Rob Smith of Rivelin explains the pros and cons of the various fuel types.
Outdoor fires have been rising in popularity in the UK thanks to home-improvement shows on TV, but credit must also be given to our American cousins, for whom outdoor fires have been part of the culture for decades.
They are available in various shapes and sizes and can vary in price from tens of pounds to thousands of pounds. Currently outdoor fires can be split into 3 categories based on the fuel they burn:
- Solid fuel – generally Wood
- Bioethanol –Liquid or gel
- Gas -LPG or Natural gas
Solid Fuel Fires – Solid fuel fires are the most common and cheapest outdoor fire to get hold of. Any fire which runs on wood, charcoal, briquettes or biomass would be categorised as solid fuel. Solid fuel fires are incredibly flexible and a quick trip to any garden centre or search on the internet will reveal hundreds of options.
Most outdoor fire pits sold run on wood and are simply dropped into place requiring no installation expertise. Although ease of installation is an obvious benefit, this must be balanced with the smell and smoke produced by the fire, the inconvenience of building the fire and its maintenance once lit. In addition, once you’ve put out the fire and you retire, there’s the lingering smell of smoke on your clothes and hair never mind the bed clothes in the morning. If cost is the deciding factor then a solid fuel fire has to be the front runner.
Bioethanol Fires – These are a more recent entrant to the outdoor fires market. Bioethanol is alcohol which has been produced using the by-products of sugar beet and other foods. The only by-products of the fire are water vapour and carbon dioxide, making the fuel very friendly to the environment.
Unfortunately, most bioethanol fires are for decoration only with limited heat output of a few kw’s. With approx 6.7kw of energy per litre of bio-ethanol, a fire manufacturers claimed heat output and burn duration can be quickly verified. If a fire claims to have a 9kw output and a 2 litre tank, then it will run for approx 1.5 hrs before it needs refilling. All bio-ethanol fires require around 0.5hr’s or more to cool down before refilling. The advantages of bio-ethanol fires are that they are dropped into place often requiring no installation requirements and unlike wood fires they don’t smell. The disadvantages are limited heat output, they require refilling often, and generally have a lack of control over the flame size in addition to relatively high fuel costs.
Gas Fires – Outdoor gas fires can be fuelled by LPG or Natural gas. We are all familiar with LPG from using a gas fired BBQ. Which gas one selects, depends on the installation circumstances.
If a mobile unit is required, then LPG is the most likely candidate. In this case, the key question is where will the gas bottle be located. In the USA, gas bottles are often stored horizontally inside the unit allowing units below 50cm in height to be manufactured. Here in Europe we have to by law stand gas bottles vertically when the LPG is used as a gas and not as a liquid; as in the case of a forklift. The smaller the gas bottle, the lower the recommended Kw off take before the valve can potentially freeze. LPG has around 13.6kw of energy per kg so a 6kg bottle; which has a recommended off take of 10kw ; will last around 8hrs at 10kws.
One can quickly see that the inevitable conclusion is that here in Europe mobile units with gas bottles contained within its structure, will have a limited heat output. To achieve the typical 18kw (60,000btus) associated with a gas fire pit which is to be used for heat, requires a larger gas bottle of 19kg or greater. These stand around 800mm and cannot fit underneath a product so have to be located away from the gas fire. Flexible rubber pipes can be used for short runs where is it visible or permanent hard piping can be installed beneath the deck or patio for a cleaner look. If a permanent installation is the preferred option then Natural Gas can also be considered.
LPG has more installation considerations than Natural Gas because it is heavier than air, in addition it is also generally more expensive p/kw than Natural Gas but cheaper than bio-ethanol. If you are considering a gas fired unit , ensure that it is a CE approved unit. Most imported American units aren’t CE approved and aren’t legal here in the UK. Gas fires should be serviced annually so make sure spare parts are easily available and ask about the build quality.
The advantages of gas powered outdoor fires are that they can be clean burning with no smell, instant heat with no preparation, no cleaning out, completely controllable with manual or remote ignition, heat outputs of 18kw and greater and can be instantly turned off. The disadvantages are that mobile units with contained gas bottles tend to have relatively low heat outputs and higher Kw output units require a larger gas bottle which needs hiding or a commitment to a permanent gas pipe. This commitment to a permanent installation obviously adds to the cost the job and should be considered before the patio is laid.
Outdoor fires are a great way to add drama to a garden and with something available for every budget, there’s no excuse to not include fire in your next project.
About Rivelin – Rivelin are based in Sheffield and design and build outdoor gas fire tables and fire bowls for architects, landscapers and garden designers. These fires have been installed in gardens and penthouses from Cornwall to John O Groat’s and have been exported throughout Europe and further afield.