How to use fire pits more sustainably this summer

Is there still a place for real-flame, responsible patio heating? Here is a guide on how to use fire pits carefully and more sustainably - plus some ideas on how to build your own

You can enjoy a gas fire piped directly to your pit position from a 9kg tank. There are still greenhouse gases, but no smoke to annoy the neighbours. 

As fossil fuel and even wood-burning come under attack for its role in damaging air quality, there’s still a place for real flame patio heating. 

Still, we need to ignite this controlled blaze as an occasional, well-planned, responsible treat. I’ve ranted and raved about propane patio heaters for years in these pages. Sadly, they are still for sale. 

Wildly inefficient, they have been described by Friends of the Earth as “gratuitously damaging” to outright “planet wrecking”. The use of commercial-level, propane umbrellas surged in the mid-noughties due to their snap-to convenience. Gas patio heaters are highly carbon emissive. 

A 12.5kW heater will produce almost 35kg of CO2 before the fuel runs out, and a standard 11kg propane patio cylinder runs out fast — in about 10 to 13 hours (Energy Savings Trust). The trouble with outdoor heating, is it tends to linger on, long after the barbecue has been put to sleep once cooking is over.

There are some situations where burning wood or charcoal at any time outdoors is questionable. If you live in a dense, urban area with sustained heavy traffic, prickling with operating chimneys — you are already aware of the problem.

The low-level ozone layer laced with dust and toxins released by barbecue and solid fuel heaters can be indirectly affecting the lungs of your neighbours forced to breathe in smoke, dioxins, nitrogen oxide, and other trace nasties. 

Limiting damage

Electric (outdoor rated) Infra-red heaters (lumpen and industrial as they are) and thermally useless bio-ethanol fires are less damaging to air quality at point-of-use in the suburbs than charcoal and its release of the dreaded tiny particles termed PM2.5 (Particulate Matter 2.5).

I’m not advocating for an outright prohibiting the primal joy of twisting, real flame. The thing is not to be blithe about it. Snaking grey plumes rising from every back garden, every weekend? We could tick on a geansaií or snuggle bare thighs up under an Irish lambswool throw, and limit the hours we enjoy a fire pit, bowl, or chiminea to a two-hour show. 

Going ahead with a period of outside combustion — let’s do this in as considered a way as possible. By the way — smoke-less fire-pits designs are just fire-pits designed with increased airflow through surrounding cavity walls, to burn dry fuel efficiently, and to cut down on smoke — they are not completely smokeless.

This Sierra cast-iron chiminea is suited to wood or charcoal and has front air venting for a clean burn. Shop on glanbiaconnet.com

The heat released by the fuel in your fire pit or chiminea is rated in megajoules (MJ) per kg — the higher the number, the more heat you should feel. Coal has a high megajoule rating, but it releases a lot of particulate matter. 

Turning away from fossil fuels, we want dry, dense fuel that will light easily, burn as completely as possible and deliver plenty of heat to you and your party on high days and holidays. Burning dry wood might release less CO2, but it takes longer to create the equivalent heat — not an issue where we’re looking for a focal point rather than the fires of Hades.

The drier and denser the wood, the better. Look for low moisture content and use as little wood or sustainable charcoal as you can for a pleasing blaze when you genuinely need a little direct warmth and crave its shifting light. 

Wood should be 15% to 20% in moisture content to burn as cleanly and hot as possible and cut to the correct length to sit safely in your burner. Wet wood creates a dirty, smoky, sluggish fire that no one will enjoy. Dry wood will feel light in your hand and have a grey to pale yellow colour. 

When you knock it off another log or a surface it will sound almost hollow. The safest thing is to source your wood from someone who certifies its moisture content.

Sustainable sources

Sticking with any solid fuel means first ensuring it is as close to carbon-neutral in its production as possible: Waste wood products such as eco-logs made from materials that would otherwise have gone into the landfill. 

Burn charcoal from a sustainable source, and the carbon dioxide absorbed by new trees planted, is feted to offset the greenhouse gases created by its use. These will be coppiced trees grown in managed woodlands. 

If you cannot trace the source of your charcoal by flipping over the bag at the DIY or garden centre, it is very likely to come from the problematic traditional sources in Brazil, Argentina, Namibia, Nigeria, or South East Asia. Here deforestation to feed the market is continuing to spiral, adding to habitat decline in ancient tropical forests and vulnerable tidal swamps of precious mangroves.

A fire bowl based on an Indian Kadai bowl. Shop on einrichtendesign.de

Ecofuel offer 3.6kg, 8.5kg and 10kg bags of Marienburg lump charcoal prepared from FSC sources without paraffin or kerosene in alder, birch or oak (it’s €25 for a 10kg bag). They also carry 20cm Pinikay heat logs made with compressed sawdust that stack perfectly with their octagonal profile. They look similar to commercial briquettes but burn hotter and cleaner (€8.50 for 12, ecofuel.ie). 

To light the fire or barbecue, there are a number of natural alternatives, including Big-K FSC wood and vegetable oil lighters in a handy kindling form (€6.50 for 96 from a range of suppliers). If You Care do an efficient, biomass firelighter (€7.55 for 72 from evergreen.ie and selected suppliers).

Safety first

Stage the heater with some shelter to prevent even light wind whipping the comforting joules away. A windy, drizzling night could prove a misery for adjoining properties penetrated by open flues and open windows — a choking nuisance. 

Have a bucket of water on stand-by, and never-ever place a fire-pit or bowl on decking or right by a wooden fence. No open flame should be set under an awning. 

When you have finished with any dished fire pit or bowl, put a fireproof cover on it to ensure that its extinguished safely and hot embers don’t blow around.

You can choose a number of burner designs that balance direct, fiercer heat against radiant background warmth and light. Build your own pit from bricks and gravel (there are dozens of good guides on YouTube). Washing machine drums are regularly up-cycled as fire-pits, as the pierced sides deliver a nicely distilled glow.

Be prepared to add a stable iron stand, and keep in mind they will be dangerously hot with their thin metal sides. Masonry and ceramic chimeneas are affordable and stylish, and in frost-proof bodies — you can leave them out all year.

The body of the device holding the fuel in its belly, stores and radiates heat even when the flames have long diminished. It can also be turned to sit with its back to any prevailing wind, increasing that thermal efficiency.

Dish forms taken from the Indian Kadai cooking bowls sit on legs, a trestle or directly into a table. Suitable for cooking, they are lethal at drunken gatherings with floaty frocks, so set them with a good boundary and guard once alight.