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How important is AFUE?

The least efficient gas furnace available today has a AFUE of 78%. All furnace manufacturers today build two efficiency ranges of gas furnaces. Their standard gas furnace will be between 78%-81% efficient (called "80% AFUE") and their high efficiency gas furnace will be between 90%-96% efficient (called "90% AFUE). To be practical, most homes will have some factor that will justify one efficiency range or the other. In very few homes are both efficiency ranges equally practical.

The 80% AFUE gas furnaces require some type of masonry or metal vertical chimney. A home with an existing chimney is usually a candidate for the 80% AFUE furnace. A home that currently has no chimney (ie, existing heat pump home that may be switching to natural gas) or a home that has a very old defective chimney, probably would be the best candidate for a 90% AFUE gas furnace. Other factors also play into the choice.

My gas furnace is no longer heating properly. What is the most likely problem?
  Most of our "replacement" gas furnaces are sold because the old furnace developed a crack in the heat exchanger. The crack is seldom visible to the untrained eye. Sometimes it is not visible to the most experienced technician but he is able to make a judgement call based upon the operation of the system. Maybe the pilot light keeps going out. Maybe a safety switch sometimes cuts the furnace off. Then the homeowner resets the furnace and it seems to work for a few days. Both of the above could be due to a cracked heat exchanger. As the "crack" gets larger, the chance that the furnace will malfunction becomes much greater. If the homeowner fails to see the symptoms, eventually a technician will be called for repairs.
Should I keep running my old system until it wears out or replace it sooner?
  Because newer equipment usually is more energy efficient than older central air conditioning or heat pump systems, you may actually save money by replacing your old system before it wears out. In some cases, the money you save in reduced utility costs might pay back your purchase price of a new system years earlier than you might think.
What air conditioner works best with a gas furnace?
  Any efficiency air conditioner (or heat pump) will operate with a gas furnace. There is no one type or efficiency that is "better". In most parts of the country the heating system runs more than the air conditioner and is, therefore, the more expensive item to operate. For this reason, We recommend that your choice of a furnace is more important than the air conditioner. You will benefit from purchasing the best, lowest operating cost, gas furnace. If this stretches the budget, then purchase the more standard model air conditioner.
What is "AFUE"?
  The Annual Fuel Utilization Efficiency. In a general sense, it is a measure of the amount of heat that you actually get inside of the home compared to the amount of heat that is being used by the system. As an example, a 100,000 BTU, 80% AFUE gas furnace will provide 80,000 BTU's of heat into the home if it runs for one hour. The other 20,000 BTU's of heat will go up the chimney as products of combustion.
What is a cracked heat exchanger?
  The heat exchanger is the area of the furnace where "heat" is exchanged-from the fire at the gas burner to the air that is recycled into the home through the duct system. The heat exchanger is sealed so that the products of combustion from the gas burner never come into contact with the air that goes back into the home. When a "crack" develops, the seal between the two sides has broken and the products of combustion (including carbon monoxide) can mix with the air going into the home.
What is the best type of system to meet all indoor comfort needs?
  The best system depends on many variables, including family size, house location, design, and utility costs. The optimum indoor comfort system might include high efficiency air conditioning, high efficiency heating, high efficiency air cleaning, air purification, and humidification.
What is the difference between manufacturers products?
  First, you are probably aware that most manufacturers market their gas furnaces under several different brand names. Often these furnaces are identical. Carrier markets under several brand names including Bryant. Rheem markets under the name Ruud. American Standard markets under their own name plus Trane. The list goes on and on. The differences between truly competing gas furnaces can be significant. The thickness of the metal used for the equipment jacket (quietness), the thickness of the heat exchanger (quality), the construction of the inner parts of the furnace (quietness), quality of the internal components, warranty, insulation, packaging, availability of parts-all are areas where a gas furnace can be made into a quality product or just a commodity.
What is the difference in a Manufacturer's Limited Warranty and an Extended parts and labor Warranty?
  A limited warranty covers specific parts (i.e. compressor, coil, electronics, etc.); therefore, it is limited by the language in the warranty. Extended warranties are generally purchased in addition to the equipment. Extended warranties cover all parts and may also include the labor for the service call. An extended warranty protects you for unexpected and unbudgeted service calls for the duration of the warranty. Be aware that no warranty includes maintenance, shipping costs, and related parts (parts not provided by the manufacturer). Most labor warranties do not include labor for diagnostics. Most of the better manufacturer's now require proof that routine maintenance has been performed on the equipment. If a contractor offers a labor or long parts warranty, you should remember that it is only good as long as the dealer is in business.  HVAC Distribution offers only the manufacturer's warranty.
When do I know it's time to replace my system?
  When the system starts giving more problems than seem cost-effective to fix, particularly when major components such as the gas valve or heat exchanger fail. When faced with major repairs, consider that a new system will eliminate costly repairs and will save money on your monthly power bill because of the increased efficiency. The average life of a gas furnace is 18-20 years. We recommend that any gas furnace over 12 years old only be repaired as a last resort. The newer models are so much more efficient that often they will help pay for themselves with the fuel they save.