MHUniversity Unit Utility Heaters

The Big Maxx Forced Air Unit Heater is efficient and effective convection heat for your garage or workshop for residential or commercial use. If you are looking to turn your garage or barn into a work space you can use all year-round, you will have to find a safe quiet and reliable heat source. The heaters use a built-in electric high velocity fan to pull cool air into the rear of the heater, across a heat exchanger, then force warm air into the surrounding areas. These heaters only require 115v AC power and can be vented vertically or horizontally - please check local codes and restrictions. With a mounting clearance of only 1 inch, the supplied brackets, external access to power, and thermostat connections - installation is a cinch. With the durable spark ignition and robust factory standard self-diagnostic control module, we offer a 3 year factory warranty on all parts and burners and a 10 year warranty on any defects in the heat exchanger. This heater offers the operating versatility and safety that you have come to expect from Mr. Heater.

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Unit Heater FAQs
Unit Heater Manuals and Troubleshooting Guides
Unit Videos
Unit Heaters
Unit Heater Accessories
Parts Ordering

Unit Heater FAQs

Where do I connect the thermostat wires?

The connections are on the terminal strip on the circuit board marked in white, R for red and W for white.

Connections on Unit Heater

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I can not get my heater to come on. There is no green light on, on the circuit board.

Check the 3amp fuse on the upper left portion of the Circuit Board.

Unit Heater Circuit Board

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The green light is flashing slowly but my heater is not turning on.

Check your connection at your thermostat. Check for broken wire to the thermostat. If the wires are good disconnect from the thermostat and jumper them together to start the heater automatically. If the heater runs the thermostat is bad.

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What is the amp usage for my Big Maxx?

MHU50 uses 2.3amps, MHU80 uses 2.3amps, and the MHU125 is 3amps

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What is the efficiency of the heater?

The Unit Heaters are 80% efficient.

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Why does your Horizontal Vent Kit cost more than your Vertical Vent Kit?

Horizontal Vent Kit has to be stainless steel, which is more expensive.

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Can I test my gas outlet pressure with compressed air?

No. If you use compressed air through your pressure valve on any gas heater, you will blow out the gasket and it will destroy the gas valve and will void your warranty.

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I am getting a 3 flash code; does that mean my pressure switch is bad?

Most likely not. The pressure switch being faulty is the least likely issue. Please execute the following tests to eliminate all possibilities. First, pull the vacuum tube off the pressure switch and blow into it. If it does not have good flow or no flow at all, then clean out the vacuum hose connector with a 5/64in drill bit. If it is not that, then turn the heater on with the vacuum hose connected to the pressure switch. Turn the thermostat on then suck on the hose to create a vacuum and pinch the hose to keep the pressure. If the heater fires up, reconnect the hose to the hose connecter on the vent motor. Once that is done, if this shuts the heater down then you have something blocking your exhaust. If after these steps the heater still does not function, then replace the pressure switch.

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What is an ODS?

An ODS is an Oxygen Depletion Sensor. This device senses the amount of oxygen in the air surrounding the device. When the oxygen level drops below a specific level, the device will shut off automatically.

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What does the heating area square feet mean?

Square footage is the length of an area times the width of an area. Knowing the square footage of an area allows you to estimate the amount of BTUs necessary to heat the area most effectively. A generally accepted formula is: Square Footage x 40 = required BTUs. This is just a starting point. Ceiling height, building layout, and level of insulation will also factor into your BTU needs.

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What is W.C. (Water Column) and how do I measure it?

All gases are measured in W.C. because it is used to measure small differences in low pressure across an orifice or pipeline. Low pressure is any pressure below 1 Pound per Square Inch (PSI). When dealing with pressures below 1 PSI, you will see the term inches or inches of water column. This refers to the amount of pressure it takes to raise a column of water 1 inch. There are 27.7 inches of water column (W.C.) pressure in 1 PSI of pressure. W.C. is measured with a manometer (pressure gauge), which measures the pressure of gases and vapors. If you need to measure your W.C., we highly recommend you contact your local gas company to send out a professional or have someone who is HVAC certified to test it.

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What is a High Limit Safety shut-off?

A High Limit Safety is a switch located inside the device which will turn it off if the internal temperatures of the device rise above a specific level.

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Do you need to order parts?

For your convenience please enter your serial number below to access Mr. Heater’s interactive schematic & parts ordering system. This system will allow you to browse your specific product schematic to order the correct service parts as well as download a complete manual for your make & model year.  If your product was produced any year prior (2011 and earlier), please call our Service Department at 1-800-251-0001, where our technicians will gladly assist you.


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Don't see your question?

We try to make our FAQs as comprehensive as possible but sometimes things are missed!  We apologize for the inconvenience and ask that you contact us so we may assist you.  You have multiple options to get a hold of us:

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Unit Heater Manuals and Troubleshooting Guides

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Unit Heater Videos

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Parts Ordering

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