QUESTION: I am researching 2009 superefficient gas furnaces, which I hear can cut my gas bills in half. I am confused by the terms like "stages," "variable blower speeds," "condensing," etc. Please explain these?ANSWER: There have been some significant design changes in many of the 2009 gas furnace models. Just two years ago, an AFUE (annual fuel efficiency ratio) of 95 percent was about the highest. This efficiency was targeted by manufacturers to meet the now expired federal energy tax credit.Now some of the multistage models reach AFUEs as high as 98 percent.This means only two cents of every dollar you spend on gas or propane is lost out the flue. They don't use chimneys any longer, just a plastic vent pipe. All of the gas models can be converted to burn propane with very minor, inexpensive modifications.Cutting your gas bills in half might be a bit of an exaggeration, but a 40 percent savings is certainly possible. The enhanced indoor comfort with some of the multistage gas furnaces could allow you to set the wall thermostat lower. If you do this, you actually might be able to cut your bills in half.All gas furnaces with an AFUE of 90 percent or above have a secondary condensing heat exchanger. In this extra heat exchanger, the hot water vapor in the exhaust gases is condensed into water. When this occurs, additional latent heat is captured to heat your house. These furnaces have an induced draft exhaust fan to force the flue gases outdoors.A one-stage furnace is the simplest design. The gas burner is either full on or off. This is how furnaces have been made for the past 100 years. About a decade ago, furnace manufacturers started using a two-stage gas valve, which creates a low- and high-output burner. This allows the furnace to produce less heat when less heating is required.By doing this, the room temperature varies less between furnace cycles and its efficiency is improved.Within the past several years, some furnaces added a third stage to even out the room temperature even more. The gas burner heat output operates at 40, 65 or 100 percent. These require a thermostat designed for the particular furnace controls to make it all work properly.Some very new modulating-stage furnaces can vary the heat output from 15 percent to the full 100 percent in several percent increments. Every 60 seconds, the instantaneous heating needs of your house are measured and the heat output percentage is adjusted. Other designs make the changes in just one percent increments from 40 to 100 percent. Either design yields excellent comfort.The multistage gas furnaces use an efficient variable-speed blower motor. Becuase the heat output from the burner changes, the air flow rate through the duct also must change or the air would blow out too cool.These blowers also start quietly and greatly improve summer comfort when air-conditioning.Write for (or download at www.dulley.com) Update Bulletin No. 698 — the 2009 buyer's guide of superefficient modulating and two-stage gas furnaces listing AFUE's, capacities, blower types, warranties, and sizing and savings charts. Please include $3.00 and a business-size SASE.

QUESTION: I need to get replacement windows for my house. The price quotes I have gotten vary greatly. With today's economic climate, does it make sense to buy from a smaller local window manufacturer?ANSWER: Generally, it is fine to purchase replacement windows from a small local manufacturer. I did at my own home. With today's poor economy, there no doubt will be some of these companies going out of business. With long window warranties, this can be a potential problem.Other than considering the size of the manufacturer, also consider how long they have been in business. Well-established companies, even small ones, are more likely to weather this economic storm.Send inquiries to James Dulley, Butler Eagle, 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit www.dulley.com.James Dulley has a degree in mechanical engineering. His column is published in more than 400 newspapers.