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Glossary of Glossary of Zero Energy Terms

Advanced Framing

A construction method (also known as “Optimum Value Engineering” or “OVE”) that uses less material in the framing of a home and can reduce labor and material costs, improve structural integrity, and improve energy efficiency.

Air Source Heat Pump

A home comfort system using refrigeration technology to either heat or cool a building. An outdoor unit exchanges heat with the outdoor air while an indoor unit delivers conditioned air to the occupied space. Air source heat pumps can deliver between two and four units of heat for every unit of electricity used, making them far more energy efficient that other mechanical comfort systems.

Blower Door Test

A test that measures the air tightness of a building and helps reveal air leaks. To run the test, the house is depressurized using a fan mounted in one of the doors. Test results are expressed as air changes per hour at 50 Pascals (ACH50). Pascals are units of air pressure. Typical values for new construction range from 5 to 7 ACH50, while energy-efficient homes can be in the 1 to 2 ACH50 range. The tightest houses can reach less than 0.25 ACH50.

Building Envelope

The building envelope is like a six-sided box that separates the interior and exterior environment of a building.  The six sides consist of a floor or basement, a ceiling or roof, and 4 walls including windows and doors. The goal is to keep that box as airtight and insulated as feasible.

Carbon Footprint

A calculation of the amount of greenhouse gases produced as a result of commercial, industrial, and individual activities. An individual’s carbon footprint is a calculation of the amount of greenhouse gases they produce from daily living, home energy use and transportation.

Ceiling Fans

Fans attached to ceilings that circulate air within living spaces. In rooms with high ceilings, where warm air collects near the ceiling, a fan can mix the air to improve comfort and reduce winter heating costs. In summer, they can cut cooling costs when they are used in lieu of air conditioners.

Cellulose Insulation

Plant fiber insulation that is used in wall and roof cavities to separate the inside and outside of the building thermally and acoustically. Typically, cellulose insulation is made by recycling old newspapers and telephone directories. Borates and ammonium sulfate are included to retard fire and pests.

Certified Zero Energy Home

These are zero net energy homes that have been certified to be net zero by third party certifiers, such as Earth Advantage, Living Building Challenge, or independent energy analysts. Certification is based on energy modeling, on-site inspections and sometimes energy use monitoring.

Compact Fluorescent Lamp (CFL)

Small fluorescent light bulbs that can be used in place of incandescent light bulbs. CFLs consume about 75 percent less electricity and last 8-10 times longer than incandescent bulbs. All fluorescent lamps contain a small amount of mercury. See LED lamps below for the most efficient, durable and safest type of lighting.


Designing a building with building orientation and window placement to take advantage of natural sunlight illumination.

Double Pane Windows

Double pane glass windows often contain argon, krypton, or other gases between two panes of glass to reduce heat flow and improve insulation.

Double-stud Walls

A method to increase the insulating value of exterior walls by making them thicker so they can hole more insulation material. Walls are generally between 10 and 16 inches thick. Not only do they save energy, but they also block sound making for a quieter home.

Dual Flush Toilets

Toilets with two flush options, one for liquid and another for solid waste. The button for liquid waste uses less water per flush.

Energy Audit

A building inspection to determine how energy is used in a home or building and how energy use can be reduced. A qualified inspector first measures the dimensions of various building components, such as walls, ceilings, floors and windows, and the type and amount of insulation is recorded. The inspector conducts a visual assessment and uses methods and measurements, such as blower door tests, that comply with industry standards. A written report should include recommendations and a detailed cost and savings analysis.

Energy Efficient Appliances

Products that use less energy than conventional models. The ENERGY STAR® label is a credible third-party certification of a product’s energy efficiency. Consumers can also refer to the FTC’s Energy Guide label, a yellow label affixed to most appliances today.

Energy Efficient Light Fixtures

Fixtures holding high-efficiency bulbs, such as compact fluorescent lights (CFLs) or light emitting diodes (LEDs), and designed to emit a high proportion of the energy generated by the lamp as light rather than as heat.

Energy Efficient Mortgage (EEM)

Loan products that take a home’s energy efficiency into account when determining the qualifying ratios for a buyer. The rationale is that an efficient home will result in lower monthly energy bills, making more funds available for the mortgage payment. Also, occupants of energy efficient properties have proven to have a lower risk of default. EEMs primarily apply to new construction. In some markets, an energy improvement mortgage (EIM) can be used to make energy improvements in existing homes.

