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Energy and Energy Efficiency Dictionary
This dictionary contains definitions for most popular energy efficiency and other technical terms used on this site as well as many other energy efficiency related terms.
Heat loss
– All fuel-burning systems (natural gas, oil, propane, wood) lose heat because of stopping and starting, cold start-up, incomplete combustion, heat carried away in combustion gases, and warm house air drawn up the chimney. The extent of these losses determines the efficiency of a furnace or boiler, given as a percentage indicating the amount of original heat that actually warms the house. Electric space heating equipment, which uses electric resistance heating, is typically 100 per cent efficient because all the electrical energy used is converted into heat and there are no combustion losses through the chimney.
Steady-state efficiency
– measures the maximum efficiency of the furnace after it has been running long enough to reach its peak operating temperature. This is an important standardized testing procedure that is used by a serviceperson to adjust the furnace, but the figure it gives is not the efficiency achieved by the furnace or boiler in actual use over the course of a heating season. Think of the difference between the fuel consumption figures for city and highway driving published for cars. Steady-state efficiency in a furnace is like the best fuel mileage you can get when driving on the highway.
Seasonal efficiency (also known as the annual fuel utilization efficiency (AFUE)
– takes into consideration not only normal operating losses, but also the fact that most heating equipment rarely runs long enough to reach its steady-state efficiency temperature, particularly during milder weather at the beginning and end of the heating season. This figure is useful because it is a good indication of how much annual heating costs will be reduced by improving existing equipment or by replacing it with a higher efficiency unit.
Cost-Effectiveness
- A measure of the relevant economic effects resulting from the implementation of an energy efficiency measure. If the benefits outweigh the cost, the measure is said to be cost-effective. An indicator of the relative performance or economic attractiveness of any energy efficiency investment or practice. In the energy efficiency field, the present value of the estimated benefits produced by an energy efficiency program is compared to the estimated total costs to determine if the proposed investment or measure is desirable from a variety of perspectives (e.g., whether the estimated benefits exceed the estimated costs from a societal perspective).
Effective Useful Life
- An estimate of the median number of years that the efficiency measures installed under a program are still in place and operable.
Decoupling
- A mechanism that weakens or eliminates the disincentive for EE by breaking the relationship between sales and revenue (or more narrowly the revenue collected to cover fixed costs) and allows a utility to adjust rates to recover authorized revenues independent of the level of sales.
Lost Revenue Adjustment Mechanisms
- Mechanisms that attempt to estimate the amount of fixed cost or margin revenue that is “lost” as a result of reduced sales. The estimated lost revenue is then recovered through an adjustment to rates.
Program Cost Recovery
- Recovery of the direct costs associated with program administration (including evaluation), implementation, and incentives to program participants.
Straight Fixed-Variable
- A rate structure that allocates all current fixed costs to a per customer charge that does not vary with consumption. Such a rate structure is undesirable because conservation incentive for customer is lost.
Throughput Incentive
- The incentive for utilities to promote sales growth that is created when fixed costs are recovered through volumetric charges without a decoupling mechanism. Many have identified the throughput incentive as the primary barrier to aggressive utility investment in energy efficiency.
Baseline
- Conditions, including energy consumption and related emissions that would have occurred without implementation of the subject project or program. Baseline conditions are sometimes referred to as “business-as-usual” conditions. Baselines are defined as either project-specific baselines or performance standard baselines.
Baseline Period
- The period of time selected as representative of facility operations before the energy efficiency activity takes place.
Deemed Savings
- An estimate of an energy savings or energy-demand savings outcome for a single unit of an installed energy efficiency measure that (a) has been developed from data sources and analytical methods that are widely considered acceptable for the measure and purpose and (b) is applicable to the situation being evaluated.
