How Many Patio Heaters Do I Need? Size Calculator for Watts, BTU and Mounting Height
Quick answer
Plan on about 40 watts per square foot for an electric heater or 240 BTU per square foot for gas on a covered patio. Add about a quarter more for a partly open space and about half more for an open patio with moderate wind. Most mounted heaters cover 64 to 144 square feet each, so a 12 x 16 ft. seating area usually needs two.
Sizing comes down to three numbers: the area you actually sit in, how much heat it needs, and how high you can mount the heater. Electric models are rated in watts and gas models in BTU per hour. Use the size calculator below, then read on for the rules behind it, mounting heights and winter use.
Patio Heater Size Calculator
Enter your seating area, fuel, setting and mounting height. Results update as you type.
How much heat does your patio need?
Results show watts for electric, BTU for gas, the number of heaters and the mounting height.
192Square feet
7,700 WHeat needed
2Heaters
2 x Infratech 61 in. Single Element 4000W, mount at 8 to 11 ft.
Each is rated for about 100 sq. ft. Total 8,000 watts, about 16.7 amps per heater at 240V, roughly $1.46 per hour for both at full power.
The calculator uses rules of thumb built from the coverage ratings in our product listings. Wind, cold and layout change real results, so use it as a starting point and check the manual for your exact model.
Step 1: Measure the Area You Actually Sit In
Heat the seating, not the whole patio. Measure each seating zone, multiply length by width, and size a heater for each zone.
- Multiply length by width for square feet
- Size a dining table and a lounge as separate zones
- Skip the grill area. The cook is already warm
Electric Patio Heaters: Watts per Square Foot
Electric heaters are rated in watts. To size one, multiply your seating area in square feet by the watts each square foot needs. Infratech rates its 4000 watt heater for a 10 x 10 ft. area, which is about 40 watts per square foot under a roof. Open sides and wind need more.
Electric heater sizing at a glance
Square feetxWatts per sq. ft.=Watts you need
Covered patio
40watts per sq. ft.Solid roof with one or more walls.
12 x 12 ft. patio: about 5,800 WPartly open
50watts per sq. ft.Pergola roof or open on most sides.
12 x 12 ft. patio: about 7,200 WOpen patio
60watts per sq. ft.No roof, with a moderate breeze.
12 x 12 ft. patio: about 8,600 WElectric heater sizes we carry
Infratech 39 in. Single Element
2,500 W
Coverage64 sq. ft. (8 x 8 ft.)
Mounting height7 to 9 ft.
Best forA bistro table or bar seating for 2 to 4. Fits lower porch ceilings.
Infratech 61 in. Single Element
4,000 W
Coverage100 sq. ft. (10 x 10 ft.)
Mounting height8 to 11 ft.
Best forThe go-to size for a 6-seat dining table under a covered patio.
6,000 W
Coverage121 sq. ft. (11 x 11 ft.)
Mounting height9 to 12 ft.
Best forHigher ceilings and larger lounge or dining areas.
Bromic Platinum Smart-Heat 3400W
3,400 W
Coverage108 sq. ft.
Mounting height8 ft. min. ceiling, 6 ft. min. wall
Best forA slim, low-profile look on modern patios, with Smart-Heat controls.
Bromic Tungsten Smart-Heat 4000W
4,000 W
Coverage130 sq. ft.
Mounting height8 ft. minimum
Best forBigger coverage per heater, with a mirror-finish reflector that pushes heat forward.
Bromic Tungsten Smart-Heat 6000W
6,000 W
Coverage160 sq. ft.
Mounting height8 ft. minimum
Best forLarge dining areas and restaurant patios that need the most heat per heater.
Compare the two brands in our Bromic vs Infratech guide, or see our picks for the best electric patio heaters. Most electric patio heating runs on a dedicated 240V circuit. Watts divided by 240 equals amps, so a 4000 watt outdoor heater draws about 16.7 amps. Our Infratech wiring and controls guide covers breakers and switches.
