MODULE 5

1. MODULE 5 Validating Combustion Air

2. LESSON 1 Validating Combustion Air

3. Introduction In the previous lesson, you learned to validate the venting of a vapor distribution system and any appliances before placing them into operation. Next, you will need to validate that every appliance in the building has enough combustion, dilution, and ventilation air available to support combustion, to assist with venting flue products, and to help ventilate the appliance. This lesson will focus on where this air will come from. After completing this lesson, you will be able to: • Define “air for combustion.” • Determine whether the space is large enough to support combustion. • Identify methods for supplying indoor and outdoor air.

4. Combustion and Ventilation Air Air for Combustion “Air for combustion” is the air needed at the gas burner to support proper combustion. Do you remember the ideal combustion ratio of propane to air? Approximately 24 cubic feet of air is needed for one cubic foot of propane to burn. If gas appliances do not receive enough air to burn properly, combustion is incomplete. This can create a potentially hazardous condition, such as carbon monoxide build up. Ventilation Air “Ventilation air” is the air needed at the gas appliance to help prevent its housing and components from overheating. Appliances located in small confined areas may get too hot if there is not enough ventilation air to keep them cool.

5. Dilution and Makeup Air Dilution Air “Dilution air” is the air needed at the appliance draft hood to mix with flue gases on all natural draft appliances equipped with a draft hood. Without the proper amount of dilution air supplied at the draft hood, the appliance’s ability to vent the flue products to the outside may be affected. Makeup Air • “Makeup air” is the air that replaces air used in a space. Once air is burned and the flue products are vented outside, more air must come into the space to “make up” or replace the air leaving the room. The space must have access to makeup air to support combustion, assist with venting, and help keep the appliances from overheating. Let’s discuss where this makeup air can come from.

6. Outdoor Air Makeup air is supplied to propane appliances through normal building infiltration and may be sufficient to support combustion for most appliances. However, if it is not enough, outdoor air will need to be supplied to the gas appliances in the building. The various methods you can use to supply outdoor air will be discussed later in this lesson and in greater detail in a separate CETP course. Infiltration needed to supply air for combustion occurs when outside air leaks into a building through cracks around doors and windows. It also occurs in the gaps between building components. Infiltration is the result of two pressures. The first is the pressure caused by wind blowing against the building.

7. Infiltration The second pressure that causes infiltration is the pressure caused by the temperature difference between indoor and outdoor air in cold weather. This pressure is called "chimney effect” and is the same kind of pressure that pushes flue gases up and out of a vent. During cold weather, outdoor air is colder and heavier than indoor air. The warmer air, being lighter, is pushed up and out of the house. In an attempt to reduce heat loss, customers may add weather stripping, caulking, or insulation to cracks, windows, and doors. Although these measures are effective in reducing energy consumption, they may also reduce the air infiltration rate of a building to levels below those required for adequate gas appliance air supply.

8. Negative Air Pressure When the air pressure inside a building is lower than the air pressure outside, air is forced into the building through any opening it can find, including the venting system. If gases are not properly vented from the space, unburned gases, such as carbon monoxide, could remain in the structure. This phenomenon is called “negative air pressure.” Negative air pressure occurs in a room or building that cannot supply a sufficient amount of air to meet appliance combustion requirements. Appliances need the correct ratio of air-to-propane for combustion. This ratio can be disrupted by exhausting air, either by natural causes or mechanical devices.

9. Negative Air Pressure (cont.) Appliances that have a natural draft venting system, such as a chimney or gas vent, can allow negative air pressure to occur if the low pressure inside the building draws air in through the vent. When this occurs, the appliance cannot operate properly and can cause safety issues such as a build up of carbon monoxide. Kitchen and bathroom exhaust fans, fireplaces, or other exhaust devices can also cause a build up of negative air pressure. One way to identify a negative air pressure problem is by conducting a spillage test, which we will discuss later in this course.

10. Avoiding Negative Air Pressure Negative air pressure can be avoided by: • Ensuring that all appliances are the correct size for the application. An appliance that is too large for a room or structure will cause air to exhaust in an amount that will cause negative air pressure build up. • Ensuring normal infiltration can supply adequate air for all appliances in a building. • Providing makeup air to maintain the proper air-to-propane ratio when normal infiltration is not enough.

11. Determining Adequate Indoor Air Supply When inspecting a vapor distribution system to determine if enough indoor air is supplied, a simple calculation must be made. This lesson explains a couple of ways to do this. A more in depth explanation of how to calculate the proper amount of combustion, dilution, and ventilation air is covered in a separate CETP course, as well as in NFPA 54. When an appliance is installed in a space that does not supply adequate air flow, the air needed may come from a different space within the building, for example, from an adjoining space with no door. In this example, the adjoining cubic feet of space may be added to the cubic feet of space where the appliance is located to determine if there is adequate air supply.

12. Determining Adequate Indoor Air Supply (cont.) Other interior spaces may also be used to supply air to an appliance space. Air is normally supplied through a louver at the floor and one at the ceiling or through a louvered door. If the air available inside a building is insufficient, then additional air from outside will need to be provided. If you determine there is an inadequate air supply, contact your supervisor or refer to your company policy for specific instructions.

13. Standard Method Calculation One method to determine adequate air supply is the Standard Method calculation. This is used where structures have an air infiltration rate of 0.40 air changes per hour (ACH) or greater. Where the Standard Method is applicable, the minimum combustion air requirement is 50 cubic feet (ft3) room air volume per 1,000 Btu/hr for the total input rating of all gas appliances located in the space. On the next page, you will see a calculation worksheet with an example of determining the required volume for a 125,000 Btu/hr furnace and a 38,000 Btu/hr water heater installed in a 32 x 28 ft basement with an 8 ft ceiling height. You can see an alternative method of calculating adequate indoor combustion air in this same example in the lower portion of the worksheet.

