The design of kitchen hoods can vary greatly depending on what they are going to be used for. In general, there are two main types of kitchen hoods. The first type of kitchen hoods are designed to reside above appliances for cooking and that create laden vapors, like smoke or grease. The second type of kitchen hoods are installed above dishwashing or cooking appliances that create steam, heat, and/or by-products of combustion.

The purpose of this second type of hood is to control the amount of moisture and waste heat that is produced, as this can affect the HVAC system and promote a generally unsafe living and working space. The design, installation, and operation of kitchen hoods is governed by the applicable code(s).

How Do These Hoods Activate?

Typically, the first type of hood we discussed is automatically activated whenever cooking operations happen, and the kitchen hood in turn activates the exhaust fan. In general, the hood is activated by a heat sensor that detects the heat when a cooking appliance is turned on. Another way of achieving automatic activation of the kitchen hood is to interlock the fan with the cooking appliance in question, or interlock it with infrared technology, lights, or light beam interference detection.

How Big Are The Hoods, And Where Do You Put Them?

The size of a kitchen hood is directly proportional to the size of the cooking appliance that the hood is serving. The kitchen must extend more than six inches outside of the edge of the cooking appliance below on every side, and the kitchen hood cannot be more than four feet above the appliance as well. There are various types of hood designs that affect the exhaust air requirements for the hood.

For instance, there are type of hood design that have side panels, these types of hood need less exhaust air than hoods that do not have side panels. Some of the different types of hood designs are: back-to-back, island, eyebrow hood, canopy with side panels, and pass-over/back-shelf. The exhaust air requirement for any of these hoods is also dependent on the cooking equipment below.

Kitchen Hood Equipment

The cooking appliance that kitchen hoods serve can be split up into four different categories based on the amount of contaminants that it produces. Cooking appliances that produce the most grease laden vapors will demand more exhaust air. Along with the cooking appliances that the hood serves, and the type of hood itself, the exhaust air requirements are also dependent on the front face of the hood’s length. The longer the front face of the hood is, the more exhaust air that is needed.

Make-up Air, Do We Need It?

Kitchen hoods must also bring in make-up air with the exhaust air. The reason why the make-up air is needed is to flow across the front face of the hood, take away the contaminants in the air and force them into the kitchen hood. This make-up air can either be brought into the space where the hood is, or it can be delivered directly to the kitchen hood, where it can be used to flow across the face of the hood. This air is delivered by the HVAC system.

Kitchen Hood Requirements

Field constructed hoods and shop bought hoods alike are both subject to make-up and exhaust airflow requirements that are set forth by the Mechanical Code. A kitchen hood that is factory built and for commercial exhaust purposes, has been tested in accordance with UL710, and has been labelled by an approved agency does not have to meet these requirements. They already demonstrate that they meet design and commercial requirements so that is why they are exempt from the code.

So, what do you think of the two types of kitchen hoods and their uses? Do you have experience with kitchen hoods and have something to add to this article? Engineering Solutions would love to hear your thoughts and opinions in the comments below, and don’t hesitate to contact us for your next project!