Chapter 24. Types of Heating Systems

There are many kinds of equipment used to heat houses. Because the fireplace is the most ancient it should be considered first, although as heating equip­ment it deserves little consideration. A fireplace exists to warm your soul and to make a room cheerful; do not count on it to raise the room temperature much except in its immediate vicinity. Whether you in­clude a fireplace in your new home depends largely on whether you like a fireplace or not. If you con­sider a fireplace to be a nuisance, if you feel that it is liable to be a source of ashes and dirt, and that the wood will bring litter into the house, and that sparks might damage the carpet, and that all this will inter­fere with your immaculate housekeeping, then you do not want and should not have a fireplace.

If you like to sit before the open fire during the long winter evenings and "toast your shins," or if you like to entertain guests by the fireplace, maybe even with "fireplace snacks," and if you do not mind too much the minor litter caused by wood and ashes, then you should by all means have a fireplace and a good one at that. Be sure the fireplace is built so that it will draw well enough to not smoke.

An imitation fireplace is hardly worth the effort of building it, but a small gas-fired fireplace with imitation logs, if properly vented, can be very cozy where a wood-burning fireplace is not feasible.

Heating stoves, still used in many rural areas, do a very efficient job of heating a house. The fuels most commonly used are wood or oil. A brick chimney will be required for a stove of this kind.

Portable gas heaters that are not connected to a vent through the roof are entirely unsafe and should never be used.

Radiant panel heaters installed in the wall and connected to a proper vent or flue will give fairly satisfactory inexpensive heating. The usual fuel for these is gas, natural or manufactured.

The central heating system is coming into use as the most effective and economical way of heating the house. There are several types of these on the market, both as to fuel used and the means of getting the heat where it is wanted.

If a house has a basement, the gravity warm-air system is the least expensive and the easiest to in­stall. The furnace will function most efficiently if it is placed near the center of the house. Heat ducts are made as short as possible and run to registers near the floor. The cold air returns are cut through the floor under the windows or where the cold air is most likely to enter the room. Often the space be­tween the joists can be utilized for the return ducts by merely enclosing the bottom, letting the joists form the sides of the duct and the floor the top. A certain amount of metal work will be necessary to get the air from these ducts to the furnace, where it enters near the bottom of the furnace. The heated air is taken off near the top of the furnace. Thus the difference in temperature of the air will cause it to circulate as the warm air rises and the cold air natur­ally flows in a downward direction. No additional force is needed to cause the air to circulate.

The fuel used in a furnace will be governed by the local conditions and the relative price of the various kinds. Where natural gas is available, it is usually the first choice; next comes fuel oil, coal, manufactured gas, and coke. Wood is seldom used in a furnace as it requires too much hand firing, and people want their furnaces automatic nowadays. Coal is easily handled by an automatic stoker.

If you feel that a gravity warm-air heating sys­tem will not meet your needs, the next step is a forced-air furnace. This has ducts similar to the gravity system, but the ducts can be slightly smaller and longer. The furnace can also be on the same level with the rest of the house, as the air is moved by a fan and not entirely by gravity. Often with a forced air system, the heat registers are placed under the windows or in the coldest parts of the room so they can warm up the cold air before it can crawl across the floor and chill your feet. The cold air returns are then placed on the inside walls. A very comfortable house can be made by this method of "perimeter heating," as it is called.

There are too many variations in the duct ar­rangements, each with its own advocates, to list them all here.

Heat is sometimes distributed to the various rooms by circulating hot water, which comes to ra­diators in the room by means of pipes, one to bring the hot water and another to take it back to the fur­nace to be reheated. The first cost of this type of in­stallation is higher than that of the circulating hot-air systems, but it gives a very uniform heat and is a good system. It is best installed by those experi­enced in doing so.

Steam is widely used to distribute the heat through buildings. In a large house this might be the best system, but it is seldom used in a small house. The steam does not require as large a piping system as the hot water, but requires more automatic con­trols and would probably cost more to install. The cost of operation would be about the same. This type should be installed by regular steam fitters and furnace men.

Heating the House

The first step in planning the heating of the house is to find out how much heat you will need. There are three factors to consider in arriving at the heat needed. The first is the climate. What will be the maximum difference between the inside temperature and the outside temperature on the coldest days of the year? The inside temperature will prob­ably not exceed 75°; some people keep their houses nearer 70°. If you live in a place where the outside temperature will drop to 40° below zero, you should use that figure in calculating the maximum heat needed. This would make a difference of 110°. In other places the coldest days seldom see the thermo­meter lower than 25°; this would make a maximum difference of 50°. All temperatures used in calculat­ing heating are in the Fahrenheit scale. In Florida and Southern California a maximum difference might be calculated at 40°.

Once you have decided what temperature range you will have to consider in heating, you have one of the important factors to use in calculating the heat­ing requirements of your house.