Evaluation, Measurement, And Verification (EMandV)
- The performance of studies and activities aimed at determining and documenting the results, benefits, and effects of an EE program; any of a wide range of assessment activities associated with understanding or documenting program performance, assessing program or program-related markets and market operations; any of a wide range of evaluative efforts including assessing program-induced changes in energy efficiency markets, levels of demand or energy savings, and program cost-effectiveness. “Evaluation” refers to any real time and/or retrospective assessment of the performance and implementation of a program. “Measurement and verification” is the subset that includes data collection, monitoring, and analysis undertaken in the calculation of energy and demand savings from individual sites or projects.
Free Driver
- A non-participant who has adopted a particular efficiency measure or practice as a result of the evaluated program.
Free Rider
- A program participant who would have implemented the program measure or practice in the absence of the program. Free riders can be total, partial, or deferred.
Impact Evaluation
- An evaluation of the program-specific, directly induced changes (e.g., energy and/or demand usage) attributable to an energy efficiency program. Used to determine the actual savings achieved by different programs and specific measures.
Market Effects Evaluation
- Used to estimate a program’s influence on encouraging future energy efficiency projects because of changes in the energy marketplace. All categories of programs can have market effects evaluations; however, these evaluations are primarily associated with market transformation programs that indirectly achieve impacts.
Net Penetration Rate
- The difference between the anticipated adoption rate of the efficiency measures after intervention and the “business as usual” adoption rate absent efficiency intervention.
Persistence Study
- A study to assess changes in program impacts over time (including retention and degradation).
Process Evaluation
- Used to verify whether the energy efficiency program is correctly implemented and to understand any problems or issues that arise in program implementation.
Appliance Efficiency Standards
- Standards that regulate the minimum performance requirements for appliances sold, including refrigerators, freezers, room air conditioners, central air conditioners, gas space heaters, water heaters, plumbing fittings, fluorescent lamp ballasts and luminaries, and ignition devices for gas cooking appliances and gas pool heaters.
Base Load
- The lowest level of power production needs during a season or year. And: The minimum amount of electric power delivered or required over a given period of time at a steady rate.
Base Load Plant
- A plant, usually housing high-efficiency steam-electric units, that is normally operated to take all or part of the minimum load of a system, and which consequently produces electricity at an essentially constant rate and runs continuously. These units are operated to maximize system mechanical and thermal efficiency and minimize system operating costs, and are intended to run constantly at near capacity levels, as much of the time as possible.
Building Efficiency Standards
- Standards that regulate energy efficiency of buildings constructed.
Capacity Factor
- A percentage that tells how much of a power plant’s capacity is used over time. For example, typical plant capacity factors range as high as 80 percent for geothermal and 70 percent for co-generation.
Co-Benefits
- The impacts of an energy efficiency program other than energy and demand savings.
Combined Cycle
- An electric generating technology in which electricity is produced from otherwise lost waste heat exiting from one or more gas or combustion turbines. The exiting heat is routed to a conventional boiler or to a heat recovery steam generator for utilization by a steam turbine in the production of electricity. This process increases the efficiency of the electric generating unit.
Demand
- The time rate of energy flow. Demand usually refers to electric power measured in kW (equals kWh/h) but can also refers to natural gas, usually as Btu/hr, kBtu/hr, therms/day, etc. The level at which electricity or natural gas is delivered to users at a given point in time.
Demand-Side Management (DSM)
- Planning, implementation, and evaluation sponsored programs to influence the amount or timing of customers’ energy use. Includes conservation, efficiency, load management, demand response, and fuel substitution.
Distributed Generation
- A distributed generation system involves small amounts of generation located on a utility’s distribution system for the purpose of meeting local (substation level) peak loads and/or displacing the need to build additional, or upgrade, local distribution lines.
Distribution
- The delivery of electricity to the retail customer’s home or business through low voltage distribution lines.
End-Use
- A category of equipment or service that consumes energy (e.g., lighting, refrigeration, heating, process heat).
Energy Efficiency (EE)
- The use of less energy to provide the same or an improved level of service to the energy consumer in an economically efficient way; or using less energy to perform the same function.
