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A Guide to Understanding Furnaces

Many people confuse furnaces with central heating. They operate on the same general systems, and many central heating sets have furnaces or boilers that provide their heat. However, unlike central heating systems themselves, which are separated into different units that can oftentimes be placed outdoors, furnaces can be placed either indoors or outdoors, depending on convenience for the owner.

Furnaces are the sources of heat for central heating systems and for general household heating. They pump heat into the air, which is funneled through the installed piping system and, in the case of central heating, filtered into an entire home using an air handler. The exact operation varies by furnace type and model. Some furnaces can even double as a tankless water heater when connected to vent pipes with running water in them.

Types of Furnaces

  • Gas floor furnace: Gas floor furnaces work based on a system where heat rises from a grill flush with the floor. They are relatively inexpensive when installed for the first time, but replacements can be extremely costly. They heat using a pilot light.
  • Self-contained, vented, gas wall furnace: These furnaces provide hot air directly to the surrounding space. They often have higher ranges in energy efficiency and are slightly cheaper than gas floor furnaces. Like gas furnaces, wall furnaces heat using a pilot light.
  • Indoor wood furnace: Uncommon in the U.S., indoor wood furnaces run on fires that are maintained mostly by wood and fuel. Due to extraneous heat escape and other health concerns, indoor wood furnaces are not regularly used anymore.
  • Outdoor wood furnace: Also sometimes called an outdoor wood-fired boiler, outdoor wood furnaces are very popular in the U.S. They often look like a small metal shack, and the furnace provides heat to the nearby house through an underground insulated water pipe. They are appealing because they accommodate more fuel than other forms of wood heat, decreasing the number of times an owner has to add fuel to the fire. However, some people complain that outdoor wood furnaces emit too much smoke and find it bothersome.

Important Furnace Features

  • Burners are the most important components in furnaces. It is where inside the furnace that the air and fuel is burned to produce heat. They are usually lit by a pilot flame, which is lit by an electrical spark. Some furnace burners include a pre-mixer to mix the fuel and air prior to entering the burner, providing better combustion.
  • Insulation is important for many different reasons. Based solely in law, local building codes often have regulations on insulation requirements for energy efficiency purposes. Otherwise, poorly insulated ducts result in cool blows of air that lose the heat provided by the furnace. This not only makes your house heat slower, but it also deducts your furnace's efficiency, costing you money.
  • AFUE (annual fuel utilization efficiency) is a thermal efficiency measure. It measures the actual amount of heat that is delivered to your house compared to the amount of fuel that you use to operate the furnace. For example, a furnace that has 75 percent AFUE converts 75 percent of the fuel that you use to heat, while the other 25 percent is wasted to the outside world. Obviously, you want an AFUE rating that is as high as possible, so take these ratings into consideration when shopping for a furnace.

Furnace Cost

A gas floor furnace costs between $900 and $1,500, and self-contained furnaces range anywhere from $500 to $1,500 depending on capacity and energy efficiency. Installation for either of these adds another $1,000 to $2,000 to the overall cost. Replacing older gas furnaces start at about $1,700, but depending on efficiency ratings and location complexity, that can get as high as $7,500 or more. When energy efficiency is at its highest (90 to 97 percent), the cost rises to as much as $10,000.

Furnace To-Do List

  1. Always consult a professional before purchasing or installing a unit. They will audit your home for not only a cost estimate, but also the size and efficiency level that you will need for your device to be the best deal. Without consulting a professional, you run the risk of having a highly inefficient or over-sized device, both of which will cost you money in the long run.
  2. Understand the investment. Furnaces are expensive, whether you're buying new or replacing. Upfront costs range in the high thousands. Installation, insulation and utilities costs also tack on more dollar signs. Unless you have a home where you (and your furnace) will be staying for a long while, then don't get one. Wait until you've found the home you'll be settled in for a long while.
  3. Turn your furnace on within a week of installing it. Determine if it works, how well it works and how much you are satisfied by it. If it is not up to your standards or does not operate correctly, call both the installer and the manufacturer immediately to arrange for a replacement. You should never have to pay for this replacement out of pocket. As long as it was professionally installed, you should be covered under warranty
Last Updated: January 18, 2012
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About Emelie Battaglia Emelie Battagila is a contributing writer for Idealhomegarden.com

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