The thesis

Keeping the patio usable past October

Most people solve this in the wrong order and spend more than they needed to. The heater is the fourth decision, not the first, and the first three are cheaper.

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It goes the same way most years. Late September, the evenings turn, and the patio you used four times a week stops being somewhere anyone goes. So you buy a patio heater — usually the biggest one that seems reasonable, because bigger must be warmer.

It arrives. It is impressive. On the first calm evening it works well. On the second evening there is a breeze, and it is much less impressive. By November it is standing in a corner with an empty cylinder, and the conclusion is that patio heaters do not really work.

They do work. The purchase was the fourth step done first, and the three steps that should have come before it are cheaper than the one that got done.

The most under-appreciated fact in outdoor heating is that a breeze does not reduce a heater's output. It removes the warmed air that output produced, continuously, and replaces it with cold air. A heater on an exposed patio is working against an unlimited supply of cold.

Our sizing model puts a number on it: exposure raises the heat a patio needs by about 55 percent relative to shelter. To put that in context, the entire spread between the smallest and largest propane tower in this category is about four percent.

Which makes the ranking clear. A run of screening on the prevailing windward side does more than any heater upgrade, costs a fraction as much, and lowers every future running-cost figure too. Windbreaks covers what to buy, the DIY version covers building one, and both start with the same free step: tie a ribbon to the railing and watch which way it points for a week.

Almost nobody does this, and it takes a minute. Measure the seating area, multiply by 20 BTU per square foot, and correct for whether there is a roof and how exposed the spot is.

The number that comes out surprises people in both directions. A small covered patio often needs less than a single 1,500 W electric heater produces, which means the whole propane conversation was unnecessary — and 28 cents an hour instead of $1.40. A large exposed patio often needs more than one tower can sensibly deliver, which means the answer is shelter or two heaters rather than a bigger one.

Either way you have replaced a guess with an arithmetic, and every subsequent decision gets easier. The calculator page shows where each factor comes from, including where published sources disagree with each other.

Heat outdoors is directional, and the placement decisions are free.

• A heater covers a circle; a patio is a rectangle. On a long, narrow space two smaller units beat one large one, whatever the total output says. The geometry.
• Radiant heat needs line of sight. A parasol, a planter or a chair back between the heater and a person blocks it entirely.
• Mounted heat wants to be seven to nine feet up, aimed at the chairs — not at the geometric middle of the patio, where nobody sits.
• Move the chairs. The cheapest fix on this entire site, and it resolves a surprising share of complaints.

With the first three done, the choice narrows to almost nothing. Look up: if there is a roof, a pergola or a porch ceiling, you want a mounted electric infrared unit, and the clearance arithmetic on the covered patio page will tell you it fits where a tower does not.

If there is open sky, you want propane, and the number from step two tells you what size. If the answer was under about 5,000 BTU/h, electric will still do it and will cost a fifth as much per evening.

Cylinders run out faster than anyone expects

A 20 lb cylinder holds about 431,500 BTU. At 48,000 BTU/h that is nine hours — two or three evenings, not a season. The arithmetic is on the runtime page, and the practical answer is a second cylinder, which costs less than most accessories and eliminates the problem entirely.

The heater goes over on the first windy night

Seven feet tall, forty pounds, base the size of a dinner plate. Most towers ship with a ballast reservoir or anchor stakes and no instruction anyone reads. Fill the base, secure the cylinder, and put it in a corner rather than the open. The full list.

Everything above assumes you want a seating area that is comfortable. If what you actually want is a fire to gather around, that is a different product and a legitimately different answer — heater versus fire pit works through where the line falls, and the short version is that it depends on whether people sit in a ring or spread out.

It will, and it will almost certainly be a thermocouple — the part that holds the gas valve open, which costs very little and fails from soot and corrosion. The fault tree diagnoses it in one symptom, and the storage routine is what stops it happening in the first place.