5-i

CHAPTER 5. ENGINEERING ANALYSIS

TABLE OF CONTENTS

5.1 INTRODUCTION ........................................................................................................... 5-1

5.2 PRODUCT CLASSES ANALYZED.............................................................................. 5-1

5.3 EFFICIENCY LEVELS................................................................................................... 5-2

5.3.1 Baseline Units.................................................................................................................. 5-2

5.3.2 Incremental Standby Power Levels ................................................................................. 5-3

5.4 METHODOLOGY OVERVIEW.................................................................................... 5-5

5.4.1 AHAM Data Submittal .................................................................................................... 5-6

5.4.2 Manufacturer Interviews.................................................................................................. 5-6

5.4.3 Product Teardowns .......................................................................................................... 5-6

5.4.3.1 Selection of Units........................................................................................... 5-7

5.4.3.2 Generation of Bill of Materials...................................................................... 5-7

5.4.3.3 Cost Structure of the Spreadsheet Models..................................................... 5-8

5.4.4 Product Testing ................................................................................................................ 5-9

5.5 ANALYSIS AND RESULTS.......................................................................................... 5-9

5.5.1.1 AHAM Data................................................................................................... 5-9

5.5.1.2 Product Testing and Teardowns................................................................... 5-11

LIST OF TABLES

Table 5.3.1 Standby Power Levels for Microwave-Only Ovens and Countertop 

Combination Microwave Ovens.......................................................................... 5-4

Table 5.3.2 Standby Power Levels for Built-In and Over-the-Range Combination 

Microwave Ovens................................................................................................ 5-5

Table 5.4.1 Engineering Analysis Methods............................................................................ 5-6

Table 5.4.2 Major Manufacturing Processes .......................................................................... 5-8

Table 5.5.1 Microwave Oven Standby Power Comparison.................................................. 5-11

Table 5.5.2 Microwave-Only Oven Features (Table 1 of 4)................................................. 5-13

Table 5.5.3 Microwave-Only Oven Features (Table 2 of 4)................................................. 5-14

Table 5.5.4 Microwave-Only Oven Features (Table 3 of 4)................................................. 5-14

Table 5.5.5 Microwave-Only Oven Features (Table 4 of 4)................................................. 5-14

Table 5.5.6 DOE Microwave-Only Oven Standby Power (Table 1 of 4)............................. 5-15

Table 5.5.7 DOE Microwave-Only Oven Standby Power (Table 2 of 4)............................. 5-16

Table 5.5.8 DOE Microwave-Only Oven Standby Power (Table 3 of 4)............................. 5-16

Table 5.5.9 DOE Microwave-Only Oven Standby Power (Table 4 of 4)............................. 5-16

Table 5.5.10 DOE Standby Power Requirements among Similar Microwave-Only 

Ovens with Different Options............................................................................ 5-24

Table 5.5.11 Incremental Manufacturing Costs for Microwave-Only Oven and 

Countertop Combination Microwave Oven Standby Power ............................. 5-26
5-ii

Table 5.5.12 DOE Countertop Combination Microwave Oven Standby Power .................... 5-27

Table 5.5.13 Control Power Supply Transformer Standby Power Test Results..................... 5-29

Table 5.5.14 DOE Built-In and Over-the-Range Combination Microwave Oven 

Standby Power ................................................................................................... 5-29

Table 5.5.15 DOE Built-In and Over-the-Range Combination Microwave Oven 

Disaggregated Components Standby Power Consumption ............................... 5-31

Table 5.5.16 Built-In and Over-the-Range Combination Microwave Oven Incremental 

Manufacturing Costs.......................................................................................... 5-32

LIST OF FIGURES

Figure 5.4.1 Manufacturing Cost Assessment Stages.............................................................. 5-8

Figure 5.5.1 AHAM Microwave Oven Standby Power......................................................... 5-10

Figure 5.5.2 DOE Microwave-Only Oven Standby Power Consumption as a Function 

of Rated Output Power....................................................................................... 5-18

Figure 5.5.3 AHAM Microwave Oven Standby Power Consumption as a Function of 

Rated Output Power........................................................................................... 5-19

Figure 5.5.4 DOE Microwave-Only Oven Standby Power Consumption as a Function 

of Display Size................................................................................................... 5-20

Figure 5.5.5 DOE Standby Power Consumption as a Function of Display Size for 

Microwave-Only Ovens with LED Displays..................................................... 5-21

Figure 5.5.6 DOE Standby Power Consumption as a Function of Display Size for 

Microwave-Only Ovens with VFD Displays..................................................... 5-22

Figure 5.5.7 DOE Standby Power Consumption as a Function of Display Size for 

Microwave-Only Ovens with LCD Displays..................................................... 5-23

Figure 5.5.8 DOE Standby Power Consumption Associated with Different Design 

Options............................................................................................................... 5-25

Figure 5.5.9 DOE Standby Power Consumption as a Function of Display Size for 

Countertop Combination Microwave Ovens..................................................... 5-28

Figure 5.5.10 DOE Standby Power Consumption as a Function of Display Size for 

Built-In and Over-the-Range Combination Microwave Ovens......................... 5-30
5-1

CHAPTER 5. ENGINEERING ANALYSIS

5.1 INTRODUCTION

After conducting the screening analysis, the U.S. Department of Energy (DOE) 

performed an engineering analysis based on the remaining design options. The engineering 

analysis consists of estimating the standby energy consumption and costs of products at various 

levels of increased efficiency. This section provides an overview of the engineering analysis 

(section 5.1), discusses proposed product classes (section 5.2), establishes baseline unit 

specifications (section 5.3.1), discusses incremental efficiency levels (section 5.3.2), explains the 

methodology used during data gathering (5.4) and discusses the analysis and results (section 5.5) 

The primary inputs to the engineering analysis are baseline information from the market 

and technology assessment (chapter 3 of the technical support document (TSD)) and technology 

options from the screening analysis (chapter 4.) Additional inputs include laboratory testing and 

reverse-engineering of representative microwave ovens. The primary output of the engineering 

analysis is a set of cost-efficiency curves. In the subsequent markups analysis (chapter 6), DOE 

determined customer (i.e., product purchaser) prices by applying distribution markups, sales tax 

and contractor markups. After applying these markups, they serve as the input to the building 

energy-use and end-use load characterization (chapter 7) and the life-cycle cost (LCC) and 

payback period (PBP) analyses (chapter 8).

DOE typically structures its engineering analysis around one of three methodologies. 

These are: (1) the design-option approach, which calculates the incremental costs of adding 

specific design options to a baseline model that will improve its efficiency (i.e., lower its energy 

use in standby mode and off mode); (2) the efficiency-level approach, which calculates the 

relative costs of achieving increases in energy efficiency levels (in this case, levels of reduced 

standby power), without regard to the particular design options used to achieve such increases; 

and/or (3) the reverse engineering or cost-assessment approach, which involves a “bottom-up” 

manufacturing cost assessment based on a detailed bill of materials (BOM) derived from 

teardowns of the product being analyzed. Deciding which methodology to use for the 

engineering analysis depends on the product, the design options under study, and any historical 

data that DOE can draw on.

5.2 PRODUCT CLASSES ANALYZED

DOE separated residential microwave ovens into product classes. Because DOE 

formulated a separate energy conservation standard for standby power consumption for each 

product class, the criteria for separation into different classes are (1) type of energy used (natural 

gas or electricity), and (2) capacity or other performance-related features such as those that 

provide utility to the consumer, or others deemed appropriate by the Secretary that would justify 

the establishment of a separate energy conservation standard. (42 U.S.C. 6295 (q)) 
5-2

For the reasons discussed in chapter 3 of this TSD, DOE has analyzed for the purposes of 

this supplemental notice of proposed rulemaking (SNOPR) the following two product classes for 

microwave ovens:

• Microwave-only ovens and countertop combination microwave ovens

• Built-in and over-the-range combination microwave ovens

5.3 EFFICIENCY LEVELS

5.3.1 Baseline Units

DOE selected baseline units as reference points for each product class, against which 

DOE measured changes resulting from energy conservation standards. The baseline unit in each 

product class represents the basic characteristics of equipment in that class. Typically, a baseline 

unit is a unit that just meets current required energy conservation standards and provides basic 

consumer utility. 

DOE used the baseline units in the engineering analysis and the life-cycle-cost and 

payback-period analysis. To determine energy savings and changes in price, DOE compared 

each higher energy efficiency design option with the baseline unit. 

