Viessmann Vitocrossal 300 CU3A Series Technical Data Manual
Product Overview
The Vitocrossal 300 CU3A is a floor-mounted, gas-fired condensing boiler featuring a modulating MatriX gas burner. It is designed for operation with natural gas and liquid propane gas, suitable for room air dependent or independent operation.
It offers unparalleled performance, reliability, and comfort, boasting industry-leading technology, high efficiency (up to 98% at full modulation, up to 95% A.F.U.E.), low emissions, and fast installation with reduced maintenance thanks to the Lambda Pro combustion management system.
Key benefits include:
- Best value in its class with advanced technology and standard features.
- Lasting performance with Viessmann-made SA240 316 Ti stainless steel Inox-Crossal heat exchanger.
- Low Emission Combustion with stainless steel MatriX burner.
- Powerful and user-friendly Vitotronic control for multi-temperature space and DHW heating.
- Zone circuit capabilities for easy integration of third-party controls.
- Expanded application range with multi-boiler installation capability (up to 8 boilers).
- Greater venting flexibility with extended vent lengths and multiple options.
- Compact, aesthetic product design with zero clearance to combustibles.
- Extremely quiet operation.
- True high-altitude operation up to 10,000 ft.
- Efficiency up to 98% through intensive condensation.
Cross-Section and Efficiency
The document includes graphs illustrating boiler efficiency based on system heating water return temperatures and load conditions, as well as boiler water/supply temperature versus outdoor temperature.
Technical Data
The following tables provide detailed technical specifications for the Vitocrossal 300 CU3A series boilers, including model numbers, input/output capacities, ratings, dimensions, pressures, temperatures, and connections.
Boiler Specifications
| Boiler Model No. CU3A | 26, 94 | 35, 125 | 45, 160 | 57, 199 |
|---|---|---|---|---|
| Natural Gas / Liquid Propane Gas | ||||
| CSA input MBH (kW) | 19-94 (5.6-27.5) | 25-125 (7.3-36.6) | 43-160 (12.6-47) | 43-199 (12.6-58) |
| CSA output / DOE heating capacity*1 MBH (kW) | 17.7-87 (5.2-25.5) | 23.3-116 (6.8-34) | 40-149 (11.7-43.7) | 40-185 (11.7-54.2) |
| Net AHRI Rating MBH (kW) | 76 (22) | 101 (30) | 129 (38) | 161 (47) |
| Heat exchanger surface area ft.2 (m2) | 16.7 (1.5) | 20.7 (1.9) | 34.1 (3.2) | 34.1 (3.2) |
| Min. gas supply pressure "w.c. Natural gas | 4 | 4 | 4 | 4 |
| Min. gas supply pressure "w.c. Liquid propane gas | 10 | 10 | 10 | 10 |
| Max. gas supply pressure *3 "w.c. Natural gas | 14 | 14 | 14 | 14 |
| Max. gas supply pressure *3 "w.c. Liquid propane gas | 14 | 14 | 14 | 14 |
| A.F.U.E. % | 95 | 95 | 95 | 95 |
| Weight lbs (kg) | 269 (122) | 275 (125) | 352 (160) | 352 (160) |
| Boiler water content USG (L) | 13.5 (51) | 13.0 (49) | 18.8 (71) | 18.8 (71) |
| Max. operating pressure psig (bar) at 210°F (99°C) | 30 (2) | 30 (2) | 30 (2) | 30 (2) |
| Boiler water temperature - Adjustable high limit (AHL) range space heating (steady state) °F (°C) | 68-194 (20-90) | 68-194 (20-90) | 68-194 (20-90) | 68-194 (20-90) |
| DHW production °F (°C) | 194 (90) | 194 (90) | 194 (90) | 194 (90) |
| - Fixed high limit (FHL) °F (°C) | 210 (99) | 210 (99) | 210 (99) | 210 (99) |
| Boiler connections | ||||
| Boiler heating supply and return | 1¼ in. NPTM | 1¼ in. NPTM | 1¼ in. NPTM | 1¼ in. NPTM |
| Pressure relief valve | ¾ in. NPTF | ¾ in. NPTF | ¾ in. NPTF | ¾ in. NPTF |
| Boiler drain | 1 in. NPTM | 1 in. NPTM | 1 in. NPTM | 1 in. NPTM |
| Gas valve connection | ¾ in. NPTF | ¾ in. NPTF | ¾ in. NPTF | ¾ in. NPTF |
Dimensions
| Model 26, 35, 94, 125 | Model 45, 57, 160, 199 | |||
|---|---|---|---|---|
| Dimension | inches (mm) | inches (mm) | ||
| Overall depth | 27 (684) | 31½ (801) | ||
| Overall width | 26 (660) | 26 (660) | ||
| Overall height (with control interface open) | 67 (1707) | 67 (1707) | ||
| Overall height | 61.5 (1562) | 61.5 (1562) | ||
Minimum Clearances to Combustibles
| Boiler model CU3A | 26, 94 | 35, 125 | 45, 160 | 57, 199 |
|---|---|---|---|---|
| Top | 0 | 0 | 0 | 0 |
| Sides (left and right) | 0 | 0 | 0 | 0 |
| Vent pipe | 0 | 0 | 0 | 0 |
| Front (alcove or closet) | 0 | 0 | 0 | 0 |
| Rear | 0 | 0 | 0 | 0 |
| Floor | combustible | combustible | combustible | combustible |
Waterside Flow - Pressure Drop
The document includes a graph illustrating pressure drop versus flow rate for different boiler models (A: CU3A 26, 35, 94, 125; B: CU3A 45, 57, 160, 199). It also provides tables for flow rates at different temperature differences (ΔT).
