Ventilation is one of the most important, yet frequently overlooked elements of kitchen design. In addition to aesthetics, proper ventilation plays the functional role of exhausting contaminants, such as oil and grease, which would otherwise float around the house and settle on your walls, ceilings, furniture and floors. Proper ventilation consists of 4 main factors: capture area, blower strength, length of duct run, and distance above the cooking surface.

1) Capture area
In general, particularly in the case of island hoods, we recommend that the width of the hood exceed the width of the cooking surface by 6”. Eg. A 42” wide hood for a 36” cooktop. Wall hoods have more flexibility on this rule as there are less draft winds and a rear wall creates a chimney effect to trap and extract the smoke and smells. It is quite common to have the width of the hood equal the width of the cooking surface for wall hood applications but a wide hood is better. One additional aspect to consider in designing the width of the hood is the adjoining upper cabinets. When the hood is the same width as the cooktop, the edge of the cabinets is directly above the edge of the cooktop and is vulnerable to damage from heat as well as from the extra cleaning that the area will require.

2) Blower strength
-For gas cooktops UNDER 60,000 BTU’s, select a blower with at least 100 CFM’s per linear foot of your cooktop width. Eg. A 30” cooktop would used of blower of at least 250 CFM’s and a 36” cooktop would use a blower of at least 300 CFM’s.

-For cooktops GREATER or EQUAL to 60,000 BTU’s, use approximately 1 CFM per 100 BTU of cooktop output. Add 200 extra BTU’s for each grill or griddle. Eg. Let’s say we have a 4 burner grill (18,000 BTU each) and a grill (15,000 BTU). The total BTU output would be 87,000. An adequate blower would be 1,100 CFM (derived by adding 870 BTU + 200 BTU for the grill, and rounding up).

3) Length of duct run
The maximum effective length of the duct run should be determined by checking the manufacturers specifications. In most cases a duct run should not exceed a total of 60 feet for the hood to be effective. The total length of the duct run is determined by adding the deduction for each turn in line to the straight run length. Eg. for an 8”-round 90 degree turn you must add 7’, for an 8”-round 45 degree turn you add 3’. Each turn in the duct run must be as far apart as possible.

4) Distance above the cooktop
For optimal performance, the distance from the cooking surface to the bottom of the range hoods for most professional style range tops is between 30 and 36”. If the hood is over an island it is often placed higher and in that situation the size should be increased in both width and depth to be effective.

An alternative for kitchens where overhead ventilation is not an option is downdraft venting. However, as heat and steam both rise up, venting from the top is a more effective and preferable method over venting down.

This article outlines the general guidelines for proper ventilation. For further details please consult your Hamai Appliance sales person.