How to Keep Warm This Winter

New Zealand Listener, Volume 30, Issue 767, 2 April 1954, Page 8

How to Keep Warm This Winter

o~ owe Ss o~ The talk reprinted below was given recently in "Science Commentary,"

bv

R.F.

BENSEMAN

of the Dominion

Physical Laboratory, who has made a special study of heating problems

WANT to talk about a problem which we will all have to face in a few months’ time. It probably seems a bit early in the year to start worrying about house heating, but if you are going to do anything about your present heating system-now is the time to do it. Generally, our New Zealand climate is not too severe in the winter. This means that central heating, as it is used overseas, is not necessary in the average home. Nor do we need the whole house heated to an even temperature. We can be satisfied with some sort of heating atrangement which will keep one room nicely warmed-and the chill off the rest of the house. So that we can examine this business with some degree of logic, I’ve divided the talk into three parts: First of all an examination of the heating arrangements in the average New Zealand home. In particular I’m going to discuss the conventional open fire..Then I’m going to suggest an alternative to the open firenamely, the slow combustion stove. And finally, I’ll deal with the economics of the two systems; I’ll compare the initial cost of installing these two methods of heating, and the amounts of fuel needed to obtain the equivalent amount of warmth from each appliance. Now, getting back to the first pointan examination of our present heating arrangements. Most houses have at least one open fireplace which is used as the main defence against the cold winter evenings. Let’s have a look at the design of the average open fire, and briefly trace its development. It’s about 18 inches wide and perhaps 2 feet high; but it wasn’t always as small as this. I remember one that I saw in action some years ago. It must have been .all of four feet

wide and the best part of three feet high. It burnt a prodigious amount of fuel, but it was certainly cheery and most effective in keeping the room warm. The modern equivalent of this old style of fireplace has been developed for economic reasons. Fuel is no longer available for the taking, as it was 50 or more years ago. As a result the fireplace has been scaled down so that

it will use less. fuel. The present day open fire is only a shadow of its former gelf-and its continued use as a heating appliance has become a luxury which few of us can really afford. Now I’m going ‘to introduce a few figures to make some of my points clearer. In the laborato-y at Gracefield, we’ve measured the efficiency of an ordinary open fire, mainly to give us results to compare with the more advanced methods of heating. The results did not surprise us, since we expected them, but they may come as something of a shock to you. For ‘evety ‘ton of coal that is burnt in the open fire-between 17 and 18 hundredweight are effec-

tively lost up the chimney in the form of smoke and heated gases. The heat into the room is obtained only from. the two or three hundredweight which are not lost in this way. At the Laboratory we would say that the open fire has an efficiency of between 10 and 15 per cent. This is bad enough in itself, but add to it an air-flow up the chimney of about 20,000 cubic feet per hour, and you have not only a most inefficient method of heating, but the makings of a good sized draught .as well. But let’s be fair, and admit that the open fire is excellent company, and forms a focal point during the winter for the family circle. For this reason, many

people ate prepared. to put up with the low efficiency; but if you are in any way concerned about the cost of keeping warm, then the open fire which you are using at present should be examined again in the light of what I’m going to say about the slow combustion stove. The slow combustion stove has been in use on the Continent for the last two hundred years. Its introduction was brought about by much the same conditions which face this country. Fuel was becoming scarcer and dearer so that an appliance which could convert more of the fuel into useful heat for the house was needed. We in New Zealand have been fortunate in that our need for stoves has come so much later. As a result, suitable stoves are already available from overseas, which will fill our requirements quite nicely. Let’s examine one of these stoves. It consists roughly of two boxes-one inside the other, The inner firebox has doors in front through which the fuel is fed. An air control governs the draught through the fire and so regulates the rate of burning and the amount of heat given off. The outer box is merely a shield, put there for safety and decorative purposes. I haven’t time to explain how a stove works, but briefly, the main heating effect is caused by the passage of air over the outside of the firebox. This warm air circulates throughout the room, and even further if the doors are left open, and brings even heating to a large part of the house. We have tested the various makes of stoves which are available in this country, in exactly the same way that we tested the open fire -- and we found several interesting features in their operation. We found, for example, that the heating efficiency is closely related to the speed at which the fuel is burnt. The slower the burning, then the higher the efficiency. By carefully limiting the supply of air to a stove, we have been able to get efficiencies of over 70 per cent. These were rather special tests and a figure of between 50 and 60 per cent. would be nearer the practical truth. Compare this with an efficiency of between 10 and 15 per cent. for an open fire-and the savings that can be made by using a stove, are immediately apparent. And here’s another point-the air requirements of a stove are usually in the neighbourhood of 200 cubic feet per hour. This is a big reduction on the needs of the open fire, which as I’ve said earlier, can be as great as 20,000 cubic feet per hour. In fact one of the first things you will notice when using a stove, is the almost complete absence of draught. "s The figures I’ve given so far have put me in a position to make a few calculations on the cost of running the open fire as compared with the slow combustion stove. Since the stove is at least four times as efficient, in one winter, where formerly you used say 20 bags of coal-with a stove you should not need more than five. This seems a straightforward calculation, and yet it is at this point that human nature defeats the logic of mathernatics. In a practical case we have generally found that about the same amount of fuel is burnt, irrespective of whether an open fire or a stove is used. Perhaps you are already ahead of me and have seen where I made a wrong assumption. The average householder will seldom light the open fire ‘before the late afternoon-generally it will burn from say 4.0 until 10.0, The stove on the other hand is seldom used for such a short time, and it is almost ‘ (continued on next page)

(continued from previous page) inevitable that the householder who experiences the warmth and comfort such a heater can give, will have it going 24 hours a day. In this way the calculated fuel saving is lost. Over a winter your fuel bills will be smaller but not much smaller than they were before. But-and this is the important thing-next spring you will remember a house that was warm right through the winter, both day and night, and not just for a few brief hours in the evening. I promised earlier to say something of the cost of installing a stove. It’s difficult to give exact values, but as a working rule you can use this example. A stove and the necessary flue pipe can be put into a new house for a little less than the cost of an open fire and the.attendent chimney. In a house which already has an open fire, the stove can be fitted to use the existing chimney. The cost of the stove becomes a straight capital charge which may be recovered by lower tuel bills in the future, although I think this unlikely. However, you will have the benefit of a far superior heating arrangement. : Although I’ve covered as fully as possible the measurable advantages o the stove as compared with the open fire, there still remain those intangible

ee qualities. which cannot be specified exactly — convenience, safety, appearance, and so on. In every respect except one, the stove is greatly superior. The one exception is appearance. Stoves are neat but they’re not attractive. They are meant to be tucked away in some inconspicuous corner of the house, to act as a heater and not as a focus for social gatherings. In the last three years I’ve been in contact with hundreds of householders, who have replaced their open fire by a slow combustion stove. In all except three cases, they have expressed ¢omplete satisfaction with the change, and only regret that they hadn’t made it earlier. Of the three exceptions, one was dug to improper insta!lation, another to a faulty stove, and the third I didn’t have a chance to examine, so I can’t say what the trouble was there. But it’s safe to say, that when a stove is operating properly, there is no question of its superiority to our conventional open fire. So there’s the position. If you’re prepared to exchange the company of your open fire for an economical, more con® venient, and safer method of heatingthen you can’t do better than install a slow combustion stove. Think it over, before it’s too late to do anything this year.