Energy Guide Label

An appliance label that provides an estimate of how much energy the appliance uses, compares energy use of similar products, and lists approximate annual operating costs. It is required by the U.S. Department of Energy on many appliances. Clothes washers, dishwashers, refrigerators, freezers, water heaters, window air conditioners, central air conditioners, furnaces, boilers, heat pumps, and pool heaters can get the label. Televisions, ranges, ovens, clothes dryers, humidifiers, and dehumidifiers do not receive such labels.

Energy Modeling

The use of a computer program to project how much energy a home will use. Modeling shows energy use by building component, such walls, and by end use, such as space heating. This allows designers and builders to focus efficiency efforts in the most cost effective areas. Energy modeling estimates for zero energy homes should come very close to zero.

Energy Monitoring

Each major electric circuit of the home is monitored to determine the energy use of appliances, heating and cooling system, lights and electronics. Based on this information, homeowners can determine how best to conserve energy and identify malfunctioning equipment.

Energy Performance Score (EPS)

A score developed by the Energy Trust of Oregon that shows the total energy use of a home.  The score allows home buyers to compare the energy use of different homes, just as MPG allows car buyers to compare the gas mileage of different vehicles. The EPS scoresheet shows total energy use in million BTUs (MMBTUs), total energy cost, and carbon footprint.

Energy Rating

An energy rating provides a ranking for building energy use along a standardized scale, providing an objective expression of the home’s energy use. Examples include Energy Performance Score (EPS) or Home Energy Rating System (HERS) rating. Energy ratings can be used to qualify for an energy efficient mortgage, compliance with building codes or conformity with green ratings.

Energy Recovery Ventilator (ERV)

A type of ventilation system in which the heated (or cooled) air being vented out of the home is used to heat (or cool) the supply air being pulled in from outdoors. The approach decreases the amount of energy needed to heat or cool the supply air and provides fresh filtered air. They are needed in very air-tight homes, such as zero energy homes, to provide fresh air. Unlike heat recovery ventilators, ERVs recover water vapor as well as sensible heat. This is useful in warm humid climates where air conditioning is common and in very dry, desert climates where the outside air has very low humidity.

Energy Star®

A certification granted by the US Department of Energy for household appliances and buildings that perform at specified levels of energy efficiency. Also see Energy Efficient Appliances.

Ground Source Heat Pump

Ground source heat pumps (GSHPs) use the constant temperature of the earth to provide cooling and heating for a home. A loop of piping is buried in the ground and fluid circulates through the loop to a heat pump compressor. The temperature of the earth is relatively stable compared to the seasonal temperature swings of the atmosphere and benefits the heat pump  as a highly effective source for heating or a sink for cooling. As a result, the efficiency of a ground source heat pump is around 400 percent.


Falsely or vaguely promoting or exaggerating the greenness of a product or service.

Grey Water System

A system to reuse wastewater from bathtubs, shower drains and sinks. Greywater systems require separate wastewater collection pipes, storage tanks, filters and other equipment. Reusing greywater reduces the use of potable water for purposes that don’t require treated drinking water, such as irrigation, toilets, and exterior washing.

Grid Tied

Connected to the electric utility system or grid. Zero energy homes are grid tied, meaning the excess energy they produce goes to utility and the homeowner is given credit that can be used when their energy production is lower than their energy use, such as at night, during cloudy days or in winter.

Heat Pump Water Heater

A very energy efficient water heater that uses refrigeration technology to extract heat from the surrounding air to heat water for household use.

Heat Recovery Ventilation (HRV)

A type of ventilation system in which the heated (or cooled) air being vented out of the home is used to heat (or cool) the supply air being pulled in from outdoors. The approach decreases the amount of energy needed to heat or cool the supply air and provides fresh filtered air. They are needed in very air-tight homes, such as zero energy homes, to provide fresh air. Unlike an energy recovery ventilator, HRVs transfer only sensible heat and not moisture.

Home Energy Rating System (HERS)

An energy scoring system established by the Residential Energy Services Network (RESNET) which uses a “HERS Reference Home” as a standard for comparing energy efficiency in other homes. Homes built to the specifications of the HERS Reference Home score a HERS Index of 100, while a net zero energy home scores a HERS Index of 0. Each 1-point decrease in the HERS Index corresponds to a 1% reduction in energy consumption compared to the HERS Reference Home. Thus, a home with a HERS Index of 85 is 15% more energy efficient than the HERS Reference Home, and a home with a HERS Index of 80 is 20% more energy efficient.

