Information about kitchen exhaust systems and range hoods.
Kitchen exhaust is an important component to maintaining indoor air quality. Exhaust fans may be part of a range hood or be an separate fan located somewhere in the kitchen. The exhaust fan removes odors, smoke and steam generated by cooking. Kitchen exhaust fans also remove heat which is an added benefit in warmer months.
It is important to note that not all range hoods remove air from the kitchen; many are merely recirculating fans with washable filter screens. Also ventilation implies that fresh air is introduced into the space which would require a make-up air unit. In most cases the air is simply exhausted to the outside and outside air in pulled in through gaps in the exterior of the home.
Importance of Kitchen Exhaust
Cooking introduces a significant amount of moisture into the air, not to mention dishwashing either by hand or machine. During winter months this moisture can condense on windows and walls and can damage the drywall and wood and accelerate the growth of mold. A properly installed exhaust fan removes much of the moisture created in the kitchen.
Types of Kitchen Exhaust Systems
There are three basic types of kitchen exhausts system, room exhaust, range hood, and down draft. In the past thru-wall units were also used frequently, but they have fallen out of favor due to their appearance. Recirculating range hoods and microwave ovens with integrated fans are not covered here, but many of them can be ducted to the outside and become a true exhaust system.
Range hoods are the most common of all kitchen exhaust systems and under cabinet range hoods are the most popular within this group. Ducting of the unit typically runs through the upper cabinet and out through the roof, wall or eave. Most units can be installed without additional ductwork so it is important to check to see if your range hood is exhausting to the exterior. Under cabinet range hoods come in a host of different styles and finishes, including painted cold rolled steel and stainless steel versions. Options include; lights and variable speed fans. The units are designed to mount under most standard wall cabinet sizes with widths from 30 to 54 inches and have exhaust air rating of between 180 and 1500 CFM. Prices range from $60 to $2,500.
A different configuration of range hoods are wall mounted or ceiling mounted systems. These are usually semi-custom or high-end units that give the kitchen a more imposing appearance. They can be installed on an exterior wall or above an island. They can be left exposed or concealed with wood, tile, or metal. They are designed to be vented to the exterior but less common ductless units are available. Lights, variable speed fans, telescoping chimneys and different size filter screens and materials are common options. Sizes range from 30 to 60 inches. Prices range from $200 to $10,000.
Ceiling Range Hood
Custom Copper Range Hood
Although it can be called a range hood, the downdraft range hood is a high powered exhaust blower that draws the air into grills that either are flush with the countertop surface or rise out of the countertop when needed. Most are installed behind the cooktop, however some are also side mounted.
The downdraft hood usually vents through a wall or into the floor joists and then to the outside. Downdraft vent hoods are found in home kitchens as well as commercial installations. The most common material for a downdraft vent hood is stainless steel. Prices range from $400 to $7,000
While range hoods are designed to directly remove excess humidity and odors produced during the cooking process, a room exhaust fan is designed to exhaust the air from the entire kitchen.
There are a few different styles of room exhaust fans. Some models come complete with a grill and are designed to be mounted between roof rafters or floor joists while other models are designed to have a blower down line in the ductwork. Price range from $25 to $150.
There are several requirements for an exhaust fan to work properly. Most importantly it should be vented to the outside of the home, either through the wall or roof. Venting to an attic space is a common but serious mistake. Terminating a kitchen exhaust into another room or attic will cause moisture to accumulate and can pose a health risks or cause structural damage.
Inspect the ductwork connected to the unit. In commercial kitchens grease is a major concern and exhaust hoods and ductwork is required to inspected and cleaned annually. In a residence, it is unlikely that the ductwork has ever been cleaned. You may want to hire a duct cleaning professional to inspect and clean your kitchen exhaust is you notice and film or build up on the inside of the hood or ductwork.
Ductwork inside Kitchen Cabinet
It is also important to make sure that the ductwork is secured and not leaking or separated. Leaking ductwork will reduce the effectiveness of the exhaust fan and cause moisture to accumulate inside the wall. Also make sure the guard for the exhaust on the outside wall or roof is in place and not clogged with debris. Small ducts make a perfect nesting place for birds.
Verify that the fan is sized properly for the ductwork. By restricting the flow of air with very long runs or numerous elbows in the duct you will reduce the amount of air being exhausted by the fan and also shorten the life of the fan. Small fans use a 3 or 4-inch round duct, where larger fans can require up to an 8-inch duct. Flexible ductwork also reduces the airflow of the fan. As an example a fan that removes 125 CFM of air needs to be 6” in diameter for a 50-foot run while a sheet metal duct can be 4” in diameter.
Remember the more air you remove the more air you have to introduce into the home to make up for the exhaust. In the extremes of summer and winter this can add to your electric bill. Energy efficient homes may have a heat recovery system for their forced air heating and cooling that brings in some outside air to ventilate the home, but most builders forget to add that to the kitchen or bathroom exhaust systems. The more airtight the home is the harder it will be for the fan to pull out the kitchen air. If this is the case you may want to crack open a window somewhere in the kitchen as far away from the fan as practical.