When Should Combustion Air NOT Be Drawn From Inside A Building?A. The Building Has 3 Stories Above Grade.B. The Building Is Built Using Tight Construction Methods.C. The Total Btu/h Input Of The Appliance Exceeds 160,000.D. The Appliance Is A Direct

Mar 12, 2025 by ADMIN 250 views

When Should Combustion Air NOT be Drawn from Inside a Building?

As an engineer, it is crucial to understand the importance of proper combustion air supply in buildings. Combustion air is the air required for the combustion process of fuel-burning appliances, such as furnaces, water heaters, and boilers. The combustion air supply must be sufficient to ensure safe and efficient operation of these appliances. However, there are certain situations where drawing combustion air from inside a building is not recommended. In this article, we will discuss the scenarios where combustion air should not be drawn from inside a building.

Understanding Combustion Air Requirements

Combustion air is essential for the combustion process, as it provides the oxygen required for the fuel to burn. The combustion air supply must be sufficient to ensure that the appliance operates within the designed parameters. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) and the International Mechanical Code (IMC) provide guidelines for combustion air supply in buildings.

Scenario A: The Building has 3 Stories Above Grade

When a building has three stories above grade, it is generally recommended to draw combustion air from outside the building. This is because the building's internal air pressure can be affected by the number of stories above grade. As the building's height increases, the internal air pressure can become more negative, which can lead to a decrease in combustion air supply. Drawing combustion air from outside the building ensures that the appliance receives a sufficient supply of air, even in situations where the internal air pressure is low.

Scenario B: The Building is Built Using Tight Construction Methods

Tight construction methods, such as those used in modern buildings, can lead to a decrease in internal air pressure. This is because the building's envelope is designed to be more airtight, which can result in a negative internal air pressure. In such cases, drawing combustion air from inside the building can lead to a decrease in combustion air supply, which can cause the appliance to malfunction or even fail. Drawing combustion air from outside the building ensures that the appliance receives a sufficient supply of air, even in situations where the internal air pressure is low.

Scenario C: The Total Btu/h Input of the Appliance Exceeds 160,000

When the total Btu/h input of the appliance exceeds 160,000, it is generally recommended to draw combustion air from outside the building. This is because the appliance's combustion air requirements increase with its Btu/h input. Drawing combustion air from outside the building ensures that the appliance receives a sufficient supply of air, even in situations where the internal air pressure is low.

Scenario D: The Appliance is a Direct Vent Appliance

Direct vent appliances, such as those used in gas fireplaces and gas stoves, require a direct connection to the outdoors for combustion air supply. Drawing combustion air from inside the building can lead to a decrease in combustion air supply, which can cause the appliance to malfunction or even fail. Drawing combustion air from outside the building ensures that the appliance receives a sufficient supply of air, even in situations where the internal air pressure is low.

Conclusion

In conclusion, there are certain situations where drawing combustion air from inside a building is not recommended. These scenarios include buildings with three stories above grade, buildings built using tight construction methods, appliances with a total Btu/h input exceeding 160,000, and direct vent appliances. Drawing combustion air from outside the building ensures that the appliance receives a sufficient supply of air, even in situations where the internal air pressure is low. As an engineer, it is crucial to understand the importance of proper combustion air supply in buildings and to follow the guidelines provided by ASHRAE and the IMC.

Recommendations

Based on the scenarios discussed above, the following recommendations can be made:

When a building has three stories above grade, draw combustion air from outside the building.
When a building is built using tight construction methods, draw combustion air from outside the building.
When the total Btu/h input of the appliance exceeds 160,000, draw combustion air from outside the building.
When the appliance is a direct vent appliance, draw combustion air from outside the building.

Future Research Directions

Future research directions in this area could include:

Investigating the effects of building height on internal air pressure and combustion air supply.
Developing new guidelines for combustion air supply in buildings with tight construction methods.
Investigating the effects of appliance Btu/h input on combustion air requirements.
Developing new technologies for combustion air supply in direct vent appliances.

Limitations of the Study

This study has several limitations, including:

The study only considered four scenarios where drawing combustion air from inside a building is not recommended.
The study did not investigate the effects of other factors, such as wind direction and speed, on combustion air supply.
The study did not develop new guidelines for combustion air supply in buildings with tight construction methods.

Future Studies

Future studies could investigate the effects of other factors on combustion air supply, such as wind direction and speed, and develop new guidelines for combustion air supply in buildings with tight construction methods. Additionally, future studies could investigate the effects of appliance Btu/h input on combustion air requirements and develop new technologies for combustion air supply in direct vent appliances.

References

ASHRAE. (2017). ASHRAE Handbook - HVAC Applications.
IMC. (2018). International Mechanical Code.
NFPA. (2018). National Fuel Gas Code.

Appendix

The following appendix provides additional information on combustion air supply in buildings.

Combustion Air Supply in Buildings

Combustion Air Requirements

The combustion air requirements for an appliance depend on several factors, including the appliance's Btu/h input, the building's internal air pressure, and the appliance's design. The ASHRAE and IMC provide guidelines for combustion air supply in buildings, including the following:

The total Btu/h input of the appliance must be considered when determining the combustion air requirements.
The building's internal air pressure must be considered when determining the combustion air requirements.
The appliance's design must be considered when determining the combustion air requirements.

Combustion Air Supply Methods

There are several methods for supplying combustion air to an appliance, including:

Drawing combustion air from outside the building.
Drawing combustion air from inside the building.
Using a combustion air blower to supply combustion air to the appliance.

Combustion Air Supply Systems

Combustion air supply systems must be designed to provide a sufficient supply of combustion air to the appliance. The system must be able to supply the required amount of combustion air, even in situations where the internal air pressure is low. The system must also be able to handle the appliance's Btu/h input and provide a sufficient supply of combustion air.

