Patio Heater Calculator
Calculate the number and BTU of patio heaters needed for your outdoor space. Enter values for instant results with step-by-step formulas.
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Total BTU requirement is calculated by multiplying the area by the desired temperature increase and a wind exposure factor. The number of heaters is the larger of the BTU-based count or the coverage-area-based count to ensure both sufficient heat output and spatial coverage.
Last reviewed: December 2025
Worked Examples
Example 1: Medium Patio with Propane Heaters
Example 2: Large Restaurant Patio
Background & Theory
The Patio Heater Calculator applies the following established principles and formulas. Structural and construction engineering is governed by fundamental load analysis, material science, and regulatory standards that ensure the safety and durability of built structures. The primary distinction in load analysis is between dead loads โ the permanent self-weight of structural elements, finishes, and fixed equipment โ and live loads, which represent variable occupancy, furniture, and environmental forces such as wind and snow. These are combined using factored load equations, such as the ASCE 7 formula U = 1.2D + 1.6L, where D is dead load and L is live load. Concrete mix design is governed by the water-cement (w/c) ratio, which is the primary determinant of compressive strength and durability. A w/c ratio of 0.40โ0.45 typically yields concrete with 28-day compressive strengths of 30โ40 MPa. Common mix ratios by weight for structural concrete are approximately 1 part cement : 1.5โ2 parts sand : 3 parts coarse aggregate. Structural steel is characterized by its yield strength (the stress at which permanent deformation begins, typically 250โ350 MPa for mild steel) and ultimate tensile strength (typically 400โ500 MPa). Mid-span deflection of a simply supported beam under a central point load is given by ฮด = FLยณ / (48EI), where F is force, L is span length, E is Young's modulus, and I is the second moment of area. Building insulation is rated by R-value, a measure of thermal resistance in units of mยฒยทK/W (SI) or ftยฒยทยฐFยทh/BTU (imperial). Higher R-values indicate greater resistance to heat flow. Foundation design depends on the allowable bearing capacity of the underlying soil, which ranges from approximately 75 kPa for soft clay to over 10,000 kPa for bedrock. Drainage gradients for surface water are typically specified as a minimum of 1โ2% slope away from building foundations to prevent hydrostatic pressure and water infiltration.
History
The history behind the Patio Heater Calculator traces back through the following developments. The history of construction engineering spans thousands of years of accumulated empirical knowledge and, more recently, rigorous scientific analysis. The ancient Egyptians built the Great Pyramid of Giza around 2560 BCE using an estimated 2.3 million stone blocks, demonstrating sophisticated logistics, geometry, and workforce organization. Roman engineers advanced the field dramatically through the use of pozzolanic concrete โ a mixture of volcanic ash, lime, and seawater โ enabling the construction of the Pantheon dome (43.3 m diameter, completed around 125 CE) and a vast network of aqueducts and roads across the empire. Cast iron emerged as a structural material during the Industrial Revolution, first used prominently in the Iron Bridge at Coalbrookdale, England, completed in 1779. Wrought iron and later steel allowed far greater spans and heights. The Eiffel Tower, completed in 1889, demonstrated the structural possibilities of wrought iron at scale and influenced the development of steel-frame skyscraper construction in Chicago and New York. Reinforced concrete was systematically developed by Joseph Monier, a French gardener, who patented iron-reinforced concrete pots and panels in the 1860s, and later by engineers including Franรงois Hennebique who created the first comprehensive reinforced concrete framing system in the 1890s. The 1906 San Francisco earthquake caused widespread devastation and galvanized the engineering profession to develop seismic design provisions. Subsequent earthquakes โ including the 1971 San Fernando and 1994 Northridge events โ drove successive improvements in seismic codes, base isolation technology, and ductile detailing of reinforced concrete and steel frames. Building codes became increasingly standardized in the twentieth century, with the International Building Code (IBC) first published in 2000 providing a unified model code adopted across much of the United States. Building Information Modeling (BIM) emerged in the 2000s as a digital workflow integrating architectural, structural, and MEP design into a unified three-dimensional model, fundamentally changing coordination practices across the industry.
Frequently Asked Questions
Formula
BTU Needed = Area (sq ft) x Temp Rise x Wind Factor x Roof Factor | Heaters = max(BTU/Heater BTU, Area/Coverage)
Total BTU requirement is calculated by multiplying the area by the desired temperature increase and a wind exposure factor. The number of heaters is the larger of the BTU-based count or the coverage-area-based count to ensure both sufficient heat output and spatial coverage.
Worked Examples
Example 1: Medium Patio with Propane Heaters
Problem: Calculate heaters needed for a 20 x 15 foot open patio, wanting a 20-degree temperature rise with moderate wind, using 46,000-BTU propane heaters.
