Product Overview

www.hotwater.com
For Technical Information and Automated Fax Service, call 800-527-1953. A. O. Smith Corporation reserves the right to make product changes or improvements without prior notice.
®
SUGGESTED SPECIFICATION
Boiler(s) for hot water supply purposes shall be Model(s) No. __________________ as manufactured by A. O. Smith or an approved equal. Boiler(s) shall be gas-fired, and design
certified by an ANSI approved/accredited independent rating laboratory, capable of supplying _____ gph at 100°F temperature rise equipped to burn __________ gas, with input rating
of _____ BTU/hr. and bearing the ASME code symbol. Boiler(s) shall be up flow type having all non-ferrous waterways, and employing a copper finned heat exchanger and a tightly
wound copper coil combustion chamber with 160 psi working pressure rating. Boiler(s) shall be equipped with an electric gas valve of the step-opening type, an adjustable limit
control which will break the electric circuit on temperature rise, intermittent ignition with one (1) second shutdown in the event of pilot flame failure, a gas pressure regulator
properly set for the gas to be supplied, and a coil limit switch for shut off in event of excessive water temperature, a certified draft diverter and a fully
illustrated instruction manual.
Certified for combustible flooring. Outer jacket shall be of baked enamel finish. The coil, heat exchanger and burner shall have a five year limited warranty as outlined in the written
warranty.
Domestic Hot Water
Boilers
Revised November 2012
Page 2 of 2
AOSDG25600
DIMENSIONS IN INCHES
MODELS
HW-300 HW-399 HW-420 HW-520 HW-670
A Overall height 65 (1651) 57-1/8 (1451) 57-1/8 (1451) 68-5/16 (1735) 68-5/16 (1735)
B Height to Top of Jacket 43-1/4 (1099) 45-1/8 (1146) 45-1/8 (1146) 56-1/4 (1429) 56-1/4 (1429)
C Floor to Center Line Water Inlet 36 (914) 38-3/4 (984) 38-3/4 (984) 46 (1168) 46 (1168)
D Diameter of Jacket 25-1/4 (641) 27 (686) 27 (686) 27 (686) 27 (686)
E Floor to Center Line Water Outlet 12 (305) 12 (305) 12 (305) 12 (305) 12 (305)
F Draft Diverter Outlet Diameter 8 (203) 10 (254) 10 (254) 10 (254) 12 (305)
G Floor to Center Line Gas Inlet 16-1/2 (419) 16-3/4 (425) 16-3/4 (425) 18 (457) 18 (457)
H Overall Depth 29-5/8 (753) 31-1/2 (800) 31-1/2 (800) 36-1/2 (927) 36-1/2 (927)
J Support Height 9 (229) 9 (229) 9 (229) 9 (229) 9 (229)
K Width of Control String (approx.) 14 (356) 14 (356) 14 (356) 11 (279) 11 (279)
L Pipe Size of Water Inlet (NPT) 1-1/4 1-1/2 1-1/2 2 2
M Pipe Size of Water Outlet (NPT) 1-1/4 1-1/2 1-1/2 2 2
N Pipe Size of Gas Inlet (NPT) 3/4 3/4 1 1 1
P Control String Plus 1/2 Jacket Diameter (approx.) 26-5/8 (676) 27-1/2 (699) 27-1/2 (699) 24-1/2 (622) 24-1/2 (622)
S Horizontal Length between Water Inlet and Outlet 5-3/8 (137) 5-1/2 (140) 5-1/2 (140) 5-3/4 (146) 5-3/4 (146)
T Control String from Jacket 5 (127) 5 (127) 5 (127) 7 (178) 7 (178)
Approximate shipping weight lbs. (Kilograms) 250 (113) 301 (137) 301 (137) 381 (173) 381 (173)
NOTE: All dimensions in inches (millimeters) except pipe size which is NPT
TABLE 1. DIMENSIONS AND CAPACITY DATA
EXTRA OPENING
FOR THERMOMETER
AND PRESSURE
RELIEF VALVE
HW-520 AND
HW--670
FIGURE 1. DIMENSIONS
BTU INPUT/OUTPUT
TEMPERATURE RISE AND PRESSURE DROP
20 DEG. F
RISE
30 DEG. F
RISE
40 DEG. F
RISE
MODELS INPUT RATING BTU/HR
NATURAL & PROPANE (LP) GAS
OUTPUT RATING BTU/HR
NATURAL & PROPANE (LP) GAS
GPM PD-FT
HEAD
GPM PD-FT
HEAD
GPM PD-FT
HEAD
HW 300
300,000 240,000 24 8 16 3 12 2
HW 399
399,000 319,200 32 16 21 7 16 5
HW 420
420,000 336,000 34 18 22 8 21 5.5
HW 520
520,000 416,000 42 12 28 5 26 4
HW 670 Nat
660,000 528,000 53 22 35 10 26 5.5
HW 670 Prop
670,000 536,000 54 22 36 10 27 5.5
TABLE 2. FLOW, HEAD AND TEMPERATURE RISE
TABLE 3. RECOVERY CAPACITIES
o
F
20 40
Btu/hr kW
o
C
(11) (22)
Natural GPH 1,455 727
Propane LPH 5,506 2,753
Natural GPH 1,935 967
Propane LPH 7,323 3,662
Natural GPH 2,036 1,018
Propane LPH 7,708 3,854
Natural GPH 2,521 1,261
Propane LPH 9,544 4,772
GPH 3,200 1,600
LPH 12,113 6,057
GPH 3,248 1,624
LPH 12,297 6,148
HW 420 420,000 123
HW 399 399,000 117
HW 300 300,000
Input
88
Type of
Gas
Models
HW 520 520,000 152
HW 670 660,000 193
HW 670 670,000 196
Natural
Propane
50 60 70 80
(28) (33) (39) (44)
582 485 416 364
2,202 1,835 1,573 1,377
774 645 553 484
2,929 2,441 2,092 1,831
815 679 582 509
3,083 2,569 2,202 1,927
1,008 840 720 630
3,818 3,181 2,727 2,386
1,280 1,067 914 800
4,845 4,038 3,461 3,028
1,299 1,083 928 812
4,919 4,099 3,513 3,074
252258_AOSDG25600.indd 2252258_AOSDG25600.indd 2 11/29/12 10:55 AM11/29/12 10:55 AM