Patio Heater Coverage, Explained: Why the Warm Circle Is Smaller Than the Box Says

A full-size propane patio heater can claim a 20-foot circle on the box, yet on a calm night it genuinely keeps people comfortable in a circle only about 6 to 8 feet across — enough for four to six people around one table, and the gap between those two numbers is physics, not fraud.

One patio heater actually keeps about four to six people warm — the people seated around a single table, inside a circle roughly 6 to 8 feet across, on a calm night. That is the answer behind the question our patio heater ranking hears most, and it is much smaller than the coverage printed on most boxes, where claims of up to 20 feet across are common. Both numbers can be defended, because they measure different things: at the edge of a 20-foot circle you may detect a trace of warmth on your face, while inside 6 to 8 feet you can stay for dinner and forget the cold. Comfort, not detectability, is what you are buying.

The comfort circle is 6 to 8 feet, whatever the box says

Compare the claims inside one category and the pattern shows itself. In our ranking, an EAST OAK model rated at 50,000 BTU states a 20-foot range, a Fire Sense model at 46,000 BTU sits in the 18-foot class, and a Hiland model at 48,000 BTU states a more cautious 10 to 15 feet — three heaters of nearly the same power whose printed circles differ by almost two to one. The mounted electrics, whose makers publish engineering tables instead of marketing copy, are plainer: Bromic rates its Tungsten Electric 4000W at 120 square feet and its 3000W at 100 square feet, Infratech rates its C-3024 at roughly 8 by 8 feet from 7 to 9 feet up, and Dr. Infrared publishes no coverage figure at all for its DR-238. Even 120 square feet is only about 11 feet on a side — nowhere near a 20-foot circle, which would cover more than 300 square feet.

Our methodology therefore treats every coverage claim as the distance at which some warmth can be felt, not the distance at which a guest stays comfortable. Plan around the smaller number: one heater, one table, four to six chairs pulled in close. A second seating group needs a second heater, not a bigger claim.

Two kinds of heat leave a patio heater

According to the U.S. Department of Energy, radiant heating delivers heat directly from a hot surface to the people and objects in front of it via infrared radiation, rather than warming the air first. It feels like sunshine on a cool day: skin and clothes warm while the air stays cold. Electric infrared panels work almost entirely this way, which is why they feel effective outdoors, where no ceiling holds warm air in.

A propane mushroom heater is a hybrid. Its burner and reflector send useful radiant heat outward and down, but a large share of its output simply heats air — and heated air rises, straight up and away. That convective share is the fragile part: indoors it would collect at the ceiling and slowly help; on an open patio it is gone in seconds. Judging a heater means judging how much of its output is radiant and aimed at people, and how much is warm air donated to the night sky.

BTU measures total output, not warmth delivered to you

A BTU rating counts all the heat a burner releases, in every direction, before any is lost upward, sideways or to the wind. It says nothing about how much arrives at your chair. The proof sits in the claims above: heaters at 46,000, 48,000 and 50,000 BTU — a spread of under 10 percent — carry printed circles from 10 feet to 20 feet. If BTU determined coverage, those numbers would move together. They do not, because coverage depends on the reflector's shape, the radiant share, the height, and the conditions the maker chose to assume.

Distance then applies its own tax, the inverse-square rule from the box above: twice as far means one divided by two squared — one quarter the intensity — and three times as far means one ninth. No reflector repeals it. Mounting height is therefore a coverage specification, not an installation detail: Bromic requires a minimum of 96 inches from floor to heater for a ceiling-mounted 4000W unit, and Infratech's 8-by-8-foot figure assumes a mount 7 to 9 feet up. Mount higher and the same watts spread thinner over a wider, cooler pool.

Wind matters more than BTU

Ask owners when a patio heater fails and few say "on the coldest night." They say "on the windy one." Wind strips away the mushroom heater's rising warm air before it can help anyone, and it cools skin and clothing faster than the radiant share can replace the loss, so even infrared warmth feels thinner in a gust. A sheltered patio can make a mid-output heater feel generous; an exposed deck can defeat a 50,000 BTU unit.