High Efficiency Furnace

Furnaces that have an Annual Fuel Utilization Efficiency (AFUE) of 85% (oil) and 90% (gas) or higher. In general the higher the AFUE, the more efficient the furnace. The Energy Guide label on the equipment can be consulted to determine whether a furnace is efficient. More information on the Energy Guide label is available at

High Efficiency Water Heaters

Water heating models with an ENERGY STAR rating are considered highly efficient. Heat pump water heaters are the most energy efficient water heaters available.

Hot Water Circulation Loop

A water-conservation device that rapidly moves water from a water heater to fixtures. This is desirable when one or more fixtures is a long distance from the water heater. Instead of turning on the hot water tap and running clean water down the drain until hot water arrives, a circulation loop rushes hot water to the fixture. Typically the circulation loop operates continuously or during certain periods of the day controlled by a timer. These typical systems waste energy with unnecessary pump operation and heat loss from the hot water as it circulates around the loop.

An on-demand system uses less energy than continuous or timed pump operation. Hot water recirculation systems can be activated by a push button, or motion sensor. When activated the pump pushes water that has been sitting in the hot water line back to the water heater through the cold water line, while quickly bringing in hot water to the fixture.

Insulated Concrete Forms (ICF)

Rigid plastic foam forms that hold concrete in place during curing and remain in place afterwards to serve as thermal insulation for concrete walls. The foam sections are lightweight and result in energy-efficient, durable construction. The approach decreases the number of breaks in the thermal barrier of the building envelope. It also can save on construction costs because it is fast, especially compared with “stick built” homes.

Indoor Air Quality (IAQ)

A measurement of the overall cleanliness of the air within a building or home. Indoor air may contain a number of contaminants, including carbon monoxide, formaldehyde, mold, lead, volatile organic compounds, and many others. Even water vapor can be considered undesirable when it reaches high levels that support mold and decay. The EPA has a builder program called Indoor airPLUS.

Induction Stove Top

A highly energy efficient electric stove top that heats more quickly and with more precise settings than a gas stove. It uses an electromagnetic field to heat the metal pan directly, so the stove top stays relatively cool, making it easy to clean up spills and less likely to burn skin.


Used with solar PV systems, inverters are necessary to change the direct current (DC) produced by the solar panels into alternating current (AC) that can be used in the home and sent to the grid. Grid-tied inverters also include safety measures to protect the grid during power outages. Stand-alone inverters work with off-grid homes.

Insulation – Blown-In

Fiberglass, cellulose, or wool insulation that is blown into building cavities. It is often easier to install than batts of fiberglass insulation. Blown-in insulation fills cavities completely with less chance for gaps and other flaws.

Insulation – Spray Foam

Spray foam acts as insulation and air sealing in one step. Most foam insulation products have a higher R-value per inch than fiberglass, making it more energy efficient. Closed cell foam insulation has the highest R-value. Open cell and rigid foam board insulation is also available.

LEED (Leadership in Energy and Environmental Design)

The green building certification program created by the United States Green Building Council (USGBC). The comprehensive rating system (based on prerequisites and points) takes a whole building approach factoring in community resources & public transit, site characteristics, water efficiency, energy efficiency, materials & resources, indoor environmental quality, awareness & education, and innovation.

LED (Light-Emitting Diode) Lamp

A semiconductor device that emits light when a current passes through it. LEDs are highly efficient and last longer than any other commercially available light source. Unlike CFLs, they contain no mercury.

Living Building Challenge

The International Living Future Institute has created the most rigorous performance standards for homes and buildings, called Living Building Challenge. Their standards call for the construction of buildings that operate as cleanly, beautifully, and efficiently as nature’s architecture. To be certified under the Challenge, buildings must meet a series of stringent performance requirements, such as zero net energy and zero off-site water use. Monitoring is required over a minimum of 12 months of continuous occupancy.

Low Flow Toilet

A toilet that combines efficiency and high performance. The toilet must average no more than 1.28 gallons per flush. Design advances enable these toilets to save water with no trade-off in flushing effectiveness. Such toilets often have the EPA’s WaterSense label.

Low Flow Fixture

A faucet with aerator installed to reduce the flow of water but not reduce water pressure. A low-flow showerhead uses 2.0 gallons per minute (GPM) or less. A faucet uses 1.5 GPM or less. However, some products have lower flow rates.

