by a given amount of electricity.  SEER refers to the “Seasonal Energy Efficiency Ratio”, which considers long-term usage over variable weather conditions.  The higher the number, the better – a higher SEER number indicates better efficiency.

Solar Energy

Literally, energy from the sun.  As a renewable energy source, solar power can be considered either “active” or “passive”.

Solar Gain

The increase in heat in a particular location (such as a home or office) when warmed by the sun.

Tankless Water Heater, Demand Water Heater

System that uses a powerful heat source to heat water as it is used, instead of maintaining a tank full of heated water.  Tankless heaters can be very energy efficient, since they avoid the wasted energy of keeping water heated while being stored.

Volatile Organic Compounds (VOCs)

A category of chemical compounds which tend to vaporize into the air from their source, thereby affecting indoor air quality.  Substances like paints and finishes may contain toxic VOCs, which can “off-gas” into the air and cause health-related side effects.



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