The identification of baseline units required establishing the baseline standby power

level. For microwave oven standby power, energy conservation standard levels are expressed as 

a maximum standby power consumption, in watts (W). As discussed in chapter 3 of this TSD, 

DOE is not aware of any current microwave ovens that are capable of operation in off mode. As 

a result, the standards do not include off mode power. Based on product testing (see section 

5.6.1.3), DOE selected a baseline standby power level which was the highest typical standby 

power for a microwave oven to provide full consumer utility for each product class. For the 

purpose of this rulemaking, DOE determined consumer utility to be the ability to display 

complex characters, brightness, and viewing angle of the display as well as the ability to 

automatically control the cooking operation (i.e., through the use of an absolute humidity 

cooking sensor). For the built-in and over-the-range combination microwave ovens product 

class, consumer utility also included a sufficiently sized power supply capable of operating 

additional features required to handle the thermal loads associated with their installation and to 

provide consumer utility, such as additional exhaust fan motors, convection fan motors and 

heaters, and additional lights. For both product classes, the baseline power supply used a 

conventional linear power supply with an efficiency of approximately 55 percent. DOE selected 

a baseline standby power level of 4.0 W for the microwave-only ovens and countertop 

combination microwave ovens product class. For the built-in and over-the-range combination 

microwave ovens product class, DOE selected a baseline standby power level of 4.5 W. As 

discussed in section 5.5.1.2, DOE noted that the built-in combination microwave ovens in its test 

sample consumed more standby power than the over-the-range combination microwave ovens. 
5-3

However, DOE notes that built-in and over-the-range combination microwave ovens have 

essentially the same features (i.e., exhaust fans and convection heaters). DOE also noted that the 

two built-in combination microwave ovens in its test sample were high-end units with large 

displays and a larger number of cooking settings and options. As a result, DOE believes that the 

standby power level of 4.5 W for the built-in and over-the-range combination microwave ovens 

product class provides full consumer utility and that the higher levels observed in DOE’s test 

sample for built-in combination microwave ovens are not appropriate for establishing the

baseline standby power levels. 

5.3.2 Incremental Standby Power Levels

For the product classes presented in section 5.2, DOE analyzed several standby power

levels and obtained incremental cost data at each of these levels. Table 5.3.1 and Table 5.3.2

provide standby power levels and the reference source of each level. DOE conducted the

engineering analysis for microwave oven standby power for the two product classes DOE 

identified for microwave ovens. To analyze the cost-energy use relationship for microwave oven

standby power, DOE defined standby power levels expressed as a maximum average standby 

power, in W. For the reasons noted above in section 5.3.1, the standard levels do not include off 

mode power.

For the microwave-only ovens and countertop combination microwave ovens product 

class, the standby power levels were derived from review of the Federal Energy Management 

Program (FEMP) procurement efficiency recommendation, the International Energy Agency’s 

(IEA) One-Watt program to lower standby power consumption below 1 W for various electrical 

appliances, and the current maximum microwave oven standby technology (i.e. lowest standby 

power) that DOE believes is or could be commercially available at the time the energy 

conservation standards become effective. The max-tech microwave-only oven and countertop 

combination microwave oven standby power level of 0.02 W corresponds to a unit equipped 

with a default automatic power-down function that shuts off certain power-consuming 

components after a specified period of user inactivity. The standby power at max-tech was 

obtained from a microwave oven currently on the market in Korea which incorporates such a

feature. DOE also added a standby power level as a gap-fill between the FEMP Procurement 

Efficiency Recommendation and IEA One-Watt Program levels. Table 5.3.1 provides the 

microwave-only ovens and countertop combination microwave ovens product class standby

power levels and the reference source for each level that DOE has analyzed. 
5-4

Table 5.3.1 Standby Power Levels for Microwave-Only Ovens and Countertop 

Combination Microwave Ovens

Standby

Power Level Standby Power Level Source Standby Power (W)

Baseline Baseline 4.0

1 FEMP Procurement Efficiency Recommendation 2.0

2 Gap Fill 1.5

3 IEA 1-Watt Program 1.0

4 Max-Tech 0.02

For the built-in and over-the-range combination microwave oven product class, the 

standby power levels were determined based on reverse-engineering analyses on a representative 

sample of built-in and over-the-range combination microwave ovens to analyze the various 

components that contribute to the standby power consumption of the unit. DOE also measured

the standby power consumed by these components individually.

In its analysis, DOE observed that the absolute humidity cooking sensor used in these 

combination microwave ovens on average consume 0.9 W of standby power. For standby power 

level 1, DOE believes that standby power can be reduced by incorporating a zero-standby 

cooking sensor. For standby power level 2, DOE analyzed potential improvements to the power 

supply design. DOE noted that microwave ovens at the baseline standby energy use incorporate a 

linear power supply. DOE measured the standby power consumption of the power supply and 

found that the transformer used to step down the line input voltage contributes most significantly 

to the standby power consumption. DOE then performed a power budget analysis to determine 

the size of the transformer needed to operate a microwave at full load, and the results suggest 

that replacing the conventional linear power supply with a more efficient switch mode power 

supply will eliminate the need for a large transformer and effectively reduce the standby power 

associated with the power supply. DOE thus estimated the standby power for standby power 

level 2 based on the improvement associated with changing from a conventional linear power 

supply with an efficiency of 55 percent to a switch mode power supply with an efficiency of 75 

percent. DOE developed this estimate for the efficiency of a switch mode power supply based on 

research of such power supply designs for appliance applications.a

 

a Information on the design and efficiency of switch mode power supplies can be found at 

For standby power level 3, 

DOE analyzed the impact relays have in determining the size of a power supply. DOE compared 

the power budget of a control board with electromechanical relays to that with solid state relays, 

and observed that the power requirement of a control board, with similar input and load, is lower 

with solid state relays than with electromechanical relays. Therefore, DOE estimated the standby 

power at standby power level 3 based on design improvements associated with using more 

efficient components in a switch mode power supply that incorporates solid state relays. For 

standby power level 4, DOE analyzed an automatic function that turns off power to standby 

power consuming components after a certain period of inactivity and that uses a transformerless 

power supply to maintain the microcontroller chip while the microwave oven is not powered on. 

http://www.powerint.com/en/applications/major-appliances.
5-5

DOE estimated the standby power at standby power level 4 based on the standby power 

requirements of the controller microcontroller chip.

Table 5.3.2 presents the proposed standby power levels for built-in and over-the-range 

combination microwave ovens.

Table 5.3.2 Standby Power Levels for Built-In and Over-the-Range Combination 

Microwave Ovens

Standby

Level Standby Power Level Source Standby Power (W)

Baseline Baseline 4.5

1 Zero W Cooking Sensor 3.7

2 Switch Mode Power Supply 2.7

3 Improved Relay Power Supply Design 2.2

4 Max-Tech (Automatic Power Down) 0.04

5.4 METHODOLOGY OVERVIEW

In order to develop the cost-efficiency relationships for microwave ovens, DOE 

performed detailed product teardowns and reverse-engineering analyses on a sample of product 

models spanning a range of standby power levels and product features. DOE also conducted 

detailed standby power testing to gain insights into energy performance in standby mode and to 

evaluate individual components contributing to standby power consumption. AHAM also 

submitted data to DOE on standby power testing that it conducted. DOE supplemented this 

information by conducting interviews with manufacturers of microwave ovens. Table 5.4.1

below shows which methods DOE used for each product class. 
5-6

Table 5.4.1 Engineering Analysis Methods

Method

Microwave-Only Ovens and 

Countertop Combination 

Microwave Ovens

Built-In and Over-theRange Combination 

Microwave Ovens

AHAM Data √

Product Teardown √ √

Product Testing √ √

Manufacturer 

Interviews √

5.4.1 AHAM Data Submittal

In support of this rulemaking effort, AHAM submitted data regarding standby power in 

microwave ovens. The AHAM submittal contained general descriptions of components related to 

standby power as well as data from standby power testing. The data provided to DOE by AHAM

are contained in appendix 5A.

5.4.2 Manufacturer Interviews

DOE conducted confidential interviews with microwave ovens manufacturers to develop 

a deeper understanding of the various combinations of technologies used to reduce standby 

power consumption, and their associated manufacturing costs. Sample questions asked during 

the follow-up interviews, which were also conducted in support of the manufacturer impact 

analysis, are contained in appendix 12B. 

During the interviews, DOE also gathered information about the capital expenditures 

required to reduce the standby power consumption of the baseline units to various standby power 

levels (i.e., conversion capital expenditures by standby power level). The interviews provided 

information about the size and the nature of the capital investments. DOE also requested 

information about the depreciation method used to expense the conversion capital.

5.4.3 Product Teardowns

Other than obtaining detailed manufacturing costs directly from a manufacturer, the most 

accurate method for determining the production cost of a piece of equipment is to disassemble 

the equipment piece-by-piece and estimate the material and labor cost of each component using a 

process commonly called a physical teardown. A supplementary method, called a catalog 

teardown, uses published manufacturer catalogs and supplementary component data to estimate 

the major physical differences between a piece of equipment that has been physically 

disassembled and another piece of similar equipment. DOE performed physical teardown 

analysis on microwave ovens for this rulemaking. The teardown methodology is described in 

detail in section 5.5.3.1 through section 5.5.3.3.
5-7

5.4.3.1 Selection of Units

During the process of selecting units for teardown, DOE considers three main questions:

 What standby power levels should be captured in the teardown analysis?

