Most households water is heated in a boiler fired with coal, coko, anthracite, or gas, and stored in a hot-water tank. The boiler may be one built into the back of the kitchen range, or a fireplace which also heats a room; or – this alternative is becoming increasingly popular – is an independent boiler having the fire more or less completely surrounded by water.
A range boiler, even if of the boot or L type, is far less efficient than an enclosed boiler, which in many cases is adopted for the slow-combustion burning of anthracite or coke. It may be said without fear of contradiction that a pound of coal, etc., consumed in an enclosed boiler does as much heating as two or even three pounds burned in a range. Where the latter is built against an outside wall, one has only to stand near the outer face of the wall when a good fire is on to realize how much heat is being dissipated uselessly.
The charge usually brought against the enclosed boiler is one of cheerlessness, as compared with the kindly glow and room-heating power of a range. It is obvious that the heat cannot be in two places at once; the more of it that goes into the water, the less of it there will be for warming the room.
It is possible, however, to get boilers which, when not needed for water-heating, can be manipulated to give a very good imitation of an open fire as regards both cheeriness and radiation.
It may be added that it is very feasible to harness range and independent boiler together, or to use either separately. The one which is not doing duty will merely be a dead end and not affect the general circulation of the system.
The, Cylinder System
The cylinder, in which the hot water is stored, is near the boiler; say, in a cupboard. Hot water is drawn off from tha flow pipe leaving the cylinder at the top – where the hottest water, being lightest, collects. This pipe is continued upwards above the level of the cold-water tank, fed automatically from the main through a ball-cock, and its end is bent over so as to discharge any water and steam that may be thrown out if the water boils, into the tank. This pipe should never be closed, since it acts as a safety-valve.
As fast as hot water is drawn off it is replaced in the eylinder by cold water from the feed pipe entering at or near the bottom. The cold water, be it noted, should not be able to flow directly upwards and chill the hot water collected in the upper part of the cylinder. If the feed pipe is vertical as shown, a spreading plate, p, should be fitted to deflect it horizontally.
The hot-water taps n and c are on dead ends. If water has not been drawn off for some time, that in the branches and the flow pipe will have chilled. Consequently hot water will not issue from a tap till this cold water has been drawn off and the pipes have been heated up. If a return pipe (indicated by broken lines in the diagram) is fitted, a constant circulation of water near taps can be produced; and as soon as a tap is opened, hot water issues.
The existence of a return pipe makes it possible to supply house-heating radiators off the hot-water system in the manner shown. It may be added that, where hot water piping is fitted, the branches, if left unjacketed, act as small radiators. In winter this may be an advantage, but at all times it tends to drill the hot-water supply.
A stop-cock on the feed pipe for interrupting the feed when taps have to be rewashercd is a convenience, if each branch is not provided with its own stopcock – which is the better plan. And there should be a drain-cock at a lower level than the bottom of the cylinder, to empty the cylinder when the boiler requires cleaning out. If the cock has a threaded nozzle to lit the collar of the garden hose, emptying becomes a simple and cleanly business.
Elevated Hot-water Tank Sistem. – In some houses the hot-water storage system is on an upper floor, and connected by two pipes with a range or enclosed boiler. Hot water is drawn off from the flow pipe, which is hotter than the return pipe, below the tank.
This arrangement, has two disadvantages: the first, that the long connections between boiler and tank allow a considerable escape of heat, unless they are well insulated. The second, that if the cold-water supply should fail, the tank could be emptied unawares.
This would interrupt the circulation through the boiler and, as the only water Outside the boiler would be that standing in the flow and return pipes, the water in the boiler would soon boil itself dry. A sudden inrush of cold water would damage the boiler and might cause an explosion.
To provide for rewashering of taps without emptying the tank, stop-cocks A and B are fitted on both flow and return pipes. This is a dangerous practice, as if both were accidentally left closed, an erplosion uright result.
The arrangement is therefore a bad one. The draw-off for an elevated tank should, as in the case of a cylinder, be from a joint above it, say, from the expansion pipe, through a separato pipe; and the flow and return pipes should be used only for circulating purposes, and be left free of stop-cocks.
Wherever a stop-cock on a hot-water system may be fitted, it should be marked in a way which will show clearly whether it is closed or open.
It may be mentioned here that frost can have the effect of stop-cocks by freezing up expansion and feed pipes. This is an argument in favour of emptying cold-water tanks and pipes in very severe weather if there is any doubt as to their ability to resist frost.
Pipes. – The pipes used on a hot-water installation, being necessarily of iron, are liable to rust internally, and have their effective bore reduced. Pipes connecting the boiler with cylinder or tank are subject to furring. If the flow and return pipes are of small bore, the turning on of a tap starves other taps at a higher level; and a person wanting hot water in the bathroom may have to wait patiently till somebody else has ceased drawing from the scullery tap.
