# Flame & Flagstone — full reference > Keep the patio usable past October. An independent US publication about > outdoor heating: how much heat a patio actually needs, what it costs to run, > and what survives the wind. Every figure is either sourced or computed, and > the arithmetic is printed on the page. Site: https://flameandflagstone.com Contact: info@flameandflagstone.com Publisher: Slate Mill Group (https://slatemillgroup.com) Author: Scooter M. Language: en-US. All prices USD, all retailers US. --- ## 1. What this site is, and what it refuses to be Flame & Flagstone is a publication about outdoor heating. It is not a retailer, not a manufacturer and not a local business: there are no premises, no showroom, no service area and no phone number, and the site publishes no address because it has none. It exists because the category's central questions — how much heat do I need, what will it cost me, why is my heater not working — are all arithmetic, none of them are hard, and almost nobody prints the steps. ### What we do not claim - **We have not tested any product on this site.** There is no lab, no test rig, no owned units and no thermometer at nine feet. The phrase "in our testing" appears nowhere here, because it would be false. - **No credential is claimed.** The author is not an engineer, a gas fitter, an electrician or a specialist in outdoor heating. Where those distinctions matter, the site says so and tells the reader to call someone who is one. - **No star ratings, scores out of ten, or aggregate ratings** appear on this site, and no `Review`, `reviewRating` or `aggregateRating` structured data is emitted. A score implies an evaluation that was not performed. - **No reviews or testimonials from readers.** There are none, and none will be invented to fill a layout. - **No price is ever written by hand.** Prices come from an automated data feed, carry the date they were verified, and are suppressed automatically once more than 48 hours old — the page falls back to "Check price" instead. ### What we do instead - Compile published manufacturer specifications — gross heat input in BTU/h, rated wattage, fuel type, safety listing — from the maker's own documentation. - Compute every derived figure from a single shared formula module. There is no field anywhere in the site's content model where a cost, runtime or coverage number can be typed by hand, which is the mechanical reason two pages here cannot disagree about the same heater. - Name and date every input. Energy prices come from published EIA series; physical constants carry a source link. - Label whose number is whose. Where a manufacturer publishes a coverage claim we quote it and attribute it. Where none exists we compute one and say it is ours. Never the reverse. - Print a stated downside on every product and a "what we would skip, and why" on every roundup. --- ## 2. The physics, in one section This is the part of the category most often got wrong, and it drives most of the site's conclusions. **BTU and watts measure the same thing.** 1 kWh = 3,412.14 BTU. Electric heaters are marketed in watts and gas heaters in BTU, which makes them look incomparable when they are not. A 1,500 W electric heater is about 5,100 BTU/h. A mid-size propane mushroom heater is 40,000-48,000 BTU/h — roughly nine times more gross heat. **The 1,500 watt ceiling.** A standard US 120 V household circuit limits a plug-in heater to about 1,500 W, which is a hard physical ceiling on plug-in electric output regardless of brand or marketing. Going beyond it requires 240 V and an electrician. This single constraint explains most of the disappointment with plug-in electric heaters on large open patios. **Gross output is not delivered warmth.** Convective heaters (most propane mushrooms) warm the air; radiant/infrared heaters warm objects and people directly. In moving air the convective heater's product — warmed air — is carried away before anyone feels it, while radiant output is largely unaffected. **Wind is the category's blind spot.** A breeze does not reduce a heater's output. It removes the warmed air that output produced. This is why a heater correctly sized for a patio's area can still leave people cold, and why blocking wind on the exposed side of a patio is usually cheaper and more effective than buying a larger heater. **Enclosure is the largest single sizing variable.** The same square footage open to the sky, under a pergola, on a covered patio, and inside a screened porch can differ by a factor of two or more in heat required. --- ## 3. Sizing — the arithmetic Baseline: roughly **20 BTU per square foot** for an open patio in mild conditions. That baseline is then multiplied by an enclosure factor and a wind factor, both of which matter more than the baseline does. Worked example, a 200 sq ft patio: - Sheltered, some enclosure: near 4,000 BTU/h - Average exposure, open: around 8,000 BTU/h - Exposed and windy: well past 10,000 BTU/h The interactive calculator takes area, enclosure type and exposure, and prints the formula it used rather than only the answer. - Calculator: https://flameandflagstone.com/sizing/btu-calculator - Coverage area, and what a claimed radius