 Are there units on the market that capture all potential standby power levels and design 

options?

 Which of the available units are most representative?

In responding to the preceding questions, DOE adopts the following criteria for selecting 

units for the teardown analysis:

 The selected products should span the full range of standby power levels for each product 

class under consideration;

 Within each product class, if possible, the selected products should come from the same 

manufacturer and be within the same product series;

 The selected products should primarily come from manufacturers with large market share in 

that product class, although the highest efficiency products were chosen irrespective of 

manufacturer; and

 The selected products should have non-standby power-related features that are the same as, 

or similar to, features of other products in the same class and at the same standby power 

level.

5.4.3.2 Generation of Bill of Materials

The end result of each teardown is typically a structured bill of materials (BOM). The 

process is discussed here in the context of the general methodology used for teardown analysis, 

although it should be noted a more limited approach was used for microwave ovens due to the 

substantial uniformity in design and construction among the sample units. Structured BOMs 

describe each equipment part and its relationship to the other parts, in the estimated order of 

assembly. The BOMs describe each fabrication and assembly operation in detail, including the 

type of equipment needed (e.g., stamping presses, injection molding machines, spot-welders, 

etc.) and the process cycle times. The result is a thorough and explicit model of the production 

process. 

The BOMs incorporate all materials, components, and fasteners, classified as either raw 

materials or purchased parts and assemblies. The classification into raw materials or purchased 

parts is based on DOE’s previous industry experience, recent information in trade publications, 

and discussions with high- and low-volume original equipment manufacturers (OEMs). 

For purchased parts, the purchase price is an estimate based on volume-variable price 

quotations and detailed discussions with suppliers. For fabricated parts, the price of intermediate 

materials (e.g., tube, sheet metal) and the cost of transforming them into finished parts are an 

estimate based on current industry pricing. 
5-8

The cost of raw materials is determined using prices for copper, steel and aluminum from 

the American Metals Market.1

5.4.3.3 Cost Structure of the Spreadsheet Models

 The price of steel drastically increased in 2005, and the price of 

copper has increased steadily since 2004. Because DOE is using a 5-year average in material 

prices from 2005–2009, these price increases are normalized, which better represents long-term 

material prices.

The manufacturing cost assessment methodology used is a detailed, component-focused 

technique for rigorously calculating the manufacturing cost of a product (direct materials, direct 

labor and some overhead costs.) Figure 5.4.1 shows the three major steps in generating the 

manufacturing cost.

Figure 5.4.1 Manufacturing Cost Assessment Stages

The first step in the manufacturing cost assessment is the creation of a complete and 

structured BOM from the disassembly of the units selected for teardown. The units are

dismantled, and each part is characterized according to weight, manufacturing processes used, 

dimensions, material, and quantity. The BOM incorporates all materials, components, and 

fasteners with estimates of raw material costs and purchased part costs. Assumptions on the 

sourcing of parts and in-house fabrication are based on industry experience, information in trade 

publications, and discussions with manufacturers. Interviews and plant visits are also conducted 

with manufacturers to ensure accuracy on methodology and pricing.

Following the development of a detailed BOM, the major manufacturing processes are

identified and developed for the spreadsheet model. These processes are listed in Table 5.4.2.

Table 5.4.2 Major Manufacturing Processes

Fabrication Finishing Assembly/Joining Quality Control

Fixturing Washing Adhesive Bonding Inspecting & Testing

Stamping/Pressing Powder Coating Spot Welding

Brake Forming De-burring Seam Welding

Cutting and Shearing Polishing

Insulating

Fabrication process cycle times are estimated and entered into the BOM. For this 

analysis, $24.00 per hour was used as the average fully-burdened labor rate based on typical 

annual wages and benefits of industry employees. In the final step of the cost assessment, 
5-9

assembly times and associated direct labor costs are estimated. Once the cost estimate for each 

teardown unit is finalized, a detailed summary is prepared for relevant components, 

subassemblies and processes. The BOM thus details all aspects of unit costs. 

Design options used in units subject to teardown are noted in the summary sheet of each 

cost model and are cost-estimated individually. Thus, various implementations of design options 

can be accommodated, ranging from assemblies that are entirely purchased to units that are made 

entirely from raw materials. Hybrid assemblies, consisting of purchased parts and parts made on 

site are thus also accommodated. 

5.4.4 Product Testing

DOE conducted product testing on microwave ovens to develop a better understanding of 

the potential standby power improvements associated with various design options. As part of this 

testing, DOE measured the power consumption of components contributing to standby power 

individually to further evaluate the strategies manufacturers may take to reduce standby power.

5.5 ANALYSIS AND RESULTS

5.5.1.1 AHAM Data

AHAM provided data on microwave oven standby power for a sample of microwave 

ovens currently available in the U.S. market.2

Figure 5.5.1

 Standby power was tested in accordance with the 

International Electrotechnical Commission (IEC) Standard 62301-2005, Household electrical 

appliances – Measurement of standby power (IEC Standard 62301 (First Edition)).

displays AHAM-measured microwave oven standby power data as a function of rated cooking 

output power. Unlike efficiency, these data show a wide range of standby power, but there is no 

correlation between standby power and cooking output power. Standby power ranged from 1.5 to 

5.8 W, with 9 of the 21 microwave ovens meeting the FEMP recommendation of 2.0 W or less. 

The average standby power measured was 2.9 W. AHAM did not provide any information with 

which DOE could correlate standby power with other features such as cooking sensors or 

displays. The data did not indicate the product type (i.e., microwave only, combination) or the 

installation configuration (i.e., countertop, over-the-range, built-in). 

DOE notes that microwave oven standby power consumption is impacted significantly by 

the digital clock display, with more complex graphical displays drawing more power. According 

to AHAM, the three major types of displays used in microwave ovens are (1) LED displays, (2) 

VFDs, and (3) LCDs. Typically, LCDs without back-lighting use the least amount of energy 

while VFDs use the most. Energy consumed by LCDs would depend on whether back-lighting is 

present or not, and if present, the number of LEDs used for back-lighting. For LED displays, the 

number of segments, color, and operating temperature affect energy consumption. The size of the 

display (number of digits and icons) also affects the energy consumed by the display. For VFDs, 

the size of the display is a major factor in energy consumption.3

 Standby power consumption 
5-10

may also be affected by the electronic controls required for features such as cooking sensors, 

along with associated power supplies.

Figure 5.5.1 AHAM Microwave Oven Standby Power4

Table 5.5.1 compares the AHAM-measured microwave oven standby power data with 

data from other studies that have examined standby power in the United States and Canada. It 

can be seen that average standby power has remained relatively constant since 1997 even though 

minimum and maximum levels have varied by a greater amount.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

600 700 800 900 1000 1100 1200 1300 1400

Rated Output Power (W)

Standby Power (W)
5-11

Table 5.5.1 Microwave Oven Standby Power Comparison

Source

Microwave Oven Standby Power

Min (W)

Average 

(W) Max (W)

Std Dev 

(W) # Samples

AHAM 20065 1.5 2.9 5.8 0.8 21

CBEEDAC 20066 0.4 1.9 3.3 0.8 19

CREEDAC 2001 (New Stock)7 0.8 3.8 12.6 - 4

CREEDAC 2001 (Existing Stock)8 0.0 2.1 7.3 - 64

LBNL 20089 1.4 3.1 4.9 - 18

Florida Solar Energy Center 199810 - 3.0 - - 25

LBNL 199711 - 3.1 - - -

DOE recognizes that annual energy consumption can be significantly affected by standby 

power in real-world usage. For example, a 1-W increase in standby power corresponds to an 

increase of 8.76 kilowatt-hours (kWh) in annual energy consumption. Prior to it being repealed 

in a final rule published on July 22, 2010 (75 FR 42579), the microwave oven test procedure 

assumed an annual useful cooking energy output of 79.8 kWh. For a baseline microwave oven 

that operates at 55.7 percent efficiency, annual energy consumption not including standby power 

would be 143.3 kWh. Therefore each W of standby power included in the annual energy 

consumption metric would increase it by 6 percent for a baseline microwave oven. Since the 

highest measured standby power was 5.8 W, the increment of 3.8 W over the FEMPrecommended level of 2.0 W would represent a 23-percent increase in annual energy 

consumption for a baseline microwave oven. 

5.5.1.2 Product Testing and Teardowns

Microwave-Only Ovens and Countertop Combination Microwave Ovens

Section 310 of the Energy Independence and Security Act of 2007 (EISA 2007) (Pub. L. 

