REPORT: DOE MICROWAVE OVEN ACTIVE MODE TEST PROCEDURE 

INVESTIGATIONS 

September 2010 

Summary 

 During its most recent energy conservation standards rulemaking for microwave ovens, 

the U.S. Department of Energy (DOE) evaluated test procedure methodology to measure 

microwave energy use in cooking (i.e., active) mode. Specifically, DOE conducted 

measurements of output power and cooking efficiency according to the International 

Electrotechnical Commission (IEC) test procedure incorporated by reference until recently in the 

DOE microwave oven test procedure, as well as the most recent IEC test procedure addressing 

microwave oven active mode. Test data were used to investigate the suitability of these test 

procedures for measuring microwave oven active mode energy use in an accurate, representative, 

and repeatable manner. DOE identified key test conditions, instrumentation requirements, 

methods, and calculations impacting the cooking efficiency metric, and outlined additional 

specificity to certain provisions that improved the accuracy and repeatability of the test 

measurements. Based in part on the information developed during this investigation, DOE 

repealed the active mode provisions in its microwave oven test procedure and is currently 

considering a rulemaking to address new active mode methodology.

Historical Background: DOE Testing According to IEC Standard 705 

Prior to the test procedure final rule published in the Federal Register on July 22, 2010 

which repealed the active mode test procedure for microwave ovens (75 FR 42579), DOE’s

microwave oven test procedure incorporated by reference testing provisions from IEC Standard 

705-1988 and Amendment 2-1993, “Methods for measuring the performance of microwave 

ovens for household and similar purposes” (hereafter “IEC Standard 705”). As discussed in 

detail below, the test procedure consists of heating 1 kilogram (kg) of water in a borosilicate 

container from about 10 degrees Celsius ( 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. 

 As part of the energy conservation standards for residential dishwashers, dehumidifiers, 

and cooking products (including microwave ovens), and commercial clothes washers (hereafter 

“Home Appliance Group 1”), the Association of Home Appliance Manufacturers (AHAM) 

provided cooking efficiency data on 21 microwave ovens tested according to DOE’s test 

procedure (using IEC Standard 705). In addition, as part of the Home Appliance Group 1 

standards rulemaking, DOE conducted testing on a sample of 32 microwave ovens according to 

the DOE test procedure. DOE noted that IEC Standard 705 does not precisely specify the 

temperature measurement device, how the temperature measurement device is to be used, or how 

to ensure test-to-test consistency. In order to increase this consistency while remaining within the 

conditions specified in the test procedure, DOE included additional provisions for its testing: 
- Using a slotted, low-mass plastic cup with four thermocouples attached at even intervals 

around the circumference of the cup, approximately 3⁄4 inch from the rim. By inverting 

the cup in the water and swirling the water with it, a multi-point temperature distribution 

could be measured at a known and repeatable distance from the bottom of the borosilicate 

test vessel, avoiding direct contact with the thermocouples. The slots in the cup ensured 

that the water could be well stirred prior to the temperature measurement in order to 

minimize temperature gradients that could provide misleading results. 

- Insulating the glass test vessel from the test bench surface with a small piece of foam to 

ensure that the bench would not influence the test vessel temperature when it was outside 

of the microwave oven. 

 On December 13, 2007, DOE held a public meeting for the Home Appliance Group 1 

energy conservation standards Advanced Noticed of Proposed Rulemaking (ANOPR) during 

which DOE presented the measured range in cooking efficiency for individual models tested for 

the data submitted by AHAM (which followed IEC Standard 705 with no modifications) as 

compared to the measured range in efficiency for units tested by DOE following IEC Standard 

705 with the additional modifications within the conditions of the test procedure (as presented 

above). The results, shown below in Figure 1 and Figure 2, show that the test-to-test repeatability 

could be improved with additional specifications that are within the conditions specified by the 

test procedure. 