Energy Efficiency Measure
- Installation of equipment, subsystems or systems, or modification of equipment, subsystems, systems, or operations on the customer side of the meter, for the purpose of reducing energy and/or demand (and, hence, energy and/or demand costs) at a comparable level of service.
Energy Service Company (ESCO)
- A company that offers to reduce a client’s electricity consumption with the cost savings being split with the client.
Gross Savings
- The change in energy consumption and/or demand that results directly from program-related actions taken by participants in an efficiency program, regardless of why they participated.
Integrated Resource Planning
- A public planning process and framework for developing an approved utility resource plan for utility investments in supply and demand side resources. Costs and benefits of both demand- and supply-side resources, as well as attributes outside the basic provision, or reduction, of electric capacity and energy, are evaluated to develop the least-total-cost mix of utility resource options. In many states, integrated resource planning includes a means for considering environmental damages caused by electricity supply/transmission and identifying cost-effective energy efficiency and renewable energy alternatives.
Load
- An end use device or an end use customer that consumes power. Load should not be confused with demand, which is the measure of power that a load receives or requires. Or: The amount of electric power supplied to meet one or more end user’s needs.
Load Factor
- A percent telling the difference between the amount of electricity a consumer used during a given time span and the amount that would have been used if the usage had stayed at the consumer’s highest demand level during the whole time. The term also is used to mean the percentage of capacity of an energy facility such as power plant or gas pipeline that is utilized in a given period of time.
Load Management
- Steps taken to reduce power demand at peak load times or to shift some of it to off peak times. This may be with reference to peak hours, peak days or peak seasons. The main thing affecting electric peaks is air conditioning usage, which is therefore a prime target for load management efforts. Load management may be pursued by persuading consumers to modify behavior or by using equipment that regulates some electric consumption.
Load Profiles
- Representations such as graphs, tables, and databases that describe energy consumption rates as a function of another variable such as time or outdoor air temperature.
Loading Factor
- Ratio of actual electricity consumed and total potential consumption. Used when analyzing electricity consumption in a large population. A loading factor of 0.5 means that 50% of homes are consuming all of the electricity they are able or that, on average, all of the homes are only consuming 50% of the power they have the potential to consume.
Local Distribution Company (LDC)
- A utility that delivers natural gas to end-use customers through its own distribution system.
Market Transformation
- A reduction in market barriers resulting from a market intervention, as evidenced by a set of market effects, that lasts after the intervention has been withdrawn, reduced, or changed.
Net Savings
- The total change in load that is attributable to an energy efficiency program. This change in load may include, implicitly or explicitly, the effects of free drivers, free riders, energy efficiency standards, changes in the level of energy service, and other causes of changes in energy consumption or demand.
Net-To-Gross Ratio (NTG)
- A factor representing net program savings divided by gross program savings that is applied to gross program impacts to convert them into net program load impacts. This ratio accounts for only those energy efficiency gains that are attributed to, and the direct result of, the energy efficiency program in question. Consequently, it gives evaluators an estimate of savings that would have occurred without program incentives.
Peak Demand
- The maximum level of metered demand during a specified period, such as a billing month or a peak demand period.
Program Administrators
- Typically procure various types of energy efficiency services from contractors (e.g., consultants, vendors, engineering firms, architects, academic institutions, community-based organizations), as part of managing, implementing, and evaluating their portfolio of energy efficiency programs. Program administrators in many states are the utilities; in some states they are state energy agencies or third parties.
Public Goods Charge (PGC)
- A non-bypassable surcharge imposed on all retail sales to fund public goods research, development and demonstration, and energy efficiency activities, and support low-income assistance programs.
Rebound Effect
- A change in energy-using behavior that yields an increased level of service and occurs as a result of taking an energy efficiency action.
Resource Acquisition Program
- Programs designed to directly achieve energy and or demand savings.
