Vitocrossal 300 CA3B

Outstanding versatility, performance and reliability

Vitocrossal 300 CA3B

Our most powerful gas condensing boiler

Vitocrossal 300 CA3B is a commercial gas-fired condensing boiler with stainless steel Inox-Lamellar heat exchanger and fully-modulating burners. Rated input: 2500 to 6000 MBH.

Outstanding thermal efficiency
Ideal for commercial buildings
Common venting up to four boilers
No dedicated boiler pump required

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Low emissions & quiet operation

With fully-modulating Viessmann pre-mix cylinder burners (up to 3).

Easy fuel changeover

From NG to LP with a simple turn of a key (on Dual Fuel models).

Fully assembled boiler

Simplifies installation and commissioning.

Large water content

Reduces wasteful burner cycling which increases system efficiency and overall durability.

Seamless integration

With building management systems.

Venting flexibility

Venting through the sidewall or chimney, and combustion air options of sealed combustion or room dependent.

Image courtesy of The Atmospheric Fund and Ecosystem.

Advanced condensing technology and flexibility

With its unique synthesis of proven Viessmann technology and innovative features, the Vitocrossal 300 CA3B takes a bold step forward while retaining the superior Viessmann quality you know and trust.

The boiler combines unparalleled flexibility with maximum efficiency, making it your ideal choice for a new installation or economical retrofit in multi-family, commercial or light industrial applications.

Exceptional performance and reliability

The SA240 316Ti stainless steel Inox-Lamellar heat exchanger surface provides maximum heat extraction while maintaining a compact size. Its smooth, corrosion-resistant surfaces allow condensate to simply run off – a "self-cleaning" process that ensures continuous condensing efficiency, reduced maintenance costs and longevity.

Combined with our fully-modulating pre-mix cylinder burners, the Vitocrossal 300 CA3B achieves outstanding thermal efficiencies over 96% and delivers exceptional performance and reliability at an attractive price.


Stainless steel Inox-Lamellar heat exchanger

User-friendly control system

The Vitotronic 300, GW6C control system is an  advanced digital boiler and system control with outdoor reset function that ensures reliable, efficient performance of the entire heating system. The Vitotronic 300 GW6C will modulate input and rotate boilers to meet the heating system's load. The control will regulate supply water temperature for one high temperature circuit, two mixing valve circuits and one DHW circuit with the standard control package.


Vitotronic 300, GW6C control system

A versatile solution

With multiple venting options and seamless integration into building management systems, the Vitocrossal 300 CA3B offers a solution for almost every commercial application. The boiler comes fully assembled and is easy to install. For buildings with narrow entrances or small elevators, the boiler can be disassembled into sections to fit.

Check out the time-lapse video below to see the installation process in action at our largest project yet – First Canadian Place in Toronto.


Vitocrossal 300 CA3B installation at First Canadian Place

Advantages of the Vitocrossal 300 CA3B

Total burner modulation turndown ratio of up to 16:1 precisely matches load per boiler.
Vitotronic 300 GW6C can be used as a single boiler control or as a cascade primary/secondary control system.
Low inlet gas pressure capability as low as 4" w.c. (NG) for compatibility with a range of supply pressures.
Burners and supply header can be easily removed to facilitate transportation through smaller doorways.
No dedicated boiler pump required due to extremely low water pressure drop through heat exchanger.
160 psi pressure rating allows for this boiler to be installed in almost any building.
Dual fuel (NG and LP) models available.
High-altitude operation up to 10,000 ft (3,000 m).

Look inside the boiler

  1. Vitotronic 300, GW6C control system
  2. Fully-modulating cylinder burners
  3. Inox-Lamellar heat exchanger surfaces
  4. Highly effective thermal insulation
  5. Wide water passageways

Product details

Fuel type

Natural gas (NG) or liquid propane gas (LPG)

Min. input (single fuel NG)

250,000 BTU (73 kW) for CA3B 2.5
300,000 BTU (88 kW) for CA3B 3.0, 3.5, 5.0
400,000 BTU (117 kW) for CA3B 4.0, 6.0

Max. input (single fuel NG)

2,500,000 BTU (733 kW) for CA3B 2.5
3,000,000 BTU (879 kW) for CA3B 3.0
3,500,000 BTU (1026 kW) for CA3B 3.5
4,000,000 BTU (1172 kW) for CA3B 4.0
5,000,000 BTU (1465 kW) for CA3B 5.0
6,000,000 BTU (1758kW) for CA3B 6.0

Thermal efficiency *

96.1% for all models

* Tested to ANSI/AHRI standard 1500 Performance Rating of Commercial Space Heating Boilers / DOE Test Procedure 81 FR 89276 / U.S. Standards ANSI Z21.13/CSA 4.9 / AHRI, BTS-2000 Testing Standard Method to determine the efficiency of Commercial Heating Boilers.

Weight (single fuel boiler)

4233 lbs (1920 kg) for CA3B 2.5, 3.0
4696 lbs (2130 kg) for CA3B 3.5
4806 lbs (2180 kg) for CA3B 4.0
6261 lbs (2840 kg) for CA3B 5.0
6894 lbs (3127 kg) for CA3B 6.0

Overall dimensions (single fuel boiler)


88¾ inches (2251 mm)  for  CA3B 2.5, 3.0
99½ inches (2526 mm)  for  CA3B 3.5, 4.0
136 inches (3449 mm)  for  CA3B 5.0, 6.0


34 inches (860 mm)  for  CA3B 2.5, 3.0
39½ inches (1000 mm)  for  CA3B 3.5, 4.0,  5.0, 6.0


78¾ inches (2000 mm)  for  CA3B 2.5, 3.0
84 inches (2131 mm)  for  CA3B 3.5, 4.0,  5.0, 6.0


Limited 10 year commercial warranty. See warranty sheet for details.

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