Friday, 1 February 2008

Cold Shoulder for Patio Heaters

There's been another small victory in the battle against energy waste, as British leisure retailers are falling over themselves in a rush to stop selling patio heaters. These heaters are designed to help people stay warm in their gardens on chilly summer evenings and generally work off a 13kg LPG cylinder in the base, which also helps to provide stability. Switched on to maximum output and left to run until a full cylinder runs out, they are reckoned to burn for around 13 hours - enough for even the longest party! FoE and the Energy Saving Trust have calculated that this would release some 34.8kg of CO2, the main gas contributing to climate change. That's the same as the emissions from 15 litres of petrol - or enough to drive 120 miles in a typical family car.

What's more, most of this energy (and CO2) is wasted. The typical heater burns across a circular grill at a high level; although some radiant heat is generated, most of the heat simply rises up above the device, or is convected around the "cap".

Enter the DIY retailers. So far, they have sold an estimated 1.2 million of these highly inefficient and quite ineffective units. But suddenly they have come over "all green" and are trumpeting their concern for the environment by stopping sales. Wyevale took the lead last May, saving its customers from a complete summer of patio heating. B&Q followed last week, with Homebase jumping on the bandwagon this week. This is to be welcomed, but B&Q admit they have 20,000 of the things still waiting to be sold - and they are not going to be scrapped.

The cynic in me wonders if there's another reason. Patio heaters are ineffective: they may impress the neighbours, but they don't keep you warm. The Government's Market Transformation Programme have compared cumulative sales of heaters (1.2mn) with annual sales of "alfresco" gas canisters - and deduced that the average unit is used between 10 and 21 hours a year: many heaters, they suspect, are rarely or never used, staying locked inside the garden shed. And if B&Q have such a large stock now, I suspect that sales may not be what they used to be, as the public have cooled on the idea of patio heating. Axe a slow-selling line and claim greenie points - it's almost to good to be true!

Hiding behind the consumer patio heater is a much more pernicious heater - the pub patio heater. These are used, especially since the smoking ban, and - unlike domestic heaters - are use year-round, not just on balmy evenings. Although some are the same as domestic LPG units, most are electric to befit from lower running costs. Electric units are also more controllable: they can be centrally switched on or off by the pub staff with a second point-of-use push button for use by customers, which will give a 10 minute burst of heat. Unlike gas heaters, they are primarily radiant, and use a rear reflector to direct the heat in a narrowly focused pool. But they're not all good; a typical 1.5kW heater in use for 2371 days a year and 2 hours on a day (assuming good controls) will still result in almost 400kg of CO2 annually. And most pubs will have several such heaters, to cater for several different groups of smokers. When you realise that around half Britain 51,000 pubs (not the mention its 48,000 restaurants) may have installed these heaters to beat the smoking ban, that's a lot of CO2! Estimates vary, but they could lead to anywhere between 100,000 and 200,000 tonnes of CO2 - perhaps equivalent to the emissions from 50,000 cars.

1 These figures come from the MTP (


heater patio said...

There's been another small victory in the battle against energy waste, as British leisure retailers are falling over themselves in a rush to stop selling Patio Heaters

EnergyDon said...

Sneakily, @heater_patio added a link to his site selling these devices. However in the interests of free speech I am leaving it in place. This gives us the opportunity of seeing just how much energy these guzzle. Firstly, the electric ones appear to use 1.5kW - that's half the level of a traditional 3 bar fire for indoors, and I don't think that these would actually make much impact on a cold evening (apart from on your energy bills, but even there they may be manageable).

The LPG ones are another matter altogether, going up to a massive 13.48kW. Sure, they'd keep you a bit warmer outside (a fleece might do the same, of course) but assuming perfect combustion, they'd emit CO2 at the rate of 2.9kgCO2/hour - that's about the same as driving a modern supermini car about 14 miles. OK, individually it's not going to destroy the planet, but I don't think that the damage/reward ratio is especially good. And it does help place this in context: if you can persuade your visitors to cycle to your barbecue rather than drive their Chelsea tractor, perhaps you can feel smug about having a high power patio heater.

plumbing said...

It is warmer in direct sunlight than in the shade because the shade blocks out a lot of the light, and like our natural big outside heater, infrared heaters in your home will only warm areas directly in front of it.

EnergyDon said...

That's a good point, @plumbing. In a room, a 1.5kW heater will over time warm up the room because the warm air is effectively trapped inside (OK, some may leak through doors, windows etc.). Indeed most of the perceived heating effect is by coming into contact with warmed air, rather than by direct infra-red radiation from the heater.

However on a patio, there is nothing to trap any warm air and so you can only get a warming effect by standing directly in front of an infra-red heater. This makes it even less efficient as a way of keeping warm. Arguably, if there are a group of three or four people all standing in a huddle in front of the infra-red heater, they will get as much benefit from the heat being generated by the other people, and a shelter effect from any reduction in wind chill from standing in a group.

The logical conclusion is that maybe someone should sell a dummy infra-red heater (a bit like a dummy speed camera); people will stand in front of it and feel warmer because of the effects of each other, and also because they think they are are being warmed by it!