Exhaust Fans

Using Exhaust Fans to Keep Indoor Air Clean

According to the Environmental Protection Agency, indoor air can be two to five times more polluted than air from outdoors. To keep air quality optimal for homeowners and employees, various methods of ventilation can be used to exchange stale indoor air with fresh outdoor air. The American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) suggest air circulation in the amount of 15 cubic feet per minute (CFM), per person to maintain a safe balance of indoor and outdoor air.

Equipment, installation, operation, and maintenance are key to striking a balance in air quality. The overall design of a system can make a difference when it comes to intermittent air flow, healthy distribution of clean air, and proper supply and exhaust locations. Consider the following variables when striving to maintain quality air control:

• Intermittent air flow rates (when a system is in use or turned off) can be determined by building type, size, and use, as well as recommended rates of air flow, air distribution, temperature, and humidity for each variable.
• Air distribution capability is determined by the efficiency of air intake systems and exhaust fan ventilation. Static pressure measurement can help determine system capacity.
• Supply and exhaust locations control air quality. Air supply vents installed near exhaust vents and intake vents installed close to sources of outdoor pollution can cause air supply contamination.
• Ductwork design will determine the overall efficiency of the system. Straight-path ventilation will work better than a system that has sharp bends and angles.

It’s not only important to consider system design, but also the capability and reliability of the equipment used for HVAC applications. Look for a knowledgeable and reliable vendor of HVAC equipment and supplies to make the most of a building’s capacity to supply air quality and comfort.

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Defining Exhaust Fans

Exhaust fans play a major role in air quality and temperature controls for residential, commercial, and industrial applications. They work by drawing stale air out of homes and buildings to be replaced with fresh, outdoor air to meet HVAC industry-recommended air quality standards.

Ventilation exhaust fans can help provide a healthful living environment by removing toxic gases, chemicals, and odors. Mold and mildew caused by heat and moisture (particularly in bathrooms, kitchens, and other areas that generate heat and moisture) can cause health problems and compromise the structural integrity of a home or building. Similarly, areas that generate smoke, chemicals, and toxins can be detrimental to health and can cause fires.

Exhaust fans can help to keep building occupants comfortable, safe, and healthy. There are three main types:

• Axial fans (also known as propeller fans) draw air through the fan and are often designed for wall- or ceiling-mounts to cool a space. Ceiling fans, variable pitch fans, small cooling fans, and wind turbine fans are examples of axial fans.
• Centrifugal fans (also known as blowers) have a squirrel-cage design and work by drawing air in and exhausting it at a 90-degree angle. They are often noisier than axial fans but are used effectively in air conditioning systems and industrial ventilating and cooling.
• Mixed flow fans look like axial fans with curved blades and can provide air supply and return air under high pressure. They operate with less noise than centrifugal fans.

Exhaust fans can be mounted in an inline system, at the ceiling, on the wall, or on the exterior of a building. They can be used in bathroom ventilation, kitchen range hood exhaust, whole house exhaust, commercial exhaust, and industrial exhaust. In commercial kitchens, exhaust is extremely important for maintaining cleanliness, reducing odor, and maintaining building safety. In industrial settings, exhaust fans can keep workers cool, help provide fresh air, and keep harmful chemicals from causing health and safety problems.

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Residential Exhaust Fans

Residential ventilation is important for supplying quality airflow and ventilation to homeowners. Since most modern homes are built to be airtight, and because windows are often shut at certain times of the day, circulation is essential to keep stale air, humidity, and contaminants at bay. Maintaining or improving the quality of indoor air can be achieved by evaluating and updating mechanical ventilation. Operating an efficient HVAC system that employs ductwork, vents, and exhaust fans will result in proper circulation.

There are several types of residential exhaust fans:

• The most common type of modern household exhaust fan is a ceiling-mounted exhaust fan. This type of fan is installed directly into the ceiling of a room and works to remove stale air through exhaust ducts to an external vent.
• Combination exhaust fans are generally ceiling-mounted units combined with a light fixture and/or heater. These types of fans can offer convenience and comfort in one unit.
• Household kitchen, dryer, and bathroom exhaust fans are intermittent fans. They work when turned on or when ventilation is needed in a room.
• Kitchen range exhaust fans are used to vent heat, cooking odors, smoke, and chemicals from a kitchen. They can be mounted above a cooking surface and come in many styles. Many modern kitchens are designed around decorative vent hoods.
• Inline exhaust fans are similar to ceiling-mounted fans, except in terms of placement—they are mounted along the ductwork line to save space and/or reduce fan noise. Noise can be reduced even further by using insulated flex duct materials between the intake vent and the fan.
• Wall-mounted exhaust fans are installed on an exterior wall of a home. No ductwork is required as air is vented directly outside.
• Exterior remote mounted exhaust fans operate outside of the home and pull— rather than push—air outside. This type of fan is quiet due to its location, but should be installed away from air intake vents to prevent airflow contamination.
• Continuous whole house fans can provide ventilation to an entire home with singe or multi-port exhaust vents. It pulls out hot air into the attic area and pushes it outdoors. Cool air can be drawn into the home through open windows.
• Attic fans are often confused with whole house fans. Attic fans vent hot air from an attic, but do not offer direct cooling.

Knowing building size, room size, and ductwork layout is essential before buying equipment to install, replace, or update ventilation. Fan type, duct length, and vent location will depend on the existing HVAC framework.

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Following the Rules: Commercial Kitchen Exhaust and Compliance

A commercial ventilation exhaust system is designed to vent smoke, fumes, grease, and odors through a hood to the outside of a building and provide fresh replacement air from outdoors. Solid commercial kitchen ventilation design, installation, use, and maintenance are essential to foodservice for public health and safety, fire prevention, and emissions control. Exhaust fans need to meet the specific criteria for the intended application and provide adequate air quality controls. Without proper use and care, even the most superior equipment can fail to provide adequate ventilation to meet certain local, state, and federal guidelines.

