Air infiltration - Air that leaks into a home through any opening in a home's structure. This may include seams where walls meet other walls, window or door frames, chimneys; and holes where wires or pipes penetrate walls, floors or ceilings/roofs. Air infiltration is one of the major causes of unwanted heat loss or gain in a home.

Caulk - A substance used to seal air infiltration points between areas where exterior and interior wall surfaces meet window and door frames and at corners formed by siding. There are various forms of caulk. Most come in tubes and are applied using a caulk "gun".

Compact Fluorescent Lamps (CFLs) - A light bulb using fluorescent technology that can be used on many of the same fixtures traditionally used by standard incandescent bulbs. CFLs light levels are comparable to 20- to 150-watt traditional bulbs but use 70 to 75 percent less energy. They also last 10 to 13 times longer.

Composite Wood - A product consisting of wood or plant particles or fibers bonded together by a synthetic resin or binder. Examples include plywood, particleboard, oriented-strand board (OSB), medium-density fiberboard (MDF) and composite door cores.

Conduction - Transfer of heat through solid objects - glass, drywall, brick or other building materials. The greater the difference between temperatures, the faster the conduction occurs and the more heat a home can lose or gain.

Convection - Transfer of heat to or from a solid surface via a gas or liquid current. In terms of home heating loss or gain, convection is caused by the gas (in this case air) currents that carry heat from occupants' bodies, furniture, interior walls and other warm objects to windows, floors, ceilings, exterior walls and other cooler surfaces.

Drip Irrigation System - A network of pipes and valves that rest on the soil or underground and slowly deliver water to the root systems of plants. Drip irrigation saves water by minimizing evapotranspiration and topsoil runoff.

Dual-flush Toilets - A toilet with two flush volumes - one for solid waste and a reduced volume for liquid waste.

Energy Efficiency Ratio (EER) - Measures how efficiently a cooling system will operate when the outdoor temperature is at a specific level (95°F). The higher the EER, the more efficient the air conditioner is.

Green Rater - An individual who performs field inspections and performance testing of LEED for homes measures.

Heat Pump - An air conditioner with a reversible valve, allowing it to operate in reverse - removing heat from your home to the outdoors in the summer, and removing heat from the outdoor air and passing it through into your house during the winter. Heat pumps do not actually create heat - they just move it from one place to another - which make them more efficient than other forms of heating.

Home Energy Rating System (HERS) - A system for evaluating the energy efficiency of a home using an energy simulation model. A HERS index of 100 represents the energy efficiency of a home that meets basic IECC code requirements. Each additional index point represents a 1-percent increase in energy use, and lower index numbers indicate the percentage savings in energy use.

Insulation - A product that inhibits heat transfer. Some materials are better insulators than others; however, if processed properly, any product - including glass, cotton, paper and plastic can be used to make insulation.

Low-E Glass - Low-E (low emissivity) refers to a transparent metallic coating applied to a surface of insulated glass. During the winter, Low-E reflects some interior light back into the home. During the summer, Low-E glass reduces the amount of the sun's heat entering the home.

Payback Period - The amount of time it takes to get a full return on an investment. For example, if a high-efficiency air conditioner costs $300 more than a lower-efficiency version but saves $100/year in energy costs, the payback period would be three years.

R-value - A measurement of a material's ability to resist heat transfer. Insulation products are rated according to the R-value. The higher its R-value, the greater the product's ability to resist heat flow.

Radiant Barrier - Thin sheets of highly reflective material, such as aluminum, that reduce heat transfer from thermal radiation across the airspace between the roof and attic floor.

Radon - A radioactive gas that naturally vents from the ground. Not all homes have problems with radon. High levels of radon are known to be carcinogenic.

Reclaimed Materials - Building components that have been recovered from a demolition site and reused in their original state (i.e., not recycled). Also known as salvaged or reused material.

Seasonal Energy Efficiency Ratio (SEER) - Used to measure the efficiency of a central air conditioner. It measures how efficiently a cooling system will operate over an entire season. The higher the SEER, the more efficient the air conditioner is.

Settled Density - The depth of insulation remaining after it has settled. Most often used with loose-fill insulations. To ensure insulation maintains its desired insulating value (R-value) once settled, the recommendation depth at installation should be 20 to 25 percent deeper than what the settled density R-value requires.

Solar Gain - Heat that builds up inside a structure from sunlight that enters through windows and is converted to heat after striking other surfaces inside the home. During summer months, solar gain can cause as much as 50 percent of the interior heat gain in a home.

Thermal Envelope - The thermal enclosure created by the building exterior and insulation.

U-value - The measurement of heat can flow through glass, brick, drywall and other building materials. The higher the U-value, the less efficient the building material.

Vapor Barrier - Material designed to resist the migration of moisture through a wall or other building component. The most common vapor barriers are made of plastic, but can also include oil paint.

Volatile Organic Compound (VOC) - A carbon compound that vaporizes (becomes a gas) at normal room temperatures. VOC's contribute to air pollution directly and through atmospheric photochemical reactions to produce secondary air pollutants, usually ozone and peroxyacetyl nitrate.