It heats up to 1,250 sq. Starting it up was fun! or Best Offer. Easily the most attractive feature of the Big Maxx 50,000 Natural Gas heater is that it can put out a whopping 50,000 BTU per hour, which can heat a garage ranging in size from 700-1250 square feet. Additional information for residents of Quebec only: The regular annual rate for persons applying for the Triangle Mastercard and the Triangle World Elite Mastercard is 22.99% for cash transactions and related fees and 19.99% for all other charges. To replace it simply pull off the old knob and secure the new one over the shaft. For larger spaces or fast heat up the forced air heater is an awesome product. Increase Quantity. Skip to main Your eCTM will be stored in that account. Mr. Heater 80,000 BTU Big Maxx Natural Gas Garage/Workshop Heater - Model MHU80NG (6) $398.99. These notices may be given to you by postal mail, e-mail, facsimile, telephone, text message or other form of electronic messaging using the contact information that you provide to us.