 

Figure 1 AHAM Cooking Efficiency Test Results Using IEC Standard 705 with No 

Modifications 

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650 750 850 950 1,050 1,150 1,250

Measured Output Power (W)

Cooking Effciency (%)
Figure 2 DOE Cooking Efficiency Test Results Using IEC Standard 705 with Additional 

Specifications 

 

 At the December 2007 ANOPR public meeting presentation, DOE also presented 

modifications to IEC Standard 705 that could be considered for improving repeatability, which 

included: 1) increasing the water sample weight to 2 kg for better test vessel coating and longer 

run time, and 2) requiring the test vessel to be insulated from surfaces and hands outside of the 

microwave oven. 

DOE notes that as microwave ovens on the market become more powerful, the alreadyshort cooking times associated with the test procedure will shrink even further because the mass 

of the water sample (1 kg) becomes smaller in relation to the output of the magnetron. Past 

research has shown a relationship between tested efficiency and the loading factor.1

 The greater 

the water mass inside the microwave oven, the better the load’s ability to absorb all the 

microwave radiation put out by the magnetron. DOE notes that doubling the water sample 

weight to 2 kg could potentially improve load matching at higher magnetron outputs, and that 

such an increase in water mass would not necessitate a new test vessel and would roughly double 

cycle times. This could be beneficial for testing certain microwave ovens whose user interfaces 

only allow 10 second cooking time increments. Such long increments may make the test sample 

under- or over-shoot the allowable final water test load temperature on units with high-powered 

magnetrons. For example, a typical 1,200 watt (W)-rated microwave oven needs only about 42 

seconds to heat the present 1 kg sample by the requisite 10 oC. 

 

1

 Houšová, J. and Hoke, K. 2002. “Microwave Heating – the Influence of Oven and Load Parameters on the Power 

Absorbed in the Heated Load. Czech Journal of Food Science, Vol. 20, No. 3, pp. 117 – 124, 2002. 

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

Measured Output (W)

Cooking Efficiency (%)
In addition, DOE notes that the volume of a 1 kg water load is only sufficient to fill the 

test vessel about half full, resulting in about 64 percent of the test vessel surface being in contact 

with the water sample. By doubling the water sample weight, 94 percent of the test vessel surface 

area is in direct contact with the water sample during the test. This may reduce calculation error 

and improve test-to-test consistency. DOE understands that the IEC Standard 705 cooking 

efficiency calculation assumes that the entire test vessel changes uniformly in temperature. 

However, based on testing, DOE believes that this may not be the case. Because conductive heat 

transfer through thin cross-sections of borosilicate glass is relatively slow, the non-wetted 

portion of the test vessel may have a significant temperature gradient across it. Therefore, DOE 

believes that the IEC assumption of a consistent vessel temperature may not be valid. By 

doubling the water sample weight, the test vessel is filled to the point where this temperature 

gradient effect is minimized, since the sections of the test vessel that are not in direct contact 

with water would then represent only about 0.2 percent of the heat load instead of 2.2 percent at 

present. DOE believes that this change could improve test accuracy. 

DOE also believes that using thermal insulators whenever the test vessel is handled or 

measured outside of the microwave oven could improve test accuracy and repeatability. Both the 

weighing scale and the test bench could be thermally insulated from the vessel to limit heat gain 

via conduction through the base of the test vessel. In addition, the test vessel should be handled 

with insulated gloves to limit heat transfer via the hands. 

 DOE does not have data quantifying the cumulative effect of these potential revisions to 

the test procedure. 

Comparison of IEC Test Procedures for Measuring Efficiency 

As part of the Home Appliance Group 1 energy conservation standards rulemaking, DOE 

conducted an analysis to compare the cooking efficiency testing procedures in IEC Standard 705 

and IEC Standard 60705-2006 (hereafter “IEC Standard 60705”). The following analysis was 

presented in chapter 5 of the Home Appliance Group 1 energy conservation standards’ Technical 

Support Document (TSD) of the Notice of Proposed Rulemaking (NOPR). 

