If you could build a perfectly insulated house, you'd never have to heat it during the winter. It wouldn't even need a furnace. Just the heat created by your body and electrical appliances would be enough to keep you warm through any weather.

Of course, perfectly insulated houses don't exist. But they are becoming more nearly a reality than anyone would have expected just a few years ago, and "superinsulated" houses are starting to pop up across the United States and Canada.

In one example, the attic has more than 16 inches of fiberglass insulation for an R-value of 55. In the floor are six-inch batts. But it's the walls that are actually the equivalent of two regular house walls, stuffed full of insulation. The result is R-32, well over twice the value found in the typically insulated home.

There's more to these walls than just a lot of insulation. Using double walls instead of a single thick wall means that the studs framing the interior wall of the house never touch the exterior wall. Thus the studs can't conduct heat directly through the wall -- bypassing the insulation -- as they can with single-wall construction.

How will a house of this type perform? One of them has made it through a Canadian winter on the amount of fuel that would heat a normally insulated house for two weeks. Typical energy savings for superinsulated houses run somewhere around 75 percent.

To really perform well, these houses need a few other refinements in addition to superinsulation. One is triple glazing. Another is careful sizing and placement of the windows. Most windows are located on the south side of the house so they can gather solar heat. Windows on the east and west walls are kept small, and windows on the north face are usually omitted altogether.

Also important is an all-out attack on air infiltration. Many such homes feature a continuous plastic film vapor barrier that also helps to seal out drafts. Others have vestibule or "air lock" entries. To enter the home you open the door and step into a small vestibule or mud room. You close the outer door to seal out the cold, then open the inner door and enter the house.

The house is also very carefully weatherstripped and caulked. The result of all this sealing may make the house so airtight that the air inside becomes stale or even polluted. The solution to this is an air-to-air heat-exchanger, which exhausts stale air from the house and pulls in fresh air. The two air streams pass on the opposite sides of thin plates, and in doing so pass the heat from the outgoing air to the fresh air. Result? Ventilation without heat loss.

It's surprising that more houses of this type are not being built. Sure they cost more to build than conventional houses, but they can quickly make up the difference in fuel savings. Cutting fuel costs by 75 percent is about all you can expect from a solar home. But a solar home will probably cost more to build, and it will rely on mechanical systems that need maintenance and repairs. Insulation does its job without attention, and it never wears out.

Of course, insulation can do more than keep the heat in your home during the winter -- it can also keep it out during the summer, resulting in significant savings on cooling costs. Q: We are remodeling an old house and have run into several areas where the woodwork has been painted over. The paint is finely cracked, like a dry lake bed. We would like to keep these areas painted, but are afraid that the new coat will also crack. Is there any way of dealing with this short of stripping down to bare wood?

Also, we plan to finish the floors with polyurethane, but would like them to match the baseboards, which are reddish. Can stain or other pigments be added to the urethane to make this a one-step process?

Finally, we would like to install a wood stove and make use of an existing chimney, but the chimney is unlined. Any suggestions? A: I have some old woodwork in my home with the same lake-bed appearance. About a year ago I troweled on a thin coat of wallboard compound to fill the cracks. Then I sanded lightly to scuff up the paint and remove any excess compound. Over that I painted. So far, things look good, but I am not sure how well the treatment will hold up over the years. My guess is that the original cracking was due to lack of compatibility between two coats of finish that were applied before you bought your house. Those two coats should be through shifting by now, and I doubt you will get any further cracking. No guarantees, though. If you don't like to gamble, strip down to the bare wood and start over.

Yes, you can mix stains and pigments into polyurethane, but I wouldn't do it, especially on a floor. The depth of the color will depend on the thickness of the finish. Spots that get a slightly thicker coat will be darker. Brush marks will show, too. Then as the floor starts to wear in high-traffic areas, the color will begin to wear away and lighten up.

Best bet is to put on the stain separately. This will give you better control, a wider slection of stains, a better orginal match, and better color stability over the long haul.

Now for the chimney: You are right not to use the unlined chimney as is. Some masons can add clay liners, a section at a time, into unlined chimneys, but this is tricky work, and it is hard to be sure the seams between the tiles are properly mortared. Best solution here is to lower sections of single or double-wall stainless-steel stovepipe into your chimney, using the existing flue as nothing more than a space to run the new flue. The sketch shows how the installation should look, with an air space all around the new pipe. Do not use ordinary steel stovepipe for this job. It will rust out in a season or two, leaving you with no protection. Most local codes do approve of stainless steel for this application, though. Check first with your local building inspector to see what he approves, however. He may be able to give you further advice, and will surely steer you away from techniques that are not approved in your locality.