Comparison Bosch DHI 655 F stainless steel vs Bosch DHI 635 H stainless steel

Modes supported by the hood.

— Extraction only. The device draws in the air in the room and takes it to the ventilation shaft or directly to the street. It is a very effective way to clean the air from pollution: all impurities, including odours, are simply removed. However, when the hood is operated in this mode, you must either open windows or provide adequate ventilation. Because of this, this mode is not always appropriate: for example, in the cold season, not only pollution but also heat can fly out into the chimney. Therefore, in most modern hoods, a recirculation mode is also provided.

— Recirculation. An operating mode in which the hood does not draw air from the room but drives it through its own filters. This mode is not as effective in terms of air purification as extraction. To effectively remove odours you need to use absorbent filters, that have a limited service life. On the other hand, recirculation does not require an intensive flow of outside air, which in some situations is important — for example, in the cold season, when it is undesirable to blow out the heated air from the room.

The vast majority of modern hoods support both modes of operation. Occasionally, some models are not compatible with carbon filters and work only in extraction mode; even rarer — devices with recirculation only mode.

The power of the hood at maximum speed.

The more powerful the device, the more performant it is, usually. However, there is no rigid dependence here, and hoods of the same power may differ in actual performance. So it is worth evaluating power consumption in terms of power first of all: the lower this indicator, the more economical the device. And when evaluating performance, you need to look not so much at power as at the directly claimed flow of the air (see below).

The maximum flow of air or motor flow of air indicates the theoretical capability of the device. This parameter of the hood (motor) is measured during idle operation. By connecting the duct and working in the appropriate mode of extraction, the flow of air will be lower. However, high-performance motors will also give a high flow of air in extraction mode.

The performance of the hood in extraction mode at maximum speed shows the real possibilities for air purification. Since this parameter is several times less than the motor performance (maximum performance), not all manufacturers indicate this value, trying to present large and beautiful numbers. A similar situation can be observed among other devices. For example, in vacuum cleaners, the total power is many times greater than the suction power; in acoustics, mediocre brands prefer to list peak power instead of nominal power. Therefore, motor performance and extraction performance can not be compared. However, high-performance motors will also give high performance in extraction mode. And it may well be that the conditional Bosch with an extraction performance of 300 m³/h will be better than another hood with a maximum motor performance of 500 m³/h.

The volume at which the device operates in the quietest mode. Usually (but not necessarily) it is the minimum power mode.

The decibels in which the noise level is measured are non-linear units, so it is easiest to use comparison tables to estimate a specific value. Here is the simplest table for minimum noise in modern hoods:

— 20 dB. Almost inaudible. The volume of a whisper at a distance of 1 m, the sound background in an open field on a calm day.
— 30 dB. The whisper, the ticking of the clock. The maximum noise level allowed for residential premises at night.
— 40 dB. The volume of normal human speech. The maximum permissible sound background (permanent) for living quarters during the day.
— 50 dB. Conversation of several people in medium tones.
— 60 dB. Loud talk.
— 65 – 68 dB — background noise on a city street, a vacuum cleaner engine at a distance of 2 – 3 m. The highest noise level among modern hoods is typical for powerful performant models.

When choosing according to this indicator, note that, other things being equal, a quieter device will, accordingly, cost more.

The level of noise produced by the hood in the loudest mode of operation. Usually (but not necessarily) it is the maximum power mode. It affects the comfort during operation of the device, so quiet hoods will be more preferable, but also more expensive.

The decibels in which the noise level is measured are non-linear units, so it is easiest to use comparison tables to estimate a specific value. Here is the simplest table for the values relevant in this case:

— 35 dB. The volume of a conversation in an undertone (but not a whisper). The lowest maximum noise value in modern hoods. Devices with such characteristics are almost guaranteed not to cause inconvenience: such noise is often blocked by other sounds, for example, the background noise of the street in an open window.
— 40 dB. The volume of a normal conversation. The maximum noise level allowed in a residential area during the day. If the hood is bought for home use, and it is supposed to be turned on often and for a long time, the noise level in the selected device shouldn't exceed this indicator.
— 50 dB. Conversation volume at medium tones.
— 60 dB. Raised conversation.
— 70 dB. Sound background on a busy street, in a crowd of people talking loudly, the sound of a vacuum cleaner motor at a distance of 2 – 3 m.
— 75 dB. Scream or loud laughter at a distance of about a metre.
— 78 – 79 dB. Loud mechanical alarm clock, motorcycle o...r truck engine. The highest level in modern consumer-grade hoods.

Note that the actual comfort of using the device depends not only on the volume but also on the timbre (tonality) of the noise: for example, a low, even rumble is generally perceived easier than high frequencies with clanging notes. If the hood installation is unsuccessful, the actual noise level may be higher than stated in the specifications. For example, additional noise can be caused by the hum of air in the ducts or rattling from the contact of the vibrating body with the wall. However, when choosing, it is worth focusing on the noise level claimed in the specifications.

The number of speeds at which the hood can operate.

The more speeds, the more accurately you can adjust the device's operating mode to a specific situation. At the same time, the vast majority of modern hoods have only three speeds which are enough for most occasions.

The number of motors provided in the hood.

For most modern models, one engine is enough — this is enough even for fairly high performance. Models with two motors are somewhat less common — usually, these are powerful performant hoods. One of the advantages of this design is that only one motor can be used at low speeds, and the second one can be connected only when maximum power is required. It has a positive effect on the minimum noise level (see above); on the other hand, the maximum noise level can be quite high, and such devices are usually more expensive than single-motor ones.

It is technically possible to use more than two motors. However, such models are single exceptions.

The ability to install an additional carbon filter in the hood — in addition to the grease filter (see above).

It provides finer air purification than a grease mesh: the carbon filter is capable of retaining impurities literally at the molecular level. Due to this, it is possible to effectively clean the air from not only kitchen fumes but also odours that are not associated with smoke, steam and other relatively large impurities. However, the carbon filter has a limited service life, and it has to be changed from time to time (cleaning, in this case, is not an option).

Note that, in this case, we are talking only about the compatibility of the hood with a carbon filter. The filter itself may not be supplied. However, in many models with this function, it is available as an option (included or not included in the kit at the request of the user).