Designing and selecting a suitable Carbon Monoxide/ Diesel Exhaust System. 

Below you will be able to get a good idea of which system is right for your situation or application. 

Cars, trucks, small trucks, specialty vehicles, construction equipment, off-road recreational, military vehicles.

  • Dedicated service bays for cars, light trucks and other areas for larger vehicles.
  • Bays designated for different types of work, such as transmission work, interior work, tune-up bays, oil change, etc.
  • Running engines at idle, high idle, or higher RPMs.
  • Length and conditions of engine running.
  • Whether engines are placed under load while testing AC units, transmissions, hydraulic testing or other Power Take Off operations.
  • Type of fuel being used.
  • Service bays for cars or “small work areas” do not generally require long hoses.
  • Open plan service areas or “large work areas” may require a swing boom arm or motorized hose reels with long exhaust hoses.
  • Number of mechanics vs. the number of service bays.
  • Whether exhaust flow is needed for every service bay at once.
  • Whether a single hose/hose reel can serve two work areas that are side by side.
  • Ceiling height, light fixtures, HVAC ductwork, overhead cranes, and building structure.
  • Take photos if possible.
  • Spring recoil hose reels are mounted at 12-16′ AFF.
  • Motorized hose reels can be mounted higher.
  • It may make sense to initially mount the reel lower so a shorter hose can be used, thereby lowering future hose replacement cost if needed.
  • Determine the number of fans needed.
  • Consider whether a fan should be provided with each hose/hose reel or if a centrally located fan is the better choice.
  • Consider whether the fan should be located inside or outside.
  • Proper controls provide required ventilation where and when it is needed.
  • Consider adding a DCV controller and dampers to an older system, or expand an existing fan capability.
  • Determine what kind of tailpipes the fleet has.
  • Consider tailpipe accessibility, diameter, and shape.
  • Determine whether one standard nozzle, multiple tailpipe adapters, or a custom solution is needed.
  • Consider the wall or column to which you can attach the hose reel or swinging boom arm.
  • Steel columns and masonry walls are ideal for mounting hose reels or boom arms.
  • Consider whether there is sufficient amperage and slots for new breakers in the electrical panel.
  • Consider the electrical power requirements for the system, based on the number of hoses and the CFM required.

An automotive repair shop typically requires 275-300 CFM through a 4 in. hose. In most cases, automotive garages do not have excessive exhaust temperatures, given that the exhaust must flow all the way down the tailpipe before it gets to the hose and nozzle. This volume can also be applied to pick-up trucks.

General Recommendation: COEXHAUST TYPE E hose (350°F / 170°C continuous – 400°F / 205°C Spike) is the typical hose used for automotive shop conditions.

Motorcycles: Motorcycle repair facilities typically require 600-650 CFM through a 6 in. hose (This may be split into two five-inch legs for dual exhaust).
General Recommendation: COEXHAUST EG type hose (350°F / 170°Ccontinuous, 400°F / 205°C Spike) is the typical hose recommended. If the repair team loads the engine or is Dyno testing, then the EF2/SNF2 hose (550°F / 260°C continuous, 660°F / 350°C Spike) can be used.
Note: Two cycles make twice the exhaust volume as four cycle engines.

COEXHAUST Recommendations

CoExhaust recommends that the airflow through the hoses  at least exceeds the exhaust volume of the vehicle. We want to ensure that your systems properly capture both the exhaust fumes AND ambient shop air into the hose. This additional airflow ensures that exhaust from the engine is captured and the additional air flow provides cooling as it mixes with the hot exhaust fume. Too much airflow through the hose is far better than too little. These items should be considered when designing and laying out a Vehicle Exhaust removal system. COEXHAUST experts can help you select the right system based on your exhaust volume.


Repair garages could include public works (DPW), department of transportation (DOT) garages, rental fleets, delivery fleet repair, etc. These typically require 500-550 CFM through a 5 in. hose.
General Recommendation: COEXHAUST EF2 or SNF-2 (550°F / 260°C continuous, 660°F / 350°C Spike) hose is often recommended. However, diesel engine repair shops may conduct tests that generate higher temperatures. Engine loading for operation of the power take-off (PTO) to power hydraulic pumps or AC unit testing can raise the temperature and volume, as the engine is under load. It’s important to learn how much time the engines are tested under load before determining the right hose.

