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Internet # 305089829

Model # MHU80NG

Store SKU # 1003143329

80,000 BTU Black Big Maxx Natural Gas Unit Heater-Space Heater

$549.99
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  • Indoor 80,000 BTU forced air propane or natural gas unit heater
  • Heats up to 2,667 sq. ft., or approximately a 3- or 4-car garage
  • Ceiling mounted forced air unit heater for garages, barns, etc.
  • View More Details

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Product Details

About This Product

The Mr. Heater Big Maxx 80,000 BTU unit heater will turn your garage or barn into a work space you can use all year round. Uses a built-in high-velocity electric fan to pull cool air in and across the heat exchanger, then forces warm, comfortable air out. Its low profile design requires only a 10 ft. minimum ceiling height and 1 in. mounting clearance. Features a high-temperature safety shut-off, gas safety shut-off flame sensor, and an electric spark ignition with a self-diagnostic control module, to bring you peace of mind and years of comfortable, safe heat. Comes as natural gas and includes a propane conversion kit and ceiling mounting brackets. Requires 120-Volt AC power and can be vented vertically or horizontally - please check local codes and restrictions. This heater offers all the operating versatility and safety you have come to expect from Mr. Heater.

Highlights

  • Compatible with standard 24-Volt or new wi-fi enabled thermostats (sold separately)
  • Ceiling mounted forced air propane unit heater turns garages, barns and workshops into heated work spaces
  • 80,000 BTUs heat up to 2,667 sq. ft. or approximately a 3 or 4-car garage
  • Spark ignition features self-diagnostic control module
  • Low profile design 10 ft. minimum ceiling height with 8 ft clearance required from base of heater to floor
  • Return Policy
  • California residents
     see Prop 65 WARNINGS

Product Information

Internet # 305089829

Model # MHU80NG

Store SKU # 1003143329

Specifications

Dimensions

Product Depth (in.)

21.75 in

Product Width (in.)

30.25 in

Details

Area Heated (sq. ft.)

2667 sq ft

Color

Black

Color Family

Black

Control Type

Mechanical

Features

Adjustable Thermostat

Fuel Rate (gallons/hour)

0 gal (US)/min

Fuel Tank Capacity (gal.)

0 gal

Heat rating (BTU/hour)

80000 Btu/h

Heater Type

Natural Gas

Heating Method

Forced Air

Ignition Type

Electrical

Indoor/Outdoor

Indoor

Location Use

Garage

Maximum Temperature Setting (F)

0 °F

Number of Heat Settings

1

Portable Heater Features

Thermostat

Power/Fuel Type

Natural Gas

Product Weight (lb.)

87.6 lb

Returnable

90-Day

Room Size

Extra Large

Runtime (hours)

0 hr

Vent Type

Ventless

Warranty / Certifications

Certifications and Listings

ETL Certified

Manufacturer Warranty

3 Years parts, 10 year Heat Exchanger

Questions & Answers

Does this unit include a propane conversion kit
ByAug 6, 2026
1 Answer | 
Answer This Question

Thank you for your inquiry. Yes, this unit comes with a conversion kit, so you can run it on propane or natural gas. Have a great day!

By|Aug 7, 2026


    What voltage amps for the 125,000 heater?
    ByJun 8, 2026
    1 Answer | 
    Answer This Question

    Thank you for your inquiry. This heater requires 3 amps of power. Have a great day!

    By|Jun 9, 2026


      Does this need dedicated electrical circuit
      ByJun 3, 2026
      1 Answer | 
      Answer This Question

      Thank you for your inquiry. Yes, this heater should be wired in on its own circuit. Have a great day!

      By|Jun 4, 2026


        Can this be converted from Natural gas to propane?
        ByApr 13, 2026
        2 Answers | 
        Answer This Question

        My garage is 12ft wide, 20ft long,9ft ceiling how many sq ft is that

        By|Apr 23, 2026

          Thank you for your inquiry. Yes, this heater includes a conversion kit if you would like to switch to propane. Have a great day!

          By|Apr 14, 2026


            need it to be lp gas
            ByMar 31, 2026
            1 Answer | 
            Answer This Question

            Thank you for the inquiry. These heaters come with a conversion kit inside. Have a great day!

            By|Mar 31, 2026


              Does the fan shut off once temp the thermostat is set to is reached
              ByDec 6, 2025
              1 Answer | 
              Answer This Question

              Thank you for your inquiry. Yes, the fan will run for a few minutes after the heat shuts down, and then will stop itself until the heater starts back up. Have a great day!

              By|Jun 27, 2026

                (1)

                Can you vent this into a chimney that has a liner?
                ByDec 1, 2025
                1 Answer | 
                Answer This Question

                Thank you for your inquiry. Yes, this heater can be vented into a lined chimney. For full instructions on how to do so, consult the heater's owner's manual. Have a great day!

