Heaters drink propane. Plan for it.
A standard mushroom-style patio heater runs at something like 40,000 BTU on full, which empties a 20lb cylinder in roughly ten hours. A grill might last you most of a summer on one tank. A heater running every evening will not last you a week.
This catches people out every autumn. The heater arrives, it gets used nightly, and the tank dies on the first genuinely cold Friday, which is the exact night the terrace was full. If you are running a heater regularly, the question is not whether you will need another tank, it is how many and how often.
For restaurants, bars and cafes
Sidewalk and backyard seating is the difference between a full house and an empty one from October onward, and it only works if the heaters are lit. Most of the hospitality customers on the route take several tanks at a time and set up a standing swap, so a fresh set arrives before the old ones run dry rather than after.
Tell Rodrigo how many heaters you run and how many hours a night, and he will tell you roughly how many tanks a week that works out to. Then you can just book the swap and stop thinking about it.
For terraces and backyards at home
One heater, used on weekend evenings, is a tank every few weeks in the depths of winter. The practical move is the same as with a grill: keep a spare, swap the empty when it empties, not when you next need heat.
Bear in mind that propane heaters are for outdoor use. Never run one indoors, in a garage, or in a space you have enclosed with plastic sheeting or tarps to keep the cold out, which is a common and genuinely dangerous mistake in this city. Carbon monoxide is the reason.