What Size Patio Heater Do I Need? Heaters by Patio Size and Hours per Propane Tank

One 46,000 BTU tower heater on a 16 × 24 ft deck warms about two-thirds of it. The maker says it heats an 18-foot circle, which is 254 sq ft, and the deck is 384.

Quick pick: count heaters by heat circle, not BTU per square foot. Use the smallest coverage figure the maker gives, and plan on about 9 hours of high heat per 20 lb tank.

What size patio heater do I need

Heaters by area (minimum), plus heaters to put every corner inside a circle. Amazon Basics 46,000 BTU spec, 18 ft circle (254 sq ft):

10 × 12 ft patio (120 sq ft): 1 minimum, 1 full coverage

12 × 16 ft patio (192 sq ft): 1 minimum, 2 full coverage

16 × 20 ft deck (320 sq ft): 2 minimum, 3 full coverage

16 × 24 ft deck (384 sq ft): 2 minimum, 3 full coverage

20 × 30 ft patio (600 sq ft): 3 minimum, 6 full coverage

Maker claims vary a lot. Mr. Heater says its 48,000 BTU tower "heats up to 1,200 square feet," almost five times the Amazon Basics circle for nearly the same BTU. Plan on the smaller number.

The math, step by step

☐ Patio area = length × width. 16 × 24 = 384 sq ft.

☐ Heat circle = 3.14 × radius × radius. 18 ft across means a 9 ft radius: 3.14 × 9 × 9 = 254 sq ft.

☐ Heaters = patio area ÷ heat circle, rounded up. 384 ÷ 254 = 1.5, so 2 at minimum.

☐ Full coverage: Slice the deck across its long side into equal strips that span the full width (if the width is over 18 ft, split it in half too). One heater in the center of each piece. A piece is covered when its diagonal is 18 ft or less. 16 × 24: two 12 × 16 strips = 20 ft, three 8 × 16 = 17.9 ft, so 3. 20 × 30: four 10 × 15 cells = 18.03 ft, six 10 × 10 = 14.1 ft, so 6.

☐ Tank energy = 4.6 gallons × 91,452 BTU = 420,679 BTU.

☐ Hours on high = tank energy ÷ heater BTU per hour. 420,679 ÷ 46,000 = 9.1 hours.

How long a 20 lb tank lasts

AmeriGas says a full 20 lb grill tank holds 4.6 gallons; the EIA puts propane at 91,452 BTU per gallon.

46,000 BTU on high: 9.1 hours

48,000 BTU on high: 8.8 hours

18,000 BTU heater: 23.4 hours

Party example: two 46,000 BTU heaters for 3 hours burn 276,000 BTU, 66% of one tank. Bring a spare.

Covered patio? Read this first

From the Amazon Basics manual (the heater linked below):

☐ Keep 3 ft from combustibles on all sides and 3 ft above the top. Plants and awnings count. The heater is 91.3 in tall, so a roof must be about 10.6 ft up.

☐ Outdoors only, never in a building, garage or other enclosed area.

☐ Covered areas: walls on all sides with no overhead cover; or a roof with no more than two side walls; or a roof and three walls if 30% or more of the wall edge is permanently open.

☐ Not above 2,000 ft altitude. Wind under 10 mph, so it won't tip.

☐ Carbon monoxide: never in a camper, tent, car or home.

Electric instead of propane

A 1,500 W electric heater puts out 5,118 BTU per hour (EIA: 1 kWh = 3,412 BTU), about a ninth of a tower heater. It costs about 27 cents an hour at the U.S. average rate of 18.16 cents per kWh (EIA, August 2026).

Propane and electric heaters (#ad)

As an Amazon Associate, Curb Calc earns from qualifying purchases.

Amazon Basics 46,000 BTU Outdoor Propane Patio Heater: heats up to an 18 ft circle, with a tilt shut-off valve and a water box for the base, per the maker. Uses a 20 lb tank (not included). Not for use above 2,000 ft. See it on Amazon

Dr Infrared Heater DR-222, 1500W: carbon infrared, wall or ceiling brackets, rated for indoor and outdoor installs, per the maker. See it on Amazon

Patio heater FAQ

Can I use a propane patio heater on a covered porch?

Only under the manual's rules. Amazon Basics allows a roof with no more than two side walls, plus 3 ft clear on all sides and above (a roof about 10.6 ft up).

How many heaters for a 16 x 24 ft deck?

At least two; three to put every corner inside the 18 ft circle.

Firewood instead? Firewood for winter. Building the patio first: paver calculator. All tools: calculators.

Watch Curb Calc on YouTube: youtube.com/@curbcalc

Sources: Amazon Basics heater manual; Mr. Heater; AmeriGas; EIA BTU units; EIA Table 5.6.A, Oct. 23, 2026.