A trend toward larger rooms in homes inspires many do-it-yourselfers to consider tearing out interior walls to create bigger spaces.

Removing a wall is always a major undertaking, however, and should never be done without careful planning. Do-it-yourselfers should also be certain to learn the difference between the load-bearing and nonbearing walls in their homes so that the structural strength of the house is not damaged in the room-enlarging project.

Load-bearing walls or supporting walls are those that help hold the weight of the construction above them. Normally these walls run at right angles to the ceiling joists and often joists are jointed or tied together directly over such walls.

Interior load-bearing walls can often be safely removed, but some other means of supporting the construction, such as a girder, must be provided. Therefore, removing a load-bearing wall is a project that should be left to experienced carpenters or should be undertaken only by advanced do-it-yourselfers who know exactly what they are doing.

Nonbearing walls, however, can be removed without harming the structure of the house, since they are simply partitions. This type of wall normally runs in the same direction as the joists.

Even a nonbearing wall must be removed with care, since it might contain wiring or plumbing that will have to be rerouted. Some patching and refinishing of the ceiling, floor and any abutting walls will also be necessary.

For clues to whether any specific wall is load-bearing or nonbearing, do some detective work that starts by checking the direction of the joists of the house. Normally, the joists run across the house's narrow dimension, but they can often be visually inspected in the basement, crawl space or attic of the house.

Overlaps or other types of joints at the midpoint of attic joist are a certain sign that a perpendicular wall underneath is a load-bearing wall.

If the joists are in one piece but rest on a perpendicular wall, it's still possible the wall is helping support the load. This is especially true if the span or length of the joists is long or if the joists are shallow, such as 2-by-6s. The best bet, in a doubtful case, is to get the opinion of an experienced carpenter.

In some newer houses, the roof is supported by unitized sections of joists and rafters called trusses. These trusses run from one outside wall to the other and need support only from the outside walls, so any interior walls on the level under them are nonbearing walls. It is usually easy to recognize trusses by their triangular bracing system.

In a one-story, truss-built house, therefore, all interior walls are non-bearing walls. In a two-story house with a truss-supported roof, however, there can be bearing walls on the first floor.

In general, any wall that runs through the middle area of a house and is at right angles to the joists, should be suspected of being a load-bearing wall unless it is directly under trusses.

Here are a couple of additional steps to take before removing a non-bearing wall:

If there are toilets, sinks or other plumbing fixtures in rooms above the wall, it is probable that the wall is a conduit for pipes. Make plans for rerouting the piping before removing the wall; it could be a major project. If in doubt, call in a plumber and get some expect advice.

Note the location of any electrical outlets or switches on the wall. Relocating these and rerouting wiring is not as difficult as making plumbing changes, but it's possible an electrician's help will be needed at some point in the project.

Remove any doors, moldings and baseboard first. If carefully removed, these can often be reused.

Removing either plaster or wallboard is messy, so furniture and rugs in the vicinity should be moved or protected.

If you're fed up with the high cost and crisis atomosphere of heating your home with oil or gas, but aren't quite ready for solar energy, you'll be interested in "Heating With Coal" by John W. Bartok Jr. (Garden Way, $5.95 paperback). This excellent new book, which points out that the United States has enough coal reserves to last several hundred years even if demand increases, is a primer on selecting, installing and using all types of coal heaters and accessories.

The author, a professor and agricultural engineer at the University of Connecticut, doesn't attempt to romanticize his subject. He concedes that tending a coal stove or furnace requires at least half an hour per day of hard, messy work. "You can also expect to have more dirt and dust in the house," Bartok adds.

However, coal does have advantages over most other fuels, particularly in price and supply, and an automatic stoker can take some of the work out of owning a central coal heater. Coal also comes out well when compared with wood. It is cheaper than wood in most areas, takes less space to store, is relatively free of dangerous creosote and, of course, it doesn't need to be chopped and seasoned.

Among the dozens of valuable tips in this book is a warning not to attempt to burn coal in a stove designed for wood. Coal burns hotter than wood and requires more air, and problems could result.

"Heating With Coal" is well-illustrated and well-organized, and Bartok makes some thought-provoking points. An example: "For every tone [of coal] burned, 150 fewer gallons of oil will have to be imported."