Staying in compliance means avoiding fines and costly retrofits later. One way to keep up with code is to maintain a balance between the exhaust device, filters, the replacement air system, variable airflow, duct cleaning, duct access, duct pitch, duct drain, stack outlets, and the entire system’s impact on the internal and external environment.

Specific to the exhaust device is filtration and its external impact on the environment. A good system will keep grease from draining onto roofs or outside of buildings and polluting waterways and drainage systems. Changing pads and filters and scheduling timely maintenance will prevent this type of exhaust failure.

Commercial kitchen owners and operators who hire professionals to maintain and clean exhaust systems should find out if service is within parameters of EPA and applicable regulatory agency guidelines. Hiring a compliant-friendly service can cost more, but it also keeps business owners and operators from paying fines for violations of health and safety guidelines.

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Exhaust Fan Sizing for Commercial and Industrial Applications

Finding high-quality, low-maintenance exhaust and air movement equipment can save money for agencies and business owners. Commercial and industrial ventilation can be expensive to install or update, and finding the right type and size of fan will keep companies and industries in compliance with codes and regulations and make working conditions safe for employees. Whether an industrial exhaust fan is used in a school, commercial kitchen, storage facility, gymnasium, factory, or outbuilding, getting the right equipment can make a difference.

There are different types of fans to consider for ventilation and exhaust. Local exhaust ventilation fans, for example, can help prevent indoor air contamination by capturing fumes and pollutants before they are spread. These type of hooded systems can be found in restrooms, commercial kitchens, chemical industrial environments, wood-working factories, and metal shops, just to name a few.

Size exhaust systems based on room or area dimensions, the type of environment, and the acceptable temperature and humidity range. ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) defines acceptable indoor air quality by: (1) the dilution of odors, (2) the concentration of airborne pollution, (3) heat, and (4) humidity. Exhaust fans and equipment can help provide ASHRAE-acceptable indoor air quality in terms of ACH (air changes per hour). According to ASHRAE standards, a rate of .35 or 3 CFM (cubic feet per minute) per each 100 square feet in a space is an adequate rate of airflow.

Along with sizing, ventilation exhaust should be designed and fitted with pollution control in mind. Exhaust ducts should be laid out in the most direct route possible to outdoor vents. Exhaust vents should never be located near supply air vents to avoid contaminating fresh outdoor air with polluted exhaust air. Improper design and installation can cause static pressure imbalances, indoor air contamination, odors, drafts, and inefficient environmental control.

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Limiting Chemical Exposure in Commercial and Industrial Applications

Workers exposed to harmful levels of heat, humidity, fumes, and chemicals can be at risk for health problems. Among the common worker complaints and medical problems from overexposure are allergies, asthma, confusion, headaches, and nausea. In plants and factories where painting, blasting, welding, high temperatures, and fumes from chemical processes are the norm, it is the owner/operator’s responsibility to ensure employee comfort and health by meeting federal, state, and local guidelines for environmental controls.

There are a few types of ventilation strategies for the workplace that can limit chemical exposure:

• Air conditioning and heating provides fresh air and temperature control, but is not practical or cost-effective for all environments.
• Dilution ventilation reduces the amount of polluted air in a room or building by exhausting stale air and supplying a source of fresh air. This can be done with wall exhaust fans or roof exhaust fans, open windows, and cooling fans. Dilution works best when exhaust fans are in close proximity to workers.
• Spot exhaust ventilation pulls contaminants, heat, and smoke from specific areas like kitchens and heavy equipment. In situations where toxic airborne chemicals are present, spot ventilation is a necessity. It requires less make-up air than dilution ventilation. Spot exhaustion can be conducted through hoods (commercial range hoods) and vent ducts.
• Some systems incorporate air cleaners to remove contaminants like dust and chemicals. These systems may be required by federal, state, or local agencies for pollution control.
• Fans provide air pressure for moving clean air indoors and contaminated air outdoors through ducts. Centrifugal fans are used in spot exhausting in atmospheres of high resistance (where there may be high level of dust). Axial fans are wall- or ceiling-mounted and can pull large amounts of air through a space, but cannot draw air through a ventilation system.

Contact federal, state, and local regulatory agencies for guidelines and policies where environmental safety and employees are concerned.

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Exhaust Fans and Safety

Exhaust fans can promote healthy and safe air quality for residential, commercial, and industrial settings; however, they can be hazardous if they’re not maintained or installed properly. Faulty exhaust can provide insufficient removal of humidity, toxic substances, and fumes. Faulty exhaust fan ventilation is also responsible for a number of fires each year.

One major safety hazard from exhaust fans is as simple dust accumulation. Dust collects on fan blades and inside the housing unit. If fans are left to collect dust over long periods of time, the motor will labor or seize. The fan will continue to generate heat, but may fail to maintain the amperage to trip the circuit. If left in this state, the wiring and any plastic or lint inside the housing could catch fire.

Keep a maintenance schedule to avoid accidents related to exhaust fan buildup. At specific intervals (these will vary depending on the fan application), turn off the circuit breaker and clean the fan motor and blades. Professional cleaning is recommended for commercial and industrial exhaust vent fans.

Faulty exhaust placement can also lead to safety hazards. An exhaust fan vented too close to an air uptake vent can contaminate indoor air. Keep air intake and output vents apart, and be sure that intake vents are located away from other sources of contaminants.

Older fans and exhaust systems may need to be updated or replaced to make the most of home, commercial, or industrial ventilation.

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