No. 110-140) amends Section 325 of the EPCA to require DOE to incorporate standby mode and 

off mode energy use into a single amended or new standard, if feasible, for covered products, 

including microwave ovens, for any final rule establishing or revising a standard adopted after 

July 1, 2010. If such a single standard is not feasible, DOE shall prescribe a separate standard for 

standby mode and off mode energy consumption, if justified. (42 U.S.C. 6295(gg)(3)) As 

discussed in chapter 3 of this TSD, DOE published a final rule on July 22, 2010 repealing the 

provisions in the existing microwave oven test procedure relating to the measurement of cooking 

efficiency and energy factor (EF). 75 FR 42579. DOE notes that the absence of active mode 

testing provisions in the microwave oven test procedure results in a de facto separate energy use 

descriptor for microwave oven standby mode and off mode energy use. Therefore, DOE 

conducted microwave oven standby power testing to supplement the AHAM-supplied data,

investigated design options, and developed a relationship between incremental manufacturing 

cost and standby power levels.
5-12

As discussed in chapter 3 of this TSD, in the March 2011 TP Interim Final Rule, DOE 

adopted definitions of standby, off, and active mode based on the provisions in IEC Standard 

62301 Second Edition, Final Draft International Standard (IEC Standard 62301 FDIS). 76 FR 

12825, 12834–37 (Mar. 9, 2011). DOE defines “standby mode” as the condition in which an 

energy-using product is connected to a mains power source and offers one or more of the 

following user oriented or protective functions which may persist for an indefinite time –

(I) a remote switch (including a remote control), internal sensor, or timer to facilitate the 

activation of other modes (including activation or deactivation of active mode); and

(II) continuous functions, including information or status displays (including clocks) or 

sensor-based functions. 76 FR 12825, 12836 (Mar. 9, 2011).

DOE defines “off mode” as the condition in which an energy-using product is connected 

to a mains power source, is not providing any active or standby mode function, and may persist 

for an indefinite time. Off mode would also include an indicator that shows the user only that the 

product is in the off position. Id.

DOE defines “active mode,” as the condition in which an energy-using product is 

connected to a main power source, has been activated, and provides 1 or more main functions.

Delay start mode is a one off user initiated short duration function that is associated with an 

active mode. Id.

DOE considers “main functions” for a microwave oven to be those operations in which 

the magnetron and/or thermal element is energized for at least a portion of the time for purposes 

of heating, cooking, and/or defrosting the load. According to these definitions, standby mode 

would thus comprise the conditions in which the microwave oven is plugged in and consuming 

power for features including displays, cooking sensors, and sensors to reactivate the microwave 

oven from a low-power state after a period of user inactivity. For reasons discussed later in this 

section, DOE does not believe that any microwave ovens currently for sale in the United States 

are capable of operation in off mode.

General Microwave Oven Construction

All microwave-only ovens examined by DOE contain a metal cavity that is mechanically 

attached to the front and rear chassis frames. Each of these pieces had been formed by stamping,

joined, and then the assembly is painted. To this frame, a bottom panel is attached. This bottom 

panel covers the turntable motor and also acts as an electrical ground for the magnetron power 

supply and the magnetron. The inner cavity occupies, on average, about 70 percent of the width 

and height of the microwave oven. The remaining space is used for cooling channels, the 

magnetron, the magnetron power supply, the cooling fan, the microwave oven controller, and 

other miscellaneous components. 

All of the microwave-only ovens examined have a door that is hinged on the left side of 

the unit. Beneath the right edge of the door, a latch mechanism with three switches ensures that 

the microwave oven cannot operate its magnetron without the door being closed. To the right of 

the door, the user interface frame typically features a foil-based button array under a flexible 
5-13

plastic cover, along with the display. The display may be either attached directly to the user 

interface frame or integrated into the main control board for the microwave oven. The main 

control board typically consists of a single-sided printed circuit board (PCB) which features a 

small alternating current to direct current (AC-DC) power supply, several relays, and control 

logic. All power coming into the microwave oven is filtered through a separate power filtration 

board to which the power cord is attached.

In addition to the aforementioned components, microwave-only ovens contain a 

magnetron power supply featuring a microwave oven transformer, a high voltage diode, and a 

high-voltage aluminum electrolytic capacitor. A single-speed fan keeps the magnetron and 

microwave oven transformer cool during operation, while a turntable may rotate the food load 

inside the cavity while the microwave oven is operating. A single incandescent light bulb (20 W 

and higher) typically provides cavity illumination during operation and when the door is open. 

More sophisticated microwave ovens may contain cooking sensors, larger and multi-colored 

displays with more complex graphics, and/or inverter-based magnetron power supplies.

Test Units

DOE conducted standby power testing and reverse engineering analyses on a 

representative sample of 32 microwave-only ovens. DOE noted key parameters for each test unit, 

presented in Table 5.5.2 through Table 5.5.5. Since manufacturers are not required to report 

standby power for microwave ovens, DOE could not select its sample test units on the basis of 

standby power consumption. Instead, DOE selected its sample microwave ovens to cover a wide 

range of cavity sizes and output power, as well as other features such as display type, power 

supply type, and presence of cooking sensors. DOE was unable to identify any microwave oven 

models with an automatic powerdown feature. Within the test sample, DOE observed significant 

standby power differences which it believes are attributable to specific design options or design 

option combinations.

Table 5.5.2 Microwave-Only Oven Features (Table 1 of 4)

DOE1 DOE2 DOE3 DOE4 DOE5 DOE6 DOE7 DOE8

700 700 700 700 800 800 800 800

0.7 0.7 0.7 0.7 1 1 0.8 0.8

- - - - Y - - -

- - - - - - - -

Type LED LED LED LED VFD LED LCD LCD

Characters #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 A, 1 x 7 #, 1 x 4 #, 1 x 4 #, 1 x 4

# of LEDs for backlighting N/A N/A N/A N/A N/A N/A None None

Size 1.50" x 

0.43"

1.50" x 

0.43"

1.45" x 

0.70"

1.90" x 

0.83"

2.25" x 

0.75"

1.50" x 

0.80"

1.87" x 

0.83"

1.87" x 

0.83"

- - - - - DOE5 - -

DOE Unit Number

Rated Output Power (W)

Stated Volume (ft3)

Cooking Sensor

Inverter Power Supply

Unit is Similar to Display
5-14

Table 5.5.3 Microwave-Only Oven Features (Table 2 of 4)

Table 5.5.4 Microwave-Only Oven Features (Table 3 of 4)

Table 5.5.5 Microwave-Only Oven Features (Table 4 of 4)

Three different display technologies were observed to be incorporated in the sample 

units: 1) LED; 2) LCD; and 3) VFD. The display format for each microwave oven was 

characterized as either numeric (#), alphanumeric (A), or dot matrix (D). Whereas numeric 

displays can only show time, alphanumeric displays can also display letters (though usually in 

simplified format). Dot matrix displays can show various fonts, letters, and symbols via matrices 

of pixels, making them the most flexible display technology. Since display power consumption is 

a function of not only the type of technology used but the overall size and number of digits in the 

display as well, the dimensions of each display were measured and the number of rows and 

columns of digits were recorded. Finally, some LCDs use LEDs for backlighting, allowing a 

microwave oven user to read the display both at night and in daylight.

DOE9 DOE10 DOE11 DOE12 DOE13 DOE14 DOE15 DOE16

900 1000 1000 1000 1000 1100 1100 1100

0.9 1.1 1.1 1 0 1.1 1.1 1.8

- - - - - - Y Y

- - - - - - - -

Type LED LED LED LED VFD LED LCD VFD

Characters #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 A, 1 x 6 A, 1 x 7

# of LEDs for backlighting N/A N/A N/A N/A N/A N/A 5 N/A

Size 2.00" x 

0.65"

1.85" x 

1.10"

1.75" x 

0.85"

1.75" x 

0.70"

2.20" x 

0.65"

2.00" x 

0.65"

2.53" x 

0.95"

2.25" x 

0.75"

- - - - - - DOE14 -

Display

Stated Volume (ft3

)

Cooking Sensor

Inverter Power Supply

Unit is Similar to

DOE Unit Number

Rated Output Power (W)

DOE17 DOE18 DOE19 DOE20 DOE21 DOE22 DOE23 DOE24

1100 1100 1100 1100 1100 1100 1150 1200

1 1.4 1 1.3 1.1 1 1.4 2.2

- - - - - - Y Y

- - - - - - - Y

Type LCD LCD LCD LED LED LCD VFD LCD

Characters #, 1 x 4 A, 1 x 5 #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 A, 1 x 7 A, 1 x 6

# of LEDs for backlighting 3 4 None N/A N/A 3 N/A 10

Size 1.83" x 

0.80"

2.03" x 

0.81"

1.87" x 

0.83"

1.50" x 

0.80"

1.47" x 

0.80"

2.00" x 

0.83"

2.25" x 

0.75"

2.05" x 

1.10"

- - DOE17 - - DOE17 DOE16 DOE30

DOE Unit Number

Rated Output Power (W)

Stated Volume (ft3

)