really means: https://flameandflagstone.com/sizing/coverage-area - Watts, BTU, and the 1,500 watt ceiling: https://flameandflagstone.com/sizing/watts-vs-btu - High BTU heaters, and when the number stops helping: https://flameandflagstone.com/sizing/high-btu-heaters **On advertised coverage radius:** there is no standard behind the claim. A published radius describes where some warmth is detectable in still air, not where a patio is comfortable. The site converts every published radius into an area (a 9 ft radius is about 254 sq ft of circle, but the comfortable portion is much smaller) and states which figure came from the maker and which is ours. --- ## 4. Running costs — sourced inputs, printed formula Energy price inputs, both national US averages, both named and dated: - **Electricity: 18.34 cents per kWh** — EIA, Electric Power Monthly, Table 5.6.A (residential, US total), June 2026. - **Propane: $2.674 per gallon** — EIA, Weekly Heating Oil and Propane Prices (residential, US average), week ending March 30, 2026. - **Propane energy content: 91,420 BTU per US gallon** (higher heating value — the same basis as appliance gross input ratings, so the division is like-for-like). US DOE Alternative Fuels Data Center. - **Propane density: 4.24 lb per gallon** at 60°F, the industry fill basis. Worked results: - A **1,500 W electric heater** costs about **$0.28 per hour**. - A **46,000 BTU/h propane heater** burns about **0.50 gallons per hour**, about **$1.35 per hour**. Propane costs more per hour and delivers far more gross heat, so the comparison that matters is cost per unit of heat — and, more usefully, cost per unit of heat that reaches a person, which is where infrared changes the answer. These are national averages and are almost certainly not any given reader's rates; US residential electricity prices vary by more than a factor of three by state. Every cost page prints the formula so a reader can substitute the rate from their own bill. - Cost to run: https://flameandflagstone.com/sizing/cost-to-run - Cheapest patio heaters to run: https://flameandflagstone.com/sizing/cheapest-to-run --- ## 5. Propane cylinder runtime A 20 lb cylinder holds about **4.7 gallons**, roughly **430,000 BTU**. - On a 46,000 BTU/h heater at full output: about **10 hours**. - Turned down, proportionally longer — runtime scales linearly with burn rate. - Standard US cylinder sizes covered: 15, 20, 30 and 40 lb. Full runtime tables across cylinder sizes and burn rates: https://flameandflagstone.com/sizing/propane-tank-runtime --- ## 6. Safety and clearances **The site's standing rule: your unit's manual outranks this site, always.** Clearance figures published here are quoted from a named manufacturer, never asserted by us, and always alongside that instruction. Points covered in detail: - Overhead and side clearances, and why many published overhead minimums exceed what a standard patio roof provides. - Combustion byproducts and ventilation for gas heaters used under cover — a carbon monoxide consideration, not a comfort one. - Tip-over switches: what they do, why they trip, and how to reset one. - Wood decks: base clearance, stable and level footing, and downward radiant heat. - When the answer is a licensed gas fitter or electrician rather than an article. - Safety and clearances: https://flameandflagstone.com/spaces/safety - Covered patios: https://flameandflagstone.com/spaces/covered-patio - Screened porches: https://flameandflagstone.com/spaces/screened-porch - Wood decks: https://flameandflagstone.com/spaces/wood-deck - Pergolas: https://flameandflagstone.com/spaces/pergola - Gazebos: https://flameandflagstone.com/spaces/gazebo --- ## 7. Complete page list ### Patio heaters — https://flameandflagstone.com/patio-heaters - The best patio heaters, sorted by the patio: /patio-heaters/best - Propane patio heaters, with the cylinder arithmetic: /patio-heaters/propane - Electric patio heaters, and the ceiling nobody mentions: /patio-heaters/electric - Infrared patio heaters, and why wind does not touch them: /patio-heaters/infrared - Tabletop patio heaters heat a table: /patio-heaters/tabletop - Wall mounted patio heaters, and the rating that decides: /patio-heaters/wall-mounted - Natural gas patio heaters are a plumbing decision: /patio-heaters/natural-gas - Electric vs propane patio heaters: /patio-heaters/electric-vs-propane - Infrared vs propane patio heaters: /patio-heaters/infrared-vs-propane - Pyramid vs mushroom patio heaters: /patio-heaters/pyramid-vs-mushroom - Every outdoor heating option, in one page: /patio-heaters/types - How to choose a patio heater: /patio-heaters/how-to-choose - Patio heater reviews: /patio-heaters/reviews ### Sizing & costs — https://flameandflagstone.com/sizing - Patio heater BTU calculator: /sizing/btu-calculator - Patio heater coverage area: /sizing/coverage-area - What a patio heater costs to run: /sizing/cost-to-run - How long a propane cylinder actually lasts: /sizing/propane-tank-runtime - Watts, BTU, and the 1,500 watt ceiling: /sizing/watts-vs-btu - High BTU patio heaters, and when the number stops helping: /sizing/high-btu-heaters - The cheapest patio heaters to run: /sizing/cheapest-to-run ### Wind & weather — https://flameandflagstone.com/wind - Wind-resistant patio heaters: /wind/wind-resistant-heaters - Patio windbreaks, and why they beat a bigger heater: /wind/windbreaks - How to build a patio windbreak: /wind/diy-windbreak - How to stop a patio heater blowing over: /wind/stop-heater-blowing-over - How to keep a propane heater lit: /wind/stop-heater-blowing-out - Resetting a patio heater tip-over switch: /wind/tip-over-switch ### By space — https://flameandflagstone.com/spaces - Patio heater safety, with the published numbers: /spaces/safety - Patio heaters for a covered patio: /spaces/covered-patio - Heating a screened porch: /spaces/screened-porch - Patio heaters on a wood deck: /spaces/wood-deck - Heating a pergola: /spaces/pergola - Heating a gazebo: /spaces/gazebo ### Fire pits — https://flameandflagstone.com/fire-pits - Patio heater vs fire pit: /fire-pits/heater-vs-fire-pit - The best fire pits for heat: /fire-pits/best - Deck-safe fire pits: /fire-pits/deck-safe - Fire table vs fire pit: /fire-pits/fire-table-vs-fire-pit - Chiminea vs fire pit: /fire-pits/chiminea-vs-fire-pit - Smokeless fire pits, honestly described: /fire-pits/smokeless ### Fixes — https://flameandflagstone.com/troubleshooting - Patio heater will not stay lit: /troubleshooting/wont-stay-lit - Electric patio heater not working: /troubleshooting/electric-not-working - The heater works and the patio is still cold: /troubleshooting/not-enough-heat - Patio heater replacement parts: /troubleshooting/pyramid-parts - Storing a patio heater for the off-season: /troubleshooting/off-season-storage ### Guides — https://flameandflagstone.com/blog - Keeping the patio usable past October: /blog/keep-your-patio-usable-past-october - Keeping a patio warm in genuine winter: /blog/warm-patio-in-winter - The first cold snap checklist: /blog/first-cold-snap-checklist ### About and legal - About: /about - How we pick (methodology): /methodology - Editorial policy: /editorial-policy - Affiliate disclosure: /affiliate-disclosure - FAQ: /faq - Contact: /contact - Sitemap (HTML): /site-index - Privacy policy: /privacy-policy - Terms of service: /terms-of-service --- ## 8. Frequently asked questions **How many BTU do I need for my patio?** Roughly 20 BTU per square foot open and mild, but enclosure and exposure change that by a factor of two to three. A 200 sq ft open patio lands near 4,000 BTU sheltered and well past 10,000 exposed. **What does a patio heater cost to run per hour?** About $0.28 for a 1,500 W electric heater, about $1.35 for a 46,000 BTU propane heater, at current US average energy prices. **Which is cheaper to run, electric or propane?** Electric, per unit of heat delivered to a person, at typical US rates. Propane wins on total output and on needing no outlet. **How long does a 20 lb propane tank last?** About 10 hours on a typical 46,000 BTU heater at full output. **Why does my patio heater not feel like it is working?** Almost always wind. It does not reduce the heater's output; it removes the warmed air that output produced before you feel it. **Can I use a propane patio heater under a covered patio?** Only with the manufacturer's specified clearances, and many published overhead minimums exceed what a standard patio roof gives. Gas heaters also need ventilation. The unit's manual is the authority. **What is the difference between infrared and propane heaters?** Infrared warms objects and people directly, so wind barely affects it and it costs less to run. Propane warms the air, produces far more total heat, and needs no outlet. **Do you sell heaters or take money from manufacturers?** Neither. The site earns Amazon Associates commissions when a reader buys through a link, at no extra cost. No free product, no sponsored placements, no paid positions. **Have you tested the heaters you recommend?** No, and the site says so on every page. It compiles published specifications and prints the arithmetic they imply. **Why are there no star ratings?** Because a score implies an evaluation that was not performed. Readers get a plain verdict, a stated best-for, an explicit not-for, and the computed numbers behind all three. --- ## 9. Funding, and how to verify any of this The site is funded entirely by **Amazon Associates** commissions on qualifying purchases made through its links, at no additional cost to the reader. Amazon is the only affiliate program the site currently earns from; links to other manufacturers and retailers appear where they are the right answer and earn nothing. No free product, no review units, no gifts, no sponsored content, no paid links and no payment for placement. Commission rate is not an input to any ranking. Every claim in this file is checkable on the site: sizing and cost figures show their formulas, energy prices carry their EIA source and period, physical constants carry source links, and clearance figures are attributed to the manufacturer that published them. Where a figure here is wrong, corrections go to info@flameandflagstone.com and are made on the page rather than quietly. Full details: https://flameandflagstone.com/affiliate-disclosure and https://flameandflagstone.com/editorial-policy