CHAPTER 5. ENGINEERING ANALYSIS 

TABLE OF CONTENTS 

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

5.2 TECHNOLOGIES UNABLE TO BE INCLUDED IN THE ENGINEERING 

ANALYSIS...................................................................................................................... 5-2 

5.3 PRODUCT CLASSES ANALYZED.............................................................................. 5-4 

5.4 EFFICIENCY LEVELS................................................................................................... 5-5 

5.4.1 Baseline Units .................................................................................................................. 5-5 

5.4.2 Incremental Efficiency Levels ......................................................................................... 5-6

5.5 METHODOLOGY OVERVIEW .................................................................................... 5-9 

5.5.1 AHAM Data Request..................................................................................................... 5-10 

5.5.2 Manufacturer Interviews................................................................................................ 5-10 

5.5.3 Product Teardowns ........................................................................................................ 5-11 

5.5.3.1 Selection of Units......................................................................................... 5-11 

5.5.3.2 Generation of Bill of Materials.................................................................... 5-11 

5.5.3.3 Cost Structure of the Spreadsheet Models...................................................5-12 

5.5.4 Review of Previous Technical Support Documents ...................................................... 5-13 

5.5.5 Product Testing .............................................................................................................. 5-13 

5.6 ANALYSIS AND RESULTS........................................................................................ 5-14 

5.6.1 Cooking Products........................................................................................................... 5-14 

5.6.1.1 AHAM Data................................................................................................. 5-14 

5.6.1.2 Review of Past TSDs...................................................................................5-17 

5.6.1.3 Product Testing and Teardowns................................................................... 5-24 

LIST OF TABLES 

Table 5.4.1 1996 TSD Baseline Energy Factors for Cooking Products ................................. 5-6 

Table 5.4.2 Efficiency Levels for Residential Gas Cooktops................................................. 5-7 

Table 5.4.3 Efficiency Levels for Residential Electric Cooktops........................................... 5-7 

Table 5.4.4 Efficiency Levels for Residential Gas Ovens ...................................................... 5-8 

Table 5.4.5 Efficiency Levels for Residential Electric Ovens................................................ 5-9 

Table 5.4.6 Efficiency Levels for Residential Microwave Ovens .......................................... 5-9 

Table 5.5.1 Engineering Analysis Methods.......................................................................... 5-10 

Table 5.5.2 Major Manufacturing Processes ........................................................................ 5-13 

Table 5.6.1 Gas Cooktop Manufacturing Cost and Efficiency Increments .......................... 5-18 

Table 5.6.2 Electric Coil Cooktop Manufacturing Cost and Efficiency Increments ............ 5-19 

Table 5.6.3 Electric Smooth Cooktop Manufacturing Cost and Efficiency Increments....... 5-19 

Table 5.6.4 Gas Standard Oven Manufacturing Cost and Efficiency Increments ................ 5-20 

Table 5.6.5 Gas Self-Cleaning Oven Manufacturing Cost and Efficiency Increments ........ 5-21 

Table 5.6.6 Electric Standard Oven Manufacturing Cost and Efficiency Increments.......... 5-21 

5-i 

EERE-2006-STD-0127 COMMENT 64.2
Table 5.6.7 Electric Self-Cleaning Oven Manufacturing Cost and Efficiency 

Increments.......................................................................................................... 5-22 

Table 5.6.8 Slopes and Intercepts for Oven Energy Factor versus Cavity Volume

Relationship ....................................................................................................... 5-23 

Table 5.6.9 Microwave Oven Manufacturing Cost and Efficiency Increments ................... 5-24 

Table 5.6.10 Microwave Oven Features (Table 1 of 4).......................................................... 5-25 

Table 5.6.11 Microwave Oven Features (Table 2 of 4).......................................................... 5-25 

Table 5.6.12 Microwave Oven Features (Table 3 of 4).......................................................... 5-25 

Table 5.6.13 Microwave Oven Features (Table 4 of 4).......................................................... 5-26 

Table 5.6.14 Microwave Oven Input, Output, and Cooking Efficiency (1 of 4).................... 5-28 

Table 5.6.15 Microwave Oven Input, Output, and Cooking Efficiency (2 of 4).................... 5-28 

Table 5.6.16 Microwave Oven Input, Output, and Cooking Efficiency (3 of 4).................... 5-28 

Table 5.6.17 Microwave Oven Input, Output, and Cooking Efficiency (4 of 4).................... 5-28 

Table 5.6.18 Microwave Oven Rated versus Measured Output for AHAM and DOE 

Tests................................................................................................................... 5-30 

Table 5.6.19 Key Differences Between IEC Standard 705 and IEC Standard 60705 ............ 5-33 

Table 5.6.20 IEC Standard 705 versus IEC Standard 60705 Test Results ............................. 5-34 

Table 5.6.21 IEC Standard 705 versus IEC Standard 60705-2006 Test Results, Without 

Rounding............................................................................................................ 5-37 

LIST OF FIGURES 

Figure 5.5.1 Manufacturing Cost Assessment Stages ............................................................ 5-12 

Figure 5.6.1 AHAM Microwave Oven Efficiency versus Rated Output Power.................... 5-16 

Figure 5.6.2 AHAM Microwave Oven Efficiency versus Oven Cavity Volume .................. 5-17 

Figure 5.6.3 DOE and AHAM Microwave Oven Efficiency versus Rated Output Power.... 5-29 

Figure 5.6.4 DOE and AHAM Microwave Oven Efficiency versus Measured Output 

Power ................................................................................................................. 5-31 

Figure 5.6.5 DOE Non-Rounded versus Rounded Test-to-Test Efficiency Variation 

Measured Using IEC Standard 60705................................................................ 5-35 

Figure 5.6.6 DOE Non-Rounded versus Rounded Efficiency Measured Using IEC 

Standard 60705 .................................................................................................. 5-36 

5-ii 

EERE-2006-STD-0127 COMMENT 64.2
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 energy and water consumption and costs of products at 

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

analysis (section 5.1), considers technologies that are unable to analyzed for this rulemaking 

(section 5.2), discusses proposed product classes (section 5.3), establishes baseline unit 

specifications (section 5.4.1), discusses incremental efficiency levels (section 5.4.2), explains the 

methodology used during data gathering (5.5) and discusses the analysis and results (section 5.6) 

As described in section 1.3 of chapter 1 of this technical support document (TSD), DOE is 

continuing the energy conservation standards rulemaking for commercial clothes washers and 

microwave oven standby power, and analyses related to these products will be published in 

subsequent TSDs. As a result, this chapter presents results for residential cooking products, 

including microwave oven energy factor. 

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

and technology assessment (chapter 3 of the TSD) and technology options from the screening 

analysis (chapter 4.) Additional inputs include cost and energy efficiency data, which DOE 

received from the Association of Home Appliance Manufacturers (AHAM), obtained from the 

previous rulemaking analysis, and qualified and supplemented through testing, teardown analysis 

and manufacturer interviews. The primary output of the engineering analysis is a set of costefficiency curves. In the subsequent markups analysis (chapter 7), 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 6) 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; (2) the efficiency-level approach, which calculates 

the relative costs of achieving increases in energy efficiency levels, 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. 

5-1 

EERE-2006-STD-0127 COMMENT 64.2
5.2 TECHNOLOGIES UNABLE TO BE INCLUDED IN THE ENGINEERING 

ANALYSIS 

In performing the engineering analysis, DOE did not consider for analysis certain 

technologies that met the screening criteria but were unable to be evaluated for one or more of 

the following reasons: (1) data are not available to evaluate consumer usage of a product 

incorporating the technology and, therefore, the test procedure conditions and methods may not 

be applicable; (2) data are not available to evaluate the energy efficiency characteristics of the 

technology; and (3) available data suggest that the efficiency benefits of the technology are 

negligible. In the first two cases, DOE is unable to adequately assess how these technologies 

impact annual energy consumption. 

For technologies that lack consumer usage details, including operating conditions, 

duration, and frequency, DOE believes that the existing test procedures may specify conditions 

and methods that are not representative of actual usage. DOE further believes that even if data 

were available to amend the test procedures, such changes could be extensive enough to require 

total revision, which in turn could warrant the creation of a separate product class for that 

technology in the event that the test procedure changes indicated unique utility. 

Furthermore, certain technologies cannot be measured according to the conditions and 

methods specified in the existing test procedure. 

In other cases, available data suggest that some of the design options would result in such 

small energy savings as to be negligible. Because DOE intends to focus on the technologies with 

measurable impact on efficiency, design options with negligible energy savings have been 

eliminated from further consideration. 

 Several technologies are available for cooktops that allow the burners or heating elements 

to automatically adjust in response to cooking-state setpoints, such as cooking vessel 

temperature. These include thermostatically controlled gas cooktop burners as well as 

electronic controls for electric cooktops. However, DOE is unaware of any data to 

quantify the energy efficiency effects of such technologies. Further, efficiency benefits 

of these design options can only be realized under variable burner or element conditions. 

Because the cooktop test procedure does not account for consumer usage patterns, the 

energy savings of these technologies cannot be adequately measured. Therefore, DOE 

did not consider these design options for further analysis. 

 Similarly, DOE is unaware of any data that indicates a measurable energy efficiency 

impact of insulation in gas and electric coil cooktops, so DOE did not analyze this design 

option for these product classes. 

 Induction cooktops require ferromagnetic cookware in order to transfer energy to the 

food contents. While the test block specified in the DOE test procedure is aluminum and 

thus is unable to measure the efficiency of induction cooktops, the National Bureau of 

Standards (NBS), now called National Institute of Standards and Technology (NIST), 

5-2 

EERE-2006-STD-0127 COMMENT 64.2
proposed an alternate method of measuring the energy consumption of such cooktops by 

simply attaching a ferromagnetic material to the bottom of the test block. Data obtained 

by this method suggested an efficiency improvement over baseline electric smooth 

cooktops. However, this test method has not been rigorously validated for incorporation 

into the DOE test procedure and therefore, due to the unresolved nature of the NIST data, 

DOE eliminated induction elements for electric smooth cooktops from further 

consideration. 

 Some electric cooktops and microwave ovens with electronic controls consume standby 

power, but the efficiency metrics (i.e., energy factor (EF)) do not incorporate such power 

in their calculation. Even though DOE considers the consumer usage of these products to 

be well-defined, the current test procedure does not measure standby power. Thus DOE 

is unable to quantify the impact on energy savings of low-standby-loss electronic controls 

for these products and did not consider these design options during the analysis. 

 The only currently available gas ovens that DOE is aware of that incorporate radiant 

burners do so for broiling, which is a secondary cooking function that is not the focus of 

the DOE efficiency measurement; energy efficiency is instead measured during the 

primary bake function. Thus the energy benefits are not captured by the test procedure 

under these conditions. Accordingly, DOE eliminated radiant burners in gas ovens from 

further analysis. 

 While there are several residential steam ovens currently on the market, DOE believes 

that the existing test procedure may specify conditions and methods that are not 

representative of actual usage. DOE further believes that even if data were available to 

amend the test procedure, such changes could be extensive enough to require total 

revision, which in turn could warrant the creation of a separate product class in the event 

that the test procedure changes indicated unique utility. Thus, DOE did not consider 

steam cooking in the analysis. 

