Electric Patio Heater BTU to Watt Conversion Chart (2026): Infratech, Bromic, Heatstrip

The one formula you need: watts × 3.412 = BTU per hour

Multiply any electric patio heater's wattage by 3.412 to get its BTU per hour rating. That's the whole conversion. It's defined by the SI unit relationship between watts and BTU, so it's exact. The only reason you'll see a brand like Bromic publish 15,300 BTU for a 4,500W unit instead of 15,354 is rounding.

Where gas and electric diverge isn't the formula, it's the share of input that reaches a seated guest. Gas heaters burn fuel below an open flame, which dumps a meaningful chunk of BTU into rising hot air before it ever hits the radiant zone. Electric infrared converts near-100% of its input to radiant and convective heat, and the beam is aimed. That's why a 15,354 BTU electric infrared heater can heat the same footprint as a 40,000 BTU propane heater on a sheltered patio. The spec sheets look mismatched; the warmth at the chair is closer than the numbers suggest.

For planning, I treat electric infrared as roughly 2 to 2.5 times more efficient per rated BTU than freestanding propane for a seated group. That's a working rule, not a published figure, and it swings with wind, mount height, and whether a solid roof catches the rising warmth.

Full watt-to-BTU conversion chart

Here's the chart most sizing pages don't publish. Common patio-heater wattages on the left, exact BTU/h on the right, and the real-world amp draw on 240V that you'll need to plan a circuit around.

What Infratech, Bromic and Heatstrip actually publish

Infratech, Bromic and Heatstrip all publish watts as the primary rating and treat BTU as a secondary number, if they list it at all. Here's what every current firepits.com electric patio heater converts to, with coverage claims included so you can size one correctly.

Infratech wattage ranges by series

Infratech's electric infrared lineup spans 1,500W to 6,000W across the W, SL/Slimline, C, and CD series. The dividing line is single-element versus dual-element. Single-element units hit 2,400W to 3,000W. Dual-element units (the CD series) pair two elements on one housing for 3,000W to 6,000W total output in a single mounted unit.

Two models most buyers compare:

Infratech Slimline Series 42.5-inch 2,400W is single element, 8,189 BTU/h, draws 10A at 240V. The compact mounted option when the seating zone is roughly 7 by 7 feet. Fits on a 15-amp dedicated circuit.

Infratech CD-Series 33-inch 3,000W Dual Element is twin elements on one housing, 10,236 BTU/h, draws 12.5A at 240V. The jump to 3,000W buys you about 25% more coverage from a shorter housing than a 2,400W single-element, which matters for pergolas where mounting length is tight.

Bromic: Platinum, Tungsten, Eclipse and Cobalt

Bromic organizes its electric lineup into four families with distinct wattages:

Platinum Smart-Heat is the flagship. Offered in 2,300W, 3,400W, and 4,500W, all 240V (208V variants available for commercial applications). The 4,500W Platinum is the headline model at 15,354 BTU/h with 143 sq ft of published coverage. The 3,400W hits 11,601 BTU/h and covers about 108 sq ft, and the 2,300W hits 7,848 BTU/h at 75 sq ft.

Tungsten Smart-Heat is the 4,000W Tungsten, the design-forward fixture, slimmer housing, 13,648 BTU/h, 130 sq ft coverage. Nearly identical warmth to the top Platinum in a cleaner installation profile for pergolas and architectural beams.

Eclipse Smart-Heat is the pendant or portable form factor. The Eclipse 2,900W portable at 9,895 BTU/h plugs into a 240V outlet and rolls where it's needed. Not hardwired, which is the whole point: you can test placement before committing.

Cobalt Smart-Heat is the Cobalt dual-element infrared heater, Bromic's compact dual option. Positioned for tighter installs where a Platinum won't fit on the mounting surface.

Heatstrip single wattage with app controls

The Heatstrip Classic 54-inch 2,400W is the easy pick when you want app control and a remote on a 2,400W / 8,189 BTU/h mounted heater. 240V. One SKU, well-tuned. Pairs well for a two-zone covered patio when a single 4,500W unit won't reach both seating groups.