Combustion Air Supply Components

Combustion air supply components must be designed to provide a sufficient supply of combustion air to the appliance. The components must be able to supply the required amount of combustion air, even in situations where the internal air pressure is low. The components must also be able to handle the appliance's Btu/h input and provide a sufficient supply of combustion air.

Combustion Air Supply Installation

Combustion air supply installation must be done in accordance with the ASHRAE and IMC guidelines. The installation must be done by a qualified technician and must include the following:

The combustion air supply system must be designed to provide a sufficient supply of combustion air to the appliance.
The combustion air supply system must be installed in accordance with the ASHRAE and IMC guidelines.
The combustion air supply system must be tested to ensure that it is functioning properly.

Combustion Air Supply Maintenance

Combustion air supply maintenance must be done regularly to ensure that the system is functioning properly. The maintenance must include the following:

The combustion air supply system must be inspected regularly to ensure that it is functioning properly.
The combustion air supply system must be cleaned regularly to ensure that it is functioning properly.
The combustion air supply system must be repaired or replaced as needed.

Combustion Air Supply Troubleshooting

Combustion air supply troubleshooting must be done to identify and resolve any issues with the system. The troubleshooting must include the following:

The combustion air supply system must be inspected to identify any issues.
The combustion air supply system must be tested to identify any issues.
The combustion air supply system must be repaired or replaced as needed.

Combustion Air Supply Safety

Combustion air supply safety must be a top priority when working with combustion air supply systems. The safety must include the following:

The combustion air supply system must be installed and maintained in accordance with the ASHRAE and IMC guidelines.
The combustion air supply system must be tested to ensure that it is functioning properly.
The combustion air supply system must be inspected regularly to ensure that it is functioning properly.

Combustion Air Supply Codes and Standards

Combustion air supply codes and standards must be followed when working with combustion air supply systems. The codes and standards must include the following:

The ASHRAE and IMC guidelines must be followed when designing and installing combustion air supply systems.
The National Fuel Gas Code must be followed when designing and installing combustion air supply systems.
The International Mechanical Code must be followed when designing and installing combustion air supply systems.

Combustion Air Supply Training

Combustion air supply training must be provided to technicians and engineers who work with combustion air supply systems. The training must include the following
Frequently Asked Questions (FAQs) about Combustion Air Supply

As an engineer, it is essential to understand the importance of proper combustion air supply in buildings. However, there are many questions and concerns that arise when it comes to combustion air supply. In this article, we will address some of the most frequently asked questions (FAQs) about combustion air supply.

Q: What is combustion air supply?

A: Combustion air supply is the air required for the combustion process of fuel-burning appliances, such as furnaces, water heaters, and boilers. The combustion air supply must be sufficient to ensure safe and efficient operation of these appliances.

Q: Why is combustion air supply important?

A: Combustion air supply is essential for the safe and efficient operation of fuel-burning appliances. If the combustion air supply is insufficient, the appliance may not operate properly, or it may even fail.

Q: What are the consequences of inadequate combustion air supply?

A: The consequences of inadequate combustion air supply can be severe. They include:

Reduced appliance efficiency
Increased risk of appliance failure
Increased risk of carbon monoxide poisoning
Increased risk of fires

Q: How do I determine the combustion air requirements for my appliance?

A: The combustion air requirements for your appliance depend on several factors, including the appliance's Btu/h input, the building's internal air pressure, and the appliance's design. You can consult the appliance's manufacturer instructions or contact a qualified technician for assistance.

Q: What are the different methods for supplying combustion air to an appliance?

A: There are several methods for supplying combustion air to an appliance, including:

Drawing combustion air from outside the building
Drawing combustion air from inside the building
Using a combustion air blower to supply combustion air to the appliance

Q: What are the benefits of drawing combustion air from outside the building?

A: Drawing combustion air from outside the building has several benefits, including:

Reduced risk of carbon monoxide poisoning
Reduced risk of fires
Increased appliance efficiency
Increased appliance lifespan

Q: What are the benefits of drawing combustion air from inside the building?

A: Drawing combustion air from inside the building has several benefits, including:

Reduced risk of drafts and air leaks
Increased appliance efficiency
Increased appliance lifespan

Q: What are the benefits of using a combustion air blower to supply combustion air to the appliance?

A: Using a combustion air blower to supply combustion air to the appliance has several benefits, including:

Increased appliance efficiency
Increased appliance lifespan
Reduced risk of carbon monoxide poisoning
Reduced risk of fires

Q: How do I install a combustion air supply system?

A: Installing a combustion air supply system requires careful planning and execution. You should consult the appliance's manufacturer instructions or contact a qualified technician for assistance.

Q: How do I maintain a combustion air supply system?

A: Maintaining a combustion air supply system requires regular inspections and cleaning. You should consult the appliance's manufacturer instructions or contact a qualified technician for assistance.

Q: What are the safety considerations when working with combustion air supply systems?

A: When working with combustion air supply systems, you should always follow safety guidelines and precautions, including:

Wearing personal protective equipment (PPE)
Ensuring proper ventilation
Avoiding electrical shock
Avoiding fires and explosions

Q: What are the codes and standards that govern combustion air supply systems?

A: The codes and standards that govern combustion air supply systems include:

ASHRAE guidelines
IMC guidelines
National Fuel Gas Code
International Mechanical Code

Q: Where can I find more information about combustion air supply systems?

A: You can find more information about combustion air supply systems by consulting the following resources:

ASHRAE guidelines
IMC guidelines
National Fuel Gas Code
International Mechanical Code
Manufacturer instructions
Qualified technicians and engineers