A standard gas mushroom heater covers a radius of around 3 to 4 metres. This guide explains how to calculate the number of heaters you need based on your space and covers placement and heater types.
A standard gas mushroom heater covers a radius of around 3 to 4 metres. This guide explains how to calculate the number of heaters you need based on your space and covers placement and heater types.
Patio heaters are sold on wattage or BTU output, but for practical planning purposes the most useful figure is the coverage radius. A standard 13kW gas mushroom heater covers a radius of approximately 3 to 4 metres, which gives a usable heated area of roughly 28 to 50 square metres. On a cold evening, guests need to be within that radius to feel the benefit.
Start with the floor area of the outdoor space in square metres. For a covered terrace or marquee side, measure the width and length and multiply them together. For an open outdoor area, estimate the area where guests will stand or sit. Divide the total area by 35 square metres to get a starting number of heaters. Round up, not down, and add one or two extras for the areas where guests tend to cluster, such as near the bar or at the entrance.
Example: a 10x8 metre outdoor terrace is 80 square metres. Dividing by 35 gives approximately 2.3 heaters, so order three. If guests will also gather on a path or decking area outside the terrace, add another heater for that zone.
Gas mushroom heaters (propane or butane) are the most common type at outdoor events. They are portable, work without a mains connection, and produce warmth that guests associate with a pub garden. The drawback is that they need gas bottle management. Each bottle lasts approximately six to eight hours at full output, so for long events you need spare bottles on-site and a plan for the swap.
Infrared heaters run on electricity and are better suited to covered outdoor spaces such as marquees or canopies. They heat objects and people directly rather than warming the air, which makes them more efficient in slightly enclosed areas. They do not work well in exposed open-air settings where the wind carries heat away. Infrared heaters need a mains supply and should be rigged or mounted rather than placed at ground level.
Place heaters at even intervals across the space rather than clustering them at one end. For a rectangular terrace, space them on a grid pattern. Avoid placing heaters directly over seating or under low ceilings. Keep a clearance of at least one metre between the heater and any overhead structure or fabric.
At events with high guest density, heaters at the perimeter of the space are often more effective than heaters in the middle. Guests standing at the edges of the crowd feel the cold more than those at the centre, and perimeter placement reduces the risk of guests knocking the heaters over.
For a four-hour outdoor event with gas heaters, order one spare gas bottle per heater as a minimum. For an event running six hours or more, order two spares per heater. Store spare bottles in a secure area away from the event footprint, with a clear handover process for whoever is managing the heaters during the event.
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