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All Categories > Commercial Water Heaters > Ultra-Low NOx Commercial Water Heaters > A.O. Smith® Ultra-Low NOx Commercial Water Heaters > Master-Fit® Ultra-Low NOx Commercial Gas Water Heaters > Item # BTL-310(A)  

Item # BTL-310(A), Master-Fit® Ultra-Low NOx Commercial Gas Water Heaters

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Unit of Measure: Imperial Metric Both

Specifications  · Dimensions  · Maximum Recovery (ºF)  · Maximum Recovery (ºC)  · Electrical Characteristics  · Features  · Other Standard Features  · Testing and Certifications  · Warranty  · Note



A. O. Smith®

Equipment Grade


Input Power

310000 KBTU/hr


85 U.S. gal

Thermal Efficiency

82 %


Natural Gas

Minimum Gas Supply Pressure

0.87 kPa

Maximum Gas Supply Pressure

14 inWc

Sides and Rear Clearance to Combustibles

0 in

Top Cover Clearance to Combustibles

12 in

Sides and Rear Clearance to Non-Combustibles

0 in

Top Cover Clearance to Non-Combustibles

12 in

Top Inlet Water Connection

1-1/2 in

Front Inlet Water Connection

1-1/2 in

Back Inlet Water Connection

1-1/2 in

Top Outlet Water Connection

1-1/2 in

Front Outlet Water Connection

1-1/2 in

Back Outlet Water Connection

1-1/2 in

Standard Approximate Shipping Weight

850 lb

ASME Approximate Shipping Weight

900 lb

Industry Standards

ANSI Z-21.10.3 - CSA 4.3

ASME Certified



Dimension A

76 in

Dimension B

16-1/4 in

Dimension C

78-1/4 in

Dimension D

65-3/4 in

Dimension E

25-3/4 in

Dimension F

21 in

Dimension G

3/4 NPT

Dimension H

66-1/4 in

Dimension I

6 in

Dimension J

27-3/4 in

Dimension K

1-1/2 NPT

Dimension L

1-1/2 NPT

Dimension M

41 in

Maximum Recovery (ºF)

Recovery at 36 ºF Temperature Rise

849 gal/h

Recovery at 40 ºF Temperature Rise

765 gal/h

Recovery at 50 ºF Temperature Rise

612 gal/h

Recovery at 54 ºF Temperature Rise

566 gal/h

Recovery at 60 ºF Temperature Rise

510 gal/h

Recovery at 70 ºF Temperature Rise

437 gal/h

Recovery at 72 ºF Temperature Rise

425 gal/h

Recovery at 90 ºF Temperature Rise

382 gal/h

Recovery at 100 ºF Temperature Rise

306 gal/h

Recovery at 108 ºF Temperature Rise

283 gal/h

Recovery at 110 ºF Temperature Rise

278 gal/h

Recovery at 120 ºF Temperature Rise

255 gal/h

Recovery at 126 ºF Temperature Rise

243 gal/h

Recovery at 130 ºF Temperature Rise

235 gal/h

Recovery at 140 ºF Temperature Rise

218 gal/h

Maximum Recovery (ºC)

Recovery at 20 ºC Temperature Rise

3216 L/h

Recovery at 22 ºC Temperature Rise

2894 L/h

Recovery at 28 ºC Temperature Rise

2315 L/h

Recovery at 30 ºC Temperature Rise

2144 L/h

Recovery at 33 ºC Temperature Rise

1929 L/h

Recovery at 39 ºC Temperature Rise

1654 L/h

Recovery at 50 ºC Temperature Rise

1286 L/h

Recovery at 56 ºC Temperature Rise

1158 L/h

Recovery at 60 ºC Temperature Rise

1072 L/h

Recovery at 61 ºC Temperature Rise

1052 L/h

Recovery at 67 ºC Temperature Rise

965 L/h

Recovery at 70 ºC Temperature Rise

919 L/h

Recovery at 72 ºC Temperature Rise

890 L/h

Recovery at 78 ºC Temperature Rise

827 L/h

Electrical Characteristics


120 V


60 Hz


<5 A

82% thermal efficiency means lower operating costs.

Fan Assisted Combustion - The blower is built into the Low NOx burner assembly for Ultra-Low NOx readings that comply with SCQAMD rule1146.2 of 14 ng/j or 20 ppm.

Metal Venting - Rated Category I Appliance. Uses standard double wall type "B" vent. Can be commonly vented with other Category I appliances. Vent connects directly to the vent connector outlet. No Draft hood or barometric damper required. Perfect choice for retrofit and upgrade installations.

Water Connections - For ease of installation, all BTLs feature water connections on the top, front, and rear. "The Eliminator™" inlet water connection eliminates harmful scale buildup, extending the life of the product. The front inlet connection must be used for the Eliminator™ benefits.

Glass Lined Tank - Permaglas® Ultracoat is the proprietary ceramic coating developed by A. O. Smith®’s ceramic engineers specifically for the heater. It is applied after the complete tank has been assembled to give a seamless barrier against hot water corrosion.

Installed Cost Savings - When multiple BTL units are exclusively used in a vent manifold, use the National Fuel Gas Code Table 13 Vent Sizing information to determine vent diameter and specifications. The BTL often uses a smaller vent diameter than a natural draft water heater which saves on installation cost.

Fully Automatic Digital Controls with Safety Shutoff - Accurate, dependable control system. Features a two speed blower control for smooth main burner light-off. Manual reset gas shutoff device for added safety. Maximum inlet gas pressure is 14" W.C. Minimum gas pressure is 3.5" W.C. Natural Gas.

Foam Insulation - Saves fuel, helps reduce standby heat loss.

Jacket - Heavy gauge steel finished with a baked enamel finish over a bonderized undercoat.

Easy Cleaning - Handhole cleanout allows access for easy cleaning.

Intermittent Ignition Device - Eliminates standing pilot. Provides flame failure response in less than one second. Spark igniter and power ON/OFF switch.

Easy-to-install - Completely factory-assembled. Only gas, water, vent and electric connections need be made. Provided with drain valve.

Anodes - CoreGuard™ long-life, stainless steel core anode rods.

Plug Kits - Pipe nipples and caps are included to plug unused water connections.

Other Standard Features
  • Integral automatic gas shutoff system prevents excessive water temperature
  • CSA Certified and ASME Rated T&P Relief valve are factory-installed
  • Maximum working pressure is 160 psi standard
  • Adjustable thermostat with a 120 to 180 ºF range.
  • All models certified up to 7700 ft.

Testing and Certifications
Fully Tested for Safety and Performance - Design certified by the Underwriters Laboratory for 180°F hot water service. Meets rigid requirements of the National Sanitation Foundation when equipped with optional leg kit. Certified for use on combustible flooring.

Approval Ratings and Certification - All models meet ANSI Z21.10.3 - CSA® 4.3 standards and the thermal efficiency and standby loss requirements of the U.S. Department of Energy and current edition of ASHRAE/IESNA 90.1.

  • Meets NSF Standard 5 with optional leg kit - Part #9008214005
Models available for sale in California only.

  • 3-Year Tank Warranty / 1-Year Parts Limited Warranty.

A after model number designates ASME construction.

Dimensions and specifications subject to change without notice in accordance with our policy of continuous product improvement.


·  Standards for Master-Fit® Ultra-Low NOx Commercial Gas Water Heaters


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