Heavy Duty Trucks

This would include over the road tractors, Kenworth/Detroit Allison/ Cummings/ Mack truck repair garages. General Recommendation: These facilities often demand 650-800 CFM through a 6 in. hose. COEXHAUST EF2 or SNF-2 hoses will meet these airflow and temperature requirements. Exhaust temperatures may be higher if the engines are under load during shop operations (this could be caused when the PTO is operating hydraulic pumps, A/C unit testing, or brake or transmission testing). In these cases, the facility may require combination hoses, such as 20 ft. of the EF2 or SNF-2 hose coupled to a lower section of 5-10 ft. of

Off-Road Equipment and Construction Equipment:
Examples of these facilities are construction equipment, compressor/generator/ pump repair shops, etc.
General Recommendation: These facilities demand a 6 in. hose at 700-800 CFM through the hose. For larger applications an 8 in. hose can be utilized. You must confirm the exhaust temperatures to determine the proper hose, fan and airflow selection. The 8 in. hose supports exhaust volumes from 1200- 1400 CFM. Whenever

engines are operating under load, the exhaust flow and temperature increase dramatically.

Dyno Testing:
Dyno testing requires a much larger volume exhaust system as it often generates
extremely high temperatures within the hoses and the fan. The text box on the
right provides more details.

Select the Right Exhaust Removal SYSTEM

The Fixed Extractor, sometimes referred to as the Retractable Hose Drop or Hose Dropper, is often appropriate for small to mid-size service areas in which cranes and other equipment are not an issue.

Hose drop systems are typically available in two types:

Winch or Rope and Pulley systems: mounted several feet away from the hose location, these systems are used to pull the hose up and away via two pulleys connected to the ceiling structure. This is the less expensive option,
and while more difficult to use, they can support longer and heavier hoses than other options.

Spring Recoil Balancer: a spring cassette pulls the hose up and away when not in use. This is the more popular option. Hose lengths are typically 16 to 20 ft. long, but longer hoses are available. The hose’s weight and length need to be considered when selecting the correct recoil balancer, so that it can fully lift the exhaust hose and tailpipe adapter when not in use.

Fixed Extractors: Two Questions to Ask
Q. What if there is limited space?
A. Include a fan and mounting bracket. COEXHAUST provides a fixed extractor system (FEF) that includes a fan and mounting bracket. These are useful for small work areas and limited space. For example, a service garage may want
to locate the hose drop between two garage doors.

Q. How can I extend the reach of the system?
A. Use the Fixed Extractor on a pivoting boom. You can increase the reach and coverage of the hose by connecting it to a swing boom. The FEB swing boom positions the hose 15 to 26 feet out, away from the column or wall mounting point. This swing boom is an ideal selection within these facilities:
– A prefabricated building that has no interior columns;
– Facilities that use overhead cranes, which require that hoses reach underneath
– Facilities that have no defined work bays.

The COEXHAUST Fixed Extractor with Boom (FEB) system utilizes a single or double articulated boom with a Fixed Extractor at the end. When mounted to a column, the articulated boom version can cover almost a 270 degree arc around the mounting point. In some cases, depending on where the tailpipe is located, the swing boom can nearly cover a 360 degree arc around the column.

When to Consider a Hose Reel System

Hose reels are ideal for facilities where hoses need to be stored above the service area when not in use. Here are general guidelines for choosing the right hose reel:

Small Workshop with Multiple Service Areas: We recommend a spring recoil hose reel, depending on the hose length and mounting elevation. An operator pulls down the exhaust hose and attaches the nozzle to the vehicle and pulls on the hose again to smoothly retract the hose.

Medium Workshop with Wide Service Areas: We recommend a spring recoil hose reel on a boom arm, which is designed to cover a wide area and keep the hose out of the way when not in use. The boom arm can be attached to a central fan system or connected to a direct-mounted fan depending on the workshop situation.

Heavy Duty Vehicle Workshop with Overhead Cranes: We recommend a motorized hose reel, in some cases on a boom, which retracts the hose with the assistance of a high-torque electrical motor. We recommend this hose reel in service areas where hoses and nozzles are heavy and/or overhead cranes and other obstacles may exist.
Note: COEXHAUST does not manufacture or recommend underground exhaust removal systems. All COEXHAUST exhaust systems are “above ground” ducted systems.

Selecting the proper hose

The CoExhaust Vehicle Exhaust Extraction Extraction Rail System (VEER) is a very flexible and cost-effective solution for extracting exhaust over large areas. They can service all types of workshops and mechanical repair facilities. You simply slide the cart with the hose or reel into the problem area.


