Page 145

NORA Oilheat Technicians Manual

Chapter 7 Combustion Figure 7-19: Calculating confined space no doors or with fully louvered doors can be considered part of the unconfined space. Note: If the actual free area of the louvers is not known, wood louvers are assumed to have a 20% to 25% free opening. Metal louvers or grills are assumed to have 60% to 70% free opening. Calculating confined space Example: A room 20' by 30' with an 8' ceiling height and the heating appliance is 140,000 Btu. See Figure 7-19. Determine the maximum total input firing rate allowable in a room without modification. Example: Boiler room 20x30x8 = 4,800 cu ft. 4800 cu. ft. x 1000 Btu/50 cu. ft. = 96,000 Btu 96,000 Btu x 1 gph #2 fuel/140,000 Btu = 0.69 GPH Result: If you fire greater than 0.69 GPH or 96,000 Btus, you will need additional combustion air. Chapter 7—Combustion 7-19 outside air must be supplied to the structure to make up for the air lost from venting heating appliances, fireplaces, clothes dryers, exhaust fans and other building air losses. Insufficient combustion air can cause major problems for proper draft and operation of both gas and oilheating systems. For years it has been assumed that when a heating appliance was located in an unconfined area, there was sufficient air for both ventilation and combustion. Today, in most cases, that is not true! New construction standards, insulation, weather stripping, and energy efficient windows and doors have reduced the amount of air changes per hour. The combustion and make up air requirements in the codes are based on 1/2 air changes per hour. For newer homes and conversion of electrically heated homes, the air changes could be reduced to 1/3 or less air changes per hour. Air problems are most notable on the coldest days when heat loss is the greatest and there is a chance that windows or doors are closed for an extended period of time. When installing new equipment or troubleshooting problem equipment, the first determination that needs to be made is whether the equipment is located in a confined or unconfined space. In accordance with NFPA 31 and NFPA 54, an unconfined space is defined as follows: Any space whose volume is equal to or greater than 50 cubic feet per 1,000 Btu (or 20 Btu/Cubic Foot). This is calculated on the sum of the total input ratings of all fuel burning appliances installed in that space. Only areas connected to the space that have


NORA Oilheat Technicians Manual
To see the actual publication please follow the link above