Combustion gadgets are rubbish

Every once in a while you will come across somebody peddling fuel-conditioning devices, often containing magnets, that are “guaranteed” to improve the efficiency of your burners. They do not work.

Be careful about letting these people onto site. The less scrupulous ones can be very aggressive and will, when you disprove their claims and instruct them to remove their product, go over your head to your management board and portray you as someone who is not committed to saving energy.

They will offer testimonials; but testimonial evidence in such cases is notoriously unreliable. They may claim that their products are patented, but remember that a patent does not prove that an idea works; it is just a claim of novelty. And then there is the guarantees -- except that they aren't guarantees that the product works. They are money-back offers, i.e., a promise not to leave you worse off than before. The chicken running around our back yard could leave you no worse off than you are now, and without wasting any of your time.

The facts The efficiency of combustion (the ratio of useful heat output to chemical energy input) depends primarily on three factors: having the correct ratio of air to fuel, ensuring good mixing between them, and minimising the exhaust gas temperature. So for example although the exhaust gas needs to be hot (mainly to prevent damaging acid condensation) excessive exhaust temperatures result in more heat than necessary going up the chimney. Poor mixing, meanwhile, results in unburned fuel going up the chimney, as does having insufficient air. A lean air-fuel ratio (excess air) increases the volume of exhaust gas. All of these effects increase the exhaust losses, and hence the amount of input fuel required to deliver a given quantity of useful heat output.

Let’s think about what can cause one or more of these things to go wrong in a heating boiler. Firstly air-fuel ratio: this is set during maintenance and it may be done wrong merely through carelessness; but the lazy technician will always set high excess air because it’s a quick way to get the job done and may avoid callbacks by helping to ensure reliable ignition. Secondly, poor mixing can occur through damage or wear to burner heads. It is particularly a problem with “pressure-jet” oil burners, when microscopic damage to the nozzle can impair its ability to produce the uniform fine mist that is essential for complete combustion with minimum air. It’s a problem that can be covered up by tuning the burner with more excess air to increase turbulence and mixing – but we already know that this is bad practice. Finally, we have the question of exhaust temperature. High exhaust temperatures can and do result from fouling of the heat transfer surfaces, since this reduces the ability of the boiler to absorb the heat released from the flame. But having a burner with too high an output has the same effect, and merely derating it can improve the percentage of its heat output that the boiler is able to capture usefully. Obviously the boiler’s output goes down somewhat, but this is rarely an issue in practice, and the point is that the stack losses decrease more than proportionately.

Let us be clear. Oil and gas are not magnetic, so passing them through a magnetic field will have absolutely no physical effect. If an improvement is seen (a big “if”), what is likely to have caused it? It can only be repairs and adjustments to the burner system. So if the gadget-seller checks out the combustion system “to ensure that everything is OK” before fitting his gizmo, it will be the adjustments he makes that cause the saving, nothing else. If he does not do any adjustments he may just be dishonest and either hope that you won’t verify the results, or will accept some bogus way of “proving” the savings. Or he may trust to a combination of chance (some installations may get better, some worse; he gets his money in half the cases) and lethargy (he also gets his money from some of the installations that didn’t work).

The moral: make sure your boilers are internally clean and that your burners are well maintained and properly tuned. If you are still getting high exhaust temperatures, derate the burner. Then show the gizmo-salesman the door.

See related article on combustion efficiency which includes a link to a combustion calculation spreadsheet.

Download results of independent test carried out by John Crabb of Exeter University Centre for Energy and the Environment

Anatomy of a vendor's claims

The following extracts are taken from a fairly representative example of the sort of publicity blurb that gets into the specialist technical press:
“Amazingly within 2 days savings were apparent,” said [the customer].
Improvements to combustion efficiency would have been apparent immediately.
"Now even with a boiler load increase of 47% we are still seeing a reduction in gas consumption per kw out, of around 9.6%"
Well, duh! If you increase the load on a boiler its overall efficiency is bound to increase regardless, because its fixed standing losses become a smaller proportion of total losses. This is especially true if the higher load factor reduces the number of ignition cycles, each of which entails a minute or two of purging with cold air.

“Initially [savings] were around 1-1.5% but they increased daily." ...and... "Within a week consumption had reduced and after 6 weeks savings of 11% were being recorded"
For the effect of magnetism to be cumulative in the way implied, either the fuel would have to do something to modify the combustion system on its way through, or perhaps more plausibly the products of combustion contain excess air (because the vendor has adjusted the air:fuel ratio) and this is burning off insulating soot deposits. Which brings me to:
The magnets cause less un-burnt hydrocarbon to be released into the atmosphere.
Any unburnt fuel in the exhaust will be accompanied by carbon monoxide or (in the case of oil) smoke. Tests for these are a routine part of normal boiler servicing, when raising the air:fuel ratio may be all that is required. This simple remedy could be slipped in to a 'preliminary inspection', which brings me to:
A free inspection is carried out to ensure that the installation of ... magnets would be possible and that there would be savings. “Some sites”, says [the vendor], “are not suitable..."
The unsuitable sites are the ones where the burners and boilers have been properly maintained and adjusted.
Those companies that do give it a go have always reduced their gas consumption and saved money.
So have companies that simply insist on diligent burner maintenance.
V.V. 26 May 06
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