 For added insulation in microwave ovens, this technology will not improve the EF, since 

during the short duration of the DOE test procedure as well as during typical usage, the 

microwave oven cavity walls do not measurably heat up. Thus, the energy savings of this 

design option would be so small as to not be measurable. 

 Cooking sensors, which terminate the operation of a microwave oven based upon inferred 

cooking state, appear to promote shorter cook times and thus lower energy consumption. 

Due to the lack of consumer usage details, including operating conditions, duration, and 

frequency of use, DOE believes that the existing test procedure may specify conditions 

and methods that are not representative of actual usage. Thus, DOE did not consider this 

design option for further analysis. 

 According to AHAM, dual magnetrons in microwave ovens do not improve energy 

efficiency due to the added losses associated with two magnetron heaters. In addition, 

AHAM stated that the additional cost of dual magnetrons could not be economically 

5-3 

EERE-2006-STD-0127 COMMENT 64.2
justified. DOE does not have any efficiency data on dual magnetrons by which to 

evaluate this design option. Therefore, it did not consider dual magnetrons for further 

analysis. 

 AHAM stated that virtually no residential solo-function microwave oven still uses a 

ceramic stirrer. Almost all microwave ovens use polypropylene or mica film stirrers, 

which have lower losses than ceramic stirrers. According to AHAM, this design option 

has already been optimized so there is no opportunity for efficiency improvements. The 

stirrer cover, however, may be made of ceramic when there are browning elements that 

generate too much heat for a plastic cover. These covers absorb some microwave energy 

but are needed to prevent food splatter inside the wave guide. Eliminating the ceramic 

cover would adversely affect consumer utility by requiring cleaning of the stirrer or by 

reducing the life of the stirrer. Therefore, DOE’s analysis did not consider eliminating or 

improving the ceramic stirrer cover. 

 According to AHAM, losses associated with the wave guide are typically less than 0.5 

percent of the overall energy consumption. DOE is not aware of any data demonstrating 

efficiency improvements associated with wave guide improvement, so DOE did not 

analyze this design option. 

5.3 PRODUCT CLASSES ANALYZED 

DOE separated residential cooking products into product classes. Because DOE 

considered a separate energy conservation standard 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)) 

For cooking products, DOE analyzed product classes based on the energy source (i.e., gas 

or electric) and the cooking method (i.e. cooktops, ovens, and microwave ovens.) These 

distinctions yielded five cooking product classes: (1) gas cooktops; (2) electric cooktops; (3) gas 

ovens; (4) electric ovens; and (5) microwave ovens. DOE’s product classes are based on the list 

of product classes defined by DOE in its 1996 Technical Support Document for Residential 

Cooking Products (1996 TSD), which was released as part of the previous standards 

rulemaking.1 Gas and electric rangesa

 are not listed below as product classes. Because ranges 

consist of both a cooktop and oven, any potential cooktop and oven standards will apply to the 

individual components of the range. As a result, product classes for ranges are not necessary. 

For gas cooktops, DOE’s analyzed product class is: 

a

 DOE defines a “conventional range” under EPCA as “a class of kitchen ranges and ovens which is a household 

cooking appliance consisting of a conventional cooking top and one or more conventional ovens.” (10 CFR 430.2) 

5-4 

EERE-2006-STD-0127 COMMENT 64.2
 Conventional burners. 

For electric cooktops, DOE’s 1996 TSD determined that the ease of cleaning smooth 

elements provides enhanced consumer utility over coil elements. Because smooth elements 

typically use more energy than coil elements, DOE analyzed the following product classes for 

electric cooktops: 

 Low or high wattage open (coil) elements; and 

 Smooth elements. 

For electric ovens, the 1996 TSD determined that the type of oven-cleaning system is a 

utility feature that affects performance. DOE found that standard ovens and ovens using a 

catalytic continuous-cleaning process use roughly the same amount of energy. Self-cleaning 

ovens use a pyrolytic process that provides enhanced consumer utility with lower overall energy 

consumption as compared to either standard or catalytically lined ovens. Thus, DOE analyzed 

the following product classes for electric ovens: 

 Standard oven with or without a catalytic line; and 

 Self-cleaning oven. 

For gas ovens, DOE analyzed the following product classes based upon the same 

reasoning as electric ovens: 

 Standard oven with or without a catalytic line; and 

 Self-cleaning oven. 

For microwave ovens, DOE analyzed no further class breakdown. This product class 

can encompass microwave ovens with and without browning elements, but does not include 

microwave ovens that incorporate convection systems (combination ovens). DOE did not 

conduct an analysis of combination microwave ovens due to the inability of the test procedure to 

measure the performance of the convection component and thus a lack of data evaluating the 

energy efficiency or energy efficiency characteristics of microwave ovens incoporating 

convection systems. 

5.4 EFFICIENCY LEVELS 

5.4.1 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. 

5-5 

EERE-2006-STD-0127 COMMENT 64.2
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 or lower energy efficiency design option with the baseline unit. 

The identification of baseline units required establishing the baseline efficiency level. 

For residential cooking products (except for the prescriptive standard for gas cooking products), 

there are no existing minimum energy conservation standards, as previous analyses (i.e., from 

the 1996 TSD) failed to determine economic justification for them. The DOE test procedure 

uses EF to rate the efficiency of cooking products. The EF for these products is the ratio of the 

annual useful cooking energy output of the cooking appliance (i.e. the energy conveyed to the 

item being heated) to its total annual energy consumption. In accordance with the 1996 TSD on 

residential cooking products, DOE has selected the baseline EFs listed in Table 5.4.1 for the 

product classes DOE is using in this rulemaking. 

Table 5.4.1 1996 TSD Baseline Energy Factors for Cooking Products 

Product Class Baseline from 1996 TSD 

EF 

Gas Conventional Burner Cooktop 0.156 

Electric Open (Coil) Element Cooktop 0.737 

Electric Smooth Element Cooktop 0.742 

Gas Standard Oven 0.030 

Gas Self-Clean Oven 0.054 

Electric Standard Oven 0.107 

Electric Self-Clean Oven 0.096 

Microwave Oven 0.557 

5.4.2 Incremental Efficiency Levels 

For the majority of the product classes presented in section 5.3, DOE analyzed several 

efficiency levels and obtained incremental cost data at each of these levels. Table 5.4.2 through 

Table 5.4.6 provide efficiency levels and the reference source of each level for each of the 

products under consideration. The maximum levels identified in these tables are based on data 

developed from the design-option analysis in the previous rulemaking. 

Table 5.4.2 presents the efficiency levels analyzed for residential gas cooktops. The 

baseline and higher efficiency levels are based on the analysis performed in 1996 for the 

previous rulemaking. Since the 1996 TSD took a design-option approach to the analysis, each 

efficiency level is associated with a particular design option or combination of design options. 

Two higher efficiency levels for gas cooktops were included in the 1996 TSD that are not 

considered here due to the elimination of design options. In the current analysis, reflective 

surfaces were screened out due to impacts on consumer utility, and thermostatically controlled 

burners were not analyzed due to the inability of the DOE test procedure to adequately represent 

usage patterns and therefore energy efficiency characteristics. The combination of design 

options that produces the maximum technologically feasible EF is designated as “max-tech.” 

5-6 

EERE-2006-STD-0127 COMMENT 64.2
DOE has structured the analysis for standing pilot igntion systems as a design option 

associated with the baseline configuration because DOE has determined that cooktops 

incorporating such ignition systems do not provide unique utility for reasons stated in section 3.3 

of chapter 3 of this TSD. The first standards efficiency level corresponds to the elimination of 

standing pilot lights. 

Table 5.4.2 Efficiency Levels for Residential Gas Cooktops 

Level Efficiency Level Source Conventional Burners 

Cooking Efficiency EF 

Baseline 1996 TSD Baseline (with standing pilots) 0.399 0.156 

1 1996 TSD (without standing pilots) 0.399 0.399 

2 Max-Tech (1996 TSD) 0.420 0.420 

The 1996 TSD analyzed two efficiency levels for electric coil cooktops and three levels 

for electric smooth cooktops. Since the 1996 TSD took a design-option approach to the 

analysis, each efficiency level is associated with a particular design option or combination of 

design options. In the current analysis, however, reflective surfaces were screened out as a 

design option for electric coil cooktops due to impacts on consumer utility, and induction 

elements were not analyzed for electric smooth cooktops because the available efficiency data, 

while suggestive of energy savings, cannot be validated by the existing DOE test procedure. In 

addition, radiant elements for smooth electric cooktops, which were included in the 1996 TSD, 

were not considered as a design option for this rulemaking because manufacturer data provided 

to DOE for the 1996 TSD indicated that this technology does not offer an efficiency 

improvement over the baseline according to the DOE test procedure. Therefore, only a single 

efficiency level beyond the baseline was analyzed for both electric coil and smooth cooktops, 

and by default this level becomes the max-tech, as shown in Table 5.4.3. 

Table 5.4.3 Efficiency Levels for Residential Electric Cooktops 

Level Efficiency Level Source Open (Coil) Elements Smooth Elements 

Cooking Efficiency EF Cooking Efficiency EF 

Baseline 1996 TSD Baseline 0.737 0.737 0.742 0.742 

1 1996 TSD 0.769 (Max-Tech) 0.769 0.753 (Max-Tech) 0.753 

Efficiency levels for gas ovens, as shown in Table 5.4.4, are based on the 1996 TSD. 

Since the 1996 TSD took a design-option approach to the analysis, each efficiency level is 

associated with a particular design option or combination of design options. The oven separator 

design option from the 1996 TSD was screened out in the current analysis due to consumer 

safety and utility issues, as well as a lack of practicability to design and manufacture. Lowstandby-loss electronic controls were added as design options for both standard and self-cleaning 

gas ovens, but were not included as efficiency levels because DOE does not have efficiency or 

cost increment information on them. 

The baseline efficiency level for gas standard ovens assumes that the product is equipped 

with standing pilot lights, and the first standards efficiency level corresponds to the elimination 

of standing pilot lights based on the same reason as for gas cooktops. However, because the 

cleaning cycle of gas self-cleaning ovens requires electrical energy use, the existing energy 

5-7 

EERE-2006-STD-0127 COMMENT 64.2
conservation standard in effect requires that such ovens currently be equipped with a nonstanding pilot ignition system because such an ignition system is disallowed if there is an 

electrical cord provided on the product. Therefore, the baseline efficiency level for gas selfcleaning ovens assumes they lack a standing pilot light. Further, the first standards efficiency 

level is not based on elimination of a standing pilot, but rather on the addition of the forced 

convection design option. 

Electronic spark ignition lowers the standby power consumption as well as the cooking 

efficiency of standard gas ovens, and since the standard gas oven EF rating includes standby 

power, the use of electronic spark ignition results in an overall reduction in energy consumption. 

Electric spark ignition has the same functionality as hot surface ignition sources and is therefore 

listed as an alternate efficiency level to the hot surface (glo-bar) design option. 

