Q - I have talked to builders about building an energy efficient house, but each is recommending different features and designs. How can I evaluate which will be most effective at cutting the utility bills? P.M.

A - There are many design characteristics that can slash heating and cooling costs. With proper design utilizing passive solar energy, a house can be heated and cooled very inexpensively. Although the extremely low utility bills would pay back the higher initial building costs, it may be difficult to afford all the energy-saving features initially.Three of the major design factors affecting the energy usage of a house are basic design and shape, type and amount of insulation and airtightness, and the quality of the mechanical systems.

Many specific factors within each of these three general categories affect your utility bills to varying degrees. Under the basic design category, you should consider the type and shape of the house, the potential for solar utilization, and the amount and type of window glass area.

A square-shaped house minimizes the total outside wall area. The worst design is H-shaped. A two-story house is better than a single-story one because it reduces the amount of roof area for a given floor space area.

On a payback/efficiency-rating scale, a square house would be rated at +30 as compared to an L-shaped house at +10 and an H-shaped house at -20. This scale indicates the relative payback of the design factors so you can choose the best ones for your building budget.

For thermal protection, the higher the level of insulation, the better. Rigid foam insulation sheets on the exterior provide the highest insulating R-value per inch thickness. These also form a natural air barrier for reduced air infiltration (leakage). Pre-manufactured complete foam core building panels are an excellent super-energy-efficient choice.

Minimize the window area especially on the north wall. On the pay-back-efficiency-rating scale, total window area less than 10 percent of floor area is rated at +40. Window area greater than 20 percent is -40. It is generally worth the additional cost to get super-high-efficiency windows (glass R-values up to R-9). Shade south windows with a large roof overhang.

Select energy efficient mechanical systems - furnace, air conditioner and water heater. Locate them near the center of the house to minimize duct and hot water pipe length. Proper location is given a +8 rating.

You can write to me for UTILITY BILLS UPDATE No. 041 showing 75 payback-efficiency-rating scale values for specific building characteristics, a list of manufacturers of foam core building panels and super-highefficiency window glass. Write to James Dulley, The Deseret News, 6906 Royal Green Drive, Cincinnati, OH 45244. Please include $1 and a self-addressed STAMPED BUSINESS-SIZE envelope.

Q - I have an old water heater insulation jacket, but it is not long enough to cover my entire new water heater. Will it still be effective if the water heater is covered only three-quarters of the way down? H.K.

A - Although it is best to have the entire water heater tank insulated, your water heater jacket should still be effective. The water at the top of the tank is generally much hotter than the water at the bottom.

If you have some old fiberglass or rock wool wall insulation, wrap a layer of it around the bottom uncovered area. Face the vapor barrier to the outside and use it to staple the ends of the insulation together. Either staple or tape it to the bottom edge of the insulation jacket.