How watts translate to coverage: the number brands don't agree on

BTU to square feet isn't a fixed ratio. Bromic publishes coverage at a specific mounting height assuming a sheltered installation. Infratech publishes a rectangular foot-by-foot zone under the beam. The implied BTU per square foot across published specs runs from about 100 to 115 for electric infrared, which is useful, because gas freestanding heaters publish numbers closer to 60.

That ~100 BTU per square foot figure is a defensible planning rule for sheltered electric infrared at a sensible mounting height (8 to 10 feet). Drop it to 75 BTU/sq ft if the patio is open to wind, 85 if the ceiling is high or vaulted, and 120 if everything is tight and tucked under a solid roof with low ceilings.

Running the formula backwards: a 150 sq ft seating zone needs about 15,000 BTU/h of electric infrared on a sheltered patio, which is one 4,500W Platinum. A 100 sq ft zone needs about 10,000 BTU/h, which is one 3,000W CD-Series. A 75 sq ft zone needs about 7,500 BTU/h, which is one 2,300W Platinum or 2,400W Slimline.

Circuit planning: the step most people skip

Wattage × 1.25 ÷ 240 = the minimum circuit size in amps. Any 240V electric patio heater needs a dedicated circuit sized to at least 125% of its continuous load. That one-line math catches almost every undersized install.

The common misread: shoppers see "draws 18.75 amps" and assume a 20-amp breaker is fine. Code (NEC 210.19/210.20) treats a load that runs more than three hours as continuous, which forces the 25% buffer. A 4,500W heater on 240V is a 25-amp circuit, which in residential practice means a 30-amp breaker on 10-gauge wire.

Quick planning table for the common sizes:

If the panel is at capacity and the planned install is more than one Platinum-equivalent, a dedicated subpanel for the patio is usually the right call. It's a 90-minute electrician visit at rough-in and keeps every future outdoor circuit separate from the house load.

When BTU still matters: mixed electric and gas patios

Most of this article is about electric, because that's where the conversion math lives. But plenty of patios mix one mounted electric unit over the dining group with a freestanding gas heater at the open end of the deck. The BTU chart lets you pick the gas unit on the same scale.

A 40,000 BTU propane freestanding heater puts out roughly what a 12,000W electric would on paper, but because the electric infrared delivers more of that energy to the seating zone, the usable warmth at the chair is closer to a 15,000 to 18,000 BTU electric. That's why pairing a 4,500W electric overhead with a 40,000 BTU Patio Comfort propane unit for a secondary zone works so well: the two numbers look mismatched but the chairs feel balanced.

If you're leaning toward a propane freestanding model, the Patio Comfort lineup runs 40,000 to 41,500 BTU on propane or natural gas, and their BTU rating is the direct spec with no conversion needed, because combustion heaters publish energy input directly.

Running cost by wattage

At the US residential average of 17 cents per kilowatt-hour (2026), here's the per-hour operating cost for each common heater size running at full output:

For comparison, a 40,000 BTU propane heater running on 20-lb tanks at $25 per fill burns about 1 gallon per hour at full throttle, which is about $1.07 per hour at current propane prices. So electric at $0.17/kWh runs cheaper per hour of use on sheltered patios where the published electric coverage holds up. That math inverts in windy or open installations where the electric heater can't deliver its rated zone.

Pick one by watts, verify in BTU, size the circuit before you buy

The right order for anyone shopping an electric patio heater:

One. Measure the seating zone, not the whole patio. 100 to 150 sq ft per group is typical.

Two. Multiply that square footage by 100 BTU for sheltered, 75 for windy, 120 for tight and tucked. That's your BTU target.

Three. Divide by 3.412 to get the wattage target. 15,000 BTU divided by 3.412 equals 4,400W, so round to the nearest commercial size (4,500W Platinum).

Four. Check the circuit: wattage × 1.25 ÷ 240 = minimum amps. Call an electrician if the panel is more than two-thirds loaded before you commit to a hardwired heater.

Five. Look at the Infratech CD-Series, Bromic Platinum, Bromic Tungsten, or Heatstrip Classic depending on whether you need dual-element, flagship coverage, design-forward profile, or app control.

If the patio also includes a built-in grill island, the hood-arc and clearance math from our sister site BBQs.com matters for where the heater can mount without blocking the cook. See Built-In Grill Cutout Dimensions Chart before finalizing the heater height and placement.