Table 5.4.4 Efficiency Levels for Residential Gas Ovens 

Level Efficiency Level Source Standard Oven Self-Cleaning Oven 

Cooking Efficiency EF Cooking Efficiency EF 

Baseline 1996 TSD Baseline (with 

standing pilot light) 0.059 0.0298 0.071 0.0540 

1 1996 TSD 0.058 (Glo-bar 

ignition) 0.0536 0.088 0.0625 

2 1996 TSD 0.061 0.0566 0.088 0.0627 

3 1996 TSD 0.062 0.0572 0.089 (Max-Tech) 0.0632 

4 1996 TSD 0.065 0.0593 - -

5 1996 TSD 0.065 0.0596 - -

6 1996 TSD/Current Analysis 0.066 (Max-Tech) 0.0600 - -

1a(1) 1996 TSD (with electronic 

spark ignition) 0.058 0.0583 - -

(1) Note: Standard levels 1 and 1a correspond to designs that are utilized for the same purpose--eliminate 

the need for a standing pilot--but the technologies for each design are different. Standard level 1 is a hot 

surface ignition device while standard level 1a is a spark ignition device 

Efficiency levels for electric ovens, shown in Table 5.4.5, are primarily based on the 

1996 TSD. The oven separator design option from the 1996 TSD was screened out in the current 

analysis due to consumer safety and utility issues, as well as a lack of practicability to design and 

manufacture. The bi-radiant oven was screened out due to a lack of technological feasibility and 

practicability to manufacture, as well as impacts on consumer utility. Low-standby-loss 

electronic controls were added as design options for both standard and self-cleaning electric 

ovens in this analysis, but were not included as efficiency levels because, even though the test 

procedure accounts for the energy consumption of electronic controls, DOE does not have 

incremental efficiency or cost information on them. 

5-8 

EERE-2006-STD-0127 COMMENT 64.2
Table 5.4.5 Efficiency Levels for Residential Electric Ovens 

Level Efficiency Level Source Standard Oven Self-Cleaning Oven 

Cooking Efficiency EF Cooking Efficiency EF 

Baseline 1996 TSD Baseline 0.122 0.1066 0.138 0.1099 

1 1996 TSD/Current Analysis 0.128 0.1113 0.138 0.1102 

2 1996 TSD/Current Analysis 0.134 0.1163 0.142 (Max-Tech) 0.1123 

3 1996 TSD/Current Analysis 0.137 0.1181 - -

4 1996 TSD/Current Analysis 0.140 0.1206 - -

5 1996 TSD/Current Analysis 0.141 (Max-Tech) 0.1209 - -

For microwave oven energy factor, Table 5.4.6 lists the efficiency levels that were 

retained from the 1996 TSD, even though recent AHAM-supplied data suggests slightly different 

baseline and maximum-available efficiencies of a representative sample of current models. For 

example, the minimum efficiency among the microwave ovens recently tested by AHAM was 

54.8 percent, while the maximum efficiency was 61.8 percent, compared to 55.7 percent and 

60.2 percent, respectively, from the 1996 TSD. However, it was noted that the standard 

deviation in efficiency measurements for any given microwave oven ranged from 0.2 to 1.2 

absolute percentage points. To attempt to identify microwave oven design options associated 

with efficiency levels, DOE performed a reverse-engineering analysis on a representative sample 

of microwave ovens. DOE did not find any additional design options beyond those that were 

identified in the advance notice of proposed rulemaking (ANOPR). DOE also performed 

efficiency testing on the sample of microwave ovens, which validated data submitted by AHAM. 

Results from both AHAM and DOE efficiency testing showed no identifiable correlation 

between cooking efficiency and either cavity volume or rated output power. As part of the 

reverse-engineering analysis, DOE also evaluated microwave oven magnetrons, magnetron 

power supplies, and fan motors (identified as design options in chapter 3 of this TSD), and 

determined that efficiencies for these design options have changed little since the 1996 analysis. 

For these reasons, it was determined by DOE that the efficiency levels from the 1996 TSD were 

still representative of the state of current microwave oven technology to the extent that the DOE 

test procedure can capture performance. Further discussion of the AHAM test data and DOE 

testing and analysis is provided in section 5.6.1.1. 

Table 5.4.6 Efficiency Levels for Residential Microwave Ovens 

Level Efficiency Level Source Efficiency Level (EF) 

Baseline 1996 TSD Baseline 0.557 

1 1996 TSD 0.586 

2 1996 TSD 0.588 

3 1996 TSD 0.597 

4 1996 TSD Max-Tech 0.602 

5.5 METHODOLOGY OVERVIEW 

DOE typically uses data submitted by AHAM as the primary source of cost information 

for the engineering analysis. AHAM generally provides DOE with aggregated incremental 

5-9 

EERE-2006-STD-0127 COMMENT 64.2
manufacturing cost data from it member companies, whereupon DOE conducts an independent 

review of the AHAM data using several methods and data sources. To gain a better 

understanding of the data submitted by member companies and to be able to relate the costs of 

improving efficiency to discrete (or system) technologies, DOE typically conducts interviews 

with manufacturers of residential cooking products. For this rulemaking, however, with general 

support from interested parties, DOE reviewed the previous TSD and compared cost and 

performance information to AHAM data and other published data. For microwave ovens 

specifically, DOE performed detailed product teardowns on a sample of models spanning a range 

of efficiencies and product features. Table 5.5.1 below shows the methods DOE used for the 

engineering analysis. 

Table 5.5.1 Engineering Analysis Methods 

Method Products 

AHAM Data Microwave Ovens Only 

Review of Past TSD All Cooking Products 

Product Teardown Microwave Ovens Only 

Product Testing Microwave Ovens Only 

Manufacturer Interviews All Cooking Products 

5.5.1 AHAM Data Request 

In support of this rulemaking effort, DOE requested incremental cost data from AHAM 

for each of the product categories. The requested data would represent the average incremental 

production cost to improve a baseline unit to a specified efficiency level. In addition, DOE 

requested shipments, shipment-weighted average efficiency, and market share efficiency data. 

As discussed above, AHAM did not provide cost information, agreeing with DOE that the 

previous analysis from the 1996 TSD, updated to reflect current manufacturing costs, would be 

appropriate for this rulemaking. AHAM did, however, provide efficiency data for a sample of 

microwave ovens, as discussed in section 5.6.1. Data provided to DOE by AHAM are contained 

in appendix 5A. 

5.5.2 Manufacturer Interviews 

To better understand cost variances due to the variability in baseline units, design 

strategies, and cost structures that may exist among manufacturers, DOE supplemented the 

estimated cost data with information obtained through follow-up manufacturer interviews. These 

confidential interviews provided a deeper understanding of the various combinations of 

technologies used to increase product efficiency, 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 13B. 

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

required to increase the efficiency of the baseline units to various efficiency levels (i.e., 

5-10 

EERE-2006-STD-0127 COMMENT 64.2
conversion capital expenditures by efficiency or energy-use 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. 

5.5.3 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 only performed physical teardown 

analysis on microwave ovens. The teardown methodology is described in detail in section 

5.5.3.1 through section 5.5.3.3. 

5.5.3.1 Selection of Units 

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

 What efficiency levels should be captured in the teardown analysis? 

 Are there units on the market that capture all potential efficiency 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 efficiency 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-efficiency-related features that are the same as, or 

similar to, features of other products in the same class and at the same efficiency level. 

5.5.3.2 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 

5-11 

EERE-2006-STD-0127 COMMENT 64.2
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. 

The cost of raw materials is determined using data sources such as American Metals 

Market for prices for copper, steel and aluminum, for example.2

 DOE research suggests that the 

price of steel drastically increased in 2005, and the price of copper has increased significantly 

since 2004. Because DOE is using a 5-year average in material prices, these price increases are 

normalized, which better represents long-term material prices. 

5.5.3.3 Cost Structure of the Spreadsheet Models 

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 5.5.1 shows the three major steps in generating the 

manufacturing cost. 

Figure 5.5.1 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. 

5-12 

EERE-2006-STD-0127 COMMENT 64.2
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 5.5.2. 

Table 5.5.2 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, 

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. 

5.5.4 Review of Previous Technical Support Documents 

DOE reviewed previous rulemaking TSDs to assess their applicability to the current 

standard setting process for cooking products. These previous rulemaking technical support 

documents served as a source for design options, baseline efficiency levels, and energy 

consumption analysis, in addition to other sources. DOE utilized the 1996 TSD as a source for 

baseline unit efficiency as well as design options and incremental cost and efficiency data. This 

approach for cooking products was generally supported by interested parties. 

5.5.5 Product Testing 

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

the potential efficiency improvements associated with various design options. 

5-13 

EERE-2006-STD-0127 COMMENT 64.2
5.6 ANALYSIS AND RESULTS 

5.6.1 Cooking Products 

5.6.1.1 AHAM Data 

Conventional Cooking Products 

AHAM did not provide DOE with cost-efficiency data for conventional cooking products 

(i.e., cooking products other than microwave ovens), in part because it stated that its members 

indicated that there have been no technology breakthroughs since the last rulemaking and that its 

members were not able to adequately assess many of the design options. In concurrence with 

interested parties, DOE believes that the efficiency characteristics of gas and electric cooktops 

and ovens from the 1996 TSD are still valid. Therefore, the efficiency data provided in the 1996 

TSD are also presumed to still be valid. Furthermore, DOE believes that the cost of the design 

options investigated in the 1996 TSD are also valid once adjusted to reflect changes in the 

producer price index (PPI). The data from the 1996 TSD are detailed in section 5.6.1.2. 

Microwave Ovens 

In contrast to conventional cooking products, microwave ovens were presumed to have 

incorporated improved technology since 1996. Therefore, AHAM provided data on microwave 

oven efficiency (and standby power) for a sample of microwave ovens currently available in the 

U.S. market.3

 Microwave oven efficiency was tested according to DOE’s test procedure, which 

utilizes the International Electrotechnical Commission (IEC) Standard 705-1988 and 

Amendment 2-1993, Methods for measuring the performance of microwave ovens for household 

and similar purposes. Standby power was tested in accordance with IEC Standard 62301-2005, 

Household electrical appliances – Measurement of standby power. 

The microwave oven test procedure specified in IEC Standard 705-1998 and Amendment 

2-1993 calls for heating a glass container containing one liter of water at full power until the 

water temperature is raised by a specified amount. The starting temperature of the water T1 in 

degrees Celsius (°C) is given as: 

T1 = T0 – (10 ± 1 °C) where, 

T0 = the ambient temperature, specified as 20 ± 2 °C 

The water is heated by the operation of the microwave oven until the final water 

temperature T2 in °C is: 

T2 = T0 ± 1 °C 

The microwave power output P in W is then calculated from: 

5-14 

EERE-2006-STD-0127 COMMENT 64.2
P = (4.187 mw (T2 – T1) + 0.88 mc (T2 – T0))/t where, 

mw = the mass of the water in grams (g) 

mc = the mass of the container in g 

t = the heating time in seconds (s) 

The time to heat the water load, power input PIN in W, and the total energy consumption 

EM in watt-hours (Wh) of the microwave oven during the test period are also recorded. This test 

is repeated three times, unless the power output value resulting from the second test is within 1.5 

percent of the value obtained from the first test. The two or three values of P are averaged for 

further calculations. 

