Extraction Performance of Cooker Hoods Not Necessarily Correlated to Exhaust Airflow Rates or Fan Rotation Speed Advocating for Standardised Performance Measurement Methods to Facilitate Smart Consumption Choices | Consumer Council

Nov 04, 2024

Whether it is to “steam, stir fry, stew, deep fry or pan fry”, the more common cooking methods of Hong Kong people, it is inevitable that much cooking steam and grease would be produced, and an effective cooker hood could maintain good air quality in the kitchen. The Consumer Council tested 14 models of cooker hoods in telescopic style and chimney style. The results showed that 9 models were strong in grease extraction performance, of which 2 telescopic-style models had the best performance. As for extracting cooking steam, chimney-style models generally performed better than telescopic-style models. In providing information for consumers’ reference, manufacturers would often give information on exhaust airflow rate, and some manufacturers might also indicate fan rotation speed. However, as different manufacturers might use different standards or units for measuring the exhaust airflow rates of their products, consumers are advised not to compare products purely based on their claimed exhaust airflow rate.

In order to standardise the comparative tests, the Council made reference to the IEC international standards, and it was found that chimney-style models with the widest body (about 90cm) had the highest exhaust airflow rate on average, whereas telescopic-style models with the slimmest body (about 60cm) had the lowest exhaust airflow rate on average. At the lowest fan speed setting, exhaust airflow rate in the same group could differ by up to 56%. As for fan rotation speed, at the highest fan speed setting (operating continuously), the difference among models was nearly 70%. Consumers should bear in mind that, even though some test models had a higher exhaust airflow rate or higher fan rotation speed, that did not equate to better grease extraction performance when compared to other models, while for the same cooker hood, if the consumer presses a higher airflow button, it will increase the exhaust airflow rate and ultimately the extraction performance. Therefore, in installing a cooker hood, a shorter exhaust pipe with fewer bends and an exhaust outlet not exposed to the wind would help to improve the extraction performance. To enable consumers to make clearer comparisons, the Council proposed that in the long run, the industry could explore the feasibility of standardising the performance measurement standards and units. In the interim, product information including measurement standards should be clearly provided on the product website or promotional leaflets.

The current test covered 3 groups of models, including 5 in telescopic style with a body width of about 60cm, 5 in chimney style with a body width of about 70cm to 75cm, and 4 in chimney style with a body width of about 90cm, priced between $2,798 and $18,000. The 2 models with the highest overall rating (4.5 points) were telescopic style priced at $4,980 and $10,300 respectively, a difference of more than 1-fold, indicating that there are good choices in different price ranges.

9 Models Had Better Grease Extraction Performance

3 Chimney-style Models Had Better Steam Extraction Performance

In selecting cooker hoods, consumers would be most concerned with the extraction of grease, odour and steam (collectively called “extraction performance”). In the extraction of grease, the tests made reference to the international standard IEC 61591 in two separate tests, with the model set at the highest fan speed setting (continuously operating), whilst at the same time cooking oil and water were dripped onto a heated flat-bottom frying pan continuously for 30 minutes, thereafter the cooker hood was turned off after 10 minutes and checked for the amount of grease collected by the cooker hood as well as the amount of grease discharged through the exhaust outlet of the cooker hood. In the second test, the amount of cooking oil and water were doubled. From the average result of the two tests, 9 models (all telescopic-style models and 4 chimney-style models) had excellent grease extraction performance, scoring 4 points or above, of which 2 of the telescopic-style models performed best.

In the extraction of steam, testing technician used the highest fan speed setting (continuously operating) for the cooker hoods and used a flat-bottom frying pan to boil water, and then measured the changes in the relative humidity of the room and whether there were condensation and droplets dripping down from the cooker hoods. The results showed that in general, chimney style performed better than telescopic style. 3 chimney-style models scored 4.5 points, whereas 2 telescopic-style models only scored 3.5 points because they were slower in reducing the humidity level even though they had performed well in the extraction of grease and odour. As for the extraction of odour, all models performed satisfactorily.