Strong gusts can end the evening outright: mushroom heaters carry a thermocouple and flame-failure shutoff, documented safety hardware that cuts the gas when the flame is blown out, so a heater that keeps going out in gusts is reporting that conditions have beaten it. The responses are placement, not power: sheltered side of the seating, walls and screens as windbreaks, chairs pulled into the circle. Our wider Outdoor Living rankings return to this point across categories — outdoors, site conditions usually outrank the spec sheet.

What an evening of warmth costs

The arithmetic is simple. A 20-pound propane tank holds about 4.6 gallons, a refill typically costs $15 to $20, and a big mushroom heater on high burns through it in about 8 to 10 hours — roughly $2 an hour, or $7 to $9 for a four-hour evening. Electric heat is cheaper per hour at the U.S. Energy Information Administration's average residential prices: a 1,500-watt heater uses 1.5 kilowatt-hours an hour, roughly 25 cents, and even a 4,000-watt Bromic flat out stays under $1 an hour. Propane still goes anywhere with no wiring, but over a season of weekends the gap is real money.

At the small end, tabletop heaters rated around 11,000 BTU run on a 1-pound canister for roughly 2 to 3 hours — an honest match of fuel to job for two people sitting close. Expecting one to cover a table of six fails on the inverse-square rule: its comfort zone is the seats immediately beside it.

Plan for one table per heater

Count tables, not square feet: one full-size heater per table of four to six, chairs inside an 8-foot circle, the heater sheltered and as close as its clearance instructions allow. For a mounted electric, trust the maker's table over any diameter claim — roughly 8 by 8 feet for a 3,000-watt Infratech at its stated height, 100 to 120 square feet for the Bromic sizes in our ranking — and treat those as calm, protected-patio figures. When a listing promises a 20-foot circle of warmth, translate it as physics does: a circle in which warmth can be detected, wrapped around the 6-to-8-foot circle in which your guests will actually want to sit.

Sources

• U.S. Department of Energy — Radiant Heating (Energy Saver): radiant systems deliver heat directly from a hot surface to people and objects via infrared radiation: https://www.energy.gov/energysaver/radiant-heating
• U.S. Energy Information Administration — Electric Power Monthly, Table 5.6.A: average price of electricity to residential customers, the basis for the per-hour electric running costs above: https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a
• AmeriGas — Propane Tank Sizes: a 20 lb propane tank holds 4.6 gallons of propane when full and is the standard cylinder for patio heaters: https://www.amerigas.com/about-propane/propane-tank-sizes
• Bromic — Tungsten Smart-Heat Electric manual and specifications, as reflected in AmRank's ranking data: the 4000W model is rated at 120 sq ft and the 3000W at 100 sq ft, heating areas are based on a protected environment at a mounting height of 96 inches, and the 4000W ceiling mount requires a minimum of 96 inches from floor to heater: https://manuals.plus/bromic/bromic-tungsten-smart-heat-electric-heater-manual-tungsten-2000w-tungsten-3000w-tungsten-4000w-tungsten-6000w
• Infratech — C-Series Installation, Use & Care Manual, as reflected in AmRank's ranking data: the C-3024 (3,000W) covers an average area of about 8 x 8 ft at a mounting height of 7–9 ft, with smaller coverage in cold conditions and larger coverage in protected ones: https://manuals.plus/m/095a4c51c5b350cee97124ebd4aee1f559b593ef30ca1d3edb13e61a71a42ea6
• AmRank patio heater ranking: the category's stated coverage figures (EAST OAK RADIATE 50,000 BTU at a stated 20 ft range, Hiland 48,000 BTU at a stated 10–15 ft diameter, Fire Sense 46,000 BTU in the 18 ft class, and Dr. Infrared DR-238 publishing no coverage figure), the verified 6–8 ft comfort circle, tank endurance and running-cost figures, wind and flame-failure notes, and the source FAQ "How many people does one patio heater actually keep warm?": https://americanrankinginstitute.org/rankings/outdoor-living/patio-heaters/