14. KAIR Method The “Known Air Infiltration Rate” (KAIR) method can also be used to determine the adequacy of indoor air for combustion, ventilation, and dilution of flue gases. The KAIR method is explained in greater depth in another CETP course.

16. Supplying Additional Combustion Air If your calculation determines that there is not enough combustion air for an appliance, you must get additional air through: • Outdoor air openings. • Engineered air supply. • Mechanical air supply.

17. Construction Changes Affecting Venting Improved construction methods have resulted in more energy-efficient structures. This type of construction is often referred to as “tight construction.” Energy-saving methods often used in tight construction include: • Sealing component mating surfaces by extensively caulking door and window jams, wall joints, electrical boxes, and so forth. • Installing vapor barriers such as plastic membranes surrounding wall sheathing and attic and flooring exposures. • Weather stripping windows and doors. • Increasing attic, flooring, and wall insulation that restrict air movement. These methods can reduce building heat loss, but can also decrease infiltration air.

18. Inadequate Air Infiltration When air infiltration measures less than 0.40 to 0.60 ACH, it means that fresh air coming into the structure replaces air that is available for appliance combustion and venting less than once an hour. If naturally-vented appliances that depend on indoor air for combustion vent away more than one half of the available indoor air volume to the outside during an hour, a negative pressure is created inside the structure. The problem is compounded if exhaust venting, such as from a clothes dryer or a kitchen vent, is operating at the same time.

19. Inadequate Air Infiltration (cont.) This would create an inadequate available air supply for proper gas appliance operation and could cause the products of combustion to build inside the building. These changes in air flow and the potential for unhealthy indoor air have led to changes in the design of propane appliances, and in the requirements for determining combustion and ventilation air in NFPA 54.

20. Methods to Provide Adequate Air If your calculations determine that a building needs additional outdoor air, consult your supervisor or company policy for specific instructions. There are two basic methods to provide additional indoor and outdoor air: • Two-openings method. • Single high-opening method. Let’s examine how you can use these methods to provide adequate air supply. An in depth review of calculating these openings is provided in a separate CETP course.

21. Two-Openings Method As the name suggests, this method provides two openings into a room where a gas appliance is located: one opening for air to come into the room and another opening for air to leave the room. Both openings must be within 12" of the floor and within 12" of the ceiling according to NFPA 54. Some configurations include: • Wall Duct Air Supply: If an appliance is located near an outside wall of a structure, separate, properly-sized inlet and outlet air ducts can be installed through the exterior wall. • Attic Air or Crawl Space Outdoor Air Supply: An alternative method of providing outside air to supplement indoor air can be achieved through the use of attic air or crawl space ventilation air.

22. Code Requirements There are different NFPA 54 code requirements for sizing openings based on the amount of free space per Btu/hr input rating of the gas appliances located in an area. As an example, if the two openings are in direct communication with the outdoors or connect through vertical ducts, than each opening must have a minimum free area of 1" per 4,000 Btu/hr of the total input ratings of the appliances. The 4,000 Btu/hr pounds per square inch (psi) is cut in half when air is supplied through horizontal ducts (2,000 Btu/hr).

23. Single High-Opening Method This method has one opening for air to come into a room. This opening must be located within 12" of the top of the space and the appliances must have adequate clearance to combustibles according to NFPA 54 (1" from the sides and back of an appliance, and 6" from the front). The opening must either directly communicate with the outdoors through a vertical or horizontal duct or through spaces that freely communicate with the outdoors. The opening must also have a minimum free area that satisfies two requirements: • It is within 1"/3000 Btu/hr of the total input rating of all appliances located in the enclosure. • It is not less than the sum of the areas of all vent connectors in the space.

24. Mechanical Combustion Air Supply Systems Sometimes mechanical systems are needed to bring outside air into an appliance. These systems are often used in colder climates to help prevent water pipes from freezing. A mechanical system supplies air to a building structure on demand from the propane appliance(s) only and eliminates the need for the one or two permanent openings mentioned previously. All mechanical combustion air supply systems must be electrically interlocked with all of the gas appliances served by the device according to NFPA 54 code. This will prevent the appliance(s) main burner from operating if the mechanical air supply system is inoperative. When properly wired and installed, a typical mechanical combustion air system will first be activated by a call for heat, then once adequate outside air is supplied to the space, the system will allow the appliance to operate.

25. Check for Understanding: Combustion Air Let’s take a moment to check how well you understand the information presented in this lesson. • A 28 ft x 40 ft basement that is 10 ft high has a furnace with an input rating of 150,000 Btu/hr and a water heater rated at 40,000 Btu/hr. How much combustion air is available to the appliances, and is it adequate? • The room has 34,000 Btu/hr more than the appliances, so there is enough combustion air • The room has 17,000 Btu/hr more than the appliances, so there is enough combustion air • The room has 17,000 Btu/hr less than the appliances, so there is inadequate combustion air • The room has 78,000 Btu/hr less than the appliances, so there is inadequate combustion air

26. Check for Understanding: Input Rating A 38 ft x 32 ft basement that is 10 ft high has a furnace with an input rating of 175,000 Btu/hr and a water heater rated at 50,000 Btu/hr. The customer wants to add an additional heater to the basement. What is the highest input rating this particular heater can be without bringing in outside makeup air? • 68,200 Btu/hr • 18,200 Btu/hr • 9,100 Btu/hr • No heater can be added to this room.

27. Module Summary In this module you learned the importance of providing proper air and space to an appliance in order for combustion to occur. We also discussed how to supply additional air when needed. Next, we’ll take a look at the procedures that you must follow when performing a leak check.