Q - I have heard of conventional-looking 2,500 square-foot houses that can be heated and air-conditioned for less than $200 per year. How are these houses constructed and are they expensive to build?

- M.I.

A - You are referring to extremely energy-efficient construction called superinsulation. There are many construction techniques for superinsulated houses, and they needn't be a lot more expensive to build than any other house. While they look like any typical house, superinsulated houses cost only a fraction as much to heat and cool.

Both conventional and some new construction methods can be used to build a superinsulated house. Thick conventional studded walls are filled with new high-density insulation. The exterior, which can later be finished with brick, stucco, or siding, is covered with thick rigid foam insulation. This blocks energy-wasting thermal bridges through the wall studs.

In addition, superinsulated houses are also very airtight. This not only saves energy, but it reduces noise, dirt and allergens inside the home.

A continuous air/vapor barrier plastic film is attached and sealed under the drywall. Another method seals all the drywall joints and corners to block air leakage. Heat recovery and fresh air ventilation systems are sometimes used. Since you can control the fresh air, the air quality inside these homes is typically better than an average house.

Do-it-yourselfers have several new low-cost superinsulation construction options - concrete-filled insulating hollow foam blocks, self-supporting foam core wall panels, low-density insulating concrete blocks, etc. Doing some of the construction work yourself can really lower the overall costs.

To use the hollow foam blocks, you stack them together like a giant Lego set to build the wall. Once the wall is built, concrete is pumped into the top of the wall. The concrete fills the interlocking cavities in the foam blocks, forming a very strong superinsulated, airtight and soundproof wall.

Finish the interior and exterior surface any way you want.

Self-supporting superinsulated foam core wall panels are very effective. These lightweight 8-foot-high panels consist of up to 8 inches of rigid foam insulation bonded between plywood panels on each surface. You simply saw holes in the panels to install framing for doors and windows.

The finished panels are so strong that they can be attached directly to the foundation and to each other without any other supporting framework. This makes construction quick and simple. With the high insulation value and few joints and gaps, these houses are extremely airtight and efficient.

You can write to me for Utility Bills Update No. 319 listing addresses and telephone numbers of manufacturers of the do-it-yourself superinsulated foam blocks and foam core panels, special building materials and schematic diagrams of several new and conventional superinsulated wall construction methods. Write to James Dulley, The Deseret News, 6906 Royalgreen Drive, Cincinnati, OH 45244. Please include $1.50 and a self-addressed business-size envelope.

Q - I am in the process of installing a new medium-efficiency gas furnace in my home. I am replacing a 20-year-old furnace. My furnace contractor says I need a new flue liner. Is he right?

- H. F.

A - He probably is right. Sometimes when you install a new furnace, especially one in the 80 percent efficiency range, you must install a new flue liner. Since the new furnace is more efficient and captures more heat for your home, the exhaust flue gases are cooler. With a large older flue, the water vapor in the gases may condense and cause corrosion problems.