This post explores possibilities for making fuel savings at no cost. Some of these were established habits a few decades ago, but have been largely forgotten in the age of push-button central heating. Others arise from modern theoretical knowledge, or involve the better use of modern appliances. Such techniques include:
– making the maximum use of sunshine throughout the heating season;
– studiously avoiding over-ventilation;
– choosing your use of rooms to make the greatest possible use of ‘incidental heat’;
– applying an understanding of comfort so as to be comfortable at lower energy cost;
– getting to know the outside temperature above which no space heating is needed;
– exploiting the ‘thermal mass’ of the house;
– exploiting the buoyancy of warm air;
– using appliances in a more efficient way;
– making full use of curtains to reduce heat loss from windows;
– making the most use of heat from cooking;
– pre-heating the cold water supply from ambient air to reduce hot water costs.
You will be aware that even in mid-winter the sun can supply some useful heat to a house, but most modern houses are not designed or oriented to exploit it. Heating systems, too, are commonly designed to ignore solar gains, with the result that rooms into which the sun shines can overheat on sunny days unless you juggle with manual controls, or open a window to spill some heat, or even draw the curtains. The former may be unnecessary or it may not. Both of the latter actions are needlessly wasteful.
The following paragraphs suggest how with a little thought and the minimum of effort you can make full use of such sunshine as you are lucky enough to get. They may make little impact on your fuel costs, but they could make an appreciable difference.
Open the curtains of sunny rooms as early as possible in the day, and open them as widely as possible. Do not open the windows – that will let the heat escape. Even if you are not using such a room, open its door to let the heat percolate into the rest of the house. If there is a room heater or heat emitter, shut it off while the sunshine lasts. Even if the room overheats a little, don’t open windows or close curtains if you can avoid it. That way more heat will be stored up for later in the day when the sun has moved round or gone down.
Use only a minimum of ventilation throughout the house. The exception might be if, by ventilation, you can create a slight through draught to carry sun-warmed air through the house and distribute it. A first-floor window opened slightly on the shady side of the house may help, depending on wind conditions that day. If possible, transfer activities to sunny rooms, and if possible do without central heating. But remember that if you let the sunless parts of the house go cold, it will take time to warm them up again. Get to know what cunning you can employ with your own house to be comfortable without heating as often as possible.
With ventilation you have to strike a balance between insufficient air, leading to stuffiness and possibly condensation on walls, floors and ceilings, and over-ventilation, which is very wasteful of heat. Research has shown that British people tend to over-ventilate their houses in mild winter weather, when draughts are not so noticeable. If you habitually do this you will use a lot more heating fuel than necessary. One reason is that most windows when they are open at all let through far more air than is needed. If the outside temperature is as high as 13°C you should not need heating at all, especially if there is any sunshine. Apart from sunshine, other incidental gains may well provide all the warmth you need to achieve comfort temperatures inside, if you do not waste it through ventilation.
If it is windy outside you probably need no windows open at all. Most houses have sufficient leakage, through other routes than the cracks you may be able to block up, to ventilate them adequately in windy weather. You must, of course, provide enough air to feed any fuel-burning appliance and remove pollution: failure to do so can be dangerous.
Remember that warm air rises, and windows left open upstairs will spill out vast quantities of valuable warm air — often causing cold draughts downstairs as well.
Using naturally warm rooms
Many houses have some rooms that receive more than their fair share of incidental heat gains. The kitchen is usually one of these, especially if it has a fridge and a central heating boiler in it. Consider whether it is possible to make more use of this heat by using such rooms more and not heating the rest of the house so much. A corner of a kitchen that is clean, well-decorated and attractively lit might easily double as a living room or homework room at such times. Many people have always arranged their lives around the warm places, so such advice may seem fatuous to them. But others, with full central heating, have come to see rooms as having distinct functions, and so use each one strictly for that function and add heat and light as necessary, because it is so easy to do so. There may be economies to be made from re-thinking such habits.
Understanding the nature of comfort
Most of us have become so used to simply turning up the heat in a room if we feel chilly in it that we do not consider whether we could be equally comfortable by another means without spending more on heating. Ask yourself whether you could improve the economy of using that room by:
– eliminating or avoiding a draught;
– improving where you sit in relation to radiant warmth, or keeping away from the coldest surfaces;
– reducing the tendency for warm air to rise to the ceiling and stay there – encourage it to circulate and mix by using a radiator shelf or placing a small fan to push or pull warm air down from high level;
– preventing cold air pooling on the floor, avoiding sitting with your feet in it, or taking special measures to keep your feet warm;
– using items of furniture that maximise thermal comfort – for example, a dining chair with a blanket or jacket draped over the back for long hours of sedentary work, as protection against draughts or cold radiation; arranging furniture that people can snuggle into like cats do ;
– shutting doors to contain the incidental heat gains from lights and/or a television set;
– making sure everyone in the room is equally well placed, or those most sensitive to cold sit in the warmest places.
Getting to know the ‘no-heat’ temperature
Keep an eye on the outside temperatures in mild winter weather, and get to know at what outside temperatures, in various conditions you can be comfortable inside without adding extra heat. In some circumstances it may be a lot more economical to provide just a little heat in one room than to heat the whole house, even if you heat that one room with a relatively expensive fuel.
Exploiting the house’s ‘thermal mass’
If you only want a bit of warmth for a short period, it may be sensible in a ‘massive’ house to use a ‘local’ heat source rather than central heating if you have it, and to avoid having to heat up the whole structure.
If you have free heat from sunshine, realise that heat will stay in the room for a long while after the rays of the sun have gone, in a heavy structure. In such a room, even when the sun’s heat is no longer enough for comfort, less extra heat will be needed in the evening than in rooms that have been cold all day.
