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Drying Rate of Hair Dryers Could Vary by Almost 1-fold Longer Drying Time Might Increase Energy Consumption Over 100-time Difference in Negative Ion Concentration

  • 2023.09.14

Whether drying after a wash or for hairstyling, the drying rate and temperature of a hair dryer are crucial. As a frequently used and relatively power-consuming home appliance, its energy efficiency and safety are also worth considering. The Consumer Council tested 13 hair dryer models on the market and found that the drying rate could vary by up to 0.85 time, while models with power ratings of 1,700W or higher generally dried hair faster. The tests also revealed that 2 models recorded maximum air outlet temperatures over 96°C, of which 1 even exceeded 108°C, thus consumers should pay heed to the distance and time for drying hair as it could be potentially damaging to the hair. All models claimed to generate negative ions, but there were discrepancies between the ion concentrations claimed or presented to the Council and actual test results. 1 model was measured with only 361 negative ions/cm3, a level on par with a hair dryer without negative ion technology. Excluding this model, the model with the lowest negative ion concentration measured just over 830,000 negative ions/cm3, more than 106 times lower than that of the highest model. The Council recommends consumers to purchase products with a suitable power rating and design according to their needs, and refrain from prolonged blow-drying with high heat to prevent hair damage while conserving energy.

The Council tested 13 hair dryer models with power ratings from 1,000W to 2,300W, of which 7 models had a power rating of 1,700W or higher, while the remaining 6 had a power rating of 1,600W or lower. Among them, 2 were “travel hair dryers” with dual voltage settings. The price ranged from approximately $199 to $3,680. Test items included drying rate, outlet air temperature and uniformity, negative ion concentration, and safety assessments, etc. Results revealed that multiple models priced from over $100 to over $3,000 received an overall score of 4, suggesting that product quality may not always correlate with the price.

Around 1-fold Difference in Drying Rate Among Models

The primary function of a hair dryer is to dry hair, thus drying rate is a critical factor. The test was conducted with each model turned to its highest temperature and airflow settings. A test cloth moistened with approximately 10g of water was placed at the air outlet and blown for 1 minute at a distance of no less than 25mm and an approximate temperature of 75°C (hair drying temperature recommended by the IEC international standard). The test clothes were then measured for their decrease in weight to calculate the drying rate. Results showed that the drying rates of the 13 models ranged from an average of 3.4g to 6.3g per minute, with a difference of approximately 0.85 times in the time required to dry the same amount of moisture. By deduction based on these results, if the fastest-drying model could dry hair in 5 minutes, the slowest model would require over 9 minutes. Consumers may opt for higher temperature settings to speed up drying, but should be mindful that prolonged drying at overly high temperatures might cause more damage to hair quality.

Hair dryers with a lower drying rate would need a longer drying time, which might increase the energy consumption. Take the model with the highest measured energy consumption, assuming daily use of 15 minutes, the total electricity consumption in 30 days would be approximately 14.2kWh. Based on the tariff of $2.0 per kWh, the monthly electricity cost would be about $28. If there are more family members in the same household and the hair dryer is used more frequently, the electricity cost would naturally be higher. On the other hand, using the model with the lowest measured energy consumption for the same duration and frequency of use would halve the electricity cost. Although hair dryers with a lower power rating may seem to consume less electricity and cost less, depending on the drying rates of the hair dryers, users might need more time to dry their hair.

Over 100°C Maximum Outlet Air Temperature for 1 Model

Prolonged Use May Damage Hair

A hair dryer’s outlet air temperature and uniformity are essential factors affecting hairstyling. However, 1 model (with a power rating of 1,600W or below) had an overall lower temperature range (57.3°C-64.8°C), approximately 10°C or more below the recommended hair drying temperature (about 75°C) and may have to be placed closer to the hair during use. Additionally, 2 models recorded temperatures exceeding 96°C at certain operation distances, of which 1 reached a maximum outlet air temperature of 108.1°C, which is higher than boiling water. An overseas study has pointed out that drying hair at high heat (95°C) at a distance of 5cm could damage hair cuticle and cause noticeable cracks and holes in the hair cuticle. The Council recommends consumers to avoid treating hair at high temperatures for extended periods. If high-temperature settings are necessary, users should try minimising the duration of use to reduce the damage to hair.

Significant Discrepancies in Negative Ion Concentrations

1 Model Measured with Only 361 Negative Ions per cm3

The function of generating negative ions has become a basic requirement for many consumers when purchasing a hair dryer. According to an overseas report, negative ions could neutralise positive electric charges on the surface of hair, potentially improving issues like frizzy hair temporarily, making combing easier. However, it does not mean that the surface of hair strands can be repaired.

Test results showed that the 13 models had negative ion concentrations ranging from 361 negative ions to 89.9 million negative ions per cm3. Nearly 40% of the models (5 models) measured concentrations exceeding 45 million negative ions, indicating higher concentrations. The model with the lowest concentration was measured with only 361 negative ions, a value close to laboratory measurements of concentration (around 200 to 300 negative ions) from a control hair dryer without negative ion technology. This raises doubts about whether negative ions measured in the test were environmental rather than generated by that particular model. Excluding this model, the lowest concentration measured was just over 830,000 negative ions, which was considerably over 106 times lower than that of the highest model. Furthermore, the agent of the model with the lowest measured negative ion concentration (just over 830,000) provided the figure of 50 million negative ions per cm3 upon the Council’s enquiry, a difference of almost 60-fold when compared with the measured value. Another model claimed to produce 100 million negative ions, but the test measured only about 16 million, which was nearly 84% less than claimed.

While individual models had significant disparity in negative ion concentrations between their claimed value and actual test result, it should be noted that the negative ion concentration test in this study was conducted with reference to the latest international standard released in August 2022, meaning that this test item had not been established when manufacturers designed and tested the product models in the Council’s current test. Therefore, for fairness the differences between the claimed and measured negative ion concentrations have not been included in the overall performance rating. The Council recommends that manufacturers state the measurement method for their product’s negative ion concentration, so as to increase transparency to help consumers make informed choices.

Safe in Construction and Operations but Motor Winding Temperature Rise of

1 Model Exceeded Standard Limit by 15°C

All models passed the safety tests for construction and abnormal operations. However, in the heating test, 1 model measured a temperature rise of the motor winding that exceeded the standard requirement, measuring 130K (1K equals 1°C), which was 15°C higher than the upper limit specified in the standard (115K), failing to comply with the standard. Overheating could accelerate ageing of the product's winding insulation, thus affecting product safety and durability.

Even though hair dryers are small household appliances, there are many aspects to note during daily use and on safety. Consumers can refer to these tips:

  • Never use a hair dryer near basins containing water or with wet hands to reduce the risk of electric shock;
  • As dust and dirt can accumulate in the negative ion release outlet with frequent use, it is advisable to regularly clean the negative ion release outlet with a cotton swab to maintain continuous negative ion output;
  • After turning on the hair dryer, avoid placing it near inflammable materials such as alcohol or paper, and prevent objects from falling into the air outlet or obstructing airflow to avoid accidental fires;
  • After use, unplug the hair dryer or turn off the switch of the wall socket to prevent connection to power supply for extended periods;
  • Pay close attention to the settings before using a dual-voltage travel hair dryer, especially when returning to Hong Kong from regions with lower voltage (e.g. the United States, Japan, or Taiwan). Make sure to switch to Hong Kong voltage to prevent excessive voltage input that may affect normal operation of the hair dryer.


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