The fuels used in domestic practice may be listed as: Solid fuel: coal ; coke; wood;peat.The last two are rare in the UK and we will not pursue them in any detail.
Oil: two grades, kerosene and gas oil.
Gas: mains distributed gas is, except in some remote regions, now entirely natural. Bottled gas, as propane or butane or a mixture is readily available.
Electricity: now almost entirely standardised in characteristics, but sold under a variety of tariffs.
One of the more impressive facts about the technological evolution of domestic heating appliances is that the combustion apparatus is no longer a sort of indoor incinerator, a place to burn any old rubbish. True, an open fire will still burn nut shells if required, but its principal fuel must be selected with care, both for technical and for legal reasons. The same is true of all oil and solid fuel appliances, where there exists a choice.
The manufacturer of an appliance will name suitable fuels for use with his appliance, and the choice should be made from such a list, not only as to type of fuel but also to size and grade where applicable.
On such detail depends the efficient performance of the appliance, and in certain cases one’s immunity from prosecution under the Clean Air Acts. Let us look a little more closely at the choice of fuels.
Bituminous coal is familiar to most people as ‘house coal’, whose unregulated use was a considerable factor in causing smokeless zones to be declared. Any appliance which sets out to burn bituminous coal in a smoke control area must be specially designed to be what has become well known as ‘a smoke eater’ and must have gained exemption under the Clean Air Act 1956. Bituminous coal must not be used in boilers, where it would deposit soot on the heat exchanger surfaces and so ruin the efficiency of heat exchange. It would indeed be fair to say that bituminous or house coal, now far from being the commonest of all solid fuels, is hedged in with special conditions which greatly restrict its use.
Two ranges of smokeless solid fuels have grown up. One consists of naturally occurring fuels, the other of manufactured fuels which are derived from coals in the bituminous range by removal of most or all of their smoke producing constituents.
All these fuels are dearer per ton than house coal but not necessarily dearer per unit of heat output since they lend themselves to more efficient use. This in turn warrants the design of more efficient appliances, and sharpens the attention to be paid to correct size or grade of fuel, upon which the best operation of the combustion process depends.
The natural smokeless fuels are anthracite and Welsh dry steam coal. Anthracite is a relatively pure form of carbon, with very little ash or volatile matter. Because of the latter it is not easy to light, and anthracite burning appliances are often equipped with a gas poker or other device with a similar purpose.
The common sizes of anthracite, in descending order, are: French Nuts; Stove Nuts; Stovesse; Beans; Peas; Grains. The last two, occasionally the last three, have a fan assisted fire bed to overcome the denseness of packing due to the small size of the fuel. Such a fan performs a secondary role as a combustion controller. When the fan is off the fire will idle.
Welsh dry steam coal has a low enough volatile content to be acceptable under the Clean Air Acts without special dispensation, but not so low that it is difficult to light. It is customarily supplied in the larger size range, as Large and Small Nuts. It is incidentally known variously as Welsh Nuts, Welsh Steam, Dry Steam, or Welsh Boiler Nuts.
There are three classes of prepared or manufactured smokeless fuels. These are: coke, semi-coke and briquettes. Since the passing of gasworks there is no more ‘soft’ or gasworks coke, and the only coke now available appears under the name Sunbrite, in sizes called Singles, Doubles and Trebles. The appliance manufacturer will state which size you need. Some assistance with initial lighting of a Sunbrite fire bed is desirable.
The semi-cokes, familiarly known as ‘solid smokeless fuels’, the best known being Coalite and Rexco, are the result of giving raw coal only a part of the treatment which would yield a coke. They therefore retain enough of the original volatile matter to assist ignition and to give some flame movement in a visible fire; but not enough to make them offensive under the Act. Both Coalite and Rexco bear a resemblance to the original coal substance and are sold in the larger sizes mainly.
The third class, briquettes, are reconstituted into a convenient size and usually an ovoid shape. Phurnacite and Home-fire are both made by the National Coal Board. They are made from selected grades of coal ground very fine, and passed through a press to give the form required. Phurnacite briquettes include a proportion of pitch added as a binder, while Home-fire starts with a coal of higher volatile content and relies upon heat generated by the press to employ some of the inherent tar substances as a binder.
There is a further difference, that Phurnacite is carbonised, I.e. heat treated to drive off excess volatile matter after being briquetted. But Homefire is made from a char, which is coal substance already partly devolatilised in a fluidised bed. For the average reader it will probably be sufficient to know that Phurnacite is very well suited to solid fuel cookers, room heaters and independent boilers. Roomheat is suited to modern open fires and to glass fronted and other types of room heater.
