Sizing

How many patio heaters do I need?

Almost everyone works this out from total output, and total output is the wrong variable. The count is a geometry problem.

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The natural way to size a patio is to compute what the area needs and divide. On the 20 BTU per square foot baseline this site uses for an open patio in mild conditions, a 400 sq ft patio wants about 8,000 BTU/h — so a single 46,000 BTU tower looks like nearly six times enough, and you would conclude one heater covers it comfortably.

It does not, and the reason is that the arithmetic assumes the heat distributes evenly across the space. Outdoors it does not distribute at all. There is no envelope to hold warm air, so what reaches you is radiant — the heater's infrared output landing directly on you — and radiant intensity falls off sharply with distance from the source.

Which means a 46,000 BTU tower does not warm 400 square feet. It warms the circle it can reach, very effectively, and does approximately nothing outside it. That circle is what you are counting.

The table above is the whole argument in one place: a published radius sounds generous until it is converted into an area, and then it turns out that even a good reach figure covers a seating group rather than a patio. The coverage page works through why makers publish the figure they do.

So the useful question is not how many square feet you have. It is how many separate places people sit, and how far apart they are.

Quick picks

Ranked for fit, not for hype. Output is the maker’s published figure; reach is computed from it or from the maker’s own radius claim, and the table says which. Tap a row for the full write-up, or go straight to the listing.

#	Product	Best for	Output	Reach	Price
1	Dr Infrared 1500 WRadiant heat that a breeze cannot blow out, on a plug. 1,500 W is only 5,118 BTU/h, which sounds like nothing next to a propane tower and lands far more of itself on you.	Wind, and anywhere with a roof	1,500 W	256 sq ft	$148.98 · Check on Amazon
2	Amazon Basics 46kOne of the very few towers whose maker publishes a coverage radius rather than a vague area, and the 9 ft figure survives the arithmetic. That alone puts it ahead of most of the field.	The published-radius honesty test	46,000 BTU	254 sq ft claimed	$156.16 · Check on Amazon
3	Star Patio STP2020-AOne of the very few electric units whose maker publishes a coverage area at all — 110 sq ft — and it mounts to a wall or hangs from a ceiling on chains. No ingress rating is published, so keep it somewhere sheltered.	A published coverage figure	1,500 W	110 sq ft claimed	$199.99 · Check on Amazon

Reach marked “claimed” is the maker’s own published figure. Reach without that label is ours, computed from published output at 20 BTU per square foot for an open patio. Neither is a measurement we took.

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Top pick · Wind, and anywhere with a roof

Dr Infrared Heater DR-238 Carbon Infrared Patio Heater with Kasa Outdoor Smart Plug

Radiant heat that a breeze cannot blow out, on a plug. 1,500 W is only 5,118 BTU/h, which sounds like nothing next to a propane tower and lands far more of itself on you.

Fuel

Electric

Output

1,500 W = 5,118 BTU/h

Reach (computed)

256 sq ft · 9.0 ft radius

Cost per hour

$0.28

Reach is ours, computed from published output at 20 BTU per square foot for an open patio. Cost at 18.34 cents per kWh. We have not measured any of this in person.

What works

• Infrared warms objects, not air, so it is the only heat that survives a breeze — this is the single reason wind changes the whole buying decision
• No combustion means no flue gas, which is what makes it legal and sensible on a screened porch where propane is not
• Three settings matter more than they sound: 900 W costs a third less to run and is enough most evenings

What does not

• 1,500 W is 1,500 W. Nothing at this wattage heats faster than anything else at this wattage; the differences between electric heaters are beam shape and build, not power
• It heats what it points at. Step out of the beam and you are cold immediately — this is a fundamentally different experience from a tower
• A 120 V plug-in unit is capped by your circuit, not by the maker. See why 1,500 W is the ceiling

Published specification
Rated power	1,500 W at 120 V
Settings	900 W / 1,200 W / 1,500 W
Element	Carbon infrared lamp
Reflector	Mirror aluminum, 90% reflectivity per the maker
Housing	Anodized aluminum, rated for outdoor use
Mounting	Wall and ceiling brackets plus remote in the box
Bundle	Currently sold with a Kasa EP40 outdoor smart plug
Maker’s coverage claim	None published — the reach figure above is ours
Safety listing	ETL listed, per the maker's published product data

Who it is for

A covered patio, pergola or screened porch where you can mount it overhead and point it at where people sit, and anywhere wind ruins a flame.