Solution: Area: 20 x 15 = 300 sq ft\nBTU needed: 300 x 20 x 3.0 (moderate wind) = 18,000 BTU\nHeaters by BTU: 18,000 / 46,000 = 1 (rounded up)\nHeaters by coverage: 300 / 314 = 1 (rounded up)\nHeaters needed: 1 (BTU and coverage both suggest 1)\nNote: For better coverage, 2 heaters recommended
Result: 1-2 heaters at 46,000 BTU each | ~$1.60/hr operating cost
Example 2: Large Restaurant Patio
Problem: Calculate for a 40 x 25 foot exposed patio, 25-degree rise, using 46,000-BTU propane heaters at $250 each.
Solution: Area: 40 x 25 = 1,000 sq ft\nBTU needed: 1,000 x 25 x 4.0 (exposed) = 100,000 BTU\nHeaters by BTU: 100,000 / 46,000 = 3 (rounded up)\nHeaters by coverage: 1,000 / 314 = 4 (rounded up)\nHeaters needed: 4\nEquipment: 4 x $250 = $1,000
Result: 4 heaters needed | $1,000 equipment | ~$6.40/hr operating cost
Frequently Asked Questions
How many BTUs do I need for my patio?
The BTU requirement for outdoor heating depends on the area size, desired temperature increase, and wind exposure. A general rule is to provide 10 to 20 BTUs per square foot for sheltered areas and 30 to 40 BTUs per square foot for open, windy locations. For a typical 200-square-foot covered patio, you need approximately 4,000 to 8,000 BTUs. For an open 300-square-foot space wanting a 20-degree temperature rise, you may need 18,000 to 24,000 BTUs. Standard standing propane patio heaters produce 40,000 to 48,000 BTUs each, which is enough to heat a 20-foot diameter circle in moderate wind conditions. Always overestimate rather than underestimate because you can turn heaters down but cannot make an undersized heater produce more heat.
What type of patio heater is most efficient?
Infrared electric heaters are the most energy-efficient option because they heat objects and people directly rather than heating the air, which means wind does not immediately disperse the warmth. They convert about 90 percent of their energy input into radiant heat. Natural gas patio heaters are the most cost-efficient for frequent use because piped natural gas costs significantly less per BTU than propane or electricity. Propane standing heaters are the most versatile since they require no utility connections and can be moved freely. Electric heaters are best for covered patios and small spaces where running natural gas lines is impractical. For large open areas, multiple infrared heaters positioned strategically provide better coverage than fewer large propane heaters.
How much does it cost to run a patio heater?
Operating costs vary significantly by fuel type. A standard 46,000-BTU propane patio heater consumes approximately 2 pounds of propane per hour, which costs about 1.50 to 2.00 dollars per hour based on current propane prices. A 20-pound propane tank costs 15 to 20 dollars to refill and lasts approximately 8 to 10 hours at full output. Natural gas heaters cost about 0.50 to 1.00 dollars per hour because piped gas is cheaper per BTU than bottled propane. Electric heaters running at 1,500 watts cost approximately 0.18 to 0.30 dollars per hour depending on your electricity rate. Over a six-month season using the heater four hours per week, annual costs range from 50 to 200 dollars for electric to 200 to 500 dollars for propane.
How far apart should patio heaters be placed?
Patio heaters should be spaced based on their effective heating radius, which varies by type and BTU output. Standard 46,000-BTU standing propane heaters heat an area approximately 15 to 20 feet in diameter, so place them 15 to 18 feet apart for overlapping coverage. Tabletop heaters with 10,000 to 12,000 BTUs have a heating radius of only 4 to 6 feet. Wall-mounted infrared heaters cover 10 to 16 feet wide depending on mounting height and wattage. Position heaters so that their coverage circles overlap by about 20 percent to eliminate cold spots between units. Place heaters near the seating areas rather than at the edges of the space, and consider that wind will push heat in one direction.
Can I use a patio heater under a covered patio?
Electric and infrared patio heaters can safely be used under covered patios and are specifically designed for this purpose. Wall-mounted and ceiling-mounted electric models are ideal for covered spaces because they take up no floor space and direct heat downward. Propane and natural gas heaters require more caution under covered structures due to combustion gases and fire risk. Standing propane heaters should have at least 3 feet of clearance from the ceiling or any overhead surface. Never use unvented gas heaters in enclosed or poorly ventilated spaces because carbon monoxide buildup is extremely dangerous. Many covered patio installations use hanging electric infrared heaters that provide efficient, safe, odorless heat without open flames or combustion concerns.
How long does a propane tank last in a patio heater?
A standard 20-pound propane tank lasts approximately 8 to 10 hours in a full-size 46,000-BTU patio heater running at maximum output. At medium heat settings, the same tank can last 12 to 15 hours. Tabletop heaters using 1-pound disposable canisters last 3 to 5 hours per canister. The burn rate is calculated by dividing the BTU output by 21,600 BTUs per pound of propane. So a 46,000-BTU heater burns approximately 2.1 pounds per hour. You can extend tank life by using lower heat settings when temperatures are mild and turning heaters off during breaks in outdoor entertaining. Buying propane in bulk through tank exchange programs costs about 3 to 4 dollars per gallon versus 4 to 5 dollars per gallon at convenience stores.
References
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