Any discussion of solid fuel must touch upon storage. Solid fuel of all kinds should be stored in the dry, the importance of this increasing as the surface porosity of the fuel increases. Thus, most of the rain will run off the hard surfaces of natural fuels of all but the very small size. But coke and semi-coke will be able to absorb a very high proportion of its own weight as water, which will have to be driven off by the fire bed when it is charged, with considerable loss of efficiency.
Then we come to handling. All solid fuels degrade to some extent when handled, and even when under the weight of their own heap. Degradation leads to size reduction, and the production of fines and dust which are usually thrown away – a complete waste of money. Handling, moving from one place to another, shovelling over, even walking on top of the heap, should be avoided. And to minimise the slow degradation at the bottom of the heap it is desirable to draw off fuel from ground level so that the bottom layer does not remain unchanged for a long time.
The tendency to degrade is higher among the prepared fuels than it is in the natural fuels. Thus, long after the chemical and combustion features of briquettes had been settled, scientists were still wrestling with the question of mechanical strength. The principal problems were overcome, of course, but a briquette should still be regarded as needing care in handling and storage.
Solid fuel differs from all of its competitors in that it will not obey instantaneous commands. It cannot be switched on and off with immediate effect as can gas, oil and electricity. This feature brings with it other considerations, some good and some less good.
The kitchen based boiler, the hearth fitted appliance and the combination range, when their dampers have been shut either by thermostat or by hand, continue to ‘tick over’ at a reduced rate of combustion and when the next command comes to start work the fire picks up slowly to a full working condition. The noticeable feature, living with one of these units, is that it is always comfortably warm in the vicinity of the apparatus, which makes its own rather involuntary contribution to house heating in this way. A secondary facet of the same phenomenon is that even though the fuel may be difficult to ignite, it is a job rarely required, in some cases only at the start of the heating season.
A more limiting aspect of the lag in answering to controls is that there has to be allowance made for it, and particularly when it is being ordered to cool down. Consider a boiler, with thermostatically operated damper, which is working at normal high capacity in a small bore heating system in which the room thermostat operates the circulating pump. The house warms up, the room thermostat becomes satisfied, and stops the pump. No more hot water is going to the heating system. The boiler thermostat quickly senses this, and closes the boiler damper. But the boiler does not stop its heat output. It may even increase it temporarily, but will in any event go on delivering heat in considerable quantity for quite a time. If this heat had nowhere to go outside of the boiler it would have to be absorbed into the quite small quantity of water which the boiler holds, and almost certainly would lead to boiling and in most cases to a state of considerable danger.
In such a situation there must therefore always be a substantial buffer available, a large source of heat transfer permanently connected to the boiler which cannot be isolated from it. This is the domestic hot water system, the cylinder of water containing over 100 litres which can safely be raised about 40 degF or 20 degC.
Thus it will be clear that a solid fuel boiler cannot power a heating system only, but must include domestic hot water. It shows too that the domestic hot water system must not be fitted with a cylinder thermostat, which could stop the primary flow into the cylinder and so isolate the boiler from the cylinder.
Fuel Oil for Domestic Use
There are two grades of fuel oil sold for domestic heating. They are known traditionally as kerosene and gas oil, but it is not uncommon to find them called 28 sec and 35 sec oil or the first as domestic fuel oil. The latest, official system, by which they will be recognised in an approvals document, is as Class C and Class D fuel. We will call them C and D; C being the lighter kerosene and D the gas oil.
They are not fully interchangeable. Some appliances will burn only one of them. Other appliances, which have a ready means of varying a component of the burner, can be adapted to burn either but the adjustment is a job for an expert. Broadly speaking, boilers of the pressure jet burner type will be found using Class D, other appliances Class C. But in the first case there is often scope to adjust to the other fuel. The arrangement quoted does however fit neatly into another aspect of modern thought, namely that pressure jets are not acceptable indoors and Class D fuel is not welcomed indoors because, in the event of leakage, or spillage during filter cleaning, etc, its smell has a lingering quality beyond that of Class C. Class D and pressure jets are therefore relegated to an outhouse together.
