Combustion Air Systems - Field Controls SWG-3 Product Manual

COMBUSTION AIR SYSTEMS

EFFECTS OF INSUFFICIENT COMBUSTION AIR ON DRAFT AND HEATING SYSTEMS
For the proper operation and venting of gas or oil heating appliances, sufficient 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 oil heating 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! With new construction, standards for building insulation
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
the air changes could be reduced to
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.
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 no doors or with fully
louvered doors can be considered part of the unconfined space. 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
For a room 30' x 20' x 8' ceiling height and a heating
appliance rated at 140,000 BTU/hr.
To determine the maximum total input firing rate
allowable in this room:
Boiler room 30' x 20' x 8' = 4,800 cu. ft.
4,800 cu. ft. x 1,000 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 BTU, you will need additional combustion air.
OVERCOMING THE CONFINED SPACE PROBLEM
To add air from an adjacent room, two openings between the rooms could be made 12 inches above the floor and 12 inches
below the ceiling. The size of these openings is based on 1 square inch per 1,000 BTU input.
To add air directly from the outside of the structure, two openings could be made. The size of these openings is based on
1 square inch per 4,000 BTU input. The requirements above are based on guidelines in NFPA 31 or NFPA 54. Alternately,
if the fuel-burning appliance is operating in a confined space, additional air may be added by a duct to the outside, sized on
1 square inch per 5,000 BTU input.
OR...Add air from outside via a
Field Combustion Air System.
22
/ air changes per hour. For newer homes and conversion of electrically heated homes,
1
2
/ or less air changes per hour. Air problems are most notable on the coldest days when
1
3
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).
According to NFPA 31 and NFPA 54, an Engineered system
such as CAS-34U, CAS-34UP, CAS-4JR, CAS-6, or CAS-7
may be used to overcome a confined space.
20'
Solid Door
30'
Customer Service:
140,000 BTU/hr
Heating Appliance
252.522.3031