Best Practice Guide

Glossary

Introduction

Planning an Energy Program

Funding and Approval

Lighting

Building Envelope

Central HVAC System

Distributed Generation

Demand Response

Commissioning

Procurement Policy

Water Use

Education

Energy Efficiency in Telecommuting

Resources and Appendices

Lessons Learned

Best Practice Guide Glossary

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U-value or U-factor Return to list of terms

A measure of how well heat is transferred by the entire window - the frame, sash and glass - either into or out of the building. U-value is the opposite of R-value. The lower the U-factor number, the better the window will keep heat inside a home on a cold day.

Source: California Energy Commission