Retrofit
- Refers to an efficiency measure or efficiency program that seeks to encourage the replacement of functional equipment before the end of its operating life with higher efficiency units (also called “early-retirement”) or the installation of additional controls, equipment, or materials in existing facilities for purposes of reducing energy consumption (e.g., increased insulation, lighting occupancy controls, economizer ventilation systems).
System Benefits Charge (SBC)
- A surcharge dictated by statute that is added to customers’ bills to pay for energy efficiency programs that may be administered by utilities or other entities.
Total Resource Requirements
- Represents total expected (energy or capacity) demand in the absence of any energy efficiency measures or strategies. It can also be thought of as the sum of all supply-side and demand-side resources in the utility’s portfolio.
Transmission
- The movement or transfer of electric energy over an interconnected group of lines and associated equipment between points of supply and points at which it is transformed for delivery to consumers, or is delivered to other electric systems. Transmission is considered to end when the energy is transformed for distribution to the consumer.
Avoided Costs
- The forecasted economic benefits of energy savings. These are the costs that would have been spent if the energy efficiency had not been put in place.
Cost Of Service
- A method of using utility costs in rate design; a cost of service study measures a utility’s costs incurred in serving each customer class, including a reasonable return on investment.
Cost Recovery
- Recovery of the direct costs associated with utility program administration (including evaluation), implementation, and incentives to program participants.
Depreciation
- A means of accounting for the wearing out or gradual obsolescence of a utility plant’s equipment and buildings.
Fixed Costs
- Expenses incurred by the utility that do not change in proportion to the volume of sales within a relevant time period. E.g., steel and cement in the ground.
Independent Variables
- The factors that affect energy use and demand, but cannot be controlled (e.g., weather or occupancy).
Levelized Cost
- A constant value or payment that, if applied in each year of the analysis, would result in a net present value equivalent to the actual values or payments which change (usually increase) each year. Often used to represent, on a consistent basis, the cost of energy saved by various efficiency measures with different useful lives.
Lost Margin
- The reduction in revenue to cover fixed costs, including earnings or profits in the case of investor-owned utilities. Similar to lost revenue, but concerned only with fixed cost recovery, or with the opportunity costs of lost margins that would have been added to net income or created a cash buffer in excess of that reflected in the last rate case.
Marginal Cost
- The sum that has to be paid for the next increment of product or service. The marginal cost of electricity is the price to be paid for kilowatt-hours above and beyond those supplied by presently available generating capacity.
Performance-Based Ratemaking
- An alternative to traditional return on rate base regulation that attempts to forego frequent rate cases by allowing rates or revenues to fluctuate as a function of specified utility performance against a set of benchmarks.
Rate Of Return
- This figure, which is expressed as a percentage, reflects the utility’s weighted cost of capital.
Return On Equity
- The profits distributed to common shareholders after all expenses, interest costs, and preferred stock dividends have been paid. In ratemaking, it represents the level of revenue needed that will permit equity stockholders the opportunity to earn a fair return on their investment in the utility. Based on an assessment of the financial returns that investors in that utility would expect to receive, an expectation that is influenced by the perceived riskiness of the investment.
Revenue Requirement
- The total amount of revenue needed to pay all operating and capital costs of doing business.
Shared Savings
- Incentive mechanisms that give utilities the opportunity to share the net benefits from successful implementation of energy efficiency programs with customers.
Stranded Costs
- Prudent costs incurred by a utility that may not be recoverable under market-based deregulation. Examples are un-depreciated generating facilities, deferred costs, and long-term contract costs.
Achievable Potential
- The amount of energy use that efficiency can realistically be expected to displace assuming the most aggressive program scenario possible (e.g., providing end-users with payments for the entire incremental cost of more efficiency equipment). The result of estimating how much market barriers and program uptake limits will reduce the economic potential. This is often referred to as maximum achievable potential, which is a larger subset than program potential, but smaller subset than economic potential and technical potential. See Economic Potential, Technical Potential, Program Potential.
