Kitchen Ventilation

All kitchens that contain hobs with burners. Need airing ducts to use up air in the kitchen. Airing means adding fixed combustion air inlets. Open ducts which can be either in outside walls of the room itself. Or in a wall that connects to an adjacent room. That has a duct that leads outdoors.

Kitchen Ventilation Holes

Why are aeration holes necessary?

The quantity of air that enters the kitchen. Must be at least equal to the air used for normal gas combustion. Besides to this, one must consider. That without a flow of air from outdoors, hood extraction may generate a drop in pressure. That would prevent the complete expulsion of fumes. To avoid these two problems the air flow must come in directly. Through the permanent openings on outside walls of the kitchen. These openings follow the UNI7129 standards and must comply with the following requirements:

They must have a net cross-section of at least 6 cm for each Kw of heat capacity installed, with a minimum of 100 cm.
If the hob does not have a thermocouple (device that stops the gas flow if the flame goes out). Then it needs an additional hole to get a minimum aeration cross-section of 200 cm.
It is advisable for the second hole to be at the top of the kitchen wall. To solve problems connected with the use of LPG. Which as well as needing a greater quantity of air for combustion. Has a comparatively lower density compared to natural gas.

Kitchen Ventilation System

Standards additionally allow indirect ventilation by taking air from an adjacent room.
As long as this room is directly ventilated from outdoors, is not a bedroom. And is not at a high risk of catching fire (e.g. a carport, a garage, a warehouse etc.). In addition to this, the adjacent room must not have a lower pressure as compared to the room to be aired. Because of the presence of an appliance powered by any type of fuel (e.g. a fireplace, a stove, etc.). Or of an extraction device which do not provides any air inlet.

The air can flow in from the adjacent room through permanent openings. Or, if a door divide the two rooms. It can enter by increasing the gap between the door and the floor (min. 2 cm). Where possible, Rafael suggests making the aeration holes in a room. Next to the kitchen to avoid annoying cold air droughts (before reaching the kitchen the air has time to warm up). And to prevent odors from going towards other rooms in the home by conveying them in the right direction.

Hood hole

How can I hide the hood hose if the outlet is in the wrong place?

When you buy or rent an old house. It is likely that the fume’s outlet will be in a position that is wrong for the new kitchen plan. The above examples give you three possible solutions to conceal the hood hose.
A – If a flat hose is used it can be camouflaged by a slim shelf. Rafael does not recommend this hose because its has the disadvantage of being very noisy.
B – If a normal-sized hose is used, conceal it by an over shelf with a raised front edge.
C – Alternatively, build a plasterboard beam or false ceiling.

N.B.: If you are renovating a house. We suggest you to widen the outlet to a diameter of at least 12 cm. Or, if possible, to make one in the right position for the hood to avoid the need for a visible connecting run.
Furthermore, avoid using the exhaust pipe of the gas boiler or of the fireplace for the hood.

Check Valve

Why do I need a check valve?

For all its hood models, Rafael has adopted a special check valve. That shuts when the motor is off, preventing unwanted air from flowing in from outdoors. And opens automatically when the motor is on. Unpleasant inconveniences may occur in absence of this valve. Due to particular circumstances that may occur in the home (droughts or drops in pressure). If, the fume’s outlet hole is near other flues. It may take in the toxic gasses coming from the fireplace, stove or boiler of adjacent homes. Moreover, if a check valve is not installed, cold air may come in from outdoors.

Furthermore, because of the chimney effect, a hood without a check valve. Tends to extract the hot air from the room and convey it outdoors even when it is off. Thus increasing heating costs. In a multistory building. Usually, all the fumes conveys into a common flue pipe, and then discharges outdoors. The flue pipe must follow the UNI EN 1443 standard construction requirements. It must also be heat-insulated to prevent condensation or cooling of fumes. And it must run vertically and be without constrictions.

The hood flue pipes should run into a typical flue pipe that branches and used to this aim solely. A problem that must not be underestimated is the possible use of an extraction hood without a check valve. In this case, a flue pipes used in common with other homes. May attracts the fumes and food odors of neighboring kitchens into your kitchen. If, your hood doesn’t have an integrated check valve. Rafael suggest you to install a separate one-way valve in the outside wall.

Kitchen Hood Duct

How can I plan the fumes outlet to hide the hood duct?

If, you plan the fumes outlet and the electric cable outlet at the right height. You can avoid the connecting hose, and the socket. That is often not a pleasant sight, from being visible. The examples of flue outlet and power supply cable positions. Shown in the drawings on the next pages refer to Rafael patented hoods. For different hoods, request manufacturer for the exact measurements. For back-to-wall kitchens the height of the fume’s outlet hole, calculated by adding a variable height. That depends on the type of hood, to the height of the base unit and of the back panel.

First, calculate the electric cable outlet. By taking as a reference point the height of the top edge of the hood and increasing it by 5 cm for safety’s sake. This way you can conceal the electric socket. For island hoods, the position of the flue outlet in the ceiling must be calculated as follows:
Lengthwise, it must be centered over the hob.
Crosswise, it must be located at a distance from the edge of the base unit that varies depending on the type of hood.

Quiet Kitchen Hood

How to achieve silent extraction?

The heart of the hood is the motor which determines its extraction capacity. For good extraction, the power of the motor must be suitable for the shape, type and size of the hood. The motor can fits inside the hood. In this case, to reduce its noise level, use top quality one. If, you want to further reduce noise. Install a remote motor outside.

Taking care to fit a duct that avoids air vortex formations that could make the hood very noisy. All Rafael hoods have an inside motor of at least 750 m (volume of air extracted in an hour). If, the hood is particularly large, then increase power by fitting two motors. On request, all Rafael hoods can be fitted with a remote motor instead of an inside one. For excellent results, Rafael recommends the use of a remote motor of the same brand as the extractor hood.

Kitchen Hood Height

What is the right hood size for good extraction?

DEPTH OF THE HOOD

Kitchen Ventilation Design Calculation

A – Very often, an 80 cm deep kitchen is fitted with a less deep extractor hood (50 cm deep) that does not extract fumes well.
B – For the 80 cm depth, Rafael offers hoods with shapes and dimensions. That is enough to completely cover the cooking area thus ensuring better extraction.

WIDTH OF THE HOOD AND HEIGHT OF THE WORKTOP

A – If, the width of the hob is greater or equal to the hood. Vapors and odors cannot be completely extracted. Especially, if the hood does not have a powerful motor. For safety reasons, do not install the hood less than 65 cm above the hob.
B – Installation of a hood wider than the hob, improves extraction. And the aesthetic result is definitely more attractive. Because, the hood can become a feature. And design element that distinguishes the kitchen.