Fuel oil is almost always fed to the burner by gravity, I.e. the storage tank is at a higher level. If not – if for instance it happens to be below ground – then the oil must be delivered to the appliance by pump. In the case of a pressure jet boiler this can be arranged, by a slight modification to the oil pump which forms part of the burner, plus extra pipework to form a two-pipe system. For any but a pressure jet an independent pump must be fitted, and again a two-pipe system is required. The system operates by the pump taking fuel from and returning it to storage, the burner taking off what it needs at any given time. The system will be explained in detail when necessary by an authorised agent of one of the major oil companies – the one chosen to supply the oil, most likely – or by a competent installer. It is usual to find that practical limits are assigned to pump performance, which in the case of gravity feed are the maximum and minimum heads. Typical values for these might be 8 and 1 m. The limit at which suction can occur in a lifting system is of the order of 3m.
All pipe runs should assist flow by having true falls, and freedom from dips. Great stress is placed upon having a filter of the right type in the line. It is customary nowadays for this to be outdoors where it is more easily cleaned. Whether or not a fire valve is to be fitted as a compulsory feature is a matter for the local authority to decide in terms of their building regulations.
The size of the storage tank, and the shape for a given size, are sometimes determined by the limitations of the space available. When that factor is absent, the size of tank is usually balanced between the way tank cost increases with size, and the way oil prices can decrease in relation to the size of each consignment. It is not a matter which requires the services of a chartered accountant on each occasion. Everyone in the trade can now give sensible advice based upon long practice, and only special circumstances should be allowed to overturn this advice. If for example you live on a track which is impassable to lorries for three months each winter then your minimum capacity must be that which will last for more than 3 months.
Routine attention starts with cleaning the filter, and opening the drain cock to release any water which has collected there. Sludge too may come away, but if what comes is run into a bucket, the good oil after settlement may be returned, so run off generously.
The tank itself will need some maintenance from time to time. Rusting of a steel tank occurs quite readily when paraffin type oils are about, and it is necessary to remove all the rust, dirt and oil, and repaint, using a hard skinned top coat which will resist oil penetration for the greatest length of time. Another point to be noted about oils and metals concerns pipework. Never use galvanised pipe to convey fuel oil. Copper remains best, but any other of the usual metals may be used.
Oil, irrespective of which class, demands quite precise conditions for correct burning. Incorrect burning can lead to smell, sooting of flueways with increasing loss of heat exchange, and general loss of efficiency. Modern appliances are a long way from the old wick burner heating stove, and even that was prone to smoke if the wick was not trimmed.
The best safeguard, and really an essential feature of ownership, is skilled servicing at regular intervals to be agreed with the service engineer. If a service contract can be arranged it saves having to remember and could save money. Beyond that, the owner should be prepared to look occasionally at the appliance, in order to see that operations are normal. If for instance the flame cannot be seen through the inspection window because of soot a more thorough inspection is required.
Gas is available to all of us, in one form or another. In the form of natural gas it is expected to last until the end of the century, which is long enough for our purposes. With the exception of a very few remote districts, mainly in northern Scotland, manufactured gas is no longer distributed. There remain many places in the UK which are not within economic distance of a gas main, though in total of dwellings they do not amount to much. For them gas can be supplied in containers, principally by Calor.
Manufactured gas, natural gas, Calor gas, are all different, but the differences are really no concern of the public. Two facts alone concern the user or potential user of gas. (1) The gases are not interchangeable. An appliance, such as a boiler or a cooker, may remain structurally the same for any gas, but it will be given a wholly different set of combustion parts for each. (2) In order that the preceding point does not cause despair, the whole matter of interchangeability, the right bits for the job, and the overall safety and efficiency of the unit, are very jealously and zealously guarded by the suppliers, either British Gas or the commercial organisations. The proper functioning and safety of a domestic installation is now insisted upon by law.
There is still some noticeable reluctance to use bottled gas as an automatic alternative to a non-existent piped supply. Yet it is almost wholly equivalent, and the price shows no significant difference. In place of a perpetual on-tap situation one may enter irito a contract or arrangement with the supplier for regular refills. This is best organised by having two cylinders or containers. The one is used until empty, the supply changed over to the other, and the empty one is replaced by a full one. The only slight chore is to transfer the supply pipe from one to the other cylinder, and rural life offers far worse tasks than that. Natural gas and bottled gas are not lethal in the way that town gas was, since they do not contain carbon monoxide. In heavy enough concentration they can asphyxiate by excluding air, but that takes some doing.
