Dear Jim: You recently wrote about budget-type 80 percent gas furnaces, but I want to install the most efficient model with the best comfort. What are the best new furnaces for 2003 and will they improve comfort too? – Kim T.

Dear Kim: The most energy-efficient furnaces made are in a class often called 90 percent models. The efficiencies actually exceed 95 percent on some models. These types of furnaces have been used for more than a decade now, so reliability is excellent. Most have a lifetime heat exchanger warranty.

As compared to a typical older gas furnace, installing one of these 90 percent furnaces can cut your heating bills in half. Although the majority of the savings results from the higher efficiency, a significant amount is also realized from the improved comfort at a lower thermostat setting.

All of these efficient furnaces use two heat exchangers instead of one as in an 80 percent furnace. The second heat exchanger captures so much heat from the furnace, the exhaust gases are cool enough to vent outdoors through a plastic pipe. No expensive chimney or flue repairs are needed.

With efficiencies already at 95 percent, there are not many more combustion efficiency improvements to make for the 2003 models. The primary changes in the new models are many subtle improvements in the electronic controls and brain that affect comfort, quiet operation, air quality, and steady temperatures.

A new comfort feature is an adjustable (at the thermostat) continuous air circulation blower speed. If you have many guests, cooking odors, smoke from the fireplace, etc., set the air circulation speed higher. This will circulate more air through the furnace air cleaner even when heat is not needed.

As has been the case for several years now, two-stage gas furnaces with a ECM variable-speed blower motor provide the best comfort and lowest utility bills. These are also often used in mild climates because the special indoor blower unit with the furnace is required for the most efficient air conditioning.

The furnace starts in the low-fire stage when the thermostat calls for heat. Low-fire heat output is often 50 to 60 percent of high-fire output. The furnace operates at this low-fire stage most of the time. On very cold days, when low-fire can’t keep your house warm, it switches to high-fire.

The comfort with these furnaces is great because run cycles are longer at low-fire to produce more steady temperatures and quieter operation. With a variable-speed blower, the electricity usage is also two-thirds less.

Another lower-priced option is the same two-stage gas furnace with just a two-speed blower, but you will lose many of the comfort benefits.

Write for (instantly download – www.dulley.com) Update Bulletin No. 472 – 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.