A.O. Smith ProMax Power-Vent GPVH-50 Instruction Manual | Page 10

A.O. Smith Water Heater Instruction Manual - ProMax Power-Vent GPVH-50.
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Chemical vapor corrosion of the fl ue, blower assembly and vent 
system may occur if air for combustion contains certain chemical 
vapors.  Spray can propellants, cleaning solvents, refrigerator and 
air conditioner refrigerants, swimming pool chemicals, calcium and 
sodium chloride, waxes, bleach and process chemicals are typical 
compounds which are potentially corrosive.

A.  ALL AIR FROM INSIDE BUILDINGS: (See Figure 5 and 6)

The confi ned space shall be provided with two permanent openings 

communicating directly with an additional room(s) of suffi cient volume 
so that the combined volume of all spaces meets the criteria for an 
unconfi ned space.  The total input of all gas utilization equipment 
installed in the combined space shall be considered in making this 
determination.  Each opening shall have a minimum free area of one 
square inch per 1,000 Btu per hour (22 cm2/kW) of the total input rating of 
all gas utilization equipment in the confi ned space, but not less than 100 
square inches (645 cm2). One opening shall commence within 12 inches 
(31 cm) of the top and one commencing within 12 inches (31 cm) of 
the bottom of the enclosures.

FIGURE 6.

B. ALL AIR FROM OUTDOORS: (See Figures 7, 8 and 9)

The confi ned space shall be provided with two permanent openings, 

one commencing within 12 inches (31 cm) of the top and one
commencing within 12 inches (31 cm) from the bottom of the 
enclosure.  The openings shall communicate directly, or by ducts, 
with the outdoors or spaces (crawl or attic) that freely communicate 
with the outdoors.

1.   When directly communicating with the outdoors, each opening shall 

have a minimum free area of 1 square inch per 4,000 Btu per hour 
(5.5  cm2/kW) of total input rating of all equipment in the enclosure, 
see Figure 7.

FIGURE 7.

2.   When communicating with the outdoors through vertical ducts, each 

opening shall have a minimum free area of 1 square inch per 4,000 
Btu per hour (5.5 cm2/kW) of  total input rating of all equipment in 
the enclosure, see Figure 8.

3.  When communicating with the outdoors through horizontal ducts, 

each opening shall have a minimum free area of 1 square inch 
per 2,000 Btu per hour (11 cm2/kW)) of  total input rating of all 
equipment in the enclosure, see Figure 9.

FIGURE 8.

4.  When ducts are used, they shall be of the same cross-sectional 

area as the free area of the openings to which they connect.  The 
minimum short side dimension of rectangular air ducts shall not 
be less than 3 inches (7.6 cm), see Figure 9.

FIGURE 9.

5.  Alternatively a single permanent opening may be used when 

communicating directly with the outdoors, or with spaces that freely 
communicate with the outdoors. The opening shall have a minimum 
free area of 1 square inch per 3,000 BTU per hour (8.3 cm2/kW) 
of total input rating of all equipment in enclosure. See Figure 9A.

FIGURE 9A.

6.   Louvers and Grilles: In calculating free area, consideration shall be 

given to the blocking effect of louvers, grilles or screens protecting 
openings. Screens used shall not be smaller than 1/4 inch 
(6.4 mm) mesh.  If the free area through a design of louver or 
grille is known, it should be used in calculating the size opening 
required to provide the free area specifi ed.  If the design and free 
area is not known, it may be assumed that wood louvers will be 
20-25 percent free area and metal louvers and grilles will have 
60-75 percent free area.  Louvers and grilles shall be fi xed in the 
open position or interlocked with the equipment so that they are 
opened automatically during equipment operation.

7.   Special Conditions Created by Mechanical Exhausting or Fireplaces: 

operation of exhaust fans, ventilation systems, clothes dryers or 
fi replaces may create conditions requiring special attention to avoid 
unsatisfactory operation of installed 

gas utilization equipment.

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