Some high temperature hoses are actually woven to have small holes in the fabric which allow cooling air to be drawn in through the fabric at our recommended velocities. This provides a cooling effect to the hose fabric. Insufficient airflows may show up as black dots on the exterior of the hose. If a facility does experience hose failure,
simply upgrading to a hose that can endure higher temperatures may not solve the problem. Insufficient airflow through a hose system may be a key reason that hoses fail. Sharp bends close to the tailpipe and tailpipe adapter may also contribute to hose problems.


The most common type of fan used in vehicle exhaust removal systems is the centrifugal blower, built to Air Movement and Control Association International (AMCA) Class B construction standards. These fans are built with spark resistant materials, such as an aluminum Impeller and a steel fan housing. Backward inclined impellers are often recommended as they offer high efficiency.

Some manufacturers offer belt driven fans, while others offer direct drive. There are benefits to both. COEXHAUST recommends that you discuss your needs with your exhaust system manufacturer to identify the most appropriate fan. The fan is the heart of the system and facilities should invest in the best fan possible. You can rely on the performance and sound listings offered by manufacturers like COEXHAUST that have had their fans tested and listed by AMCA. Fans should be selected by how much airflow they can move at a given resistance, rather than horsepower, RPM, inlet diameter, etc. 


Here are three criteria for selecting a fan:
■ Volume of air that the fan needs to move at the total system static pressure resistance;
■ Exhaust air temperatures;
■ Elevation of your building above sea level – the higher the elevation or temperature the less dense the air becomes; the fan size needs to align with these measurements; this is applicable if the facility is located in a mountainous area or temperature exhaust flows are very high.
It’s worth noting that UL does not list fans. UL lists and manages electrical devices such as motors, lights, appliances and electrical controls, but not fan assemblies. Only the motor is UL listed. The UL symbol on a motor
is a backwards R and an U, as shown below.

Q. How do I determine the best fan location?

A. When selecting a location for the fan keep in mind that it may need servicing from time to time. Make sure a mechanic can access the fan when needed. Direct drive fans typically need less maintenance, especially if the motor has permanently greased and sealed bearings. Belt-driven fans need periodic maintenance for belt tightening and pillow block
lubrication. Flex connectors should be used on the fan inlet and outlet to isolate the fan from the ductwork and reducing vibration and noise levels as well as leaks and failure.

Rubber-in-shear or spring vibration isolators should be used to isolate the fan from the building structure. This will also reduce vibration and ultimately noise levels.  Also, the fan support structure should be suitable for the weight of the fan.


Understanding the Range of Nozzles Required

COEXHAUST has more variety of standard tailpipe adapters than any other manufacturer. Tailpipe adapters are often the most difficult item to select so we designed one for almost any possible application. It is
common to have many different tailpipe locations, shapes and diameters within a single fleet. Tailpipes adapters may also be referred to as nozzles, apparatus fittings, or boots. COEXHAUST offers numerous different type and sizes of nozzles, based on the hose diameter as well as tailpipe size/shape/location on the vehicle.

General Recommendation: For truck and vehicles with dual tailpipes, consider a nozzle that takes in ambient cooling air, thereby reducing the exhaust emission temperature. This type of nozzle should be composed of moulded, high temperature resistant rubber, and be equipped with a vise grip or pincher clip or tailpipe insertion spring clips to strengthen the connection with the exhaust pipe without damaging tailpipes such as chromed or the finish around the tailpipes. Consider having multiple types of tailpipe adapters available for each hose. In these cases, consider using “Quick Disconnects” so that nozzles can be easily added and swapped on the hoses.

Vertical Stack Challenges
Most trucks are made with different stacks based on the chassis and type of body attached to them. For example, a truck chassis used for over the road tractors can have a different vertical stack than if that same chassis is used for a dump truck where the dump body would cover the cab. As you are selecting tailpipe adapters for your project, you have to inspect your fleet. You may find that you need more than one tailpipe adapter.

For example, COEXHAUST offers two vertical stack adapters that can be placed onto the vertical stack from ground level. With a telescopic arm, the nozzle can be easily fixed to the tail pipe using a guide bar.