What it is not for

A big open patio with nowhere to mount it. Radiant heat needs a line of sight and a place to hang from.

$148.98 · Check on Amazon

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Sources for this entry

• Amazon listing — Dr Infrared DR-238 carbon infrared heater bundled with a Kasa EP40 outdoor smart plug
• Dr. Infrared Heater — DR-238 published specification

2 · The published-radius honesty test

Amazon Basics 46,000 BTU Outdoor Propane Patio Heater

One of the very few towers whose maker publishes a coverage radius rather than a vague area, and the 9 ft figure survives the arithmetic. That alone puts it ahead of most of the field.

Fuel

Propane

Output

46,000 BTU/h

Reach (claimed)

254 sq ft · 9.0 ft radius

Cost per hour

$1.35

Reach is the maker's own published claim, quoted rather than endorsed. Cost at $2.674 per gallon of propane. A 20 lb cylinder runs it about 9.4 hours at full output. We have not measured any of this in person.

What works

• A published 9 ft radius is a 254 sq ft circle, and 46,000 BTU is far more than that area needs — a claim on the conservative side of its own specification, which is rare here
• The water-fill base box is a real anti-tip measure, not a sticker: filled, it is the difference between a windy evening and a repair bill
• One-touch ignition and a chain for the cylinder are both small things the cheap clones drop

What does not

• The listing does not name a safety certifying body, only the tilt valve, so we cannot tell you it is CSA listed
• 91 in tall with an open flame: the same wind exposure as every other tower of this shape
• The water box has to be emptied before a freeze or it splits

Published specification
Rated input	46,000 BTU/h
Published reach	9 ft radius
Dimensions	32.1" L x 32.1" W x 91.3" H
Fuel	20 lb propane cylinder, not included
Safety	Tilt auto-shutoff valve; chain to secure the cylinder
Base	Water-fill box for ballast, wheel kit included
Maker’s coverage claim	9.0 ft radius, which is 254 sq ft
Safety listing	Tilt auto-shutoff valve; the listing does not name a certifying body

Who it is for

An open patio where you want the largest honest circle of warmth per dollar and are happy to handle cylinders.

What it is not for

Anywhere enclosed, and anywhere the base cannot be filled with water — an empty ballast box makes this a tall, light, tippy object.

$156.16 · Check on Amazon

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Sources for this entry

• Amazon listing — 46,000 BTU, 9-foot radius, dimensions and safety features

3 · A published coverage figure

Star Patio STP2020-A-RMN2025 Wall and Ceiling Electric Infrared Patio Heater

One of the very few electric units whose maker publishes a coverage area at all — 110 sq ft — and it mounts to a wall or hangs from a ceiling on chains. No ingress rating is published, so keep it somewhere sheltered.

Fuel

Electric

Output

1,500 W = 5,118 BTU/h

Reach (claimed)

110 sq ft · 5.9 ft radius

Cost per hour

$0.28

Reach is the maker's own published claim, quoted rather than endorsed. Cost at 18.34 cents per kWh. We have not measured any of this in person.