The Wider the Cooker Hood Body, the Higher the Average Exhaust Airflow Rate

While Fan Rotation Speeds Varied

In selecting cooker hoods, consumers might compare the exhaust airflow rates and fan rotation speeds as claimed by the manufacturers. However, different manufacturers might use different measurement standards or units. For example, some manufacturers informed the Council that they use the European EN standard to measure the exhaust airflow rate, whilst another manufacturer said that they use the Japanese JIS standard. Therefore, it is not appropriate for consumers to compare different products based solely on the exhaust airflow rates claimed by individual manufacturers. The Council made reference to the IEC international standard in conducting comparative tests on measuring exhaust airflow rate under the lowest fan speed setting, the highest fan speed setting (operated continuously), and the highest fan speed setting (operated temporarily, “boost”[1]) (if any). The results showed that the chimney-style models with a body width of about 90cm had a higher average exhaust airflow rate than the other two groups under all fan speed settings. Under the lowest fan speed setting, the exhaust airflow rates varied considerably among product groups, with the biggest variances found in the groups of chimney style with a body width of about 90cm and the telescopic style, by 56% and 53% respectively. Under the highest fan speed setting (operated temporarily, “boost”) (if any), the telescopic-style group had the biggest variation in exhaust airflow rate among models of 21%, while the other two groups of chimney-style models differed by only 5% and 6% respectively.

As for fan rotation speeds, at the highest fan speed setting (operated continuously), the models recorded between 781 revolutions per minute (rpm) and 2,522 rpm, a difference of up to nearly 70% if based on the highest speed. The models with the fastest and slowest rpm were both chimney styles with a body width of about 90cm. Under the highest fan speed setting (operated temporarily, “boost”) (if any), the rpm also varied, ranging from 859 rpm to 2,551 rpm, a difference of 66%. Chimney style with a body width of about 90cm had the lowest rpm in general. The measurement methods or voltage used for the tests might be different from those used by the manufacturers, therefore the 2 sets of measured values should not be compared directly.

Higher Exhaust Airflow Rates and Rpm May Not Equate to Stronger Extraction

For the same cooker hood, the higher its exhaust airflow rate, then generally the stronger its extraction performance. But across different models, despite higher exhaust airflow rates or faster rpm, some models had poorer extraction performance. Whereas on the contrary, some models with lower exhaust airflow rates or slower rpm had better extraction performance. For example, one chimney-style model at its highest fan speed setting (operated continuously) recorded an exhaust volume of 1,034m3/h, which was the highest value amongst the models, but its score of grease extraction performance was only 3.5 points; whereas a model from another group had the lowest exhaust airflow rate in the group (at its highest fan speed setting (operated continuously) recorded an exhaust volume of 388m3/h), but its grease extraction performance was the strongest, rated at 4.5 points.

As for energy efficiency, the tests made reference to the IEC international standard in calculating fluid dynamics efficiency (FDE). The higher the numerical value, the higher the exhaust energy efficiency. When the fan speed setting is at the lowest and highest (operated continuously), chimney-style models with a body width of about 90cm had the highest average FDE value. Chimney-style models with a body width of about 70cm to 75cm differed most when the fan speed setting was at the lowest, with a variance of up to 69%. When the fan speed setting was at the highest (operated temporarily, “boost”) (if any), the difference in this group was the smallest amongst the 3 groups, with only a 1% variance, and the exhaust energy efficiency was also better on average.

1 Model Outstanding in Grease Extraction but Less Easy to Clean

For consumers who cook frequently, the level of convenience in cleaning a cooker hood is of utmost importance. For each of the 14 models, technicians calculated the amount of grease collected by the oil cups and grease filters, etc. which could be taken out without the use of any tools, as a percentage of the total grease extracted, and found that it ranged from 1% to 86%. The extracted amount for 9 models exceeded 60%, indicating that the majority of the extracted grease was collected in oil cups and grease filters which could be easier to clean. However, there was 1 model with outstanding grease extraction performance, the finding was 1% only, perhaps because there were very few parts that could be taken out for cleaning without the use of tools, and consumers would need to use tools to loosen the screws before taking out the grease filters which collected the most grease, posing some inconvenience.

5 Models Did Not Pass Some Safety Test Items

5 models did not meet the requirements of some safety test items as stipulated under the international standard IEC 60335-2-31. The earthing wires of 2 models were not long enough, and consequently if the supply cords were pulled forcefully during installation or maintenance, and the cord anchorages did not function properly, the earthing wires could possibly be loosened. The failures of 2 other models were respectively related to inadequate mechanical protection of the internal transformer component, or that the test finger could reach through a gap on the top of the cooker hood and touch the electrical components before installation. In addition, the flame resistance of the materials in 3 models had room for improvement. There were only some minor inadequacies in the user manuals of 4 models. The remaining 5 models performed well in all the safety tests. The safety test results have been referred to the Electrical and Mechanical Services Department for follow-up.

In choosing and using cooker hoods, consumers are advised to pay heed to the following:

Download the article (Chinese only): https://ccchoice.org/574-cooker-hoods

Consumer Council reserves all its right (including copyright) in respect of CHOICE magazine and Online CHOICE.

[1] Some models had a boost mode that can temporarily raise the fan speed for about 1 to 6 minutes. Under the IEC international standard, this fan speed setting is called the “Boost” fan speed setting.