Cooking Sensor

Inverter Power Supply

Unit is Similar to Display

DOE25 DOE26 DOE27 DOE28 DOE29 DOE30 DOE31 DOE32

1200 1200 1200 1200 1200 1250 1300 1300

1.2 2.2 1.2 2 2 2.2 1.2 1.2

- Y Y Y Y Y Y Y

- Y - - - Y Y Y

Type LCD LCD LCD LCD LCD LCD LCD LCD

Characters #, 1 x 4 A, 1 x 6 A, 1 x 7 D, 2 x 8 A, 1 x 7 A, 1 x 6 #, 1 x 4 A, 1 x 6

# of LEDs for backlighting 5 10 4 6 4 4 10 10

Size 1.85" x 

0.83"

2.05" x 

1.10"

2.03" x 

0.78"

2.45" x 

1.17"

2.03" x 

0.78"

2.05" x 

1.10"

1.75" x 

0.80"

2.05" x 

1.10"

DOE17 DOE30 DOE25 - - DOE31 - DOE31

Inverter Power Supply

Unit is Similar to

DOE Unit Number

Rated Output Power (W)

Stated Volume (ft3

)

Cooking Sensor Display
5-15

Microwave-Only Ovens Product Teardowns and Testing

DOE conducted product teardowns and testing in support of its standby power 

investigation for microwave-only ovens. DOE also analyzed IEC Standard 62301 (First Edition)

to determine its suitability for measuring standby power in microwave ovens. DOE found the 

results produced by IEC Standard 62301 (First Edition) to be fairly consistent for many 

microwave ovens. However, for a few microwave ovens in the test sample, the standby power 

consumption varied by more than 5 percent over the course of 5 minutes, a threshold above

which IEC Standard 62301 (First Edition) requires a longer 12-hour standby test duration. 

Investigating the source of these variations in power consumption, DOE determined that standby 

power can vary significantly with clock time, depending on the display type. 

DOE tested a sub-sample of microwave ovens over 12-hour periods and subsequently 

developed an alternate 10-minute standby power test that achieved results for average power 

consumption that were within 1 to 2 percent of the 12-hour test results (see appendix 5B). Using 

the most consistent data from: (1) the IEC Standard 62301 5-minute test, (2) the regression 

analysis as described in appendix 5B, and/or (3) 12-hour tests, standby power for each 

microwave oven in the sub-sample was characterized, the minimum, maximum, and average 

input powers were recorded, and from the average standby power, an annual energy consumption 

in kWh was calculated. Table 5.5.6 through Table 5.5.9 summarize these results.

Table 5.5.6 DOE Microwave-Only Oven Standby Power (Table 1 of 4)

DOE1 DOE2 DOE3 DOE4 DOE5 DOE6 DOE7 DOE8

700.0 700.0 700.0 700.0 800.0 800.0 800.0 800.0

0.7 0.7 0.7 0.7 1.0 1.0 0.8 0.8

- - - - Y - - -

Type LED LED LED LED VFD LED LCD LCD

Characters #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 A, 1 x 7 #, 1 x 4 #, 1 x 4 #, 1 x 4

# of LEDs for backlighting N/A N/A N/A N/A N/A N/A None None

Size 1.50" x 

0.43"

1.50" x 

0.43"

1.45" x 

0.70"

1.90" x 

0.83"

2.25" x 

0.75"

1.50" x 

0.80"

1.87" x 

0.83"

1.87" x 

0.83"

Min (W) 1.47 1.49 1.14 0.96 5.28 1.33 1.37 1.38

Average (W) 1.74 1.77 1.28 1.07 5.28 1.51 1.38 1.40

Max (W) 1.85 1.90 1.35 1.14 5.53 1.60 1.41 1.41

Annual (kWh) 15.22 15.47 11.21 9.40 46.28 13.22 12.12 12.28

- - - - - DOE5 - -

DOE Unit Number

Stated Volume (ft3)

Unit is Similar to Display Standby

Cooking Sensor

Rated Output Power (W)
5-16

Table 5.5.7 DOE Microwave-Only Oven Standby Power (Table 2 of 4)

Table 5.5.8 DOE Microwave-Only Oven Standby Power (Table 3 of 4)

Table 5.5.9 DOE Microwave-Only Oven Standby Power (Table 4 of 4)

In the course of examining the 32 microwave-only ovens in the test sample, DOE noted 

that all power supplies for the logic boards contain similar components. Incoming AC line 

voltage is reduced via a small (2 to 7 VA) transformer, input to a bridge rectifier, and 

DOE9 DOE10 DOE11 DOE12 DOE13 DOE14 DOE15 DOE16

900.0 1,000.0 1,000.0 1,000.0 1,000.0 1,100.0 1,100.0 1,100.0

0.9 1.1 1.1 1.0 0.0 1.1 1.1 1.8

- - - - - - Y Y

Type LED LED LED LED VFD LED LCD VFD

Characters #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 A, 1 x 6 A, 1 x 7

# of LEDs for backlighting N/A N/A N/A N/A N/A N/A 5 N/A

Size 2.00" x 

0.65"

1.85" x 

1.10"

1.75" x 

0.85"

1.75" x 

0.70"

2.20" x 

0.65"

2.00" x 

0.65"

2.53" x 

0.95"

2.25" x 

0.75"

Min (W) 1.26 1.09 1.11 1.42 2.46 1.16 3.08 3.08

Average (W) 1.49 1.23 1.26 1.75 2.48 1.40 3.10 3.08

Max (W) 1.58 1.30 1.33 1.88 2.49 1.49 3.12 3.31

Annual (kWh) 13.09 10.73 11.01 15.32 21.71 12.26 27.14 26.95

- - - - - - DOE14 -

DOE Unit Number

Rated Output Power (W)

Stated Volume (ft3)

Cooking Sensor Display Standby

Unit is Similar to

DOE17 DOE18 DOE19 DOE20 DOE21 DOE22 DOE23 DOE24

1,100.0 1,100.0 1,100.0 1,100.0 1,100.0 1,100.0 1,150.0 1,200.0

1.0 1.4 1.0 1.3 1.1 1.0 1.4 2.2

- - - - - - Y Y

Type LCD LCD LCD LED LED LCD VFD LCD

Characters #, 1 x 4 A, 1 x 5 #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 A, 1 x 7 A, 1 x 6

# of LEDs for backlighting 3 4 None N/A N/A 3 N/A 10

Size 1.83" x 

0.80"

2.03" x 

0.81"

1.87" x 

0.83"

1.50" x 

0.80"

1.47" x 

0.80"

2.00" x 

0.83"

2.25" x 

0.75"

2.05" x 

1.10"

Min (W) 1.64 1.64 1.30 1.46 1.32 1.70 3.05 2.57

Average (W) 1.65 1.66 1.31 1.65 1.55 1.72 3.05 2.59

Max (W) 1.67 1.67 1.34 1.73 1.66 1.73 3.18 2.60

Annual (kWh) 14.48 14.51 11.48 14.44 13.57 15.02 26.68 22.66

- - DOE17 - - DOE17 DOE16 DOE30

DOE Unit Number

Rated Output Power (W)

Stated Volume (ft3)

Cooking Sensor

Unit is Similar to Display Standby

DOE25 DOE26 DOE27 DOE28 DOE29 DOE30 DOE31 DOE32

1,200.0 1,200.0 1,200.0 1,200.0 1,200.0 1,250.0 1,300.0 1,300.0

1.2 2.2 1.2 2.0 2.0 2.2 1.2 1.2

- Y Y Y Y Y Y Y

Type LCD LCD LCD LCD LCD LCD LCD LCD

Characters #, 1 x 4 A, 1 x 6 A, 1 x 7 D, 2 x 8 A, 1 x 7 A, 1 x 6 #, 1 x 4 A, 1 x 6

# of LEDs for backlighting 5 10 4 6 4 4 10 10

Size 1.85" x 

0.83"

2.05" x 

1.10"

2.03" x 

0.78"

2.45" x 

1.17"

2.03" x 

0.78"

2.05" x 

1.10"

1.75" x 

0.80"

2.05" x 

1.10"

Min (W) 1.68 2.57 3.50 3.86 3.38 2.79 2.08 2.81

Average (W) 1.70 2.59 3.52 3.88 3.41 2.82 2.09 2.82

Max (W) 1.71 2.60 3.60 3.93 3.46 2.86 2.10 2.86

Annual (kWh) 14.86 22.66 30.84 34.02 29.90 24.69 18.28 24.72

DOE17 DOE30 DOE25 - - DOE31 - DOE31

Rated Output Power (W)

Unit is Similar to

Stated Volume (ft3)

Cooking Sensor Display Standby

DOE Unit Number
5-17

subsequently smoothed with capacitors to produce unregulated DC voltage (VDC). Multiple 

voltages for logic integrated circuits (ICs) (usually 5 VDC or less) and relay control (12 to 24 

VDC) are established either via multiple taps on the transformer or through the use of voltage 

regulators. None of the microwave ovens analyzed by DOE feature an on/off switch or 

electromechanical controls. DOE is unaware of any microwave ovens still on the market with 

electromechanical controls and no displays; DOE believes that the U.S. microwave oven market 

has completely transitioned to electronic controls with displays. Thus, all sampled microwaves 

consume standby power while waiting for user input. DOE does not believe that any domestic 

microwave ovens are capable of operating in off mode, as defined by EPCA. (42 U.S.C. 