What works

• It publishes a coverage figure. 110 sq ft is a real, checkable claim, and almost nobody in this category states one at all — which is the whole subject of our coverage page
• Wall bracket and ceiling chains both in the box, with 60 degrees of tilt, so the beam can actually be aimed at the chairs rather than at whatever the bracket decided
• 5,100 BTU/h published output is within a rounding error of the 5,118 our watts-to-BTU conversion gives, which is a maker doing its own arithmetic honestly
• Remote control on a unit mounted above head height is functional rather than a luxury

What does not

• No ingress rating is published for this model. Other units in this roundup publish one, and on a permanently mounted outdoor appliance that silence means you cannot price the weather risk. Treat it as a sheltered-position heater
• 110 sq ft is a small area — roughly a 10 by 11 ft patch, which is a seating group and not a patio
• 1,500 W, like everything else that plugs into a standard socket. The ceiling applies here as everywhere
• A 6 ft cord means the outlet has to be close, or an outdoor-rated extension has to be part of the plan

Published specification
Rated power	1,500 W at 110 V, 60 Hz
Published output	5,100 BTU/h per the maker
Published coverage	Up to 110 sq ft per the maker
Element	Golden tube
Mounting	Wall bracket or ceiling chains, up to 60 degrees of tilt
Size and weight	27.5 x 7 x 5.7 in, 7.7 lb
Element life	5,000 hours per the maker
Maker’s coverage claim	110 sq ft
Safety listing	No ingress rating published for this model

Who it is for

A sheltered wall or porch ceiling over a seating group, where you want a heater whose maker will tell you what area it actually covers.

What it is not for

An exposed wall where driving rain reaches it, since nothing is published about ingress protection, or any space much larger than a seating group.

$199.99 · Check on Amazon

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Sources for this entry

• Amazon listing — Star Patio STP2020-A-RMN2025 wall mounted and ceiling heater with remote

Where two seating areas exist, this is the real question, and the answer is consistent enough to state flatly: two smaller heaters beat one bigger one nearly every time.

• Aim beats output. Two units pointed at two groups put heat where people are. One unit between them heats the gap.
• Overlap is where the comfort is. Where two circles cross, you get radiant heat from two directions, which is noticeably more comfortable than the same total from one side — it is why restaurant terraces run several modest units rather than one large one.
• Redundancy. One heater failing in October means an unusable patio. Two means a smaller circle while you order a part.
• Turn-down. Two units is a low setting: run one for two people and both for a full table. A single large heater has no equivalent, and this is where a meaningful part of the running-cost saving comes from.

The exception is an open patio with no shelter and no power. There, output genuinely is the constraint, the 1,500 W ceiling rules electric out, and one propane tower is the answer rather than two of anything.

Placement decides more of the outcome than the purchase does, and the rules are short.

1. 1Opposite sides of the seating, not opposite corners of the patio. You want the two circles to overlap over the chairs, which means the units are closer together than most people place them.
2. 2Upwind first. If one position is more exposed, the heater goes there — the sheltered side is already doing better without help. Watch which way the air actually moves before deciding, because patios rarely behave like the forecast.
3. 3Different heights if you can. One mounted overhead and one at standing height covers seated and standing people differently, which is why terraces mix mounting types rather than buying two of the same.
4. 4Not pointing at each other. Two units facing across a gap heat the gap. Angle both inward toward where people are and accept that it looks less symmetrical.

Worth doing before rather than after, because the second unit doubles the number that matters over a season.

Two 1,500 W electric units are about 56 cents an hour together, which across a 20-week season at three evenings a week of four hours is roughly $100. Two propane towers are nearer $2.70 an hour and about $500 across the same season, plus the cylinder handling doubled.

That gap is the strongest practical argument for putting a roof over at least part of the patio, because a roof is what makes the electric option viable and the electric option is what makes two heaters affordable. The season-cost page has the full working.

Everything above assumes open sky. Put a roof over the seating and the arithmetic shifts, because a covered space does retain some warmed air rather than losing all of it upward — which is the one condition where added output behaves a little more like indoor heating.

In practice that usually means one well-aimed mounted unit does a job that would need two on the same footprint outdoors, and it means electric becomes viable where it was not. The covered patio page covers the specifics. It does not mean a covered patio behaves like a room — the sides are still open and most of the warmth still leaves — but it moves the count in your favor rather than against it.

One heater per seating group, aimed at people rather than centered in the space, with the circles overlapping where the chairs are. If that means two, buy two modest units rather than one large one. If the patio is too spread out for two to cover, move the furniture before buying a third — it works better and it is free.