Cooking efficiency EffMO is then obtained using: 

EffMO = P/PIN 

For the remainder of the calculations, the test procedure specified in 10 CFR 430 subpart 

B appendix I is utilized. Note that in the following calculations, all temperatures are expressed 

in degrees Fahrenheit. The microwave oven test energy output ET in Wh (kilo-joules (kJ))b

 is 

calculated as: 

ET = CPMW (T2 – T1) + CCMC (T2 – T0))/Ke where, 

MW = the measured mass of the test water load in pounds (lb), (g) 

MC = the measured mass of the test container before filling with test water load in lb (g) 

T1 = the initial test water load temperature in °F (°C) 

T2 = the final test water load temperature in °F (°C) 

T0 = the measured ambient room temperature in °F (°C) 

CC = 0.210 British thermal units (BTU)/lb-°F (0.88 kJ/kilogram (kg)-°C), specific heat of the 

test container 

CP = 1.0 BTU/lb-°F (4.187 kJ/kg-°C), specific heat of water 

Ke = 3,412 BTU/kWh (3,600 kJ/kWh), conversion factor of kWh to BTU. 

The two or three values for test energy output are averaged and the microwave oven 

annual energy consumption EMO is calculated in kWh per year from: 

EMO = (EM x OM)/ET where, 

EM = the test energy consumption in Wh (kJ) 

b

 Note that in order to correctly utilize the equation as specified in the test procedure to produce either watt-hours for 

standard units or kJ for metric units, additional factors must be applied. For standard units, ET must be multiplied by 

1000. For metric units, ET must be divided by 3600. 

5-15 

EERE-2006-STD-0127 COMMENT 64.2
OM = 79.8 kWh (287,280 kJ) per year, the microwave oven annual useful cooking-energy 

output 

Finally, the microwave oven energy factor RMO (equivalent to EF) is calculated from: 

RMO = OM/EMO 

EF is the metric for microwave ovens on which the DOE efficiency standard is based, 

while AHAM provided test data in terms of cooking efficiency in their data submittal for this 

rulemaking. From the above equations, it can be observed that there are several contributing 

factors that can lead to significant test-to-test variations in measured EF and efficiency. First, the 

tolerances on the temperature specifications are substantial relative to the absolute values. The 

range of allowable temperatures for ambient, starting, and final temperatures can lead to 

acceptable test load temperature rises ranging from 4–16 °C. Since the heating time is on the 

order of only a few tens of seconds, power and energy output calculations are difficult to 

measure consistently test-to-test. In addition, the efficiency calculation assumes that input power 

is constant for the duration of the test, which may not be the case. These factors make the 

existing test procedure difficult to conduct with accuracy and repeatability. 

In the recent testing for this analysis, although AHAM only tested 21 units from 9 

manufacturers, the units were selected to represent a broad spectrum of models available in the 

marketplace with varying capacities and features. Figure 5.6.1 and Figure 5.6.2 display the 

AHAM microwave oven efficiency data. 

50% 

55% 

60% 

65% 

Efficiency 

600 700 800 900 1000 1100 1200 1300 1400 

Rated Output Power (W) 

Figure 5.6.1 AHAM Microwave Oven Efficiency versus Rated Output Power4 

5-16

EERE-2006-STD-0127 COMMENT 64.2
Figure 5.6.1 illustrates a small variation in efficiency across all rated output powers, 

approximately ±3.5 absolute percentage points from the average efficiency. There is a lack of a 

correlation between microwave oven rated output power and microwave oven efficiency. Figure 

5.6.2 illustrates the relationship between microwave oven efficiency and microwave oven 

volume. Similarly, there is no correlation between microwave oven efficiency and volume. 

Figure 5.6.1 and Figure 5.6.2 confirm DOE’s approach of creating a single product class for 

microwave ovens irrespective of rated output power or cavity volume, and demonstrate that there 

is no basis to specify an efficiency standard that is a function of either rated output power or 

cavity volume. 

50% 

55% 

60% 

65% 

Efficiency 

0.0 0.5 1.0 1.5 2.0 2.5 

Microwave Oven Volume (ft^3) 

Figure 5.6.2 AHAM Microwave Oven Efficiency versus Oven Cavity Volume5 

5.6.1.2 Review of Past TSDs 

After consulting with AHAM and various interested parties and suppliers, DOE 

determined that the design options for cooking products other than microwaves have not changed 

significantly since the 1996 TSD analysis. Also, no industry-aggregated manufacturing cost data 

were supplied to DOE in the ANOPR phase of this rulemaking. Therefore, DOE decided to 

update the 1996 TSD analysis using the PPI to scale incremental manufacturing cost data for gas 

and electric cooktops, and gas and electric standard and self-cleaning ovens. For gas cooktops 

and ovens, the PPI for gas household cooking equipment was utilized. Similarly, the PPI for 

electric household cooking equipment was used for electric cooktops and ovens. 

Comparison of current microwave oven efficiency data with analogous data from the 

1996 TSD shows that the range of efficiency levels based on EF analyzed in the 1996 TSD are 

5-17 

EERE-2006-STD-0127 COMMENT 64.2
still valid, although AHAM indicated in comments provided along with its data submittal for this 

rulemaking that certain design options used to achieve those levels have already been optimized.6 

But as noted in section 5.4.2, the range of efficiency levels from the 1996 TSD is still 

representative of the performance of current microwave oven models. Therefore, for the 

purposes of this analysis, the same efficiency levels are used. As with the conventional cooking 

products, the incremental manufacturing cost data from the 1996 TSD was scaled by the PPI for 

electric household cooking equipment, which includes microwave ovens, to obtain the costefficiency relationship. 

Cooktop Test Procedure 

DOE’s cooktop test procedure is based on measuring the amount of energy required to 

raise an aluminum block test load from room temperature to a specified temperature above room 

temperature at full input heating rate, then operating the burner or element a fixed time longer at 

a reduced input heating rate. The size of the test block depends on the burner or element size, and 

the test is repeated for each burner or element. Annual energy consumption is calculated from the 

average cooking efficiency of the burners or elements. Cooktops are rated using EF, which is the 

ratio of the annual useful cooking-energy output of the cooktop to its total annual energy 

consumption. The annual energy consumption includes the energy input during the time the load 

is being heated, plus the energy consumed by any standing pilot during standby hours for a gas 

cooktop. Therefore, design options that raise the cooking efficiency of a gas or electric cooktop 

and/or reduce the energy consumption of a pilot on a gas cooktop can decrease the total annual 

energy consumption and therefore improve EF. 

Gas Cooktops 

Table 5.6.1 describes the design options and design option combinations that result in 

increased EF of gas cooktops. The design options and efficiency levels analyzed are those 

presented in the 1996 engineering analysis, with several design options (reflective surfaces and 

thermostatically controlled burners) eliminated in this analysis as described in section 5.4.2. 

Table 5.6.1 Gas Cooktop Manufacturing Cost and Efficiency Increments 

Level Efficiency Level Description Cooking 

Efficiency EF Delta Manufacturer Cost from Baseline (2006$) 

Baseline Baseline 39.9% 0.156 -

1 Baseline + Electronic Ignition 39.9% 0.399 $12.06 

2 1 + Sealed Burners 41.8% 0.420 $32.06 

Notes: 

Baseline: Cooktop cooking efficiency = 39.9%, four conventional 9,000 BTU/hr burners, two 117 BTU/hr 

standing pilot lights 

(1) Electronic Ignition: Standing pilot lights eliminated, cooking efficiency increase = 0.0% 

(2) Sealed Burners: Cooking efficiency increase = 4.8% (relative percent) 

5-18 

EERE-2006-STD-0127 COMMENT 64.2
Electric Coil Cooktops 

Table 5.6.2 describes the design option that results in increased cooking efficiency of 

electric open (coil) cooktops. The design option and efficiency levels analyzed are those 

presented in the 1996 engineering analysis, with one design option (reflective surfaces) 

eliminated in this analysis as described in section 5.4.2. 

Table 5.6.2 Electric Coil Cooktop Manufacturing Cost and Efficiency Increments 

Level Efficiency Level Description Cooking 

Efficiency EF Delta Manufacturer Cost from Baseline (2006$) 

Baseline Baseline 73.7% 0.737 -

1 Baseline + Improved Contact 

Conductance 76.9% 0.769 $2.28 

Notes: 

Baseline: Cooktop cooking efficiency = 73.7%, two 6-inch 1,250 W and two 8-inch 2,100 W elements

(1) Improved Contact Conductance: Cooking efficiency increase = 4.3% (relative percent) 

Electric Smooth Cooktops 

Table 5.6.3 describes the design options that result in increased cooking efficiency of 

electric smooth cooktops. The design options and efficiency levels analyzed are those presented 

in the 1996 engineering analysis, with one design option (induction element) eliminated in this 

analysis as described in section 5.4.2. Another design option (radiant element) discussed in the 

1996 engineering analysis was not included in this analysis because it exhibited a lower 

efficiency than the baseline cooktop. 

Table 5.6.3 Electric Smooth Cooktop Manufacturing Cost and Efficiency Increments 

Level Efficiency Level Description Cooking 

Efficiency EF Delta Manufacturer Cost from Baseline (2006$) 

Baseline Baseline 74.2% 0.742 -

1 Baseline + Halogen Lamp Element 75.3% 0.753 $89.09 

Notes: 

Baseline: Cooktop cooking efficiency = 74.2%, two 6-inch 1,500 W and two 8-inch 2,000 W solid disk elements

(1) Halogen Element: Cooking efficiency increase = 1.5% (relative percent), two small 1,200 W and two large 

1,800 W circular lamps 

Conventional Oven Test Procedure 

DOE’s oven test procedure is based on measuring the amount of energy required to raise 

an aluminum block test load from room temperature to a specified temperature above room 

temperature. Ovens are rated using EF, which is the ratio of the annual useful cooking-energy 

output of the oven (energy conveyed to the item being heated) to its total annual energy 

consumption. The annual energy consumption includes the energy input during the time the load 

is being heated plus the energy consumed by other features such as a clock, standing pilot, 

electronic ignition system, and/or self-cleaning cycles. Therefore, design options that raise the 

5-19 

EERE-2006-STD-0127 COMMENT 64.2
cooking efficiency of the oven and/or reduce the energy consumption of features not related to 

heating food can decrease the total annual energy consumption and therefore improve EF. 

Gas Ovens 

Table 5.6.4 describes the design options and design option combinations that result in 

increased EF of gas standard ovens. The design options and efficiency levels analyzed are those 

presented in the 1996 engineering analysis, with one design option (oven separator) eliminated in 

this analysis as described in section 5.4.2. 

Table 5.6.4 Gas Standard Oven Manufacturing Cost and Efficiency Increments 

Level Efficiency Level Description Cooking 

Efficiency EF Delta Manufacturer Cost from Baseline (2006$) 

Baseline Baseline 5.9% 0.0298 -

1 Baseline + Electric Glo-bar Ignition 5.8% 0.0536 $12.06 

2 1 + Improved Insulation 6.1% 0.0566 $15.64 

3 2 + Improved Door Seals 6.2% 0.0572 $16.72 

4 3 + Forced Convection 6.5% 0.0593 $38.86 

5 4 + Reduced Vent Rate 6.5% 0.0596 $40.48 

6 5+ Reduced Conduction Losses 6.6% 0.0600 $44.11 

1a Baseline + Electronic Spark Ignition 5.8% 0.0583 $15.00 

Notes: 

Baseline: Cooking efficiency = 5.92%, 2 inches of 1.09 lb/cubic foot insulation, standing pilot light ignition = 175 

BTU/hr 

(1) Baseline + Electric Glo-Bar Ignition: Cooking efficiency decrease = 0.152 (absolute percentage points), added 

electricity consumption = 176 Wh 

(2) 1 + Improved Insulation: Cooking efficiency increase = 4.9% (relative percent) 

(3) 2 + Improved Door Seals: Cooking efficiency increase = 1.0% (relative percent) 

(4) 3 + Forced Convection: Cooking efficiency increase = 4.8% (relative percent), added electricity consumption 

= 15 Wh 

(5) 4 + Reduced Vent Rate: Cooking efficiency increase = 0.5% (relative percent) 

(6) 5 + Reduced Conduction Losses: Cooking efficiency increase = 0.05 (absolute percentage points) 

(1a) Baseline + Electronic Spark Ignition: Cooking efficiency decrease = 0.09 (absolute percentage points), 

added electricity consumption = 0.0 Wh. Standard levels 1 and 1a correspond to designs that are utilized for the 

same purpose--eliminate the need for a standing pilot--but the technologies for each design are different. 