                By|Dec 2, 2025


                  Can I splice the vent into a 6" wood stove pipe in order to vent outdoors?
                  ByNov 17, 2025
                  1 Answer | 
                  Answer This Question

                  Thank you for your inquiry. No, you should not combine the venting for those two heaters. Have a great day!

                  By|Nov 18, 2025


                    Viewing 1-8 of 104

                    Customer Reviews

                    4.3 out of 5

                    • 4.3 out of 104 reviews
                    • 75% recommend this product
                    Filter by:
                    Showing 1-10 of 104 reviews
                    50000 BTU Mr Heater Big Maxx
                    I bought it in 2020 for $300+. Installed it by myself. Pretty easy to install if you know what your doing. Hanging it on the ceiling was a little challenging by myself, could have used a buddy. At this time I have used the heater for 5 winter seasons in ND. I have had no issues with it and I am very happy. I use it to heat my 20' x 24' shop that I built. Can't believe the prices on the current models.
                    by
                      • Recommended
                      This customer chose to rate the product and not provide text.
                      by
                      • Verified Purchase
                      The box was beat up when it was delivered. The fan motor was not installed and lose. Found the bolts in the bottom of the box. Removed the fan shroud and remounted it. Fan blade was bent a little. Glad we saw it before we installed the heater on the ceiling. This is a two man project to mount. Hooking it all up was straight forward. Fired right up and has been running good. Not as quite as some said. All in all I’m happy with everything.
                      by
                      • Verified Purchase
                      This customer chose to rate the product and not provide text.
                      by
                      • Verified Purchase
                      I have not installed yet, all indications it will work great
                      by
                      Care of delivery is terrible. Box smashed and unit dented. It is a shame that the shipping in this country is so bad. "Just give my your money and shut up" is the philosophy of big business any more.
                      by
                      Response from Mr. Heater Product ExpertAug 5, 2026
                      We are very sorry for the shipping inconvenience. It is certainly frustrating when an expensive purchase arrives with shipping damage. Please call s at 1-855-663-0660 so we can evaluate the situation and help to determine the best course of action to resolve this as quickly as possible. Enerco
                      • Verified Purchase
                      1 found this review helpful
                      The heater was initially out of stock but I was able to request notice when it became available. Home Depot sent me an email letting me know my item was back in stock and available to order. The Heater was hundreds less than elsewhere and has been operating flawless. In short. Great service, fast shipping, and amazing deal. Definitely would recommend both the heater and Home Depot to family and friends
                      by
                      easy and quick to install; easy to convert to propane; fired right up
                      by
                      • Verified Purchase
                      Furnace won’t stay lit
                      Brought this last month,the furnace won’t stay lit. Did some diagnostics and all the safety switches seem to be working fine. Researched this unit online and apparently some people had bad boards early after purchasing. They say to contact Mr heater tech and usually will send out new board.
                      by
                      Response from Mr. Heater Product ExpertApr 27, 2026
                      Thank you for your review and feedback. Please reach out to us directly at 1-855-663-0660 so we can determine what is going on with your stove and help get that corrected. Enerco
                        Don't, Just Don't!
                        I have one about 3 years old in Michigan, for a small attached home greenhouse. Keeps failing, they've replaced gas valve pressure valves etc. The owner of the residence is away for the winter. Parts take forever to receive by the HVAC servicer. And this has been an ongoing since November. I installed a camera pointing at a temperature gauge. It works when it wants to. Most of the time I have to go over there flip the switch to get it to reset. Spend the extra money and buy a better product.
                        by
                        Response from Mr. Heater Product ExpertFeb 2, 2026
                        Thank you for your review and feedback. We'd like to speak to you about your experience with this unit. Please give us a call at 1-855-663-0660. Enerco
                          • Recommended
                          Showing 1-10 of 104 reviews

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                          Product Snapshot

                          Ideal for homeowners looking for powerful heating, making garage use in cold climates comfortable. Heats up to 2, 667 sq. ft. with 80, 000 BTUs and features a high-temperature safety shut-off.
                          Ideal for homeowners looking for powerful heating, making garage transformations easier.
                          Ideal for transforming garages or workshops into year-round workspaces, this heater offers powerful forced air heating with a 125, 000 BTU output, ensuring optimal warmth and comfort even in large areas.
                          Ideal for large, drafty spaces like warehouses and loading docks, ensuring powerful, instant heat with its 100, 000 BTU radiant heating system.

                          Heating Capacity (BTU)

                          80, 000 BTU
                          50, 000 BTU
                          125, 000
                          100, 000

                          Heating Method

                          Forced Air
                          Forced Air
                          Forced Air
                          Radiant

                          Oxygen Depletion Sensor

                          Tip-Over Shut-Off

                          Indoor/Outdoor Use