Air Factor A - CO2/O2 Content
| Air factor A | O2 content (%) | CO2 content (%) for natural gas | CO2 content (%) for liquid propane gas |
|---|---|---|---|
| 1.20 | 3.8 | 9.6 | 11.3 |
| 1.24 | 4.4 | 9.2 | 10.9 |
| 1.27 | 4.9 | 9.0 | 10.6 |
| 1.30 | 5.3 | 8.7 | 10.3 |
| 1.34 | 5.7 | 8.5 | 10.0 |
| 1.37 | 6.1 | 8.3 | 9.8 |
| 1.40 | 6.5 | 8.1 | 9.6 |
| 1.44 | 6.9 | 7.8 | 9.3 |
| 1.48 | 7.3 | 7.6 | 9.0 |
Boiler Control (Vitotronic 200, HO1B)
The Vitotronic 200, HO1B is an on-board control unit integrated into the boiler, featuring a plain text display with graphic ability, context-sensitive help, and programmable functions for heating, DHW, and recirculation.
Key features include:
- Easy operation via display and control keys for navigation, settings, and information.
- Settings for room temperature, DHW temperature, heating programs, time programs, economy mode, party mode, holiday program, heating curves, codes, actuator tests, and test mode.
- Display of boiler water temperature, DHW temperature, operating details, diagnostic details, and fault messages.
- Functions include weather-compensated control, demand-dependent pump and burner control, anti-seizing pump protection, and integral diagnostic system.
- Time switch with individual and 7-day programming, automatic daylight savings time changeover.
- Heating programs: Heating and DHW, DHW only, Standby mode, Zone circuits, External heating program changeover.
- Frost protection function activates below 34°F (1°C).
- Summer operation mode where the burner activates only for DHW calls.
The document also details heating curve adjustments (slope and shift) and provides a graph illustrating these adjustments based on outdoor temperature.
Accessories and Optional Components
The manual lists various sensors and optional accessories for the Vitocrossal 300 CU3A, including:
- Sensors: Boiler Temperature Sensor, Outdoor Temperature Sensor, DHW Tank Temperature Sensor, Immersion Temperature Sensor.
- Optional Accessories: Supply Temperature Sensor, KM BUS Expansion Module, Mixing Valve Actuator Kit, Mixing Valve Extension Module, AM1 Extension Module, Vitotrol 200A, Vitotrol 300A, LON Communication Module, LON Connecting Cable, LON Terminal End Resistor, Fuel Conversion Label Kit, Low-Loss Header, Neutralization Unit, Neutralization Pellets.
Descriptions and specifications are provided for each component, along with diagrams where applicable.
Standard Equipment and Combustion Management
Standard equipment includes the boiler control unit, outdoor temperature sensor, power/pump module, installation fittings, pressure relief valve, and temperature/pressure gauge. The enclosure is finished in black steel, powder-coated Viessmann silver.
The combustion management system utilizes ionization current and air factor (λ) for optimal combustion quality, automatically adjusting to gas type and quality via the Lambda Pro system. The document includes a table correlating air factor with CO2/O2 content for natural gas and liquid propane gas.
Installation Examples and System Design
The document provides detailed system layouts (System Layouts 1 through 8) illustrating various installation configurations for the Vitocrossal 300 CU3A boiler, including:
- Direct-connected heating circuits.
- Heating circuits with mixing valves and system separation.
- Underfloor heating circuits.
- Multi-boiler installations (up to eight units).
- Use of low-loss headers.
- DHW storage tanks and recirculation pumps.
Each layout is accompanied by a diagram and a legend identifying components. Important notes on system separation, pump sizing, and material compatibility are included.
System design considerations cover boiler location, flue gas systems, water connections, water quality, and warranty information. It emphasizes adherence to local codes and proper installation practices.
Electrical Connections and Wiring
A dedicated section details the electrical connections for the Vitocrossal 300 CU3A boiler, including a wiring diagram and a comprehensive legend for sensors, outputs, inputs, and internal components. It stresses the importance of disconnecting power before servicing and adhering to electrical installation codes (NEC, CEC).