The second factor that needs considering is the amount of heat your house will lose for every degree difference between the inside and the outside tem­peratures. Then it is a simple matter to multiply the loss for one degree by the maximum number of de­grees difference that will occur between the inside and the outside to get the total heat needs of your house.

Heat is measured in a unit known as the British thermal unit, usually abbreviated B.T.U. This is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit. Heat loss through the various kinds of material is designated by a "U" factor, which is the amount of heat that will go through one square foot of the material in one hour if there is one degree difference between the two sides of the material. Then if you multiply the number of square feet of a material by the number of degrees difference between the outside and inside temperatures and multiply this by the "U" factor you will get the total heat loss for that area in one hour. Furnaces are rated by the number of B.T.U.'s they will produce in one hour, so you see there is a definite relation between the heat losses and the size of the furnace.

The following table will give an idea of the heat losses through several of the more common building materials.

An additional loss of heat occurs through air chat escapes around the windows and doors taking heat with it. Add up all the linear feet around the windows and doors, including the crack in the center where one window or sash joins another and mul­tiply this by 1 or 1.5 depending on how well the windows are fitted to get a factor comparable to the "U" factor previously found. This will be multiplied by the maximum temperature difference expected in the region where the house is located. This will give you approximately the heat per hour that will be necessary to make up for the loss by infiltration around the windows. Keep this figure and add it to the figure you will get when you calculate the heat loss by direct transmission through the materials your house is made of.

To find the total heat loss, find the number of square feet of each kind of material in the outside walls, ceiling, and floor of the house and multiply each area by the appropriate "U" factor given in the accompanying table. Then add all of these together and multiply by the maximum temperature differ­ence expected, and you will have the heat loss for the house. Calculate for the most unfavorable weather you can expect, since that is when the greatest de­mand will be made upon your heating system. The values given are only approximate, as construction varies so widely that greater refinement is unnec­essary. The results are only approximate, but the ca­pacity of a furnace may vary also and will be affect­ed by the quality of the fuel and the adjustment of the dampers.

Get a furnace that is just slightly larger than you think necessary, rather than one that is too small. A house that is not properly heated is seldom satis­factory.

The following example will illustrate a typical calculation of the heat losses of a house.

Multiplied by the maximum temperature difference of 70° = 103,880 B.T.U. This gives the heat required in one hour to heat the house on the coldest day. Considerable saving could be made in this if the house were well insulated.

The heat requirements then for the above house with insulation would be 60,300 B.T.U. per hour. The savings to be made by insulation need no further comment.

Keeping and Using the Heat You Generate

Heat travels by three methods: conduction, con­vection, and radiation. If one side of a piece of ma­terial is exposed to air or any substance of one tem­perature, and the other side is exposed to a lower temperature, heat will travel through the substance from the surface of higher temperature to the surface of lower temperature. This travel of heat is called conduction. The quantity of heat thus conducted will depend on the area of the surfaces, the thickness of the material, and the kind of material used. A piece of iron will conduct heat much faster than a piece of wood. Concrete or bricks will conduct heat rather rapidly, but a wall filled with good insulation will conduct very little heat. The reason for insulation in a house is to keep the heat in.

Heat will also travel in currents of air. This is called convection. If a building material lets air through, or if there are cracks through which air can flow, heat will travel with the air and will have to be replaced if the room is to be kept warm. The new air entering the room will have to be warmed up to room temperature.

Heat also travels by radiation. If you stand near a fire you can feel the heat as it strikes your skin or clothes. All surfaces radiate a certain amount of heat depending on the surface and its temperature. If our bodies radiate heat to a wall and the wall does not radiate back to us almost as much heat we feel chilly, even though the air may be warm. That's why you can feel chilly in a room having an air temperature of 80° if the walls are cold. Insulation pays off in comfort as well as in economy.

If the body gets rid of heat faster than it makes it, we feel cold, and if we cannot get rid of the heat fast enough, we get too warm. The correct balance of body heat with the surroundings is controlled by the clothes we wear and by the way we heat and cool our houses.

Heat comes into the house by radiation through the windows when the sun shines through the glass. This can be a good thing in the winter and can be very annoying in the summer. Fortunately it is pos­sible to plan the windows and the overhang of the roof so that when the sun is low in the winter the heat comes in, and in the summer when the sun is high, the roof shades the windows. You can also exclude much of the radiant heat by the use of re­flecting draperies to send the radiant heat right out through the windows through which it came in, and you can pull the draperies when you wish to wel­come the sun.

To   help  in   controlling  the   heat   that   comes through the walls and especially the roof, aluminum reflecting insulation is very effective. Of course, it does little for the conducted heat, but it can help to make the place more airtight and can help with heat transferred by convection.

In insulating, a combination of reflective insula­tion and of a rock wool or other type of blanket to catch the heat as it tries to escape by any of its three ways of getting away should be used.