 Standard level 1 is a hot surface ignition device while standard level 1a is a spark ignition device 

Table 5.6.5 describes the design options and design option combinations that result in 

increased EF of gas self-cleaning ovens. The design options and efficiency levels analyzed are 

those presented in the 1996 engineering analysis, with one design option (oven separator) 

eliminated in this analysis as described in section 5.4.2. 

5-20

EERE-2006-STD-0127 COMMENT 64.2
Table 5.6.5 Gas Self-Cleaning Oven Manufacturing Cost and Efficiency Increments 

Level Efficiency Level Description Cooking 

Efficiency EF Delta Manufacturer Cost from Baseline (2006$) 

Baseline Baseline 7.1% 0.0540 -

1 Baseline + Forced Convection 8.8% 0.0625 $11.01 

2 1 + Reduced Conduction Losses 8.8% 0.0627 $15.38 

3 2 + Improved Door Seals 8.9% 0.0632 $16.60 

Notes: 

Baseline: Cooking efficiency = 7.13%, clock power = 3.6 W, 2 inches of 1.90lb/cubic foot insulation, electronic 

ignition = 176 Wh, self-cleaning energy consumption = 43,158 BTU 

(1) Baseline + Forced Convection: Cooking efficiency increase = 23% (relative percent), added electricity 

consumption (during cooking and cleaning cycles) = 15 Wh 

(2) 1 + Reduced Conduction Losses: Cooking efficiency increase = 0.05 (absolute percentage points) 

(3) 2 + Improved Door Seals: Cooking efficiency increase = 1.0% (relative percent) 

Electric Ovens 

Table 5.6.6 describes the design options and design option combinations that result in 

increased EF of electric standard ovens. The design options and efficiency levels analyzed are 

those presented in the 1996 engineering analysis, with several design options (bi-radiant oven 

and oven separator) eliminated in this analysis as described in section 5.4.2. 

Table 5.6.6 Electric Standard Oven Manufacturing Cost and Efficiency Increments 

Level Efficiency Level Description Cooking 

Efficiency EF Delta Manufacturer Cost from Baseline, (2006$) 

Baseline Baseline 12.2% 0.1066 -

1 Baseline + Reduced Vent Rate 12.8% 0.1113 $1.63 

2 1 + Improved Insulation 13.4% 0.1163 $4.84 

3 2 + Improved Door Seals 13.7% 0.1181 $8.53 

4 3 + Forced Convection 14.0% 0.1206 $48.14 

5 4 + Reduced Conduction Losses 14.1% 0.1209 $51.69 

Notes: 

Baseline: Cooking efficiency = 12.15%, clock power = 3.9 W, 2 inches of 1.09 lb/cubic foot insulation 

(1) Baseline + Reduced Vent Rate: Cooking efficiency increase = 0.62% (absolute percentage points) 

(2) 1 + Improved Insulation: Cooking efficiency increase = 0.52% (relative percent) 

(3) 2 + Improved Door Seals: Cooking efficiency increase = 0.24 (absolute percentage points) 

(4) 3 + Forced Convection: Cooking efficiency increase = 0.33 (absolute percentage points), added electricity 

consumption = 15 Wh 

(5) 4 + Reduced Conduction Losses: Cooking efficiency increase = 0.05 (absolute percentage points) 

Table 5.6.7 describes the design options and design option combinations that result in 

increased EF of electric self-cleaning ovens. The design options and efficiency levels analyzed 

are those presented in the 1996 engineering analysis, with several design options (bi-radiant oven 

and oven separator) eliminated in this analysis as described in section 5.4.2. 

5-21 

EERE-2006-STD-0127 COMMENT 64.2
Table 5.6.7 Electric Self-Cleaning Oven Manufacturing Cost and Efficiency Increments 

Level Efficiency Level Description Cooking 

Efficiency EF Delta Manufacturer Cost from Baseline, (2006$) 

Baseline Baseline 13.8% 0.1099 -

1 Baseline + Reduced Conduction 

Losses 13.8% 0.1102 $4.37 

2 1 + Forced Convection 14.2% 0.1123 $43.98 

Notes: 

Baseline: Cooking efficiency = 13.79%, clock power = 3.8 W, 2 inches of 1.09 lb/cubic foot insulation, selfcleaning energy consumption = 5,286 Wh 

(1) Baseline + Reduced Conduction Losses: Cooking efficiency increase = 0.05 (absolute percentage points) 

(2) 1 + Forced Convection: Cooking efficiency increase = 0.33 (absolute percentage points), added electricity 

consumption = 15 Wh 

Conventional Oven Energy Use versus Volume 

The oven cost-efficiency relationships detailed above are predicated upon baseline ovens 

with a cavity volume of 3.9 ft3

. It is well documented, however, that efficiency scales with oven 

cavity volume. This variation between efficiency, and thus EF, and oven volume results from 

the fact that larger ovens have higher thermal masses and larger vent rates than smaller ovens. 

Since the test procedure for establishing EF is a transient test with a fixed test load, the increased 

energy consumption due to the increased mass of larger units yields a lower EF. The 1980 DOE 

engineering analysis for residential appliances7 established a relationship between oven volume 

and EF from data compiled by the National Bureau of Standards (which was renamed to the 

National Institute of Standards and Technology (NIST)). Using these data, linear equations were 

derived for both electric and gas ovens. No distinction was found to exist between standard and 

self-cleaning ovens for either gas or electric ovens. Intercepts for a particular baseline model or 

oven design were chosen so that the equations pass through the desired EF corresponding to a 

particular volume. Values from the 1996 TSD for the slopes and intercepts for gas and electric 

ovens are listed in Table 5.6.8. The 1996 TSD did not analyze data at every efficiency level, and 

higher efficiency levels are not included in Table 5.6.8 because certain design options have been 

eliminated in the current analysis. DOE believes the slopes and intercepts of these equations 

from the 1996 TSD to still be valid. 

5-22

EERE-2006-STD-0127 COMMENT 64.2
Table 5.6.8 Slopes and Intercepts for Oven Energy Factor versus Cavity Volume 

Relationship 

Energy 

Efficiency Level 

Electric Gas 

Slope = -0.0157 Slope = -0.0073 

Standard Self-Clean Standard Self-Clean 

Baseline - 0.1632 0.0865 0.0865 

1 0.1752 - 0.0895 -

2 0.1802 - - -

3 0.1822 - 0.0935 -

Note: EF = (Slope x Volume) + Intercept where Volume is expressed in cubic feet. 

Conventional Oven Standby Power 

In the ANOPR, DOE stated it would consider additional design options that would result 

in a lowering of the energy consumption of non-cooking features (e.g. standby power) for 

conventional ovens during the notice of proposed rulemaking (NOPR) phase. However, no data 

were received on standby power for any of these products, so no additional analysis was 

performed. 

Microwave Ovens 

Table 5.6.9 describes the design options and design option combinations that result in 

increased EF of microwave ovens. The design options and efficiency levels analyzed are those 

presented in the 1996 engineering analysis, with incremental manufacturing costs scaled by the 

PPI for electric household cooking equipment. For the NOPR, DOE sought input from interested 

parties on the approach of analyzing additional design options that would result in a lowering of 

the energy consumption of non-cooking features (e.g. standby power), even though the test 

procedure currently does not account for such usage in EF. DOE is separately considering an 

updated test procedure to incorporate a measurement of standby and off mode power, as well as 

energy conservation standards for microwave oven standby and off mode power consumption. 

5-23 

EERE-2006-STD-0127 COMMENT 64.2
Table 5.6.9 Microwave Oven Manufacturing Cost and Efficiency Increments 

Level Efficiency Level Description Cooking 

Efficiency EF Delta Manufacturer Cost from Baseline (2006$) 

Baseline Baseline 55.7% 0.557 -

1 Baseline + More Efficient Power 

Supply 58.6% 0.586 $8.68 

2 1 + More Efficient Fan 58.8% 0.588 $17.95 

3 2 + More Efficient Magnetron 59.7% 0.597 $32.53 

4 3 + Reflective Surfaces 60.2% 0.602 $51.11 

Notes: 

Baseline: Cooking efficiency = 55.7% 

(1) Efficient Power Supply: Cooking efficiency increase = 2.9 (absolute percentage points) 

(2) Efficient Fan: Cooking efficiency increase = 0.23 (absolute percentage points) 

(3) Efficient Magnetron: Cooking efficiency increase = 0.90 (absolute percentage points) 

(4) Reflective Surfaces: Cooking efficiency increase = 0.50 (absolute percentage points) 

5.6.1.3 Product Testing and Teardowns 

Microwave Oven Efficiency 

DOE conducted product testing and teardown analysis for microwave ovens to 

supplement AHAM-supplied data, to validate the approach of updating the 1996 TSD analysis, 

and to examine the microwave oven test procedure for potential updates. In order to identify 

design options, circuit designs, and display options, DOE disassembled a representative sample 

of 32 units to gain an in-depth understanding of common microwave oven design elements, 

components, and manufacturing practices. DOE also evaluated the IEC microwave oven test 

standard which is referenced by the current DOE test procedure (IEC Standard 705) in 

comparison to the current IEC test standard (IEC Standard 60705-2006, Household microwave 

ovens – Methods for measuring performance (IEC Standard 60705).) 

Test Units 

DOE conducted a market survey of microwave oven models and their associated features 

to identify the primary differentiators among commercially-available units, and to then select a 

representative range of test units which incorporate these features. DOE selected 32 microwave 

ovens based on parameters that could be identified from product literature. These included: 1) 

rated output power in W; 2) rated cavity volume in ft3

; 3) display type; 4) the presence or 

absence of a cooking sensor; and 5) magnetron power supply technology. For the latter, certain 

models were advertised as incorporating “inverter technology” that allows variable power output 

for different user-selectable cooking-level settings. The key parameters for each of the test units 

are presented in Table 5.6.10 through Table 5.6.13. In some cases, several units were selected 

from a single manufacturer that appeared to have similar construction, rated power, and volume, 

but differed in ancillary features such as the type of display or the presence of a cooking sensor. 

5-24 

EERE-2006-STD-0127 COMMENT 64.2
Such similarities are noted in the tables. Nomenclature for the display entries are described in 

the following paragraphs. 

