If this past winter's fuel bills were higher than you'd like them to be, you might need a more efficient furnace. One of the new-generation, high-efficiency heating plants can pay for itself surprisingly fast.

For instance, if you now pay $1,000 a year for fuel, a high-efficiency furnace could yield a savings of more than $300 annually. At that rate, a furnace costing $2,000 or more could pay itself off rather briskly.

Consumer Reports' engineers tested nine high-efficiency furnaces whose manufacturers claim lose no more than five to 10 percent of their fuel's heat. Most are gas-fired models for hot-air systems; one is a gas-fired hydronic (hot-water) design; another is an oil-fueled, hot-air system.

The tested furnaces are, at most, no bigger than old-fashioned furnaces, and much smaller than some. They are rated to deliver 70,000 to 90,000 Btu of heat. (A British thermal unit is the amount of heat required to increase the temperature of a pound of water one degree Fahrenheit.) However, versions of these furnaces are also available for houses that have a larger or smaller heat demand.

Old furnaces (and even new models of conventional design) waste much of the energy you buy as heating fuel -- both when the furnace is on and off.

Modern high-efficiency units narrow or eliminate one or more of the heat's escape routes. Where an old-style furnace may misdirect as much as half the heat you've paid for, the new designs deliver nearly all the heat content of their fuel to living spaces.

A measure of a furnace's efficiency is its Annual Fuel Utilization Efficiency, or AFUE. That is the percentage of the fuel's energy converted to usable heat over a full year's operation. A furnace's AFUE takes into account both on-time and off-time losses.

Where an old-style furnace may misdirect as much as half the heat you've paid for, the new designs deliver nearly all the heat content of their fuel to living spaces. AFUE figures provide a good basis for comparing furnaces and at least an inkling of what you might save in fuel by buying a high-efficiency furnace.

For instance, if you now own a 15-year-old gas furnace, its AFUE is probably about 55 percent; for a 15-year old oil furnace, about 60 percent. All of the new high-efficiency models tested will deliver AFUEs of more than 90 percent.

While a furnace's maximal efficiency is important, a comprehensive warranty and competitive installed prices are important buying guides.

A comprehensive warranty is essential to cover breakdowns or failures. In too many cases, the warranties contain "weasel" clauses that exclude the likely causes of problems.

Among high-efficiency furnaces, look first at the Amana, Hydrotherm and Yukon brand lines. In the opinion of Consumer Reports' legal counsel, their warranties provide significantly greater protection than others.

Choose Amana units for gas hot-air systems, and the pulse-combustion Hydrotherm models for gas hot-water systems. If you have an oil-fired, hot-air layout, a Yukon furnace should serve nicely.

Listed alphabetically, the models with the most comprehensive warranties were the Amana HTM Plus EGHW100DB3, at $3,125; the Hydrotherm Hydro-Pulse A100B, at $3,200; and the Yukon Ultima EX95 V900, at $2,250.

The prices shown are those paid by Consumer Reports. The Amana's price includes an optional hot-water tank; the Hydrotherm's, an optional hot-water tank and muffler kit.

There are no suggested retail prices for high-efficiency furnaces. To get a good price, ask for bids from at least three heating contractors.

1987, Consumers Union