Cream Skimming
- The pursuit of only the lowest cost energy efficiency measures, which results in leaving behind other cost-effective opportunities. Cream skimming becomes a problem when lost opportunities are created in the process.
Economic Potential
- Refers to the subset of the technical EE potential that is economically cost-effective as compared to conventional supply-side energy resources. The result of reducing the technical potential by applying cost-effectiveness and program eligibility criteria. This subset is smaller than technical potential, but larger than achievable and program potential.
Lost Opportunity
- Those energy efficiency options which offer long-lived, cost-effective savings and which, if not exploited promptly or simultaneously with other low cost energy efficiency measures or in tandem with other load-reduction technologies or distributed generation technologies being installed at the site (e.g., solar heating or photovoltaics), are lost irretrievably or rendered much more costly to achieve.
Planning Study
- A study of energy efficiency potential used by demand-side planners within utilities to incorporate efficiency into an integrated resource planning process. The objective of a planning study is to identify energy efficiency opportunities that are cost-effective alternatives to supply-side resources in generation, transmission, or distribution.
Potential Study
- A study conducted to assess market baselines and energy efficiency savings potentials for different technologies and customer markets. Potential is typically defined in terms of technical, economic, achievable, and program potential.
Program Design Potential Study
- Can be undertaken by a utility or third party for the purpose of developing specific measures for the energy efficiency portfolio.
Program Potential
- The efficiency savings that can be realistically realized from the achievable potential, given the budget, staffing, and time constraints for the efficiency program. Program potential establishes the total, or gross, savings expected from a program. This subset is the smallest of all the potentials.
Technical Potential
- The theoretical maximum amount of energy use that could be displaced by efficiency, disregarding all non-engineering constraints such as cost-effectiveness and the willingness of end-users to adopt the efficiency measures. This subset is the largest of all the potentials.
Insulation Terminology
Insulation
- Insulation is a substance that resists the transfer of heat, generally by incorporating small pockets of air. Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness.The R-value of thermal insulation depends on the type of material, its thickness and density.
Radiant barrier
- Radiant barriers are thin sheets of highly reflective material, like aluminum, which reduce heat transfer from thermal radiation across the air space between the roof and the attic floor. Radiant barrier do nothing to prevent heat transfer by conduction or convection.
U-Value
- U-Value is a measurement of heat flow. The lower the U-value the more slowly the material transfers heat in and out of your home.
R-Value
- R-value is a measurement of heat resistance. It is the inverse of the U-value, so the higher the R-value the better the insulation resists heat transfer. Many factors can affect the R-value of insulation, including the type of insulation, and the age of the insulation. To determine the R-value of the insulation in your house, first determine the type of insulation present, whether that insulation is new, and measure the depth of the insulation in inches. Look your insulation up on the table below, and multiply the R-value per inch by the number of inches present in your house.
Fiberglass
- Fiberglass is the most familiar type of insulation. It is spun from molten glass, and is pure white in its virgin state. Additives and binders often color the fiberglass, with pink and yellow being the most common. Fiberglass comes in rolls, batts and as loose insulation which is blown into place.
Rockwool
- Dirty grey, although the color can range through green and brown as well. Rockwool looks like old wool with dark flecks, and you can often find what looks like sand or small pebbles underneath the insulation. Rockwool is spun, like fiberglass, from the slag from refining metals. The debris that settles underneath the insulation is remnants of the slag, and condensed droplets of metal.
Cellulose
- Cellulose insulation is made from wastepaper, such as used newspaper and boxes. It is shredded into small particles, and chemicals providing resistance to fire and insects are added. Cellulose insulation is dusty and brown, with flat particles, on which you can frequently find legible print.
Perlite
- Perlite is a white gravelly, yet extremely light material. It is the same material found in garden centers and used as part of potting mixtures. Perlite is no longer used as an insulating material, except for the occasional do-it-yourselfer, although it is not uncommon to find it in existing houses.