Table 5.6.10 Microwave Oven Features (Table 1 of 4) 

DOE Unit Number DOE1 DOE2 DOE3 DOE4 DOE5 DOE6 DOE7 DOE8 

Rated Output Power (W) 

Stated Volume (ft3

) 

700 700 700 700 

0.7 0.7 0.7 0.7 

800 

1 

800 

1 

800 

0.8 

800 

0.8 

Cooking Sensor 

Inverter Power Supply 

- - - -

- - - -

Y 

-

-

-

-

-

-

-

Type 

Characters 

# of LEDs for backlighting 

Size 

Display 

LED LED LED LED 

#, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4 

N/A N/A N/A N/A 

1.50" x 

0.43" 

1.50" x 

0.43" 

1.45" x 

0.70" 

1.90" x 

0.83" 

VFD 

A, 1 x 7 

N/A 

2.25" x 

0.75" 

LED 

#, 1 x 4 

N/A 

1.50" x 

0.80" 

LCD 

#, 1 x 4 

None 

1.87" x 

0.83" 

LCD 

#, 1 x 4 

None 

1.87" x 

0.83" 

Unit is Similar to ---- - DOE5 - -

Table 5.6.11 Microwave Oven Features (Table 2 of 4) 

DOE Unit Number DOE9 DOE10 DOE11 DOE12 DOE13 DOE14 DOE15 DOE1 6 

Stated Volume (ft3

) 

Rated Output Power (W) 900 

0.9 

1000 1000 1000 

1.1 1.1 1 

1000 

0 

1100 

1.1 

1100 

1.1 

1100 

1.8 

Cooking Sensor 

Inverter Power Supply 

-

-

- - -

- - -

-

-

-

-

Y 

-

Y 

-

Type 

Characters 

# of LEDs for backlighting 

Size 

Display 

LED 

#, 1 x 4 

N/A 

2.00" x 

0.65" 

LED LED LED 

#, 1 x 4 #, 1 x 4 #, 1 x 4 

N/A N/A N/A 

1.85" x 

1.10" 

1.75" x 

0.85" 

1.75" x 

0.70" 

VFD 

#, 1 x 4 

N/A 

2.20" x 

0.65" 

LED 

#, 1 x 4 

N/A 

2.00" x 

0.65" 

LCD 

A, 1 x 6 

5 

2.53" x 

0.95" 

VFD 

A, 1 x 7 

N/A 

2.25" x 

0.75" 

Unit is Similar to - --- - - DOE14 -

Table 5.6.12 Microwave Oven Features (Table 3 of 4) 

DOE Unit Number DOE17 DOE18 DOE19 DOE20 DOE21 DOE22 DOE23 DOE2 4 

Rated Output Power (W) 

Stated Volume (ft3

) 

1100 1100 1100 1100 

1 1.4 1 1.3 

1100 

1.1 

1100 

1 

1150 

1.4 

1200 

2.2 

Cooking Sensor 

Inverter Power Supply 

- - - -

- - - -

-

-

-

-

Y 

-

Y 

Y 

Type 

Characters 

# of LEDs for backlighting 

Size 

Display 

LCD LCD LCD LED 

#, 1 x 4 A, 1 x 5 #, 1 x 4 #, 1 x 4 

3 4 None N/A 

1.83" x 

0.80" 

2.03" x 

0.81" 

1.87" x 

0.83" 

1.50" x 

0.80" 

LED 

#, 1 x 4 

N/A 

1.47" x 

0.80" 

LCD 

#, 1 x 4 

3 

2.00" x 

0.83" 

VFD 

A, 1 x 7 

N/A 

2.25" x 

0.75" 

LCD 

A, 1 x 6 

10 

2.05" x 

1.10" 

Unit is Similar to - - DOE17 - - DOE17 DOE16 DOE3 0 

5-25 

EERE-2006-STD-0127 COMMENT 64.2
Table 5.6.13 Microwave Oven Features (Table 4 of 4) 

DOE Unit Number DOE25 DOE26 DOE27 DOE28 DOE29 DOE30 DOE31 DOE3 2 

Rated Output Power (W) 

Stated Volume (ft3

) 

1200 1200 1200 1200 

1.2 2.2 1.2 2 

1200 

2 

1250 

2.2 

1300 

1.2 

1300 

1.2 

Inverter Power Supply 

Cooking Sensor - Y Y Y 

- Y - -

Y 

-

Y 

Y 

Y 

Y 

Y 

Y 

Type 

Characters 

# of LEDs for backlighting 

Size 

Display 

LCD LCD LCD LCD 

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

5 10 4 6 

1.85" x 

0.83" 

2.05" x 

1.10" 

2.03" x 

0.78" 

2.45" x 

1.17" 

LCD 

A, 1 x 7 

4 

2.03" x 

0.78" 

LCD 

A, 1 x 6 

4 

2.05" x 

1.10" 

LCD 

#, 1 x 4 

10 

1.75" x 

0.80" 

LCD 

A, 1 x 6 

10 

2.05" x 

1.10" 

Unit is Similar to DOE17 DOE30 DOE25 - - DOE31 - DOE3 1 

The range of rated output powers and cavity volumes were determined on the basis of 

manufacturer specifications. Rated output power, which is a measure of the power transferred to 

the food load at the full-scale cooking setting, ranged from 700 to 1,300 W. Cavity volumes, 

which typically roughly scale with output power, ranged from rated values of 0.7 to 2.2 ft3. 

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

units: 1) LED; 2) LCD; and 3) VFD. (Details of each technology are discussed later in this 

section in the context of standby power.) 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. 

All 32 microwave ovens in the DOE sample were subjected to efficiency testing via the 

current DOE test procedure, which is based by reference on IEC Standard 705, which has been 

superseded by IEC Standard 60705.c

 DOE subsequently subjected 12 of the 32 microwave 

ovens to additional cooking efficiency testing per IEC Standard 60705 to investigate the 

differences between the two test standards. DOE conducted additional testing of an inverterbased microwave oven to assess the impact of operating such a system at various power levels. 

Lastly, DOE considered possible improvement opportunities for the current cooking test 

procedure. 

General Construction 

All microwave 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 

c

 Current IEC standards may be obtained from www.iec.ch. However, IEC does not make obsolete standards 

available. 

5-26 

EERE-2006-STD-0127 COMMENT 64.2
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 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 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, baseline microwave ovens contain a 

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

high-voltage aluminum electrolytic capacitor. The user interface for these microwave baseline 

ovens is a simple LCD or LED display. 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 multicolored displays with more complex graphics, and/or inverter-based magnetron power supplies. 

Cooking sensors and displays will be discussed in more detail below in sections regarding 

standby power. 

Because the microwave field is not uniform inside microwave oven cavities (creating 

“hot” spots), manufacturers have developed various methods to improve cooking uniformity. 

Within the DOE sample, mode stirrers and turntables for the food were the only methods 

observed, although DOE is aware of other approaches that could be taken, such as utilizing dual 

magnetrons and associated wave guides. Mode stirrers temporally change the distribution of the 

microwave energy delivered to the cavity and thus cause the “hot” spots to move around the 

cavity. However, only one unit in the DOE sample (designated “DOE16”) contains a mode 

stirrer. Most manufacturers have shifted away from this approach in favor of turntables. 

Turntable motors were observed in all microwave ovens sampled by DOE. By rotating the food 

through the “hot” spots, turntables help improve cooking uniformity. Both a turntable and mode 

stirrer require a motor, as does the blower, which provides cooling air to remove the significant 

heat dissipated by the magnetron and its power supply. 

5-27 

EERE-2006-STD-0127 COMMENT 64.2
Efficiency Testing Using the Current DOE Test Procedure 

DOE conducted efficiency tests on all sampled units using the current DOE test 

procedure, which references IEC Standard 705. As can be seen in Table 5.6.14 through Table 

5.6.17, the DOE test results noted similar cooking efficiencies and input and output powers as 

the results submitted by AHAM, which were presented in section 5.6.1.1. 

Table 5.6.14 Microwave Oven Input, Output, and Cooking Efficiency (1 of 4) 

DOE Unit Number DOE1 DOE2 DOE3 DOE4 DOE5 DOE6 DOE7 DOE8 

Stated Volume (ft3

) 

Measured Input Power (W) 

0.7 0.7 0.7 0.7 

1,192.8 1,129.8 1,121.9 996.8 

1.0 1.0 0.8 

1,374.6 1,314.9 1,356.7 

0.8 

1,374.0 

Rated Output Power (W) 

Measured Output Power (W) 

700.0 700.0 700.0 700.0 

686.1 654.8 627.0 593.8 

800.0 800.0 800.0 

818.5 767.6 781.7 

800.0 

786.7 

Energy Factor 57.5% 58.0% 55.9% 59.6% 59.5% 58.4% 57.6% 57.3% 

Table 5.6.15 Microwave Oven Input, Output, and Cooking Efficiency (2 of 4) 

DOE Unit Number DOE9 DOE10 DOE11 DOE12 DOE13 DOE14 DOE15 DOE16 

Stated Volume (ft3

) 

Measured Input Power (W) 

0.9 

1,602.4 

1.1 1.1 1.0 0.0 

1,769.9 1,701.8 1,713.0 1,736.4 

1.1 1.1 

1,886.2 1,876.3 

1.8 

1,566.7 

Rated Output Power (W) 

Measured Output Power (W) 

900.0 

964.6 

1,000.0 1,000.0 1,000.0 1,000.0 

1,007.8 1,010.3 1,013.6 1,024.5 

1,100.0 1,100.0 

1,145.9 1,105.3 

1,100.0 

949.7 

Energy Factor 60.2% 56.9% 59.4% 59.2% 59.0% 60.8% 58.9% 60.6% 

Table 5.6.16 Microwave Oven Input, Output, and Cooking Efficiency (3 of 4) 

DOE Unit Number DOE17 DOE18 DOE19 DOE20 DOE21 DOE22 DOE23 DOE24 

Stated Volume (ft3

) 

Measured Input Power (W) 

1.0 1.4 1.0 1.3 1.1 1.0 

1,829.8 1,882.2 1,815.7 1,774.3 1,851.8 1,823.1 

1.4 

1,626.8 

2.2 

1,926.2 

Rated Output Power (W) 

Measured Output Power (W) 

1,100.0 1,100.0 1,100.0 1,100.0 1,100.0 1,100.0 

1,046.7 1,114.0 1,057.3 1,072.5 1,134.0 1,038.2 

1,150.0 

966.7 

1,200.0 

1,130.8 

Energy Factor 57.2% 59.2% 58.2% 60.4% 61.2% 56.9% 59.4% 58.7% 

Table 5.6.17 Microwave Oven Input, Output, and Cooking Efficiency (4 of 4) 

DOE Unit Number DOE25 DOE26 DOE27 DOE28 DOE29 DOE30 DOE31 DOE32 

Stated Volume (ft3

) 

Measured Input Power (W) 

1.2 2.2 1.2 2.0 2.0 

1,871.2 1,925.1 1,812.7 1,904.5 1,904.5 

2.2 

1,919.8 

1.2 

1,917.1 

1.2 

1,928.2 

Rated Output Power (W) 

Measured Output Power (W) 

1,200.0 1,200.0 1,200.0 1,200.0 1,200.0 

1,147.7 1,116.6 1,114.4 1,149.4 1,137.9 

1,250.0 

1,105.4 

1,300.0 

1,121.9 

1,300.0 

1,119.0 

Energy Factor 61.3% 58.0% 61.5% 60.4% 59.7% 57.6% 58.5% 58.0% 

Both DOE’s and AHAM’s microwave oven samples contained units with manufacturerrated output powers ranging from 700 to 1,300 W. DOE-tested efficiencies varied from 56 to 61 

percent. These measured efficiencies were similar to the results submitted by AHAM to DOE 

(see section 5.6.1.1), which noted cooking efficiencies of 55 to 62 percent. 

