What do I look for when choosing an efficient furnace?
How should I operate my furnace?
How do I determine furnace size

What do I look for when choosing an efficient furnace?

Select a furnace with an AFUE of 90 percent or higher.
The Annual Fuel Utilization Efficiency or AFUE measures a furnace’s overall energy performance. The higher the AFUE, the more heat you get for your heating dollar. In Alberta, a furnace with an AFUE of 90 percent or higher is a good investment.
 
Select a furnace with multi-stage firing for the right size furnace for all heating conditions.
Your furnace must have enough capacity to meet your heating needs on the coldest day of winter. However, for most of the heating season, it will be more heating capacity than you need. Unlike a furnace with single-stage firing that is either firing at full output or completely off, a furnace with multi-stage firing can selectively turn some burners off when full furnace output is not needed. Multi-stage firing gives you the right size furnace for the majority of the heating season, and a reserve capacity to meet additional heating needs on really cold days or to recover from a temperature setback period. Multi-stage furnaces are usually equipped with another efficiency feature as well: an electronically commutated motor (ECM) that uses considerably less electricity to run the fan.

Select a furnace that uses electricity efficiently.
A gas furnace uses electricity to run the fan blower motor. Furnaces equipped with an ECM have lower annual operating costs and can save you $40 to $300 per year depending on how you use the furnace fan. An ECM will save the most if you run your furnace fan all the time. Multi-stage ECM furnaces not only save you money, they are usually much quieter and less prone to producing unpleasant drafts.
 
Your new furnace must be installed properly to ensure that it operates safely and efficiently.
The contractor should adjust the air flow so the furnace fan setting is matched to the ductwork and furnace characteristics. An improperly installed furnace can result in higher energy costs and a less comfortable home.

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How should I operate my furnace?

OPERATING TIPS
How you operate your heating system will influence how much energy you use. The following tips will help lower your heating bill and ensure that your furnace functions safely and efficiently.

• Set your thermostat between 68 and 70 degrees when you are at home. Turn down the thermostat when you are away or sleeping. Regularly lowering your thermostat temperature, by five degrees for eight hours every day will save about five percent on your heating bill. Use a programmable thermostat to adjust the temperature automatically, based on the time of the day and the day of the week.
• Leave the fan switch on your thermostat set to “auto” unless you have a specific need for additional air circulation. Some customers choose to operate their fan continuously to even out warm and cold spots in their home, or to provide extra air filtration which may be beneficial where occupants have health concerns. Setting the fan to “on” will cause it to run all the time whether or not there is a need for heating or cooling. Those extra hours of operation can add several hundred dollars to your annual electric bill. If you do need to run your fan continuously, install a furnace with an ECM. Running the fan year-round will cost only about $50.
• Clean or replace furnace filters as recommended by your contractor or as noted on your filter packaging. Filters may need to be replaced as often as once a month.
• Be sure registers in occupied rooms aren’t blocked by furniture or draperies.
• Have your furnace tuned up every other year unless the manufacturer indicates otherwise. The contractor will test the efficiency, adjust the air and fuel flow, inspect the fan, and clean the unit.
• Install carbon monoxide detectors on every floor with a bedroom. Carbon monoxide detectors are not a substitute for properly maintaining your combustion appliances, but provide added protection against carbon monoxide poisoning.

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How do I determine furnace size?

The heating capacity of a furnace, also referred to as size, is measured in thousands of BTUs (British Thermal Units). Furnaces are rated by the input BTU’s, that is, the amount of fuel energy that goes into it when running. Different furnaces of the same input BTUs will have different output BTUs if the furnace efficiency ratings are different. Select a furnace for your home according to the output BTUs, as this is the actual heating capability of the furnace. You can easily calculate the output BTUs of a furnace according to the efficiency rating of the unit and the input BTUs – simply multiply the efficiency percentage by the input BTUs. For example, a 100,000 BTU furnace at 80% efficiency will produce 80,000 BTUs of heat output, whereas as 100,000 BTU furnace at 92% efficiency will produce 92,000 BTUs of heat output.

There is only one correct size furnace for your home.
You don’t want a unit that is too big, as it will turn on and off too frequently, be inefficient, and accumulate moisture in the heat exchanger which can damage the unit over time. And you don’t want a unit that is too small as it won’t properly heat the home. You want just the right size. How do you determine which one is just right? There are several ways you might go about determining the correct furnace heating capacity (or size) unit:

Manual J Load Calculation
This is the proper and scientific method as well as the most accurate. It is the method taught to HVAC technicians at school and recommended for use by professionals in the trade. It consists of taking information about your home’s constructions materials, insulation levels, sizes of rooms, etc, and then makes a calculation based on those to determine the appropriate heating and cooling requirements needed. The BTUs recommended by this tool should be close to output BTUs of the furnace you select. It should be noted, that while this is the most accurate approach for determining furnace size, according to a study by the US Department of Energy, less than half of heating and air conditioning contractors actually use Manual J Calculations to determine the proper size for heating or cooling equipment.

Compare your home to similar homes in your area.
Does you neighbor have the same size home as you? If he has a properly sized furnace, then the same size unit may also work for you.

Ask a contractor.
Most furnace professionals give free in-home estimates for installing new heating equipment during which they will recommend a unit size. While we don’t encourage using contractors for quotes if you don’t intend to hire any of them, a contractor familiar with the homes in your neighborhood will likely be able to give you an idea over the phone of what size you might need.

If you are replacing an existing furnace, look at what size you have.
If the unit you have now is the correct size for your home, replace it with the same size. How do you know what size you currently have? Look at the name plate on the furnace usually located somewhere inside the unit (remove service panel to find). Remember, furnaces are rated by input BTUs, but you will want to determine what the actual output BTU is (often also listed on name plate) when selecting the right size replacement unit.

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