Dear Jim: I have noticed my old gas furnace seems noisier and the room temperatures are not steady. I want a new superefficient model, but comfort is my primary concern. What is new among the 2002 models? – Mic R.

Dear Mic: You are in luck because the most efficient models do provide the ultimate comfort available. If you plan to install the most efficient central air conditioner now or in the future, you will need the superefficient air handler (blower) that comes with the top-of-the-line furnaces.

The AFUE (annual fuel utilization efficiency) of the new furnaces is typically in the 92 to 95 percent range. When you compare this to your old furnace, you should expect to save 30 to 40 percent on your heating bills. It may make economic sense to replace an old furnace even if it is still working.

Some of the newer models for 2002 are smaller and quieter with extra insulation and other sound-deadening features in the cabinet. Much of the noise you hear now also comes from the air blowing through the ductwork and the furnace cycling on and off. Some new models greatly reduce this noise too.

Installing a furnace with a smart, variable-speed blower motor will have a great impact on your comfort. When it starts, it slowly ramps up to speed. This reduces the noise level and the initial gust of cold air from the registers. Also, it uses 75 percent less electricity than a standard motor.

These motors are called “smart” because they sense pressure variations in the airflow and automatically adjust their speed to compensate. If you close off a register to an unused room or move a sofa against a wall register, the motor will speed up to maintain a constant overall airflow.

A furnace with two heating levels provides the best overall comfort. These models use a two-stage gas valve that fires at a low-heat-output level the majority of the time. In this superefficient mode, the furnace runs more continuously and room temperatures stay steady. Most models use a smart blower motor.

When the outdoor temperature drops and the low level will not keep your house warm, the gas valve automatically switches to the high-heat output. The smart blower motor simultaneously switches to a higher speed.

For many homes, a less expensive, single-level model often provides a faster payback. Some manufacturers offer optional smart motors in these models too.

It is wise to select a furnace with sealed combustion. This reduces drafts and wasted energy because the combustion air is drawn from outdoors, not from inside your house. Sealed combustion models are often quieter and the induced draft blower minimizes the possibility of dangerous backdrafting.

Write for (instantly download – www.dulley.com) Update Bulletin No. 925 – buyer’s guide of 16 super-efficient gas (and propane) furnaces listing efficiencies, blower speeds, heating stages, warranties, comfort features, and sizing/payback charts. Include $3 and a business-size SASE, and send to James Dulley, 6906 Royalgreen Drive, Cincinnati, OH 45244.