When I bought my home some years ago, I paid about 19 cents a gallon for heating oil. This winter there's talk of that price reaching a dollar. Even worse is the possibility there won't be enough oil to keep us warm at any price. So homeowners have been roused from their complacency and are looking for ways to save fuel.

One of the best spots to attack fuel waste is in your furnace, and one of the simplest ways is through downsizing. Downsizing is the installation of a smaller burner nozzle in your furnace. Here's how it works.

As you probably know, your furnace is controlled by a thermostat. When the temperature in your home drops below the level set on your thermostat, the furnace switches on. It runs until your home warms up and the thermostat is "satisfied." Then it shuts off.

But every time the furnace shuts off, a certain amount of heat is wasted. And the longer the furnace remains off, the more heat it wastes. Ideally, a furnace should run constantly, eliminating those fuel-wasting off periods. But that's impossible. A furnace that runs constantly might keep the house just right on a 20-degree day, but it would overheat you if the temperature outside hit 40 and give you the shivers if the temperature outside dropped to zero.

The best you can do is size your furnace to run constantly on the coldest day you can expect. But most furnaces are oversized when installed (just to make sure they can do the job, and to provide extra capacity in case the house is enlarged). And the problem can be aggravated if you added insulation, caulking and weatherstripping or storm windowns. All these steps have the effect of making your furnace too large.

Downsizing is the solution. If your furnace runs intermittently, even on the coldest day of winter, it is too large. Ask your service representative to check and see about installing a smaller burner nozzle. The smaller nozzle will burn less fuel per hour and in effct make your furnace burn longer. Thus you move closer to the ideal of constant operation.

This approach is a lot simpler and cheaper than installing a whole new furnace or burnere gun. The nozzle is a small part, selling for less than $10, and the job of installing it and returning the furnace shouldn't be more than $75 total.

But downsizing has its limitations. You can only reduce nozzle size so far. Then performance may actually begin to suffer, and you can even damage the furnace. If downsizing won't work for you, possibly a whole new burner gun will. And if your furnace is especially old, inefficient or prone to breakdowns, a whole new furnace may be the answer.

But if downsizing will work, by all means try it. After the nozzle is changed, the service representative should retune the furnace, checking draft and flue temperatures, and sampling exhaust gases. Downsizing will almost surely throw things out of tune.

Q. I would like to make some wooden toys for my son, but cannot locate the tool I need to cut threads in wooden dowels. Do you know where I could find them?

A. I know of two places, but let me warn you these tools are not cheap. Woodcraft Supply, 313 Montvale Avenue, Woburn, Mass., has the best prices on tools for cutting threads on dowels one inch in diameter and smaller. But if you want to cut threads larger than that, Leichtung, Inc., 701 Beta Drive, No. 17, Cleveland, Ohio 44143, has better prices.

Q. We get water in our cellar whenever it rains -- sometimes as deep as a foot. What's the proper way to prevent the water from leaking in, and what do you think about a sump pump?

A. I'd have to know just how the water is getting in before I could come up with a specific fix. Go to the library and check out the article on wet basements featured in the September '72 issue of Popular Science.

I think sump pumps are a good idea. They don't really solve the leaking, but they do eliminate the water. And if the problem is severe -- as yours is -- the pump is often cheaper than the type of repairs that may be necessary.