Gas Patio Heaters: BTU per Square Foot
Gas heaters are sized by heater BTU per hour. Sunpak and SunStar both rate their 34,000 to 35,000 BTU models for a 12 x 12 ft. area, which is about 240 BTU per square foot. Bromic rates its burners for a little more area per BTU, so 240 is a safe number to plan with. The same math works for natural gas and propane.
Gas heater sizing at a glance
Square feetxBTU per sq. ft.=BTU you need
Covered patio
240BTU per sq. ft.Solid roof with one or more walls.
12 x 12 ft. patio: about 35,000 BTUPartly open
300BTU per sq. ft.Pergola roof or open on most sides.
12 x 12 ft. patio: about 43,000 BTUOpen patio
360BTU per sq. ft.No roof, with a moderate breeze.
12 x 12 ft. patio: about 52,000 BTUGas heater sizes we carry
35,000 BTU
Coverage144 sq. ft. (12 x 12 ft.)
Mounting height7 to 10 ft.
Best forCovered residential patios. Natural gas or propane, with a glass face rated for winds up to 40 mph.
50,000 BTU
Coverage144+ sq. ft.
Mounting height8 to 11 ft.
Best forOpen, windy patios and colder climates. 43% more heat than the SGL35.
34,000 BTU
Coverage144 sq. ft. (12 x 12 ft.)
Mounting height9 ft. minimum
Best forHigher ceilings, with a slim 48 in. body that mounts flat or at up to a 30 degree angle.
26,000 BTU
Coverage160 sq. ft.
Mounting height8 ft. minimum
Best forMid-size patios that want smart controls and a wall, ceiling or pole mount.
43,000 BTU
Coverage215 sq. ft.
Mounting height8 ft. minimum
Best forThe most coverage per heater here. Restaurants, bars and large dining patios.
39,800 BTU
Coverage215 sq. ft.
Mounting height8 ft. minimum
Best forUpscale outdoor rooms that want a sleek gas heater with large coverage.
Every heater above comes in natural gas or propane. Shop all gas patio heaters, natural gas heaters or propane heaters.
How Many Heaters by Patio Size
These estimates are for a covered patio using the 4000 watt Infratech for electric and the 35,000 BTU SunStar for gas. For a partly open or open patio, run your numbers through the calculator.
10 x 10 ft.
100 sq. ft.
Electric4,000 W
4000W heaters1
Gas24,000 BTU
35K BTU heaters1
12 x 12 ft.
144 sq. ft.
Electric5,800 W
4000W heaters2
Gas35,000 BTU
35K BTU heaters1
12 x 16 ft.
192 sq. ft.
Electric7,700 W
4000W heaters2
Gas46,000 BTU
35K BTU heaters2
16 x 20 ft.
320 sq. ft.
Electric12,800 W
4000W heaters4
Gas77,000 BTU
35K BTU heaters3
20 x 20 ft.
400 sq. ft.
Electric16,000 W
4000W heaters4
Gas96,000 BTU
35K BTU heaters3
20 x 30 ft.
600 sq. ft.
Electric24,000 W
4000W heaters6
Gas144,000 BTU
35K BTU heaters5
Let heat zones overlap a little at the edges. Two heaters on opposite sides of a table feel warmer than two side by side. For layouts under a roof, see our guide to covered patio, porch and pergola heaters.
Mounting Height for Each Heater
Too low and the heater feels hot on your head. Too high and the warmth spreads thin before it reaches you. Most heaters land between 8 and 10 ft., and higher output models need more height.
Electric heaters
Heater
Output
Coverage
Mounting height
Gas heaters
Heater
Output
Coverage
Mounting height
If your ceiling is higher than the range, a drop-down bracket or suspension kit brings the heater down to the right height. Browse patio heater mounting brackets and wall and ceiling mounted heaters.
Covered Patio vs Open Patio and Wind
A covered patio holds warmth, so the base sizes work and electric heaters are usually the best fit. An open patio loses heat to wind and open sky, so plan on about half more heat, mount low in the range, or step up to a wind-rated gas heater.
Covered patio
VSOpen patio
Covered patio
Heat needed
Base size: 40 W or 240 BTU per sq. ft.
Best heaters
Electric, like Infratech or Bromic. Gas works with the right clearance and airflow.