5-28 

EERE-2006-STD-0127 COMMENT 64.2
62% 

61% 

60% 

59% 

58% 

57% 

56% 

55% 

54% 

Figure 5.6.3 Efficiency (EF) 

600 700 800 900 1,000 1,100 1,200 1,300 

Rated Output Power (W) 

AHAM Standard MOT 

AHAM Inverter Drive 

DOE Standard MOT 

DOE Inverter Drive 

DOE and AHAM Microwave Oven Efficiency versus Rated Output Power 

DOE is unaware of the specific microwave ovens that AHAM tested. However, it is 

possible to infer some model features on the basis of identified characteristics, such as rated 

output power. The models identified in Figure 5.6.3 as “AHAM Inverter” units were inferred as 

such because all of the microwave ovens that DOE is aware of on the market that have a rated 

output power at or in excess of 1,250 W feature an inverter driving the magnetron. DOE was 

unable to ascertain if any additional inverter units at lower output powers are contained within 

the AHAM data submittal. DOE noted that none of its microwave ovens with inverter-based 

magnetron power supplies achieved as high an efficiency as comparable microwave ovens with 

standard magnetron power supplies and high output powers. AHAM commented in its data 

submittal that inverter-based power supplies are 2 percent more efficient than standard power 

supplies (82 versus 84 percent, respectively).8 Yet, collectively, the DOE and the inferred 

AHAM inverter units have lower cooking efficiencies than the highest-efficiency non-inverter 

units. Thus, while it is possible that inverter systems are more efficient than the simple 

microwave oven transformers they can replace, the overall efficiencies of inverter-based 

microwave ovens on the market do not presently demonstrate a corresponding efficiency 

improvement. 

In considering the issue of inverter versus non-inverter power supply efficiencies, DOE 

observed that besides being much more complex, the inverter power supplies examined by DOE 

also feature large aluminum heat sinks and plastic tunnels to direct air flow over key 

components. The data sheets for the rectifiers and insulated-gate bipolar transistors used in the 

inverter power supplies note maximum heat dissipation requirements in excess of 400 W. 

During its teardown analysis, DOE also noted that inverter power supplies in its test sample use 

50 percent heavier fan motors, indicating a greater need for heat removal from such systems and 

5-29 

EERE-2006-STD-0127 COMMENT 64.2
thus implying lower efficiencies, since energy is lost through heat dissipation from the power 

supply. However, regardless of the type of magnetron power supply used, almost all units in the 

AHAM and DOE samples meet the baseline efficiency of 55.7 percent for microwave ovens 

proposed in section 5.4.1. 

DOE then investigated whether there was a correlation between microwave oven 

efficiency and measured output power. Typically, rated output powers in the test samples were 

observed to be within 50 W of measured output power, as shown in Table 5.6.18. 

Table 5.6.18 Microwave Oven Rated versus Measured Output for AHAM and DOE Tests 

Unit # 

Rated 

Output 

(W) 

Measured 

Output (W) 

Deviation from 

Rated Output 

DOE4 

DOE3 

DOE2 

AHAM10 

DOE1 

AHAM11 

700 

700 

700 

700 

700 

700 

594 

627 

655 

671 

686 

699 

-15.2% 

-10.4% 

-6.5% 

-4.2% 

-2.0% 

-0.1% 

AHAM1 

DOE6 

DOE7 

DOE8 

AHAM16 

DOE5 

800 

800 

800 

800 

800 

800 

743 

768 

782 

787 

795 

818 

-7.1% 

-4.1% 

-2.3% 

-1.7% 

-0.7% 

2.3% 

DOE9 900 965 7.2% 

AHAM22 950 907 -4.5% 

AHAM20 

AHAM12 

AHAM4 

AHAM5 

AHAM14 

AHAM19 

DOE10 

DOE11 

DOE12 

AHAM3 

DOE13 

AHAM15 

1,000 

1,000 

1,000 

1,000 

1,000 

1,000 

1,000 

1,000 

1,000 

1,000 

1,000 

1,000 

930 

967 

971 

973 

986 

999 

1,008 

1,010 

1,014 

1,015 

1,025 

1,028 

-7.0% 

-3.3% 

-2.9% 

-2.7% 

-1.4% 

-0.1% 

0.8% 

1.0% 

1.4% 

1.5% 

2.5% 

2.8% 

Unit # Inverter 

Rated 

Output 

(W) 

Measured 

Output (W) 

Deviation 

from Rated 

Output 

DOE16 

DOE22 

DOE17 

DOE19 

AHAM21 

DOE20 

DOE15 

DOE18 

AHAM13 

DOE21 

DOE14 

1,100 

1,100 

1,100 

1,100 

1,100 

1,100 

1,100 

1,100 

1,100 

1,100 

1,100 

950 

1,038 

1,047 

1,057 

1,060 

1,073 

1,105 

1,114 

1,119 

1,134 

1,146 

-13.7% 

-5.6% 

-4.8% 

-3.9% 

-3.7% 

-2.5% 

0.5% 

1.3% 

1.7% 

3.1% 

4.2% 

DOE23 1,150 967 -15.9% 

DOE27 

DOE26 

DOE24 

DOE29 

AHAM2 

DOE25 

DOE28 

AHAM17 

AHAM6 

Y 

Y 

1,200 

1,200 

1,200 

1,200 

1,200 

1,200 

1,200 

1,200 

1,200 

1,114 

1,117 

1,131 

1,138 

1,145 

1,148 

1,149 

1,152 

1,205 

-7.1% 

-7.0% 

-5.8% 

-5.2% 

-4.6% 

-4.4% 

-4.2% 

-4.0% 

0.4% 

DOE30 

AHAM8 

AHAM9 

Y 

Y 

Y 

1,250 

1,250 

1,250 

1,105 

1,142 

1,166 

-11.6% 

-8.6% 

-6.7% 

DOE32 

DOE31 

AHAM7 

Y 

Y 

Y 

1,300 

1,300 

1,300 

1,119 

1,122 

1,173 

-13.9% 

-13.7% 

-9.8% 

The measured output for the AHAM data averaged 2.8 percent less than rated output 

power, with a range in deviation from rated output of +3.1 percent to -9.8 percent). Most units 

had a measured output lower than their rated output. As mentioned previously, the AHAM data 

sample did not identify whether an microwave oven had an inverter power supply for the 

magnetron. Thus, the presence of an inverter in the AHAM data set is solely inferred by the 

DOE market survey. 

Output power measurements within the DOE sample followed a similar pattern to the 

data submitted by AHAM, though with a greater proportion of units having measured output 

5-30 

EERE-2006-STD-0127 COMMENT 64.2
power below rated output power. The divergence ranged from a high of about 7 percent above 

rated output power to a low of about 16 percent below rated output power, with the average 

divergence being about -5 percent. The results for rated output power shown in Figure 5.6.3 and 

Figure 5.6.4 indicate that the DOE efficiency data as a function of measured output power 

exhibits largely similar characteristics as the AHAM data submittal, and neither shows an 

identifiable correlation. 

54% 

55% 

56% 

57% 

58% 

59% 

60% 

61% 

62% 

Efficiency (EF) 

AHAM Standard MOT 

AHAM Inverter Drive 

DOE Standard MOT 

DOE Inverter Drive 

600 700 800 900 1,000 1,100 1,200 1,300 

Measured Output Power (W) 

Figure 5.6.4 DOE and AHAM Microwave Oven Efficiency versus Measured Output 

Power 

The maximum measured output power of approximately 1,200 W represents the practical 

limit of residential microwave ovens currently on the market, since at even the highest measured 

efficiency, input power is approaching the amperage limits of residential electrical circuits. For 

example, the maximum input power measured by DOE in its test sample was approximately 

1,925 W, while two microwave ovens in the AHAM data submittal exceeded 2,000 W of input 

power during cooking efficiency tests. For a standard 120 volts AC (VAC) circuit, these input 

powers would correspond to 16.0 and 16.7 amperes (A), respectively. Higher output powers 

may thus only be achievable with microwave ovens that have even higher efficiencies or by a 

transition to 240 VAC circuits for microwave ovens. Higher input and output powers are 

common for commercial microwave ovens, but these products require higher line voltages. 

Impacts of Design Options on Cooking Efficiency 

DOE identified the following design options present in its sample of microwave ovens 

and observed the following impacts associated with each design option on cooking efficiency: 

5-31 

EERE-2006-STD-0127 COMMENT 64.2
• Cooking sensors. There was no identifiable relationship between the absence or presence 

of a cooking sensor and the measured efficiency. The only clear impact of some cooking 

sensors was on the standby power consumption. 

• Improved fan efficiency. The units subjected to reverse-engineering all appeared to 

incorporate fans of similar type and construction, i.e. single-speed shaded-pole-motors 

(SPMs) with plastic blades and presumably similar efficiency characteristics. Therefore, 

no impacts could be quantified for the effect of improved fan efficiency on microwave 

oven efficiency. 

• Improved magnetron efficiency. Despite the range of magnetron manufacturers and 

models, there was notable consistency of rated magnetron efficiency among the data 

sheets that DOE was able to obtain. All data sheets indicated a conversion efficiency 

range of 71 to 72 percent. Therefore, no relationship between microwave oven efficiency 

and magnetron efficiency could be evaluated, nor did DOE have a means of evaluating 

the efficiency of those magnetrons for which data sheets were unavailable, since the 

magnetrons could not be tested by DOE in isolation. 

• Improved microwave oven transformer power supply efficiency. Among the units torn 

down, only the inverter-type microwave ovens had an identifiably different efficiency 

performance characteristic than the microwave ovens with standard power supplies, and 

the data indicate that overall efficiency is not improved by inverter power supplies. All 

standard microwave oven transformers appear to be similar in construction and, hence, no 

data was available to evaluate the effect of incremental improvements in conventional 

microwave oven transformers. Furthermore, DOE did not have the means of evaluating 

the efficiency of the microwave oven power supplies alone, since they could not be tested 

by DOE in isolation. 

• Low-standby-loss electronic controls. By definition, these technologies impact only 

standby power consumption rather than cooking efficiency. 

• Modified wave guide. This design option described in the market and technology 

assessment (chapter 3 of the TSD), wherein special coatings are applied to the wave 

guide interior surfaces, was not observed in the DOE test units. However, two different 

orientations of the wave guide were noted, and an attempt was made to identify any 

impact that wave guide orientation would have on measured efficiency. No such 

relationship was found. 

For more detailed descriptions of each of these design options, see chapter 3 of the TSD. 

Based on this analysis, DOE believes that the efficiency improvements associated with these 

design options has changed little since the 1996 TSD analysis. 

5-32 

EERE-2006-STD-0127 COMMENT 64.2
Comparison of IEC Test Procedures for Measuring Efficiency 

The existing DOE microwave oven test procedure references IEC Standard 705, but this 

IEC test procedure has been declared obsolete by the IEC. The current IEC test procedure is IEC 

Standard 60705. Because there are key differences between these two IEC procedures, the 

impact of which on efficiency measurements were not known to DOE, and because 

manufacturers which do conduct efficiency testing are likely to be using the current version, a 

test series was conducted on a sub-sample of the microwave ovens to compare efficiency 

measurements made using both IEC test procedures. 

