Here is what I sent James about the show because I found the "official" stance misleading. 4 burners on my range inside provides more BTUs (and uses more oxygen) than my outdoor cooker and my range is deemed "safe":
"Unfortunately Bruce has to wear this official Propane Police hat when he's answering your questions, and his although his answers are correct to the letter of the law, the common sense and real world answers may be different. Kinda like the brewing 100 gallons of beer per person law, some guys I know are breaking that law before Easter (Andy?). Or even the "only 2-1# propane bottles in one house" law.
Some propane math: 1 cubic foot (ft3) of propane requires 23.5 ft3 of air to properly burn. So lets exaggerate and say you have to use 35,000 BTUs to make a batch of beer (cuz you're not running that 35K burner full blast the whole time), you're going to need 329 ft3 of air to do so. That's a chunk about the size of a VW Bug. There's 10 times that volume in a 2-car garage. You might just pull it off in a sealed garage if the carbon monoxide (CO) didn't get you first! (don't try this!!)
But, a furnace (with a flue mind you, your burner has no flue) requires 1 SQUARE INCH of combustion air intake per 1000 BTU rating. So if your burner had a flue, you'd only need 35 in2 of opening to supply the combustion air (plus 35 more for flue dilution air) . This is an active system with air getting sucked in by the air that gets sucked out. Garages aren't like that, but opening the garage door 18" will give 100 times that area and might be safe, but I'd go half way if you don't have any cross ventilation available (another window or door open).
Can anyone legally recommend using a burner in the garage? NO
. But, that being said, I do it all the time with an open window and the garage door up about 4" - with my CO detector showing ZERO the whole time (the same detector jumps to 20 if I back a car in, so I know it works).
Just make sure you have a CO detector (with a readout) and adjust your air mixture for blue tipped flames (yellow flames = CO=death).
The most dangerous thing about the whole adventure is having the propane tank and it's rubber hose in an enclosed space (with your house attached to it). I've recently had an overfilled (3.4# in a 2.5# mini tank - despite
the overfill protection device) propane cylinder vent out through it's overpressure valve while running my BBQ. The ensuing fireball was neat looking, but being immediately adjacent to my house and my eyebrow(s), it was a little scary. It had been cold out since filling it, but the BBQ heated up the cold tank which increased the pressure and caused the purge. If a hose had melted, things could have been much worse."