Mounting
Ceiling or flush mount, 8 to 10 ft.
Watch for
Ceiling clearances in the manual, and fans blowing across the heater.
Our guide to a patio heater under a covered patio explains the options.
Open patio
Heat needed
About 50% more: 60 W or 360 BTU per sq. ft.
Best heaters
High output gas, like the SunStar SGL50 or Bromic Tungsten 500.
Mounting
Wall or post, toward the low end of the range.
Watch for
Steady wind. Screens, curtains or planters help more than a bigger heater.
For restaurants and bars, see our commercial patio heaters.
Do Patio Heaters Work in Winter?
Yes. Outdoor heaters work in winter because infrared warms you directly, the same way the sun feels warm on a cold, clear day. They will not make a patio feel like a living room in January, but they take the edge off and add real comfort.
Do patio heaters work below freezing?
They still work, but plan for it. Wind chill pulls more warmth away than the temperature alone.
- Size up about a quarter, or tick the freezing weather box in the calculator
- Mount toward the low end of the range
- Heat people from two sides
- Block the wind with screens or curtains
Propane in cold weather
Propane turns from liquid to vapor inside the tank, and that slows in the cold. In very cold weather a portable tank loses pressure and the heater runs weaker. Keep a spare tank handy. Natural gas and electric heaters are not affected, which makes them the steadier choice for regular winter use.
Running Cost and Fuel Use
Electric cost is easy to work out: kilowatts x hours x your rate. At the EIA forecast US average of about 18 cents per kWh for 2026, here is what each size costs at full power.
- 2500 watts: about 46 cents per hour
- 4000 watts: about 73 cents per hour
- 6000 watts: about $1.09 per hour
Gas use depends on BTU. A 35,000 BTU heater burns about 0.35 therms of natural gas per hour, or about 0.38 gallons of propane, since a gallon of propane holds roughly 91,500 BTU. Sunglo rates a 20 lb. tank at about 6 hours on its 40,000 BTU portable heater. Two-stage gas heaters and electric dimmers cut fuel use once everyone is warm.
Accessories and Heater Parts
A good control lets you run on low most of the night, and a cover protects the heater off season.
- Mounting brackets to hit the right height on high ceilings
- Infratech and Bromic switches, dimmers and smart controls
- Covers and heater parts for upkeep and replacements
- Patio heater accessories, including timers and wind shields
Want us to check your numbers?
Send us your seating area size, mounting height and fuel. We will confirm the heater count and placement for your outdoor space.
Get expert helpShop all patio heatersFrequently Asked Questions
How many BTUs do I need for my patio heater?
Plan on about 240 BTU per square foot for a covered patio. A 12 x 12 ft. area needs about 35,000 BTU. Add about a quarter more for a partly open patio and about half more for an open, windy one.
How much area does a patio heater cover?
Most mounted heaters cover 64 to 144 square feet. A 2500 watt Infratech covers about 8 x 8 ft., a 4000 watt covers 10 x 10 ft., and a 35,000 BTU SunStar or 34,000 BTU Sunpak covers about 12 x 12 ft.
What size patio heater do I need for a covered patio?
Multiply the seating area in square feet by 40 for electric watts or by 240 for gas BTU. A 12 x 16 ft. covered patio needs about 7,700 watts, which is two 4000 watt heaters.
How many watts do I need to heat a patio?
About 40 watts per square foot under a roof. A 10 x 10 ft. area needs about 4000 watts. Open or windy patios need roughly 50 to 60 watts per square foot.
Do patio heaters work in winter?
Yes. Infrared heaters warm people directly, so they work in cold weather. They take the edge off rather than making it feel indoors. Block the wind and size up for the best results.
Do patio heaters work below freezing?
Yes, but plan for about a quarter more heat, mount toward the low end of the range and block the wind. Portable propane tanks lose pressure in very cold weather, while natural gas and electric heaters are not affected.
How high should a patio heater be mounted?
Most mounted heaters go between 7 and 12 ft. Smaller electric heaters start at 7 ft., 4000 watt models run 8 to 11 ft., and 6000 watt models need 9 to 12 ft. Always follow the manual for your model.