As discussed above, prior to the July 2010 final rule which repealed the active mode test 

provisions (75 FR 42579), the DOE microwave oven test procedure referenced IEC Standard 

705. However, this IEC test procedure has been declared obsolete by the IEC, and 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 as part of the Home Appliance 

Group 1 energy conservation standards rulemaking. 

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 1: 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 more 

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

Standard 705 efficiency measurement can be considered strictly a cooking efficiency 

measurement. Table 2 shows the results for the test procedure comparison. Per the IEC Standard 

60705 test procedure, DOE rounded the measured output of each test to the closest 50 W and 

then averaged the rounded values. 
Table 2: IEC Standard 705 versus IEC Standard 60705 Test Results

There is a largely consistent decrease in efficiency of about 1 to 2 percentage points from 

IEC Standard 705 to IEC Standard 60705 for all of the microwave ovens. This decrease 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 heat-up 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 does IEC Standard 705. 

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 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 rounding requirement for the power output to the nearest 50 W and the efficiency to 

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

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. 

Efficiency Efficiency

(%) (%)

DOE1 700 686 57.5 1.46 650 55.3 3.57

DOE6 800 743 58.4 0.06 733 57.0 3.45

DOE5 800 795 59.5 0.4 733 58.7 3.33

DOE9 900 965 60.2 0.48 917 58.3 5.00

DOE22 1,100 1,038 56.9 0.71 1,000 55.0 3.57

DOE19 1,100 1,057 58.2 0.47 1,017 56.7 3.45

DOE15 1,100 1,073 58.9 0.77 1,083 58.0 3.39

DOE21 1,100 1,105 61.2 0.21 1,083 59.3 1.67

DOE27 1,200 1,114 61.5 1.07 1,067 59.3 1.67

DOE29 1,200 1,131 59.7 0.92 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

Test Unit 

#

Rated Power 

Output (W)

IEC Standard 705-1998 and Amendment 2-1993 IEC Standard 60705-2006 (rounded)

Measured 

Power 

Output (W)

Test-to-Test 

Efficiency Range (%)

Measured 

Power Output 

(W)

Test-to-Test 

Efficiency Range 

(%)
 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: , 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 . 

The rounded efficiencies varied from the non-rounded values by as much as 0.75 percentage 

points. 

Figure: 3 DOE Non-Rounded versus Rounded Test-to-Test Efficiency Variation Measured 

Using IEC Standard 60705 

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DOE Test Unit # Test-to-Test Range (%)

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

IEC Standard 60705 Rounded Test-to-Test Results Range
Figure 4: 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. 

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DOE Test Unit # Efficiency (%)

IEC Standard 60705 Non-Rounded Efficiency

IEC Standard 60705 Rounded Efficiency
Table 3: IEC Standard 705 versus IEC Standard 60705-2006 Test Results, Without Rounding

Based on observations and analysis of test results, DOE stated in the Home Appliance 

Group 1 energy conservation standards NOPR TSD that it 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. 

 

Efficiency Efficiency

(%) (%)

DOE1 700 686 57.5 1.46 659 56.1 0.56

DOE6 800 743 58.4 0.06 740 57.2 0.96

DOE5 800 795 59.5 0.4 722 58.0 0.70

DOE9 900 965 60.2 0.48 925 59.0 1.66

DOE22 1,100 1,038 56.9 0.71 1,012 55.6 0.50

DOE19 1,100 1,057 58.2 0.47 1,023 56.8 0.20

DOE15 1,100 1,073 58.9 0.77 1,075 57.5 0.53

DOE21 1,100 1,105 61.2 0.21 1,087 59.4 0.76

DOE27 1,200 1,114 61.5 1.07 1,061 59.3 1.05

DOE29 1,200 1,131 59.7 0.92 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

Test Unit 

#

Rated Power 

Output (W)

IEC Standard 705-1998 and Amendment 2-1993 IEC Standard 60705-2006 (no rounding)

Measured 

Power 

Output (W)

Test-to-Test 

Efficiency Range (%)

Measured 

Power Output 

(W)

Test-to-Test 

Efficiency Range 

(%)