Mini-Split Heat Pump

A type of air source heat pump with an outdoor unit to exchange heat and indoor unit to deliver conditioned air to the living space. Refrigerant moves through tubes between the units. In smaller systems, one outdoor unit drives a single indoor unit. In other cases, one outdoor unit can drive two to four indoor units. They are very quiet and provide very even heating. Mini-splits are distinguished from central split-system heat pumps in several ways. First, capacity is smaller, ranging from 8,000 BTUs per hour to 24,000 BTUs per hour. Second, each indoor unit serves a small area, so multiple indoor units may be needed for larger homes. Third, duct work is generally not used, although sometimes short ducts may be installed inside the conditioned space of the building. Fourth, current models use an inverter-drive compressor that provides variable speed operation to match output to the need of the conditioned space. Fifth, the most energy efficient mini-splits can be up to 400% efficient, exceeding the most efficient central heat pumps. Sixth, mini-splits operate efficiently at very low outdoor temperatures. Sometimes they are called ductless heat pumps.

Net Metering

A method for giving credit for excess electricity produced by a consumer’s home, often by means of solar panels. In most zero energy homes, the excess energy produced in the summer goes to the utility grid and credit is given, via net metering, for the energy supplied. Then in the winter, the home can use the credit to power the home without an energy bill. Net metering arrangements vary widely between locations and must be thoroughly researched before undertaking a zero energy home project.

Passive House Standard

A voluntary international building standard developed by the Passive House Institute (PHI). The Passive House Standard is composed of several strict performance requirements for new building construction, including a roughly 90% reduction in heating and cooling energy usage in new construction, and up to a 75% reduction in primary energy usage from existing building stock. These strict standards must be met using passive design measures before any renewable energy, such as photovoltaic panels, are added.>

Passive Solar

A type of design which takes maximum advantage of the sun’s energy to help warm the living space in winter and helps to redirect or block the sun’s energy to reduce cooling needs in the summer. Passive systems rely on the building structure to achieve greater efficiency and comfort, as compared to active systems that use mechanical devices and energy inputs to increase efficiency. Solar water heaters or photovoltaic systems are examples of active systems.

Photovoltaic (PV)

This system captures light from the sun and converts it into electricity through solar panels usually installed on roofs.

Programmable Thermostat

Programmable thermostats save energy by permitting occupants to set temperatures according to whether the house is occupied and allowing homeowners to set the temperature at different levels at different times of day. For example, in winter, it could be set to be colder while occupants sleep and warmer as occupants awaken. These thermostats typically have a digital interface that allows more precise temperature control and a wider range of options or features for saving energy.

Radiant Barrier

A barrier, installed on the underside of roof sheathing in warm or hot climates to reflect some of the sun’s radiant heat energy so it does not enter the attic. Radiant barriers can also help prevent winter heat loss from the home. Radiant barriers are most useful in cooling-dominated climates where summer heat gain is a greater concern that winter heat loss.

Radiant Heated Floors

A way to heat spaces using radiant energy that is emitted from a heat source. There are three types of radiant floor heat: radiant air floors (air is the heat-carrying medium); electric radiant floors; and hot water (hydronic) radiant floors. Hydronic radiant floors are the most energy efficient.

Radiant Floors – Hydronic

A popular and cost-effective choice that pumps heated water from a boiler through tubing underneath the floor. In some systems, the temperature in each room is controlled by regulating the flow of hot water through each tubing loop. This is done by a system of zoning valves or pumps and thermostats. The most efficient source of hot water for hydronic radiant floors is a ground source heat pump in most applications.


Adding new energy efficient features, such as added insulation or solar collectors, either in a new home after completion or in an existing home.


R-value indicates an insulation material’s resistance to heat flow. The higher the R-value, the greater the insulating effectiveness. This is the inverse of U-value, which is used for rating windows.

Sealed Combustion Fireplace / Wood Stove

A sealed combustion fireplace or woodstove gets its combustion air from outside of the home and exhausts 100 percent of the combustion by-products to the outside. This eliminates the likelihood of “backdrafting,” a situation in which combustion gases are pulled back into the home and cause health problems. It also eliminates the use of heated indoor air for combustion and sending it up the chimney.

Sealed Ducting

A way to save energy, improve indoor air quality and avoid moisture damage by sealing all the seams in newly installed ductwork or by sealing improperly installed existing ducts. Duct mastic is a paste-like sealant that is applied with a brush or a gloved hand for sealing ducts.

