Why people replace their furnaces
The number one reason why most people buy a new furnace is because their furnace has been condemned as the result of a cracked heat exchanger. The heat exchanger, which is the part of the furnace where combustion takes place, can develop tiny cracks over time, allowing deadly carbon monoxide to leak out into the house. Other reasons for replacing a furnace include the following:
- The furnace is more than 15 years old (the furnaces built today are more efficient and break down less often).
- You want to change fuel types (e.g., from electric to natural gas).
- You've renovated your house and the existing furnace cannot handle the new heating load.
- You have an older furnace that is not compatible with the new air conditioner you would like to buy.
The factors that can affect the choice of fuel for your new furnace include the following:
- The type of fuels available in your area now, as well as those expected to become available. For instance, if you have to replace your furnace now in an area that does not yet have natural gas but will within the next year or two (and natural gas is your preferred fuel), then you might consider installing a propane furnace now, which can converted to natural gas later on.
- Whether you are willing to have a storage tank on your property. Oil furnaces require a tank in the basement, which can take up quite a bit of space. Propane furnaces need a large storage tank outside the house.
- The cost of various fuels in your area now, as well as the projected cost of each fuel in the future. In many areas, natural gas is the least expensive choice when compared with the cost of electricity, oil, or propane, but this is not always the case and may not remain so where it is the case. Also, some suppliers will offer either short- or long-term incentive plans if you go with their particular fuel, so check out all of your options.
- Your gas utility, electrical utility, oil supply company, and your propane supplier will all try to make convincing cases for their respective fuels. You should look for an independent source for pricing information. What you need to do is compare the local costs for electricity, gas, oil, and propane.
A word about the environmental friendliness of different fuels: All fossil fuel-burning furnaces (natural gas, propane, oil, wood) produce by-products that include nitrogen oxide, sulfur dioxide, carbon monoxide, and carbon dioxide. However, the more efficient the furnace, the cleaner the burn, and the less pollution is produced. In general, natural gas and propane do burn more cleanly than oil, but some high-efficiency oil-fired furnaces manufactured today burn just about as cleanly. You should also note that electric furnaces are just as polluting because, although they don't produce any combustion by-products, the electricity used to fuel them comes from generators that burn coal or oil, or that produce nuclear waste
Should you replace your furnace to switch fuels?
If you don't have to replace your current furnace right now, then you should sit down and calculate how long it will take you to make up the money you'll spend on the new furnace by saving with the new fuel. Keep in mind that a higher efficiency furnace will also help you to save on the new fuel. If you're going to move in the next year or two, then it's probably not worth doing, unless you've got an electric furnace and natural gas has just come to your area, in which case the new furnace could help sell the house.
To determine the correct furnace size for a given house, a heat-load calculation must be performed. This calculation takes into account such factors as the size and orientation of the house, the local landscaping, the number of windows, and the number of occupants. Too large a furnace means you'll pay more than you need to for fuel; too little means you won't be comfortable. You'll need the advice of a good professional HVAC contractor to determine which size you need.
Shopping for energy efficiency
The measure of a furnace's efficiency is its Annual Fuel Utilization Efficiency (AFUE) rating. Furnaces manufactured today are either high-efficiency (>90% efficient) or mid-efficiency (about 70–89% efficient). Whether or not you opt for the high-efficiency furnace depends on where you live, how long you plan to live there, and what fuel you're using. In areas with long, cold winters, a high-efficiency furnace could really save you some money over time. However, if you're going to move next year, then it probably wouldn't be worth the extra investment. If you're looking at oil furnaces, then high-efficiency is the way to go, because oil is generally a more expensive fuel and, if not burned efficiently, can produce a lot of pollution. Once again, you'll have to sit down and do the math.
To ensure compatibility, it's a good idea to think about adding furnace accessories when you purchase your new furnace. Examples of furnace accessories include filters, thermostats (see the sections on each of these, below), and power humidifiers. You can find out more about power humidifiers and other indoor air quality products in the Indoor Air Quality Products section of the Buyer's Guide.
Furnace filters have two purposes: (i) to protect the inner workings of the furnace and the condenser coil of the central air conditioning system (located in the furnace) from dust and debris; and (ii) to improve indoor air quality by trapping harmful particles. The standard fiberglass filter that comes with a new furnace is next to useless in both of these areas. It should be replaced with one of the following:
- An electrostatic filter. This filter attracts particles using a static charge created by air moving over the filter. It will protect the furnace and air conditioning coil, as well as trap a wide range of bioparticles such as pet dander, bacteria, molds, and pollen. This filter has to be washed and dried monthly and lasts about 5 years.
- A pleated fabric filter. The pleats in this filter provide a large surface area for capturing particles. It can trap all that the electrostatic filter can and is somewhat more effective. This filter should be replaced every 3 months or so (but check it every month to see if it is dirty).
- A media air filter. This filter has a high-efficiency pleated medium which can trap all that the pleated fabric and electrostatic filters can. However, this filter requires minimal maintenance: simply change the media cartridge once or twice a year.
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