The products of combustion could contain carbon monoxide if combustion is interfered with and not allowed to proceed to its normal conclusion, which merely emphasises the need for ample combustion air, as detailed in a preceding post, and also the need to keep flue ways unobstructed. But, as has been pointed out, fatalities from this cause are of the order of those due to being struck by lightning; and we would point out that reasonable care gives greater chances of avoidance in the case of gas.
In all matters to do with mains gas the authority is British Gas, acting through the appropriate region and local showroom. Advice at least is free, and they make it clear that they will make no charge if summoned to attend to a situation, usually a leak, where safety is involved. Any action subsequent to the first aid might of course become chargeable. Loosely allied to the gas industry there is for installers the organisation called CORGI, the Confederation of Registered Gas Installers. Membership of CORGI gives reasonable assurance that the installer has proved his competence to deal with all matters concerning gas.
Gas appliances, like oil burning ones, should be given regular skilled service. Though sooting is not an endemic problem, gas burners can develop faults of their own, like linting, which alter the carefully arranged gas/air ratio and affect combustion efficiency.
Gas appliances are in the main capable of working without a flue or chimney, and flueless room heaters and geysers were once quite common. In recent times however the practice has become restricted to appliances of low thermal capacity, and we do not recommend it. One of the bad features of an unflued appliance, gas as well as the crude portable paraffin heater, is the amount of water vapour it produces. Sometimes installed partly to combat condensation, it does in fact encourage it. In flue matters gas is the most versatile fuel, for as well as being able to manage without, it is equally at home with conventional, balanced, Se-duct, U-duct and assisted flues.
Though gas runs second to electricity in being easy to control in a great variety of ways, it is first in modulation. This is the type of control which can vary anywhere between on and off, smoothly.
Electricity does not ‘burn’, is not a fossil fuel and so does not require a flue. But it is a fuel, since it is consumed and gives off energy as heat. In spite of the bitter warfare which occurs commercially between the fuels there is little going on in modern heating in which electricity is not present, even in a small capacity. Most control systems, for instance, are now electrical. A solid fuel boiler may be quite independent of it, but the circulating pump on the attached small bore system is not. Most oil fired boilers are wholly dependent. The point is worth making since, even nowadays, some people will weigh up electricity in terms of reliability – a throwback to the days when grid lines were often coming down. But it will be seen that failure of electricity will bring to a halt almost any central system, and perhaps the best way to insure against such a happening is to have at least one gas fire fitted.
Electricity is quite an expensive fuel. In compensation it is usually relatively cheap to install the necessary wiring; and it is very convenient, in being flueless, in appliances which are portable, and so on. There is a choice of tariffs for electricity users, and one, the off-peak tariff, owes its inception to electrical incursion into the central heating market. One other unique and disadvantageous feature of electricity is that it is unstorable. It must be made as required. But means can be found to turn it into heat first, and then store the heat. A suitable store must have several properties, which include mass and tolerance of high temperature. The first medium chosen was a concrete floor, from which came underfloor heating.
But the very mass of the subject rendered it difficult to control, almost impossible to do anything about a floor well warmed for a chilly day if Spring suddenly burst out – except open the windows wide. The system has therefore lapsed, to be replaced by the storage radiator and its big brother Elec-tricaire. This type of heater in its variants is described at length in a preceding post.
The ease of manipulation of electricity, the fact that anyone can run a cable and that the degree of expertise needed to run a gas pipe is not called for, has led to a good deal of controversy.
We have in mind particularly the type of system which is often claimed to be in some fashion Scandinavian, consists of several wall mounted heaters with controls, which will run for very low cost. If further identification is needed, it is sold by door-to-door salesmen, more often than not. And more often than not it is found to have two drawbacks. One is that the true running cost proves to be prohibitive, the other is that the instantaneous demand for electricity is beyond the capability of the average domestic service.
There may be genuine offers in this kind of system. But never, never commit yourself on the doorstep. Say that you will give a decision after you have shown the technical details to your local Electricity Board. No reputable seller can object to that.
Every electrical appliance has an opportunity to be tested for approval, and it follows that those most worth considering are the ones which have received approval. Look for the BEAB or Electricity Council label. When it comes to imported items, as increasingly it will, there is another consideration, that the item is suited to the characteristics of our current. It is not only having voltage in the range 230 to 250 volts a.c, but also having a frequency of 50 Hz, if there are moving parts.
