page 120

Heating the Home

R. J. Parry A.M.I.E.E., ASS.I.MECH.E., A.M.N.Z.I.E.

Most of us, when we are considering the heating of our houses, think only of temperature. But heating, to be comfortable, always involves another important element: humidity. ‘Humidity’, briefly, is the amount of water vapour in the atmosphere. Some forms of heating lower the humidity; in other words, they make the atmosphere dry and give rise to various physical discomforts such as parched throats and headaches. This is a matter which has to be taken into consideration.

(1) open coal fire. In British and probably all Western countries the fireplace is traditionally the focal point of the household. Apart from its function as a source of heat, it has a psychological value which often outweighs the technical advantages of other possible means. A summary of the technical features of various forms of heating is given at the end of this article, but with the open fire, the cosy appearance, the satisfying appeal of flame and glowing embers are factors which will probably leave the open fire a prime favourite for a long time.

The open fire has also the useful property of inducing a draught and thus changing the air in a room. The fireplace should preferably be sited in the middle of a building so that all the heat from the chimney is used and fresh air circulated.

Such an induced draught is, however, not an unmixed blessing. This is evident on a cold night in a poorly insulated room when the occupants grouped round the fireplace are toasted in front and frozen behind. This is one of the greatest deficiencies of the open fire, particularly when passages and bedrooms are unheated — the source of heat is too concentrated, too canalized and too limited.

Other disadvantages are dust and smoke (which lead to costly renovation of decorations); erratic quality of fuel; necessity of storage and service of fuel; the constructional expense of the fireplace and chimney.

(2) gas fire. The greatest virtue of the gas fire is its convenience. Other virtues depend too much on the local supply; that is, on cost, cleanliness, availablity and pressure.

In New Zealand, proper and effective use is not so general as in Britain, owing partly to the greater development of our electricity supply and partly to the nature of the coal resources and qualities in the two countries. Also New Zealand, a new country with its towns sparsely spread, does not lend itself to economic reticulation.

In Britain the use of gas has continued to grow in parallel with the greater utilization of electricity; strangely enough, the increasing use of electricity has in no way diminished the use of gas; evidently there is still room for both utili[gap — reason: unclear] for some years to come.

One of the main drawbacks of the gas fire is that [gap — reason: unclear] produces a dry atmosphere, which in extreme cases give rise to throat dryness and headaches; this is particularly [gap — reason: unclear] when the appliance is fitted in a fireplace or replaces a[gap — reason: unclear] open fire.

Coal gas needs oxygen for complete combustion; hence when the flame burns it absorbs the oxygen from the air, leading to the feeling of dryness and heaviness. This defect can largely be rectified by placing a humidifier (e.g., a bowl of water) near the gas fire — an expedient used much too rarely.

Advantages of gas heating are its convenience and flexibility; with proper attention it can be cleaner in use than a coal fire, and of course involves less labour. Some cleaning is necessary, depending on the cleanliness of the gas supply. A gas stove which is not regularly cleaned soon gives evidence of its owner's neglect.

In New Zealand gas fires are generally of the open or semi-open type with refractory bases and elements for the storage and distribution of heat; their most noticeable feature, as of all gas appliances, is the quick warmth they bring, a response speedier than with any other form of appliance.

Its very nature, however, restricts its variety and application, and a flue for the dispersal of the products of combustion is usually necessary. There are on the market patented proprietary appliances which dispense with the flue. Although these are not yet in very general use, they are worth further investigation and development.

Gas firing with a central heating furnace is convenient and usable with several types, but in New Zealand its full use in all forms is retarded by its high cost — high, that is, compared with the price of electricity here and of gas in overseas countries.

This is inevitably the result of the high cost and poor quality of New Zealand coal. Gas supplies are slowly improving in some places, and in normal times in the main centres there will probably be no shortage.

(3) enclosed stove. The slow combustion stove was developed in its present form in Europe, where greater extremes of temperature and the need for economy led to conservation of fuel and financial resources. This stove, enclosed, continuous burning, either inset or free standing, is already popular in Britain and is becoming increasingly so in New Zealand.

page 121

Its optimum efficiency (around 70 per cent) is obtainable only with a good slow burning coal such as Welsh anthracite. Various types of stove, however, burn other fuels such as coke, and synthetic fuel such a briquettes.

Apart from being self-contained and very clean (bearing in mind the fuel burned) stoves of this type are economical of fuel compared with the much more wasteful open fire.

Unfortunately, the poor quality, dirty coal usually found in New Zealand today, with its low calorific value and high ash content, make it poor fuel for the enclosed, slow combustion stove, but even so it is more economical.

The free standing stove is more efficient than one inset in a fireplace, unless the latter can be used for heating a room at the back — for example, where the kitchen backs on to the living room.

In this case there should be access to the chimney if coal is burned. The convenience of the stove, particularly with anthracite, is a valuable feature: a room can be warm in the early morning; plates can be warmed; with a back-of-the-grate-boiler hot water is readly available; in a back-to-back grate the oven can quickly be raised to a high temperature; there is a minimum of cleaning and attention involved; controlled heat is obtained by opening and closing door and damper.

(4) electric heating. This is the most modern, flexible and convenient of all forms of heating. But it is not at the moment as much used as it should be owing to the limitations of supply. Strangely, its very shortage has led to a greater appreciation of its value: its convenience, its flexibility and (in New Zealand) its reasonable cost.

There is no function of heating which cannot be performed electrically; no application where it cannot be used.

In the past, and today, various forms of proprietary electric fires emulate the coal fire and simulate flame and flicker effect. It would be far better, as many people are coming to realize, if the inherent features of cleanliness and convenience had been more emphasized.

Two factors which should be considered when the benefits of electric heatring are discussed: (a) Its cost. This ideally should not exceed a farthing per unit. (b) It should be the sole means of heating; full advantage can then be taken of its efficiency. If this is fully gone into when the house is being built, chimneys, storage space and fireplaces can all be eliminated with a saving in capital expenditure and a freedom from the restrictions imposed by conventional building design. Generous provision in the design stage of an electrical installation means ultimate saving, but it also presupposes an adequate electricity supply.

The most usual applications of electric heating are:

1. Tubular heater or hot pipes, working at a low surface temperature and low electrical consumption. These are usually fitted beneath windows. They are very useful for page 122 supplementing existing heating schemes and for heating halls, passages and landings, a field of application almost entirely its own.

2. Panel heating units which can be fitted on walls, on floors or on ceilings. Here again there is almost infinite choice in design and position.

3. The closed or open fire which can sit in the open fireplace or be placed anywhere convenient.

4. Wallpapers are now made containing electric elements which work at a low surface temperature.

All such forms of electric heating depend on the heating value of an electric current flowing through a wire having resistance, the energy being dissipated in the form of heat, ranging from black to cherry red.

An outstanding advantage of electric heating is that it can (best of all systems) be thermostatically controlled.

(5) central heating. This will go without more than mention because in only very few New Zealand homes can such an installation be justified on grounds of economy or climate.