A new manual to help buyers determine the energy efficiency of houses has been issued by the Department of Energy and the Department of Housing and Urban Development. It was prepared by Technology and Economics, Inc., a Cambridge, Mass. consulting firm specializing in energy conservation research.

The manual lists 12 energy-efficiency features to look for in a new home, starting with insulation and ending with outside combustion air intakes. It explains each feature and offers a quantitative measure where possible. For example, in this climate zone, it points out, the proper level of ceiling insulation for homes heated with oil, gas or heat pumps is R-26; R-13 for wall insulation. (The higher the R rating, the better the insulation.)

Each feature is also qualified as either essential, important, desirable, or capable of being added later. Insulation is described essential, for instance, while air conditioning with a high energy efficency ratio is called important.

For purchasers interested in existing houses, there are spaces to note estimated and actual fuel costs, as supplied by the former owner. The manual advises adding 10 percent if the bills are a year old. There is a second "optional" section for existing homes with seven items from weatherstripping to the state of the heating system. Ceiling insulation requirements, for instance, are expressed in terms of minimum (R-6 for this area) and recommended (R-19). In this section it is the potential for improvement that matters.

Entitled "The Energy-Wise Home Buyer," the manual is available at a cost of $2 from the Government Printing Office, Washington 20402. Specify stock number 023-000-00-528-2.