6295(gg)(1)(A)(ii)) 

The average standby power, disaggregated by display type and the presence of a cooking

sensor as shown in Figure 5.5.2, exhibits a relatively wide range of values. These measured data 

correlate well with the standby power measurements that AHAM submitted to DOE (see Figure 

5.5.3). In the DOE test sample, none of the microwave ovens with LED displays include a 

cooking sensor, and these models all consume less than 2 W in standby mode. Similar low 

standby power requirements were observed for microwave ovens with LCD displays and no 

cooking sensors. For those microwave ovens with LCD displays and cooking sensors, the 

standby power ranged from 2 to 4 W. VFD-equipped microwave ovens demonstrate fairly 

consistent power draw, and the microwave oven with the highest standby power uses a cooking 

sensor and a VFD. 

In the following figures, the legend key includes designations for the presence of a

cooking sensor (CS), backlighting (B), and inverter drive for the magnetron (I). 
5-18

Figure 5.5.2 DOE Microwave-Only Oven Standby Power Consumption as a Function of 

Rated Output Power

While AHAM did not identify specific models in its data submittal, and thus DOE could 

not derive information on display type, the data does note which microwave ovens contain 

cooking sensors. Like the microwave ovens in the DOE test sample, the microwave ovens with

cooking sensors in the AHAM sample, have on average, higher standby power consumption than 

microwave ovens without cooking sensors. 

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

650 750 850 950 1050 1150 1250 1350

Rated Power Output (W)

Standby Power (W)

LED

VFD

VFD, CS

LCD

LCD, B

LCD, B, CS

LCD, B, CS, I
5-19

Figure 5.5.3 AHAM Microwave Oven Standby Power Consumption as a Function of 

Rated Output Power12

Based on these standby power observations, DOE concludes that standby power is a 

function of features including the display, the presence of a cooking sensor, and controller power 

requirements. The following sections discuss the impact of each of these features on overall 

standby power consumption.

Impact of Display Type on Standby Power

DOE noted three different types of displays among the 32 microwave ovens in its sample. 

The sampled display capabilities ranged from only being able to display numbers, to displaying 

alphanumeric characters, to incorporating dot-matrix-based displays which allow the display of 

multiple fonts, symbols, and, in some cases, graphics. 

Display power requirements depend on the fundamental technology as well as the size of 

the display, the brightness, and the number and range of characters it can display. Figure 5.5.4

illustrates measured standby power consumption as a function of display size. 

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

650 750 850 950 1050 1150 1250 1350

Rated Output Power (W)

Standby Power (W)

No Sensor

Sensor
5-20

Figure 5.5.4 DOE Microwave-Only Oven Standby Power Consumption as a Function of 

Display Size

Figure 5.5.5 through Figure 5.5.7 show the average measured standby power with 

minimum and maximum values for each type of display. See appendix 5C for a further 

discussion of display technologies. 

• Light Emitting Diode (LED)

LED displays operate by individually lighting up each element in the display to create a 

character or number or to illuminate a symbol. DOE confirmed that the power consumption of 

such displays varies depending on how many elements (and hence diodes) are active at any given 

time. Thus, LED-display-equipped microwave ovens demonstrate the greatest variation in 

standby power consumption over the course of a day as the clock cycles.

The span between the maximum and minimum standby power consumption, based on the 

number of elements illuminated, ranges from 0.2 to 0.4 W in the DOE test sample. Figure 5.5.5

shows the average standby power consumption (with maximum and minimum values) for 

microwave ovens with LED displays as a function of the measured size of the display in square 

inches. DOE found no apparent correlation between display size and standby power 

consumption. DOE recognizes that diode energy efficiency characteristics may be an important 

variable, but one for which DOE was not able to ascertain any information.

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

0.5 1.0 1.5 2.0 2.5 3.0

Display size (in2)

Standby Power (W)

LED

VFD

VFD, CS

LCD

LCD, B

LCD, B, CS

LCD, B, CS, I
5-21

Figure 5.5.5 DOE Standby Power Consumption as a Function of Display Size for 

Microwave-Only Ovens with LED Displays

• Vacuum-Fluorescent Display (VFD)

VFDs typically require more power than LCD- or LED-based displays, but offer high 

brightness levels and wide viewing angles. Note that the three VFD models with cooking sensors 

have a feature that allows the display to be switched off, but selecting this option decreases

standby power consumption by only 0.1 to 0.25 W. According to the IEC Standard 62301 test 

procedure, standby power would be measured with the displays powered off, resulting in a 

constant average value over the 12-hour period. These data are denoted in Figure 5.5.6 by the 

symbols. DOE also measured the variations in standby power with the displays on during the 12-

hour cycle for these units, and these variations, which are all additive from the minimum standby 

power levels measured with the displays turned off, are indicated on the chart by bars on each 

symbol. 

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.5 1.0 1.5 2.0 2.5

Display Size (in2)

Standby Power (W)
5-22

Figure 5.5.6 DOE Standby Power Consumption as a Function of Display Size for 

Microwave-Only Ovens with VFD Displays

• Liquid Crystal Display (LCD), with or without backlighting

An LCD without backlighting requires some ambient light to allow a user to read it 

because it relies on reflected light to create a visible contrast. LCDs without backlighting are 

frequently found on entry-level microwave ovens, whereas more expensive units tend to have 

backlit displays. LCDs with backlighting can be read regardless of ambient lighting conditions. 

The backlighting typically consists of multiple LEDs mounted behind the LCD display on the 

same circuit board. LCDs with backlighting were found on 12 of the microwave ovens in the 

DOE sample. As shown in Figure 5.5.7, the standby power consumption for microwave ovens 

with LCDs in the DOE sample remains nearly constant over time (since the bars showing 

variation during 12-hour tests are virtually indistinguishable from the symbols denoting the 

average values.) Figure 5.5.7 also shows that the addition of a cooking sensor raises standby 

power consumption, on average, to over 2 W.

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

1.4 1.5 1.6 1.7 1.8

Display Size (in2)

Standby Power (W)

VFD

VFD, CS
5-23

Figure 5.5.7 DOE Standby Power Consumption as a Function of Display Size for 

Microwave-Only Ovens with LCD Displays

Based on its research, DOE concludes that certain display technologies such as VFDs 

inherently consume more power, on average, than comparably-sized displays using other 

illumination technologies. Standby power is also a function of the size and the complexity of the 

display; more complex and larger displays typically consume more power than smaller, simpler 

displays.

Impact of a Cooking Sensor on Standby Power

DOE noted from its testing that microwave ovens with cooking sensors typically 

consume more power than comparable models that do not feature a cooking sensor. From its 

reverse-engineering activities, DOE identified two different types of cooking sensors generally 

used in microwave ovens: (1) absolute humidity sensors; and (2) piezo-electric steam sensors. A 

literature review of identifiable absolute humidity cooking sensors indicates that such sensors 

typically supply power to a resistive heating element whose conductivity changes in response to 

the presence of water vapor or other gases associated with food cooking processes. Based on its 

standby power observations between otherwise identical microwave ovens and information 

provided by sensor manufacturers, DOE concludes that the resistive elements in the cooking 

sensors are typically maintained at operating temperature during standby mode because warmup 

times (which can be several minutes) are longer than many microwave oven cooking times.

The specification sheet for one representative absolute humidity cooking sensor notes

that the sensor requires approximately 0.9 W to remain warm and ready for use. Based on a 

typical power supply efficiency of about 65 percent, the required microwave oven input power 

associated with the absolute humidity cooking sensor is thus approximately 1.6 W. Other 

1.0

1.5

2.0

2.5

3.0

3.5

4.0

1.0 1.5 2.0 2.5 3.0

Display size (in2)

Standby Power (W)

LCD

LCD, B

LCD, B, CS

LCD, B, CS, I
5-24

microwave-only ovens in the DOE sample use absolute humidity sensors whose power 

requirements appear comparable to those for the absolute humidity sensor referenced above. 

Testing performed on the steam sensors used in a number of microwave-only ovens in the DOE 

sample revealed that these sensors do not consume power in standby mode. For further 

discussion of steam cooking sensors, refer to chapter 3 of this TSD.