There is no question but that electricity is not for taking risks with. Is it clear which connection is for earth, which for live? Does it have a fail-safe cut-off or similar device incorporated? If you are not absolutely sure about items of this kind, and did not buy the appliance from the Electricity Board do go and ask their advice before making any sort of connection.
Electric heating of the heat storage type, which employs solid floors or storage radiators of the individual or central type, is designed for use with off-peak current. This is electricity generated in ‘off-peak’ hours, taken to be 11 pm to 7 am with extensions beyond that period. It must be separately wired indoors, with its own meter, and unlike the standard supply does not have socket outlets. Each appliance designed for off-peak current is wired into the circuit.
Since the domestic hot water in a house with storage radiators is usually made by an immersion heater, and since this at standard tariff is more convenient than cheap, there would be considerable advantage in making hot water on the same off-peak tariff. This can be done, by arrangement with the Electricity Board. Since the basis of off-peak use is storage capacity, it follows that hot water made during the night must be sufficient for the day’s use, and this almost always means a larger than normal cylinder. It is possible that arrangements can be made for a cylinder to be warmed by off-peak current, with a standby heater working at standard tariff in case some top-up heat is required during the day.
A much later tariff, the White Meter, is a very different type. It might almost be called a challenge. As though the electricity people were saying ‘You’ve got a chance to win. But if you don’t get thoroughly organised it is more likely that we shall win.’ This is no bad thing, because getting organised is a sure step to economy – not only in gaining the advantage of the tariff, but in an all round saving of fuel. Getting organised means several things, the first of which, particularly for anyone with electric heating, means good insulation. It is greatly helped by planning for the automatic washing machine to perform in the small hours.
Cooking, for anyone with an electric cooker, is rarely other than an on-peak activity and weighs heavily on the wrong side of the balance. Electric heating by low temperature radiant panels is not a form of storage heating and so does not qualify for the off-peak tariff.
Electricity has proved that it is capable of competing with the other fuels on their own grounds. But in addition, electricity has two special characteristics. One is the way other fuels are dependent upon it. The other is its self-contained, flueless role, which makes it specially convenient for the type of dwelling which is necessarily self-contained and with no outlet but its door. This describes the modern flat of the sort not served by an overall heating system, or a bed sitter.
Central heating by storage radiators is the only form of central heating of which it may be said, with practical truth, that you can take it with you. The value of the circuit, which you leave behind, is a very small part of the total.
Two other fuels must be mentioned because they exist and are a practical proposition to someone, but in truth both are in a special and comparatively rare category.
There is wood, which used to be the only fuel available to our ancestors. Wood is nowadays in three classes. Anyone with access to woodland can get logs and sticks. Even when broken or sawn they are large units and best kept for the open fire. They are not suited to modern controlled apparatus such as a boiler, for several reasons. (1) The density, I.e. weight of fuel per unit of volume, is low, and refuelling must be frequent. (2) The absolute need to conform to a maximum size and often shape could impose an intolerable burden upon fuel preparation. (3) Wood usually gives off during partial distillation a light tar, which coats heat exchange surfaces and lower flues.
Next to logs there are cases where someone has access to standard offcuts as a byproduct of some process. While this might relieve the second condition listed above, it leaves the other two unchanged.
Finally there is sawdust, a much more common industrial byproduct. This has a use as a boiler fuel, but not seriously on the domestic scale. Because it is tightly packed it needs a supply of forced air for combustion, and it is usual for factories producing sawdust to use it as fuel for their own boiler plant.
The short answer about wood is that it is not suitable for burning in standard solid fuel apparatus of the kind we are discussing in this post. But there are answers for those who are lucky enough to have supplies available at little or no cosi.
Sawdust we have mentioned. But larger wood is still a standard fuel in parts of Scandinavia, and from there we import a limited amount of apparatus. There is at least one importer of Norwegian stoves, with a base in Wales and one in Scotland. And from Denmark at the time of writing there are two known to exist, one at least of them in Eire. The answer to wood must be, use suitable apparatus.
The second of the indigenous fuels is peat, widely associated with Ireland but still quite common in other areas, for example the ‘mosses’ around Manchester. Peat, like wood, is not suited to apparatus designed for coal and coke. It tends to be dense in the same way as sawdust is, but perhaps it may also be described as sluggish. There is a slow inevitability about peat which makes it easy to believe the tales of fires which have been burning for three or four hundred years. The Irish are taking a commercial interest in peat, but as a boiler fuel it must stay in the commercial and industrial region. It will not concern us here.