How Many BTUs Does Your Patio Heater Need? A Sizing Guide by Space Type

Once the sun starts setting before dinner and that first cool evening breeze rolls in, the patio heater questions start pouring in: "Will this actually heat my whole deck?" "Do I need gas or electric?" "Why does one heater cost $600 and another cost $5,000?" Almost every one of those questions comes down to the same root issue — sizing. Buy too small and you'll be huddled directly under the heater in a coat. Buy too big (or the wrong type for an open, windy deck) and you'll be paying to heat the neighborhood.

Here's how to actually size a patio heater for your space, without the guesswork.

BTUs and Watts Aren't the Same Thing — And That's Fine

Gas patio heaters are rated in BTUs (British Thermal Units); electric infrared heaters are rated in watts. You don't need to convert between the two to shop well — you just need to know which number matters for the heater type you're looking at, and how much of it your space actually needs. A "300" or "500" in a heater's name (like the Bromic Platinum 300 or Platinum 500) refers to that BTU or wattage tier, not the square footage it covers.

The Real Variable Is Exposure, Not Just Square Footage

Two patios can be the exact same size and need completely different heaters. What matters more than raw square footage is how enclosed the space is, because an open patio loses heat to the sky and wind on every side, while a covered or partially walled patio holds it in.

As a general rule of thumb from outdoor heating manufacturers: open-air patios need roughly 28–32 watts per square foot of coverage, a covered patio (roof, no walls) needs somewhere around 22–27 watts per square foot, and a patio with a roof plus two or three walls can often get away with 12–16 watts per square foot. Put in real terms, a 200 square foot covered patio — a fairly typical KOS customer setup — lands around 5,000 watts of infrared heat to cover comfortably. Wind exposure can push that number up another 20–30%, and mounting height matters too: every foot you go above the ideal ~9 feet mounting height adds roughly 10% to your wattage needs, since the heat has farther to travel before it reaches anyone.

Gas heaters follow the same logic in BTUs instead of watts, and generally shine in bigger, more open footprints — a single freestanding gas heater can often warm a wide open backyard or restaurant-style patio, where electric units are usually happiest covering a more contained space near an outlet.

Gas or Electric? Let Your Space (and Your Deck) Decide

This is the other half of the sizing question, and it's really an installation question as much as a heat-output one.

Propane gas heaters need no permanent installation, which makes them the easiest option if you're renting, still finishing your patio, or just don't want to run gas lines — you refill a tank as needed. Natural gas heaters need a permanent gas line and professional installation, but you never think about fuel again. Electric infrared heaters are the simplest of all on the setup side — plug into a suitable outlet and go — and they heat people and surfaces directly rather than warming the air around them, which is part of why they perform so well on covered patios, screened porches, and balconies where wind isn't fighting you.

If your space is large, open, and exposed, gas is usually the more efficient path to real warmth. If it's covered, moderate-sized, and near power, electric will usually get you there for less money up front and less maintenance long-term.

Sizing It Out: Three Real Patios

Small covered patio (under 150 sq ft), near an outlet: This is Bromic Cobalt or Tungsten electric territory — something in the Cobalt 4000W to Tungsten 4000W range gets a covered dining nook or small lounge comfortably warm without overheating the space or your power bill.

Mid-size covered patio (roughly 150–250 sq ft): Step up to a Bromic Platinum 3400W or the Tungsten 3000W/6000W dual-element unit. These are built for exactly this middle ground — big enough to cover a real seating and dining area, still simple to install on an existing covered structure.

Large or open entertaining space: This is where gas earns its keep. A Bromic Tungsten 500 or Platinum 500 gas heater, or the portable Tungsten Portable 500, can anchor an open patio, pergola, or fire pit area where wind and exposure would ask too much of an electric unit alone. For big open backyards, plan on more than one heater rather than one oversized unit trying to do it all — overlapping coverage from two heaters beats one heater cranked past its comfortable range.

Freestanding, Wall, or Ceiling — Placement Is Part of Sizing

The same wattage heater performs differently depending on how it's mounted. Ceiling and pendant-style units, like the Bromic Eclipse Pendant, put heat directly overhead where people are sitting, which is efficient under a pergola or covered structure. Portable and freestanding units are the most flexible — move them where the party actually ends up — but they lose some efficiency to open air on all sides. If you're mounting overhead, remember the height rule above: higher mounting means you'll want to size up slightly to compensate.

Sizing Mistakes We See Most Often

The most common one is buying a single electric heater for a fully open, uncovered patio and expecting restaurant-patio performance — electric can absolutely work outdoors, but an open, windy space usually calls for gas or for electric units mounted close and positioned to minimize wind loss. The second is ignoring mounting height and wondering why a heater "isn't as warm as it should be" — it's often just too high for its wattage. And the third is sizing for the square footage of the whole patio rather than the actual seating zone; you're heating people, not concrete.

Browse by Type

You can see the full lineup, filtered by fuel type, in our Patio Heaters collection, or jump straight to Gas Patio Heaters or Electric Patio Heaters if you already know which direction fits your space. And if you're still not sure which wattage or BTU tier is right for your exact patio, that's a five-minute conversation, not a guessing game — reach out and we'll help you land on the right heater the first time, so you're not shivering through the good part of the evening or shopping again next fall.