Table 5.5.10 shows a comparison of standby power for three pairs of microwave ovens in 

the DOE sample containing the same basic parts (power conditioner, transformer, magnetron, 

and cavity) with and without an absolute humidity cooking sensor. In all three cases, the 

microwave ovens with a cooking sensor consume at least 1.6 W more than comparable 

microwave ovens without a sensor. In the case of DOE test units #5 and #6, assuming the 

absolute humidity cooking sensor consumes about 1.6 W implies that the remaining differential 

between the two units of approximately 2.2 W of standby power consumption is attributable to 

the use of a VFD instead of an LED. The standby power consumption of other absolute humidity 

sensors, which can be inferred from units #25 and 27 with similar displays, is approximately 1.8 

W. 

Table 5.5.10 DOE Standby Power Requirements among Similar Microwave-Only Ovens 

with Different Options

Figure 5.5.8 shows the cumulative impact of each design option on overall standby 

power. The figure shows the average standby power consumption for all microwave oven models 

in the DOE sample which have the designated design options, as well as the minimum and 

maximum values for each group.

Test Unit # Display 

Type

# of LEDs used to 

backlight display Display Size Cooking Sensor Type Avg. Standby Power Consumption (W)

DOE21 LED N/A 1.47" x 0.80" None 1.55

DOE15 LCD 5 2.53" x 0.95" Absolute Humidity 3.10

DOE6 LED N/A 1.50" x 0.80" None 1.51

DOE5 VFD N/A 2.25" x 0.75" Absolute Humidity 5.28

DOE25 LCD 5 1.85" x 0.83" None 1.70

DOE27 LCD 4 2.03" x 0.78" Absolute Humidity 3.52
5-25

Figure 5.5.8 DOE Standby Power Consumption Associated with Different Design Options

Incremental Cost Data for Standby Power Levels for Microwave-Only Ovens and Countertop 

Combination Microwave Ovens

From the standby power testing and reverse-engineering, DOE observed correlations 

between (1) specific components and technologies, or combinations thereof, and (2) measured 

standby power. Costs for each of the components and technologies were estimated by DOE using 

quotes obtained from suppliers, interviews with manufacturers, interviews with subject matter 

experts, research and literature review, and numerical modeling. Preliminary incremental 

manufacturing costs associated with the standby power levels were then obtained by considering 

combinations of these components as well as other technology options identified to reduce 

standby power. Manufacturer interviews were also conducted to obtain greater insight into the 

design strategies to improve efficiency and the associated costs. As discussed above in section 

5.2, DOE believes the standby power levels and characteristics of power supply designs (i.e., 

size of the power supply) associated with microwave-only countertop and over-the-range units as 

well as countertop combination microwave ovens are similar. As a result, DOE proposed to 

analyze microwave-only ovens and countertop combination microwave ovens as a single product 

class. Therefore, DOE developed a single cost-energy use relationship for this product class.

The design options DOE considered in the engineering analysis include various display 

technologies, cooking sensors with no standby power requirement, higher-efficiency controller 

power supplies and relays, and improved control strategies. For details on the microwave oven 

standby design options, refer to chapter 3 of this TSD. DOE selected the design option(s) it 

believed manufactures would most likely implement to achieve a given standby power level for a 

given display technology. The incremental cost, then, for each display technology was weighted 

by the estimated percentage of shipments currently using that type of display in order to obtain a 

0.0

1.0

2.0

3.0

4.0

5.0

6.0

LED LCD LCD Backlit LCD Backlit,

Absolute

Humidity

Cooking Sensor

LCD Backlit,

Steam Cooking

Sensor, Inverter

VFD VFD, Absolute

Humidity

Cooking Sensor

Standby Power (W)

Maximum

Minimum

Average
5-26

weighted-average incremental cost at each standby power level above the baseline. DOE 

believes that, in order to meet standby power level 1, manufacturers would likely have to utilize 

a cooking sensor with no standby power requirements. Additionally, for microwave ovens with 

VFDs and backlit LCDs, the conventional power supplies would need to be upgraded to higher 

efficiency conventional power supplies. Standby power level 2 would likely also require LEDequipped microwave ovens to upgrade the efficiency of the existing power supply, and DOE 

believes that manufacturers would have to change to sensitive-coil relays in order to continue 

using VFDs. To move from standby power level 2 to standby power level 3, DOE believes that 

manufacturers would have to additionally incorporate the sensitive-coil relays for LED and 

backlit LCD-based microwave ovens. Optionally, manufacturers of LED-equipped microwave 

ovens could choose to change to a switching power supply without upgrading the relays. Each of 

these two LED options was assumed to be equally likely since the cost of each path was similar. 

At standby power level 3, backlit LCD-equipped microwave ovens would likely also need to be

changed to a switching power supply along with implementing the sensitive-coil relays. DOE 

believes the only way for manufacturers of VFD-equipped microwave ovens to meet a 1 W 

standby threshold would be to implement an automatic powerdown feature, in which a controller 

turns off power to standby-power-consuming components after a certain period of inactivity. 

This feature would also allow VFD-equipped microwave ovens to meet standby power level 4, 

and would be the approach for microwave ovens with the other display technologies to meet 

standby power level 4 as well. Table 5.5.11 presents the incremental manufacturing costs for 

each standby power level for microwave ovens. DOE originally developed and presented these 

costs the October 2008 NOPR, and therefore costs were presented in $2007. DOE updated these 

costs to $2010 to reflect changes in the producer price index (PPI) for electronic components and 

accessories.

Based on conversations with manufacturers and OEM suppliers, and the reverseengineering analysis, DOE believes that all manufacturers can and likely will implement zerostandby cooking sensors by the effective date of standby mode and off mode energy conservation

standards. Thus, DOE believes that consumer utility would not be impacted by a standard at 

standby power levels 1 or 2, since all display types could continue to be used. At standby power 

level 3 for VFDs and standby power level 4 for all display technologies, DOE analysis suggests 

the need for a separate controller (auto power-down) that automatically turns off all other powerconsuming components during standby mode. Such a feature would affect the consumer utility of 

having a clock display only if the consumer could not opt out of auto power-down. 

Table 5.5.11 Incremental Manufacturing Costs for Microwave-Only Oven and 

Countertop Combination Microwave Oven Standby Power

Standby Power 

Level Standby Power, W

Incremental Cost,

2007$

Incremental Cost,

2010$

Baseline 4.0 $ 0 $ 0

1 2.0 $ 0.30 $ 0.27

2 1.5 $ 0.67 $ 0.60

3 1.0 $ 1.47 $ 1.31

4 0.02 $ 5.13 $ 4.58
5-27

Countertop Combination Microwave Oven Testing and Product Teardown 

DOE also conducted standby power testing on 5 countertop combination microwave 

ovens, presented below in Table 5.5.12. Testing showed standby power levels ranging from 1.2 

W to 4.7 W, with an average of 3.0 W. As discussed above in section 5.2, these standby power 

levels are similar to the standby power levels for microwave-only ovens. DOE also noted that the 

countertop combination microwave ovens used similar display types as microwave-only ovens 

(i.e., LED displays, LCDs, and VFDs). 

Table 5.5.12 DOE Countertop Combination Microwave Oven Standby Power

DOE Countertop 

Combo MWO 

Test Unit

Rated Microwave 

Cooking Output 

Power, W

Display 

Type

Display 

Size, in.2

Cooking 

Sensor

# of 

Heaters

Average 

Standby 

Power, W

DOE CTC1 1,000 LED 2.25 - 2 1.20

DOE CTC2 900

LCD w/ 

LED 

Backlight

3.75 - 2 2.36

DOE CTC3 900 VFD 3.00 Yes 1 3.23

DOE CTC4 1,100

LCD w/ 

LED 

Backlight

2.66 Yes 1 3.55

DOE CTC5 1,000 VFD 10.86 Yes 1 4.68

Figure 5.5.9 illustrates the measured standby power consumption as a function of display 

size for countertop combination microwave ovens. Similar to microwave-only ovens, DOE 

observed that standby power tends to increase as display size increases.
5-28

Figure 5.5.9 DOE Standby Power Consumption as a Function of Display Size for 

Countertop Combination Microwave Ovens

DOE also conducted product teardowns and standby power testing of individual 

components contributing to the total standby power consumption. DOE noted that the cooking 

sensors used in these models were similar to those used in microwave-only ovens. DOE also 

investigated the requirements for the size of the controls power supply for countertop 

combination microwave ovens. DOE noted that the size of a conventional linear power supply 

depends largely on the transformer used to step down the line input voltage to operate the 

controls. DOE isolated the power supply transformers in the controls these countertop 

combination microwave ovens and measured the standby power consumption. DOE similarly 

measured the power supply transformer standby power consumption for a limited number of the 

microwave-only ovens in its test sample. The results from this testing, presented below in Table 

5.5.13, showed that the size of the controls power supplies (i.e., the standby losses associated 

with the power supply transformers) were similar for both countertop combination microwave 

ovens and microwave-only ovens. In addition, as presented above in Table 5.5.12, the total 

standby power consumption for countertop combination microwave ovens is similar to that for 

microwave-only ovens. For these reasons, DOE believes that the sizes of the power supplies for 

countertop microwave ovens are similar to those for microwave-only ovens. As a result, DOE 

did not establish a separate product class for countertop combination microwave ovens.