Vermiculite
- Vermiculite is made from expanded mica, a mineral. Vermiculite used as insulation is identical to the material found in garden centers. Like perlite, it is generally no longer used for insulation, although again, it can still be found in existing houses.
Rigid Boards
- Rigid boards are fibrous materials or plastic foams pressed or extruded into board-like forms. These provide thermal and acoustical insulation, strength with low weight, and coverage with few heat loss paths.
Heating, Ventilation and Cooling Terminology
System Capacity
- System capacity is a measurement of the total amount of heat or cooling your furnace, heat pump or air conditioner can produce in one hour. This amount is reported in Btu/hr on the nameplate of your equipment.
Btu
- Btu, short for British Thermal Unit is a unit of heat energy. One Btu is the amount of heat needed to raise the temperature of one pound of water 1°F. To get a rough idea of how much heat energy this is, the heat given off by burning one wooden kitchen match is approximately one Btu.
AFUE
- The AFUE, or Annualized Fuel Utilization Efficiency, is the ratio of the total useful heat your gas furnace delivers to your house to the heat value of the fuel it consumes.
Heat Pump
- A heat pump is basically an air conditioner with a reversible valve that allows it to operate in reverse, removing heat from your house and shunting it outdoors in the summer, and removing heat from outdoor air and shunting it into your house in the winter. Because heat pumps do not actually create heat—they just move it from one place to another—heat pumps are more efficient than other forms of heating.
COP
- Coefficient of Performance, COP, is the ratio of energy input to heating capacity. This is the instantaneous measurement of the heating performance of your heat pump. It is comparable to knowing how many miles per gallon of gasoline your car gets when it is going full speed. You can find the COP on the nameplate of your heat pump.
HSPF
- The Heating Seasonal Performance Factor, HSPF, is an efficiency rating for heat pumps. It is a measure of the average number of Btu of heat delivered for every Watt-hour of electricity used by the heat pump over the heating season. It takes into account variations due to weather conditions over a season. HSPF is comparable to knowing how many miles per gallon of gasoline your car got, over the entire year.
EER
- Energy Efficiency Ratio, EER, is the instantaneous measurement of the cooling efficiency of your air conditioner or heat pump. The higher the EER for your air conditioner or heat pump, the more efficient it is.
SEER
- The Seasonal Energy Efficiency Ratio, SEER, measures the average cooling efficiency, over the entire cooling season for your air conditioner or heat pump.
Programmable Thermostat
- A thermostat with the ability to record different temperature settings for different times for your heating and/or cooling equipment. Programmable thermostats can be electronic, or mechanical. Here is a sample schedule for both heating and cooling.
ACH
- ACH stands for Air Changes per Hour. It is the number of times in one hour that the air in your house is completely replaced with outside air.
Conduction
- The transfer of heat through a solid material.
Convection
- The transfer of heat by air flow.
Radiation
- The transfer of heat directly from one surface to another (whithout the intermediate air acting as a transfer mechanism).
Lighting Terminology
Lumen
- A lumen is the total amount of light emitted from a source. Lumens are typically used to rate the output of lamps.
Lamp
- The lighting industry uses the term lamp to refer to the source of light, the light bulb itself, not the fixture where the light bulb is located.
Fixture
- The physical item referred to as a "lamp," i.e., "table lamp" or "floor lamp," is called the fixture by the lighting industry.
Incandescent lamp
- The most common source of light, glass bulbs with a filament inside. Approximately ninety percent of the energy consumed by an incandescent lamp is given off as heat rather than light.
Fluorescent lamp
- Fluorescent lamps are up to five times more efficient than incandescent lamps, and last up to twenty times longer. They require a special fixture. Electronic ballast fluorescents are a new efficient improvement over the traditional magnetic ballast fluorescents. Fluorescent lamps are available as straight tubes, U-shaped tubes, circular tubes and compact fluorescent lamps.
Compact Fluorescent Lamps
- These fluorescent lamps are small, and are designed to fit in regular lamp sockets. They do require a special fixture. The electronic ballast-based fluorescents are more efficient, and produce better light than the older magnetic ballast models.