Lack of size also makes drawing slow when a tap is but a few feet below the level of the cold-water tank. This happens in many bathrooms. The cold water, with a short direct run through a separate pipe, rushes out merrily enough; but the hot water has to be pushed out by cold, and the pressure due to the small difference of level may be largely counteracted by the friction in the long run of piping concerned.
To draw water from it there must be movement of water downwards through the feed pipe to the cylinder and upwards through the flow pipe to the branch. Friction increases very quickly with decrease in bore.
So there are good reasons for having the mam pipes of liberal size- – 1-inch or 1£-inch bore; especially those connected directly with the boiler, the furring up of which may give serious trouble.
Gas-heated boilers, if not so economical as enclosed boilers burning solid fuel, save the user trouble and are very cleanly. The water is kept automatically at a more or less constant heat by means of a thermostat, which turns down the burners as the temperature of the water approaches the maximum allowed.
In flats to which hot water is not laid on from a central supply, the gas-heated geyser, which is in elfect a boiler with a heating surface so large that a flow of water is warmed sufficiently by a short contact with it, has much to recommend it. But the fumes must be led away into the open air through an efficient flue, fitted with a cowl which prevents back draught, or thesr may be dangerous.
Electric boilers have an efficiency of 100 per cent., if the heating element is entirely surrounded by the water to be heated. Electric heating is ideal for cleanliness and convenience, but is economical only where very small quantities of hot water are needed; or where current is supplied at A very low cost.
Cleaning Boilers. – -The efficiency of a boiler is reduced seriously if the heating surface becomes thickly encrusted with scale inside. By preventing the rapid passage of heat into the water, encrustations allow the metal to become overheated, so that a furred-up boiler will burn through quicker than one which is kept clean. If the water is very hard, it will pay to have the boiler cleaned every six months. With soft water, however, once every three or four years may suffice.
Scale is deposited most rapidly from water at or near boiling point. If heating is not allowed to go beyond, say, 180 degrees, there should be little encrustation even with hard water. As it is a bad thing in any case to let the water boil and generate steam, if a boiler shows signs of boiling, measures should at once be taken to cool it. Ashes should be throws on the fire and the draught closed down, and a hot-water tap be allowed to run until sounds of ebullition cease.
A plumber is usually called in to clean a range boiler. If the reader feels the urge to do the job himself he should proceed as follows. First, cut off the cold water by turning the stop-cock on the feed pipe from the cistern (if there be one) or plugging the inlet to the feed pipe. Then run off the water in pipes and cylinder through the drain cock. (Or turn off the supply from the main and empty cold water cistern as well.) The top plate of the range has then to be removed to get at the top of the boiler, which will probably be covered with a thick layer of asbestes or other protective material.
The handhole cover is usually round and on the outside of the boiler. It is held against the boiler by a bolt which passes through a bridge-piece on the inside. When the nut on the upper end of the bolt has been unscrewed, the cover can be prised loose. This should be done gently to allow any water that may be imprisoned to be swabbed up with a cloth as fast as it comes out.
When leakage ceases, the cover can be taken off, the bridge-piece lifted out, and most of the water baled out. The loose scale is removed with the fingers. There may be a thick fixed deposit round the arch near the front. This should be scraped or chipped away as thoroughly as possible, care being taken not to damage the metal of the boiler.
The joint between cover and boiler is first made staunch with a flat rubber ring, standard sizes of which are stocked b r most ironmongers and builders merchants. The old packing must be removed and the cover, as well as the seating on the boiler, be scraped clean. A grom-met to fit the bolt is made by bending a piece of soft string into a circle just a bib larger across than the bolt and wrapping one end round and round the ring. The grommet when completed should fit tightly. It is smeared liberally with red-lend paint.
The tip of the bolt is stepped, and has a hole through it to take a loop of wire which will be needed while replacing the cover. Having made certain that the nut runs easily on the bolt – it may need running up and down a few times and greasing – lay the rubber collar in position, push the bolt through the bridge-piece and pass the latter through the opening. Then thread over the wire the cover, grommct, washer and nut, in this order, and screw the nut down while keeping the bridge-piece in place by pulling on the wire.
The nut must be screwed down hard. The grommet, when compressed between washer and cover, should seal the small clearance round the bolt effectively.
The cover having been replaced, it is covered with fire-proofing material which, besides protecting the joint directly, prevents flames passing over the boilor if it roaches – as it should do – to the lower side of the top plate. Any spaco left here will tend to deflect flames from their proper course under the boiler.
In another article reference is made to the economy of enclosing hot-water cisterns in a jacket of non-conducting material; and practical hints on jacketing are given .
Hot water can be economized by having leaking hot-water taps rcwashered at once; and by not running the water hot from a dead-end tap when only a small quantity is needed.
A fierce fire will heat water from the cold with less expenditure of fuel than a slow fire.