Therefore, the incremental manufacturing costs listed above in Table 5.5.11 would also apply for 

countertop combination microwave ovens.
5-29

Table 5.5.13 Control Power Supply Transformer Standby Power Test Results

DOE Countertop Combo 

MWO Test Unit

Transformer 

Standby Power, W

DOE MicrowaveOnly Test UnitTransformer 

Standby Power, W

DOE CTC1 0.57 DOE28 1.44

DOE CTC2 0.95 DOE29 0.89

DOE CTC3 0.93 DOE30 1.11

DOE CTC4 1.81

DOE CTC5 1.08

Built-In and Over-the-Range Combination Microwave Ovens.

Built-In and Over-the-Range Combination Microwave Oven Testing and Product Teardown

As discussed above in section 5.2, DOE proposed to analyze a separate product class for 

built-in and over-the-range combination microwave ovens. DOE conducted standby power 

testing on a sample of six over-the-range combination microwave ovens and two built-in 

combination microwave ovens. The results from this testing are shown below in Table 5.5.14. 

Testing showed standby power levels ranging from 4.1 W to 8.8 W. DOE noted that all of the 

units in its test sample had a cooking sensor and either a LCD touch screen with backlighting or 

a VFD. DOE noted that the built-in combination microwave ovens in its test sample consumed 

more standby power than the over-the-range combination microwave ovens. However, DOE also 

noted that these two units were higher-end units with larger displays and a larger number of 

cooking settings and options.

Table 5.5.14 DOE Built-In and Over-the-Range Combination Microwave Oven Standby 

Power

DOE BuiltIn/Over-theRange Combo 

MWO Test Unit Installation

Rated 

Microwave 

Cooking Output 

Power, W

Display 

Type

Display 

Size, 

in.2

Cooking 

Sensor

# of 

Heaters

Average 

Standby 

Power, 

W

DOE OTRC1 Over-theRange 1,200 LCD Touch 

w/ Backlight 13.66 Y 4 4.19

DOE OTRC2 Over-theRange 1,200 LCD Touch 

w/ Backlight 13.66 Y 4 4.37

DOE OTRC3 Over-theRange 1,100 VFD 3.91 Y 4 4.50

DOE OTRC4 Over-theRange 1,100 VFD 3.91 Y 1 4.59

DOE OTRC5 Over-theRange 1,000 VFD 7.75 Y 1 4.14

DOE OTRC6 Over-theRange 900 VFD 4.00 Y 4 6.65

DOE BC1 Built-In 975 VFD 7.39 Y 4 8.16

DOE BC2 Built-In 950 VFD 7.39 Y 4 8.76
5-30

As discussed above for microwave-only ovens, display power requirements depend on 

the fundamental technology as well as the size of the display, the brightness, and the number and 

range of characters it can display. Figure 5.5.10 illustrates the measured standby power 

consumption as a function of display size for built-in and over-the-range combination microwave 

ovens. 

Figure 5.5.10 DOE Standby Power Consumption as a Function of Display Size for Built-In 

and Over-the-Range Combination Microwave Ovens

For each sample test unit, DOE also conducted standby power testing on individual 

components contributing to the total standby power consumption of each unit. DOE isolated and 

measured the standby power consumption of power filtration printed circuit boards, cooking 

sensors, and displays/user interface control boards. Results of this testing are shown below in

Table 5.5.15. DOE noted that the power filtration boards consumed on average approximately 

0.03 W. Similarly, cooking sensors consumed on average 0.86 W in standby mode. DOE also 

noted that display and user interface control board standby power consumption ranged from 0.75 

W to 4.24 W, with an average of 2.03 W. Note that DOE was not able to isolate every 

component consuming power in standby mode, therefore the power consumption of the 

individual components listed in the Table 5.5.15 will not add up to the total standby power 

consumption of the unit.
5-31

Table 5.5.15 DOE Built-In and Over-the-Range Combination Microwave Oven 

Disaggregated Components Standby Power Consumption

DOE Built-In/Overthe-Range Combo 

MWO Test Unit

Standby Power Consumption, W

Power Filtration 

Board

Cooking 

Sensor

Display/User 

Interface Total Unit

DOE OTRC1 0.06 0.82 1.88 4.19

DOE OTRC2 0.06 0.84 1.96 4.37

DOE OTRC3 0.03 0.82 0.75 4.50

DOE OTRC4 0.03 0.82 0.75 4.59

DOE OTRC5 0.01 0.92 1.38 4.14

DOE OTRC6 0.01 0.68 1.1 6.65

DOE BC1 0.01 1.05 4.15 8.16

DOE BC2 0.01 0.96 4.24 8.76

Incremental Cost Data for Standby Power Levels for Built-In and Over-the-Range Combination 

Microwave Ovens

DOE conducted standby power testing and reverse engineering analyses on the 8 built-in 

and over-the-range combination microwave ovens in its test sample in order to develop the costefficiency relationships. DOE used a design-option approach to determine the incremental 

manufacturing costs of combination microwave ovens for each standby power level. As 

discussed above for the microwave-only oven and countertop combination microwave oven

product class, DOE observed correlations between specific components and technologies, or 

combinations thereof, and measured standby power. Costs for each of the components and 

technologies used at each standby power level were estimated by DOE using quotes obtained 

from various component suppliers as well as interviews with manufacturers.

For standby power level 1, DOE believes that, similar to the microwave-only oven and 

countertop combination microwave oven product class, manufacturers would likely have to 

utilize a cooking sensor with no standby power requirements. DOE estimated that the 

manufacturing cost of a zero-standby cooking sensor would be the same as that of the cooking 

sensor with high standby power.

DOE believes that, in order to achieve standby power level 2, manufacturers would likely 

change the conventional linear power supply to a switch mode power supply. DOE used reverse 

engineering to determine the cost of the components used in a design of a switch mode power 

supply capable of delivering the same output power as the baseline conventional linear power 

supply. 

To move from standby power level 2 to standby power level 3, DOE estimated the cost of 

implementing a control board design with a switch mode power supply and replacing the 

electromechanical relays (used to drive components such as heaters, motors, lights, etc.) with 

solid state relays capable of driving the same loads as the electromechanical relays. Because 

implementing solid state relays would decrease the total power requirements of the control 
5-32

board, DOE also estimated the cost of changing power supply components based on the smaller 

power supply size.

For standby power level 4, DOE estimated the manufacturing cost based on the cost of 

the components needed to design an automatic power-down function that uses a transformerless 

power supply for the microprocessor chip along with a conventional linear power supply that is 

activated when the unit goes into active mode. DOE also estimated the costs associated with a 

door limit switch and Triac to control power through the transformer.

The results of this analysis for built-in and over-the-range combination microwave ovens 

are summarized in Table 5.5.16.

Table 5.5.16 Built-In and Over-the-Range Combination Microwave Oven Incremental 

Manufacturing Costs

Standby 

Power Level

Maximum Average Standby 

Power Consumption, W Incremental Cost, 2010$

Baseline 4.5 $ 0

1 3.7 $ 0

2 2.7 $ 2.29

3 2.2 $ 9.44

4 0.04 $ 5.18
5-33

REFERENCES

 1 American Metals Market. Available online at http://www.amm.com/. (Accessed May 2011)

2 Association of Home Appliance Manufacturers (AHAM). 2006. AHAM Test Data on 

Microwave Ovens. October 23, 2006. Docket No. EE-2006-STD-0127, Comment Number 

17.

3 Ibid.

4 Ibid.

5 Ibid.

6 Fish, N. et al. 2006. Standby Power Energy Use of Common Household Appliances. 

Canadian Building Energy End-Use Data and Analysis Centre, CBEEDAC 2006-RP-04-

DRAFT, July 2006.

7 Aulenback, A. et al. 2001. Stand-By Power Requirements for Household Appliances. 

Canadian Residential Energy End-Use Data and Analysis Centre, CREEDAC-2001-05-04, 

May 2001.

8 Ibid.

9 Lawrence Berkeley National Laboratory (LBNL). 2008. Low-Power Mode Energy 

Consumption in California Homes. Report CEC-500-2008-035 prepared for California 

Energy Commission, September 2008. Available online at 

http://www.energy.ca.gov/2008publications/CEC-500-2008-035/CEC-500-2008-035.PDF. 

(Accessed May 2011)

10 Floyd, D. and Webber, C. 1998. “Leaking Electricity: Individual Field Measurement of 

Consumer Electronics.” Proceedings of American Council for an Energy-Efficient Economy, 

Florida Solar Energy Center, August 1998.

11 Meier, A. and Huber, W. 1997. Results from the Investigations on Leaking Electricity in the 

USA. Lawrence Berkeley National Laboratory, Berkeley, CA, LBNL-40909, 1997.