All of the water pipes on the horizontal level in my house were changed from galvanized piping to copper with no problem. However, when it came to the ''risers'' -- the vertical pipes taking hot and cold water to the bathroom upstairs -- a problem developed with the cold water connection. It has a lot of corrosion as hard as cement caused by joining copper to galvanized piping.

Now the plumber says he will have to dig a hole in the bathroom floor and maybe into the wall to get the galvanized pipe out so he can run copper all the way.

Is there any other way to remedy this situation? -- A.T.

The corrosion at the joint where the copper was connected to the galvanized plumbing is caused by electrolysis, the rapid corrosion of pipe caused by chemical interactions between copper and iron.

To correct this problem, isolate the two metals with a 12-inch section of brass pipe, or a dielectric or insulated union. There should be no need to replace the galvanized pipe in the wall or floor, unless you suspect there are other problems with this piping.

We have central warm-air heating and air conditioning. We have an English-type walk-in basement with five heating vents, four of which are in the ceiling.

Do you have any ideas on how we can keep our finished basement from being so cold, particularly in spring and early fall when the furnace is not on? -- L.B.

Since heat rises, any heating system that has the heating vents near the top of the room or in the ceiling will continue to be very inefficient.

You might consider the installation of radiant electric heating at the baseboard level to help take the chill off this area and keep the floors warm during cooler months.

Electric radiant heating is not the most efficient heating system and is often quite expensive. However, when used on a room-by-room basis, and controlled with an accurate thermostat, it can be effective.

Or you might consider using one of the newer small room electric heaters. They can rapidly take the chill off. Even in a large room one heater can be very effective. By using a portable room heater you save on installation costs that would be required in the baseboard heating system. Cost of operation would probably also be less.

I have an old house and the water pipes are in the crawl space that has a dirt floor. In the winter they freeze. I've wrapped them with an electric tape, pipe insulation and also put regular insulation (held up by chicken wire) under there.

What else can I do to keep the pipes from freezing this winter? They do so only when it goes below 20 degrees Fahrenheit. -- M.B.

You can wrap the pipe with an electric heating cable, which should provide enough heat to keep them from freezing. Be sure to run the cable down the pipe below the frost line instead of stopping at ground level. To avoid unnecessary heat loss, you can wrap the pipe and cable with a fireproof insulation such as fiberglass.

Send inquiries to Here's How, P.O. Box 190, San Diego, Calif. 92112-0190. Only questions of general interest can be answered in the column.