The Mr. Heater Big Maxx Forced Air Unit Heater is designed to provide efficient convection heating for residential and commercial spaces, including garages, workshops, and potentially aircraft hangers or parking structures. These units utilize a 115v AC power source and can be vented either vertically or horizontally, subject to local regulations. The heaters feature a built-in high-velocity fan to circulate warm air and are available in multiple BTU output configurations. Installation requires adherence to national and local fuel gas codes, and the units come with a 3-year factory warranty on parts and burners, and a 10-year warranty on the heat exchanger.
Unit Specifications and Models
The Mr. Heater Big Maxx series offers multiple BTU output options, each with corresponding efficiency ratings and physical dimensions. The available models and their specifications, as detailed in the provided documentation, are as follows:
- 50,000 BTU with 80% efficiency
- 80,000 BTU with 80% efficiency
- 125,000 BTU with 80% efficiency
The physical dimensions (in inches) for each model are:
| Model | A (Length) | B (Width) | C (Height) |
|---|---|---|---|
| MHU 50 | 12" (305) | 5.5" (140) | 4.25" (108) |
| MHU 80 | 17" (432) | 6.5" (165) | 6.75" (171) |
| MHU 125 | 24.67" (626.8) | 8.08" (205.25) | 9.43" (239.61) |
Each unit is shipped fully assembled, including installation instructions, two mounting brackets, and a flue transition.
Installation Requirements and Safety Standards
Proper installation is critical for safe and efficient operation. The documentation emphasizes adherence to local building codes and, in their absence, the current National Fuel Gas Code ANSI Z223.1. Specific installation requirements vary depending on the application:
- Aircraft Hangers: Installation must comply with ANSI/NFPA No. 409.
- Parking Structures: Installation must comply with ANSI/NFPA No. 88A.
- Repair Garages: Installation must comply with ANSI/NFPA No. 88B.
For residential garage installations, the bottom of the heater must be at least 8 feet (2.438m) above the floor, and the unit must be protected from physical damage, such as from vehicles. The documentation also references CSA B149.1, Natural Gas and Propane Installation Code, and CSA C22.1, the Canadian Electrical Code, for installations in Canada.
Clearances to combustible materials are specified in Table 1:
| Location | Inches | Millimeters |
|---|---|---|
| Top | 1 | 25 |
| Sides | 1 | 25 |
| Access Panel | 18 | 457 |
| Bottom | 0 | 0 |
| Rear | 18 | 456 |
These clearances are based on CSA International certification and should not be superseded by local codes.
Gas Pressure Specifications
The documentation provides specific gas manifold pressure requirements for both natural gas and LP/propane, varying with altitude.
Natural Gas:
| Altitude (ft/m) | Pressure (in. W.C. / kPa) |
|---|---|
| 0-2000 (0-610) | 4.0"WC (0.99 kPa)* |
| 2000-4500 (610-1370) | 3.6"WC (0.89 kPa) |
*No adjustment is required.
LP/Propane:
| Altitude (ft/m) | Pressure (in. W.C. / kPa) |
|---|---|
| 0-2000 (0-610) | 10"WC (2.49 kPa)* |
| 2000-4500 (610-1370) | 8.5"WC (2.12 kPa) |
*No adjustment is required.
Inlet pressure requirements are:
- Natural Gas: MAX - 14" WC (3.49 kPa), MIN - 5"WC (1.25 kPa)
- Propane: MAX - 14" WC (3.49 kPa), MIN - 11"WC (2.74 kPa)
Electrical Connections and Grounding
Electrical connections require adherence to local and national electrical codes. The documentation specifies the following:
- Use 18 gauge wire or larger for line power connections.
- Connect line power to wires located in the external electrical junction box.
- Do not connect line power to the thermostat terminal strip on the outside of the heater.
- Electrically ground the unit in accordance with local codes or, in the absence of local codes, with the current National Electrical Code (ANSI/NFPA No. 70) in the USA, and the current Canadian Electrical Code, Part 1 CSA C22.1 in Canada.
- A separate disconnect switch (protected by a fuse or circuit breaker) should be installed near the unit for servicing.
- The unit utilizes a direct spark ignition system and may emit radio noise during ignition, potentially interfering with microprocessor-controlled thermostats. An isolation relay is recommended when connecting to such thermostats.
Maintenance and Troubleshooting
The documentation recommends annual maintenance, including checking gas connections for tightness and leak-checking with a soap solution. In case of a safety shutdown, the thermostat should be switched to the OFF position and then back to HEAT.
For emergency shutdown, the main gas valve should be shut down, and the main power to the unit disconnected. These devices should be clearly labeled by the installer.
If a part is damaged or missing, contact Technical Support at 800-251-0001.
Warranty and Customer Support
Mr. Heater provides a 3-year factory warranty on all parts and burners and a 10-year warranty on the heat exchanger. Warranty claims should be addressed to the Service Department at Mr. Heater, Inc., 4560 W. 160TH ST., CLEVELAND, OHIO 44135, including the purchaser’s name, address, telephone number, purchase date, and dealer information.
Customer support is available via:
- Phone: 800-251-0001 (Monday-Friday, 8:00 AM – 5:00 PM, EST)
- Website: www.mrheater.com
- Social Media: Facebook and Twitter
- YouTube: Informational videos are available on YouTube.
Important Safety Information
The documentation stresses the importance of smelling for gas leaks before lighting the unit, particularly near the floor. Users should only use their hand to move the gas control knob and avoid using tools or excessive force. The unit is equipped with an automatic spark ignition system and does not require a pilot light. Only manufacturer-approved replacement parts should be used, installed by a qualified service agency.
Conclusion
The Mr. Heater Big Maxx Forced Air Unit Heater offers a robust heating solution for various applications. Successful and safe operation relies on careful adherence to the provided installation instructions, local codes, and national safety standards. Proper maintenance and utilization of the provided warranty and customer support resources will ensure long-term performance and reliability.