Fan starters make an exhaust system easier to use because it maximizes the mechanics’ time. An exhaust system that
automatically starts or stops the exhaust fan as the hose is being used provides convenience for mechanics as they service their vehicles, and ensures consistent use.
When designing the system, the size of the project often determines the type of fan starter that should be installed. On a small system that includes two or three hoses, a manual motor starter located in a convenient position within the work area might be all that’s needed.
A larger system with four or more hose reels or fixed extractors may benefit from having a low voltage fan start/stop system included in the design. These generally include a toggle switch of some type located on the hose reel or recoil balancer that sends a start signal whenever a hose is brought down for use.

Determine the Usage Factor
As pointed out on page five, a 20 hose drop system, operating at 500 CFM per hose, would require a fan that could exhaust 10,000 CFM. But many facilities should anticipate a 40% Usage Factor (for example, only eight hoses in use at once). The Usage Factor should be determined before the design is finalized.

Automated systems may add costs at the outset of the project, but a  controller can be expected to reduce ventilation, heating, and cooling loads by 10 to 30%. In the April 2017 issue of Facility Executive, an airside efficiency
company calculated that automated projects can reduce energy by up to 38% in energy intensive environments such as laboratories.

Design the Ductwork System


When designing the ductwork for an exhaust removal system, remember that you are dealing with a carcinogenic product that may be damp. COEXHAUST recommends transport velocities to be as high as is practical given the
ductwork diameters which work the best.

General Recommendation: Transport Velocity of 3000 FPM or higher.

This may not always be possible based on airflow through the various components and duct connection fittings on the equipment. When installing the ductwork and the possibility of condensation exists, it may be
advantageous to slope the duct and include a drain.

Position Exhaust Stack Above the Roof

In some cases a louver located in the side wall of the building is selected for the exhaust system discharge. COEXHAUST does not recommend the side wall louver because this can allow the exhaust to blow back against the outside of the building – or worse – recirculate back into the building through doors or other penetrations in the building envelope. General Recommendation: In most projects an exhaust stack on the fan should discharge vertically and terminate well above the roof, away from all air intakes and air handling units.

Important precautions
Light duty lock seam HVAC duct and elbows should not be used. This type of ductwork is not strong enough to handle the negative pressure the fan will generate in these types of systems. COEXHAUST does not recommend PVC piping as ductwork. Air flowing through a pipe or duct can generate static electricity and PVC is difficult to ground.
Static electricity and flammable vapors pose a certain danger.
Do not share the ducts of the vehicle exhaust system with common shafts or ducts of other systems, such as welding exhaust systems, as the exhaust system contains flammable vapors. Follow the Sheet Metal & Air Conditioning Contractors’ National Association (SMACNA) guidelines for ductwork design.


Static Pressure is the resistance to airflow through all the components within the exhaust system. This includes the hose, hose storage device, ductwork, fan and fan exhaust stack. For example, ductwork static pressure is figured as friction loss per 100 feet of duct at a certain CFM. This resistance can be calculated by the design engineer or
the exhaust system specialists with which you are working. Pressure is measured in Pascal (Pa) / Inches Water Gauge (w.g.). Care and the manufacturers’ assistance should be sought to make sure the airflow
and static pressure is calculated correctly. When extracting vehicle exhaust, it’s important to maintain a relatively high velocity to avoid any liquids and particles from settling in the ducting system.To calculate how air pressure loss in a duct system, you must know how much air is passing through that duct, factoring in any bends in the system.
Air volume is measured in m3/h (cubic meters per hour) / CFM (Cubic Feet per Minute) or l/s (liters per second). For example, here is a chart that provides duct pressure loss and typical bends, based on the duct dimensions.

CalcuatIng Expected Exhaust Flow when engines are operating under load

Refer to the American Conference of Governmental Industrial Hygienists (ACGIH®) design manual (“Industrial Ventilation: A Manual of Recommended Practice”), which provides design criteria and a formula you can use to
calculate the expected exhaust flow at operating conditions when the engine is under load. You will need the exhaust temperature, RPM and engine size in order to make an accurate calculation (VS-85-01 and VS-85-02).


COEXHAUST offers total solutions for air cleaning For more than 40 years we have made it our business to ensure
clean air in all types of garages and facilities. We provide high quality products to protect mechanics and employees from exposure to hazardous diesel exhaust, dust and debris. We offer a broad range of exhaust extraction systems, supported by complete engineering services. Contact us to find out what genuine commitment to customer requirements really means.

COEXHAUST is not just a manufacturer. We offer professional advice and engineering services to provide a solution
tailored to your specific needs and requirements. In addition, our worldwide network of distributors offer service and maintenance to keep your system functioning optimally. For more information, please contact your authorized
COEXHAUST distributor or visit