Color Rendition or CRI
- The CRI rates the ability of the bulb to render an object's true color when compared to sunlight. Look for lamps with a CRI of 80 or higher.
Color Temperature or CCT
- The CCT refers to the color objects emit when heated to a certain temperature on the absolute temperature scale (Kelvin). The lower numbers correspond to reddish color and the higher to blue-white color. For color similar to incandescent lighting look for CCTs around 2700.
Window Efficiency Terminology
Multiple layers of glazing
- Each layer of additional glazing improves the efficiency of a window, as dead air between panes prevents conduction of heat. Proper spacing of panes prevents convection loops from occurring between the window panes, further reducing heat loss.
Tinted glazing
- Tinted glass and tinted window films reduce the amount of the sun's heat entering the building. The shading coefficient (SC) of a window is the amount by which the window reduces heat gain. The lower the shading coefficient, the less solar heat is admitted. New glazings reduce the heat gained by your house without reducing visibility as much as older tinted glass and films. Visible light transmittance (VLT) is the measure of the amount of light that comes through the window. Select a window with a VLT of 0.60 or higher.
Frame material
- Wood, vinyl or fiberglass frames conduct less heat than aluminum frames, increasing window efficiency.
Thermal break
- A material that doesn't transmit heat well, such as plastic, sandwiched inside the metal parts of the frame. This reduces the heat being transferred through the frame.Thermal breaks can be used in the spacer between panes of glass in multi-pane windows as well as in the main body of the frame.
Low-E glazing
- A special window coating that helps prevent the warmth inside your house from escaping through the glass in the winter (pyrolitic). A variation (solar control) is designed to block heat from the summer sun. Low-E coating can reduce energy use by up to 35 percent.
Gas fill
- An inert gas such as argon is used instead of air between the window panes. Inert gases have a much better insulation value than air.
Condensation
- Condensation is the buildup of water droplets on a cold window pane. This can occur on the inside of single pane windows, and in between the panes of multiple pane windows. Condensation on single pane windows can damage windowsill and wall surfaces if extensive. Condensation between the panes of multiple pane windows indicates a problem with the seal between the panes.
U-Value
- U-Value is a measurement of heat flow. The lower the U-value, the more slowly the window transfers heat in and out of your home.
R-Value
- R-value is a measurement of heat resistance. It is the inverse of the U-value, so the higher the R-value the better the window resists heat transfer.
Water Heater Terminology
Peak-hour demand
- The maximum water usage, in gallons/hour, during the time of day when your family is likely to use the greatest amount of hot water.
First-hour rating
- The ability of a water heater to meet peak-hour demands. It measures how much hot water the heater will deliver during a busy hour. The first-hour rating accounts for the effects of tank size, and how quickly cold water is heated.
Standby losses
- Storage water heaters constantly loose heat by conduction through the walls of the tank, and through the first few feet of water pipes. To reduce standby losses, insulate the tank, the first two feet of the cold water inlet pipe, and the first three feet of the hot water outlet pipe.
Energy Factor
- The efficiency of storage water heaters is indicated by its Energy Factor (EF), which is based on an average hot water consumption of 64 gallons/day. The higher the EF, the more efficient the water heater.
Recovery efficiency
- How efficiently heat from the heat source is transferred to the water. The hot water tank, the recovery efficiency for a fuel-fired water heater must be 1 or less (it represents the fraction of energy in the fuel that actually makes it into the hot water). A reasonable value to use for recovery efficiency is 0.76.
Storage capacity
- The gallons of hot water a storage water heater can hold in the storage tank.
Water Heater Temperature
- Water heaters have a thermostat which controls the temperature of the water. You can save money by lowering the temperature of your water heater to 120°F (about midway between the "Low" and "Medium" settings). If you have a dishwasher without a heating element, you should leave your thermostat on the "Medium" setting (140°F).