At the end of the evening, switch off heating as early as possible before retiring — get to know how long it takes before the room becomes perceptibly chilly, at various outside temperatures and windspeeds. Make manual adjustments to heating at or before bedtime each night, to avoid leaving an extravagantly heated living room behind when you go to bed.
Exploiting the buoyancy of warm air
Use the fact that warm air rises to help distribute solar heat around the house, if you can usefully do so. In the evening, use the buoyancy of the warm air of living rooms to boost the temperature of bedrooms at bedtime: open the living-room doors at bedtime for this purpose. Conversely, remember that you can heat downstairs rooms more economically if you shut their doors: there is no point in heating unoccupied bedrooms, except of course to warm them up before using them, or when they are in use during waking hours.
Making full use of curtains
Curtained windows, particularly if the curtains are close fitting and well lined, can be as good as or better than double-glazing at retaining heat. During the heating season, close all curtains as soon as it gets dark – or even sooner if you can bear it and there is no more sunshine around.
Some curtain tracks stand clear of the wall to which they are fixed. If possible fix hardboard or stiff card neatly across the top to reduce the flow of warm air down the face of the window. The traditional ‘box pelmet’ does this job admirably, and prevents air currents from causing warmth to be ‘pumped’ out of the room in this way.
Heat used in cooking
Some understanding of the heat output of the cooker is advisable, for three reasons:
– having understood the safety aspect, you may be able to use heat from the cooker as a source of space heating, either regularly or in an emergency;
– you may be motivated to use it more economically.
It is necessary to consider gas and electric cookers separately, because they have important differences. A gas cooker has the same order of heat output as a central-heating system. For example, assume a typical central-heating/hot-water boiler burns gas at about 50 500 BTU/hour and the gas cooker burns about 53 700 BTU/ hour. However, the central-heating boiler has a ‘rated output’ of 38 000 BTU/hour, which is about 75 per cent of its rate of burning gas. Against this, the cooker delivers all the heat value of the gas it burns into the house, because it has no flue. So the cooker is a source of heat one-third more powerful, through being about 100 per cent efficient.
It does seem rather illogical that the central-heating boiler has to have a flue while the cooker does not, especially as this flue disposes of a quarter of the power of the boiler. However, the boiler may be running continuously, while the cooker is only expected to be used for an hour or two at a time, and during waking hours. The room where the cooker is must be adequately ventilated, of course. But such ventilation does not prevent all the waste gases staying in the house. In fact it may well assist, because a strong current of hot air from the cooker, backed by a source of cool air from outside, is quite likely to pour into the rest of the house by ‘stack effect’, unless barred by a closed door.
Certain observations follow. Firstly, the cooker provides by far the biggest incidental heat gain in the house: even one large burner represents some 17 per cent of the cooker’s output, equivalent to 9000 BTU/hour or about 2V% kW. Up to a point you probably have the choice as to whether to use this heat or forcefully to reject it, e.g. by a cooker hood or extract fan. To use it all would probably be unwise, as there may be potential lung irritants in the burned gases; in any case these gases usually carry dirt, grease and smell, and almost certainly water vapour. Such health risks as there are, are small: burned natural gas consists largely of carbon dioxide and water, but also traces of oxides of nitrogen, which, in quantity, can be harmful to lung sufferers. Some people of limited means consciously use gas cookers for space heating, perhaps without realising that, leaving all other considerations aside, they are using their gas in the most efficient way possible.
Given that the cooker provides so much heat, it also follows that it will pay to use it as efficiently as possible for cooking. This matters most outside the heating season, when the waste heat is of no other benefit. If, however, your heating system and the layout of the house do not make it possible to exploit the waste heat to help warm the house, then efficient use of the cooker is doubly important.
Gas cookers are limited in their scope for more efficient cooking. The use of broad-bottomed pans with lids, and especially of pressure cookers, no doubt helps. It is certainly worthwhile, too, to cook as many dishes as possible simultaneously in the oven, which is in itself the most efficient part of the cooker because of its retained heat and thermostatic control.
Electric cooking is inherently less wasteful of heat, partly because there are no burned gases to vent off, and partly because, where boiling rings are concerned, flat solid plates in contact with the bottoms of pans and kettles inevitably put more of the heat where it is required. The maximum heat output from electric cookers is typically up to 7 kW.
There is probably scope for better insulation of ovens of all types; present insulation standards are designed to keep outside surface temperatures within safe limits rather than to conserve heat for its own sake. The gas-cooker owner can experiment to find out which common processes normally done over gas might be done more economically by purpose-built electrical appliances. The improved cooking efficiency does not, however, outweigh the present differences in tariff. Typical annual consumptions for families are 60—80 therms of gas, as against 1000-1500 kWh of electricity.
The electric kettle is an exceedingly efficient way of boiling water, being both direct and very fast. The electric slow cooker, however, loses a great deal of heat simply because it takes so long.
Helping water heating with ambient energy in summer The temperature of cold water entering the house through the main will usually vary through the seasons, but also depends on the source from which the water is drawn. The warmer the supply to the hot water system, the less your hot water will cost. If, as is usual, the water stands in a large tank in the loft before it is used, it will warm up to something approaching air temperature, especially if the loftspace is heated by the sun. Hence, for example, if by this means you can warm the cold water supply from 10 C to 15°C, it will take 12 ½ per cent less heat to raise its temperature to 50°C in the hot water system. Such a saving is unlikely to be dramatic, but would nevertheless justify removing the insulation from the cold-water tank at the start of the summer. Don’t forget to put it back when the heating season starts again.
None of the suggestions listed in this post is likely to make on its own a large difference to your consumption, but the sum of all of them might easily equal the yield from a fairly expensive modification to the house, whereas most of them will have cost nothing at all.