Net Zero Energy Homes

Imagine a home that is not only energy efficient, but also produces all the power it needs. Just like a typical home, a Net Zero Energy Home is connected to, and uses energy from, the local electric utility. But unlike typical homes, the Net Zero Energy Home makes power to send back to the utility. Annually, a Net Zero Energy Home produces enough energy to offset the amount purchased from the utility-resulting in a net-zero annual energy bill.A Net Zero Energy Home combines state-of-the-art, energy-efficient construction techniques and equipment with renewable energy systems (photovoltaic panels, solar thermal panels, wind turbines, geothermal mechanical systems, etc.) to come as close as possible to being self-sufficient in its energy usage on an annual basis. Specifically, when renewable resources cannot provide all of the home's power, e.g., at night or on a cloudy day, the homeowner purchases energy from the utility company. When renewable resources produce more than the house is using, e.g., during sunny days when no one is home, power is sent back into the utility grid. Some utilities operate the home's electric meter in reverse, essentially providing the homeowners full retail value for their energy.

Home Energy Ratings (HERs)

Home energy ratings (HERs) provide a standard measurement of a home’s energy efficiency. Ratings are used for both new and existing homes. In new homes, ratings often verify energy performance for the ENERGY STAR homes program, energy efficient mortgages, and energy code compliance. Homeowners who want to upgrade the home’s energy efficiency can use the energy rating to evaluate and pinpoint specific, cost-effective improvements.

A HERS rating results in a score that is based on national standards produced by RESNET. A HERS index of 100 is what a standard built-to-code new home would score, while a net-zero energy home would score a 0. Older, existing homes may score a higher number than 100, as they were not built to modern day building codes.Ratings are projected prior to the construction of a home, or prior to the installation of energy improvements to an existing home based on the design specification.

At the completion of the project, ratings are confirmed using data gathered from an on-site inspection, which could include performance testing of the home.The chart on the right shows the scores required for various programs and building codes in the area. The Boulder County and City of Boulder codes require better HERS scores for larger houses. The EPA's Energy Star program requires a score of 85. LEED for Homes (LEED-H) starts at HERS 85, then additional points are awarded for every HERS point above 85. Federal tax credits for builders require an approximate HERS score of 60, but the requirement is not directly tied to a HERS score.