Why do people replace their furnaces?
The primary reason most people buy a new furnace is because their old furnace has developed a cracked heat exchanger. The heat exchanger is the part of the furnace where combustion takes place. It can develop tiny cracks over time, allowing deadly carbon monoxide to leak out into the house.

You may also want to replace your furnace because:

• Your furnace is more than 15 years old. 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.

How do I decide on which fuel to use?
The factors that can affect the choice of fuel for your new furnace include

• 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. 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. Some unbiased sources of information include:
  - Your municipal government
  - The Ontario Ministry of Energy
  - The Canada Mortgage and Housing Corporation (CMHC)

What’s the most environmentally friendly fuel to use?
All fossil fuel-burning furnaces (natural gas, propane, oil, wood) produce by-products that include nitrogen oxide, sulphur dioxide, carbon monoxide, and carbon dioxide. However, the more efficient the furnace, the cleaner the burn, and the less pollution 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 can be as polluting as the fossil fuel ones. 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 I replace my furnace to switch fuels?
If you don't have to replace your current furnace right now, then you should calculate how long it would take to recover the cost of the new furnace from the savings with the new fuel. Keep in mind that a higher efficiency furnace will also help you to save on fuel costs. If you're planning to move in a year or two, then it's probably not worth doing. However, if you've got an electric furnace and natural gas has just come to your area, a new gas furnace could be a good selling feature for your house.

What’s the right size of furnace for my home?
To determine the correct furnace size for a given house, a heat-load calculation must be performed. This calculation takes into account a number of factors including 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 use (and pay for) more fuel than necessary; too little means you won't be comfortable. A good professional HVAC contractor can advise you which size is best for your situation.

Should I get a high- or mid-efficiency furnace?
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 higher) 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 money over time. However, if you're going to move next year, then it’s probably not worth the extra cost. If you're considering an oil furnace, then high-efficiency is definitely the way to go. Oil is generally a more expensive fuel and can produce a lot of pollution if not burned efficiently. Once again, you'll have to sit down and do the math.

Do I need to get anything else for my new furnace?
To ensure compatibility, it's a good idea to think about adding furnace accessories at the time you buy your new furnace. Accessories include filters and thermostats (see below), and power humidifiers. Find out more about power humidifiers and other indoor air quality products in the Indoor Air Quality section of the Home Comfort Guide.

Filters
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
• (ii) to improve indoor air quality by trapping harmful particles. The standard fiberglass filter that comes with a new furnace provides the minimum basic protection. We recommend replacement with one of the following:

Electrostatic filter - This filter attracts particles using a static charge created by air moving over the filter. It protects the furnace and air conditioning coil, and traps a wide range of bioparticles such as pet dander, bacteria, molds, and pollen. This filter must be washed and dried monthly and lasts about 5 years.

Pleated fabric filter - The pleats in this filter provide a large surface area for capturing particles. It traps all that an electrostatic filter can, and is somewhat more effective. This filter should be replaced approximately every 3 months (check it every month to see if it is dirty).

Media air filter - This filter has a high-efficiency pleated medium that can trap all that the pleated fabric and electrostatic filters can. However, this filter requires minimal maintenance – you simply change the media cartridge once or twice a year.

Thermostats
A programmable thermostat is a worthwhile investment both for comfort and energy savings. You can program the thermostat to adjust the furnace (or air conditioner) as appropriate, at night or when you are away from the house. Some programmable thermostats have special features, such as extra large numbers on the display. Others have an intelligence recovery feature that keeps track of the thermostat's performance over the course of a season. For instance, as it gets colder in the winter, the thermostat will "remember" to start operating the furnace earlier in the day. Your HVAC contractor can tell you about the thermostat options available to you.