SEER Rating

Seasonal Energy Efficiency Ratio (SEER) is a rating system used to measure the efficiency of central air conditioners and air source heat pumps. The higher the rating, the more energy efficient it is. For reference, air conditioners that are 14 or higher SEER meet ENERGY STAR criteria.

Structured Insulated Panels (SIP)

Panels made from a thick layer of foam (polystyrene or polyurethane) sandwiched between two layers of oriented strand board (OSB), plywood or fiber-cement. SIPS are often used in panelized construction and timber-frame buildings. The result is an engineered panel that provides structural framing, insulation, and exterior sheathing in a single, solid component.

Solar Hot Water

Solar thermal collectors on the roof supplement (but do not exclusively supply) the hot water to the home. Water pre-heated by solar energy is piped into the hot water heater so that less energy is required to bring the water up to the temperature setting of the conventional water heater. Solar water heaters can reduce water heating energy by around 80 percent for a family. Except in homes with many inhabitants who use a great deal of hot water, it is more cost effective to install a heat pump water heater or power a standard electric water heater with solar PV.

Solar Orientation

In northern latitudes, a home that is oriented toward the south will capture the sun’s heat during the winter, but will be shielded from overheating during the summer. Southern exposure also increases the amount of natural daylight that can be gathered by windows. Solar orientation is a key element of passive solar design.

Spray Foam Insulation

Insulation that is sprayed into place and then expands to fill cavities. It both insulates and seals air leaks. It can be used to replace standard insulation batts or in combination with other types of insulation to optimize costs and benefits. The two types of spray foam are open cell (low-density) and closed cell (high-density). Closed cell foams typically have a higher R-value and are more vapor impermeable compared to open-cell foam.


External awnings, overhangs, and plantings or internal window treatments or shades, which effectively block the sun’s heat in summer, while allowing it to enter in winter.

Sustainable Resources

Resources that are renewable or recyclable and are used in ways that do not deplete the supply, so future generations can use the same materials.

Sustainable Flooring

Flooring made from bamboo, cork, reclaimed wood, or other rapidly renewable wood sources.

Tankless Water Heater

A system that delivers hot water at a preset temperature when needed, but without requiring the storage of water. Tankless water heaters have an electric, gas, or propane heating device that is activated by the flow of water. The approach reduces or eliminates energy standby losses. Tankless water heaters can be used for supplementary heat, such as a booster to a solar hot water system, or to meet all hot water needs.

Thermal Barrier

When the building envelope is insulated and air-sealed it acts as a thermal barrier – keeping cold air out and warm air inside in winter.

Triple Pane Windows

Triple pane glass windows often contain argon, krypton, or other gases between 3 panes to reduce heat flow and improve insulation. The middle pane may be glass or a plastic film.


Also called U-factor, this is the rate of heat flow expressed as a decimal number. Higher numbers mean greater heat loss. U-value is used to express the energy performance of windows. Zero energy homes often have windows with U-values between 0.15 to 0.24. U-value is the reciprocal of R-value.

VOCs (volatile organic compounds)

Organic gases with harmful effects on air quality and health. VOCs are frequently associated with paint, pesticides, carpets, and adhesives. They are often the carrier chemicals that evaporate as the product cures. VOCs can be released into the air for months or even years after a product is installed. The VOC content of paints, coatings, finishes, adhesives and sealants is listed on the product label in grams per liter. In some products, VOCs can reach zero, while others still contain VOCs at a reduced level. To be considered low-VOC, interior or exterior house paint would need to be 50 grams per liter or less.

Water Footprint

An estimation of the amount of water used in a building.


A landscaping method used in drier areas that incorporates native plants that can tolerate infrequent watering.

Zero Energy Home

A home that uses as much energy as it produces. The home is made as air-tight and well-insulated as possible and uses highly energy efficient heating and cooling systems, hot water system and appliances. After all the energy saving measures have been taken, sufficient solar electric panels are added to balance the amount of energy produced with the amount of energy used over the course of a year.

Zero Energy Ready Home

A zero energy ready home is one that is built to the same energy saving standards as a zero energy home and has the roof space and all the fixtures installed ready for solar installation However, the solar panels and inverter are not installed at the time of construction. It is ready for solar collectors that can easily be installed at a later day.

Adapted in part from The Green Resource Council’s Green Building Glossary