The general methodology for each test procedure is largely the same, and consists of 

heating 1 kg of water in a borosilicate container from about 10 °C below room temperature to 

room temperature, using the maximum power setting on the microwave oven. The input power 

over the duration of the test, and thus energy consumed during the test, are compared to the 

energy absorbed by the test load to obtain the efficiency measurement. 

DOE conducted tests per IEC Standard 60705 on 12 selected microwave ovens from its 

original 32 unit sample with a representative range of output power, efficiency, and test-to-test 

variation observed in the DOE testing, which utilizes IEC Standard 705. The table below 

summarizes key differences noted between the test procedures that can potentially impact the 

final energy efficiency calculation. 

Table 5.6.19 Key Differences Between IEC Standard 705 and IEC Standard 60705 

IEC Standard 705-1988 and Amendment 2-1993 IEC Standard 60705-2006 

Ambient Temp.,T0 = 20 ± 2 °C 

Starting Water Temp., T1 = T0 – (10 ± 1 °C) 

Final Water Temp., T2 = T0 ± 1 °C 

Ambient Temp.,T0 = 20 ± 5 °C 

Starting Water Temp., T1 = 10 ± 1 °C 

Final Water Temp., T2 = 20 ± 2 °C 

Electrical Input Energy neglects the magnetron 

filament heat-up time, the measurement starting 

when the input current reaches 90 percent of its final 

value. 

Measurement of Electrical Input Energy includes 

the energy consumed during the magnetron filament 

heat-up time. 

No mention of rounding off efficiency or output 

power calculations 

Efficiency is rounded off to the nearest whole 

number, while output power is rounded off to the 

nearest 50 W 

Temperature measurement accurate within 0.25 °C 

and linearity better than 1 percent. Time 

measurement accurate within 0.25 seconds. 

No specifications for accuracy of temperature and 

time measurements. 

It can be noted that, for the efficiency measurement, IEC Standard 60705 includes the 

energy consumed during the magnetron filament heat-up time, while IEC Standard 705 excludes 

filament heat-up time. Thus, the IEC Standard 60705 efficiency measurement can be considered 

more accurately as an overall microwave oven efficiency measurement, while the IEC Standard 

705 efficiency measurement can be considered strictly a cooking efficiency measurement. Table 

5.6.20 shows the results for the test procedure comparison. Per the IEC Standard 60705 test 

5-33 

EERE-2006-STD-0127 COMMENT 64.2
procedure, DOE rounded the measured output of each test to the closest 50 W and then averaged 

the rounded values. 

Table 5.6.20 IEC Standard 705 versus IEC Standard 60705 Test Results 

Test Unit 

# 

Rated Power 

Output (W) 

Efficiency 

(%) 

IEC Standard 705-1998 and Amendment 2-1993 

Measured 

Power 

Output (W) 

Test-to-Test 

Efficiency Range (%) 

Efficiency 

(%) 

IEC Standard 60705-2006 (rounded) 

Measured 

Power Output 

(W) 

Test-to-Test 

Efficiency Range 

(%) 

DOE1 700 686 57.5 1.46 650 55.3 3.57 

DOE6 

DOE5 

800 

800 

743 58.4 0.06 

795 59.5 0.4 

733 57.0 3.45 

733 58.7 3.33 

DOE9 900 965 60.2 0.48 917 58.3 5.00 

DOE22 

DOE19 

DOE15 

DOE21 

1,100 

1,100 

1,100 

1,100 

1,038 56.9 0.71 

1,057 58.2 0.47 

1,073 58.9 0.77 

1,105 61.2 0.21 

1,000 55.0 3.57 

1,017 56.7 3.45 

1,083 58.0 3.39 

1,083 59.3 1.67 

DOE27 

DOE29 

1,200 

1,200 

1,114 61.5 1.07 

1,131 59.7 0.92 

1,067 59.3 1.67 

1,100 58.0 0.00 

DOE30 1,250 1,142 57.6 0.67 1,050 55.3 1.79 

DOE32 1,300 1,119 58.0 1.24 1,083 57.0 5.17 

There is a consistent decrease in efficiency of about 1 to 2 percent from IEC Standard 

705 to IEC Standard 60705 for all of the microwave ovens. This largely-consistent decrease in 

the calculated efficiency for IEC Standard 60705 was due in significant part to the requirement 

that the measured input energy include the energy consumed during the magnetron filament heatup time, whereas IEC Standard 705 specifies that the measurement of energy input begins when 

the current reaches 90 percent of its maximum value. Therefore, IEC Standard 60705 factors in 

a higher energy consumption to the efficiency calculation than IEC Standard 705 does. 

Another significant difference between test procedures is the specifications for accuracy 

of the test instrumentation. IEC Standard 705 specifies that temperature measurements be 

accurate within 0.25 °C, with linearity better than 1 percent, as well as that time measurements 

be accurate within 0.25 seconds. In contrast, IEC Standard 60705 does not provide any accuracy 

requirements for these measurements. Using a standard thermocouple, which typically has an 

accuracy no better than 0.5 °C, or a less accurate time measurement equipment could create 

significant test-to-test variation in efficiency results. 

The variation of test-to-test efficiency results per IEC Standard 60705 for an individual 

microwave oven ranged from 0 to 5 percent of the average value, which was much greater than 

the comparable variation for IEC Standard 705, whose test-to-test variation in efficiency results 

ranged from 0 to 1.5 percent for the same sub-sample of microwave ovens. This larger range 

associated with IEC Standard 60705 is believed to be attributable to the effects of the 

procedure’s requirement to round the power output to the nearest 50 W and the efficiency to the 

nearest whole number after each individual test, prior to averaging. 

5-34 

EERE-2006-STD-0127 COMMENT 64.2
The prescribed rounding under IEC Standard 60705 would make it more difficult to 

achieve an overall efficiency increase via improvements in minor components such as 

fan/turntable motors and oven light bulbs, which each consume less than 20 W. For any 

component efficiency improvements to have a measurable effect after rounding the power output 

and efficiency calculations, power consumption would have to be reduced by at least 25 W. 

To demonstrate the effect of rounding more clearly, the raw data from the IEC Standard 

60705 testing were used to calculate efficiency in the same manner as for IEC Standard 705; i.e., 

no rounding was performed on output power or efficiency from the individual tests prior to 

averaging. As shown in Figure 5.6.5, the test-to-test variation in efficiency for the rounded data 

is on average four times higher than that of the non-rounded data. The effect of rounding output 

power and efficiency also causes a significant change in the calculated efficiency, as seen in 

Figure 5.6.6. The rounded efficiencies varied from the non-rounded values by as much as 0.75 

percentage points. 

6 IEC Standard 60705 Non-Rounded Test-to-Test Results Range 

IEC Standard 60705 Rounded Test-to-Test Results Range 

5 

4 

3 

2 

1 

0 

1 6 5 9 22 19 15 21 27 29 30 32 

DOE Test Unit # 

Test-to-Test Range (%) 

Figure 5.6.5 DOE Non-Rounded versus Rounded Test-to-Test Efficiency Variation 

Measured Using IEC Standard 60705 

5-35 

EERE-2006-STD-0127 COMMENT 64.2
Efficiency (%) 

IEC Standard 60705 Non-Rounded Efficiency 60 

IEC Standard 60705 Rounded Efficiency 

59 

58 

57 

56 

55 

54 

1 6 5 9 22 19 15 21 27 29 30 32 

DOE Test Unit # 

Figure 5.6.6 DOE Non-Rounded versus Rounded Efficiency Measured Using IEC 

Standard 60705 

The non-rounded data obtained via IEC Standard 60705 still show a consistent 1 to 2 

percentage point decrease in efficiency for all of the units tested as compared to the IEC 

Standard 705 tests, which DOE believes to be attributable to the differences in the energy input 

measurement. As with the rounded IEC Standard 60705 results, the non-rounded data for IEC 

Standard 60705 also show more test-to-test variation for a given unit (0 to 2.1 percentage points) 

than the variations test-to-test during the IEC Standard 705 testing (0 to 1.5 percentage points). 

This remaining increment in test-to-test variation was likely due to the more lenient tolerances on 

the prescribed ambient and final test load temperatures. The IEC Standard 60705 test procedure 

specifies ambient temperature as 20 ± 5 °C, as compared to 20 ± 2 °C for the IEC Standard 705 

test procedure. For the final test load temperature, IEC Standard 60705 specifies 20 ± 2 °C, 

while IEC Standard 705 specifies it as ambient temperature ± 1 °C. 

5-36 

EERE-2006-STD-0127 COMMENT 64.2
Table 5.6.21 IEC Standard 705 versus IEC Standard 60705-2006 Test Results, Without 

Rounding 

Test Unit 

# 

Rated Power 

Output (W) 

Efficiency 

(%) 

IEC Standard 705-1998 and Amendment 2-1993 

Measured 

Power 

Output (W) 

Test-to-Test 

Efficiency Range (%) 

Efficiency 

(%) 

IEC Standard 60705-2006 (no rounding) 

Measured 

Power Output 

(W) 

Test-to-Test 

Efficiency Range 

(%) 

DOE1 700 686 57.5 1.46 659 56.1 0.56 

DOE6 

DOE5 

800 

800 

743 58.4 0.06 

795 59.5 0.4 

740 57.2 0.96 

722 58.0 0.70 

DOE9 900 965 60.2 0.48 925 59.0 1.66 

DOE22 

DOE19 

DOE15 

DOE21 

1,100 

1,100 

1,100 

1,100 

1,038 56.9 0.71 

1,057 58.2 0.47 

1,073 58.9 0.77 

1,105 61.2 0.21 

1,012 55.6 0.50 

1,023 56.8 0.20 

1,075 57.5 0.53 

1,087 59.4 0.76 

DOE27 

DOE29 

1,200 

1,200 

1,114 61.5 1.07 

1,131 59.7 0.92 

1,061 59.3 1.05 

1,112 58.4 0.87 

DOE30 1,250 1,142 57.6 0.67 1,074 56.0 0.82 

DOE32 1,300 1,119 58.0 1.24 1,087 56.4 2.14 

Based on observations and analysis of test results, DOE believes that IEC Standard 705 is 

more likely to produce consistent test results than IEC Standard 60705 because the measurement 

requirements in IEC Standard 705 are more stringent. Therefore, DOE believes that IEC 

Standard 705 should be retained as the basis for the DOE cooking efficiency tests. 

5-37 

EERE-2006-STD-0127 COMMENT 64.2
REFERENCES 

1 U.S. Department of Energy (DOE). 1996. Technical Support Document for Residential 

Cooking Products. Washington, DC. Available online at 

http://www.eere.energy.gov/buildings/appliance_standards/residential/cooking_products_0998_r.html 

2 American Metals Market. Available online at http://www.amm.com/. 

3 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. 

4 Ibid. 

5 Ibid. 

6 Ibid. 

7 U.S. Department of Energy (DOE). 1980. Engineering Analysis. Washington, DC, 

DOE/CS-1066, June 1980. 

8 AHAM. 2006. Op. cit. 

5-38 

EERE-2006-STD-0127 COMMENT 64.2