Furnace Terminology and Technology (source: Atco energy sense)
If you’re in the market for buying an energy efficient heating system, be prepared for the new terminology that’s emerged from the industry over the past decade.
New technologies associated with burner controls, fan motor operation, furnace efficiency, and combustion air can perplex potential buyers. Knowing what the new terminology means will help you understand the options available on today’s heating systems, and will give you peace of mind that you’re making an informed purchase.
Today’s heating systems are manufactured with single-stage, two-stage or modulating burner controls.
Single-Stage: These burners operate with very little flexibility. Basically, the burner is fully on (operating at full fire) or fully off. Older conventional furnaces in many homes still operate in this manner.
Two-Stage: Much like having two furnaces in one. During mild winter weather when the demand for heat in the home is low, the burner operates at low stage. During colder temperatures, when the heat loss in the home is at its greatest, the burner adjusts to its higher stage (full capacity). This system cycles the furnace on and off more effectively, offering increased energy savings compared to a single-stage furnace.
Modulating: These burners have the most flexibility in adjusting to heating requirements (moving up and down continuously in relation to the home’s heating demand). This system offers greater efficiency and comfort compared to single- and two-stage gas valve systems.
Fan Motor Operation
The fan motor delivers warm air throughout your home through the duct system. Today’s furnaces are equipped with single-speed, two-speed or high-efficiency, variable-speed fans.
Single-speed: These fans deliver heat at one constant speed, whether they are set to run continuously or only when the furnace is operating.
Two-speed: These fan runs at one of two levels – low or high. This system allows for continuous air circulation and more even temperatures when the furnace burners are off.
DC Variable speed: DC variable speed fans enable the heating system to operate at a continuous range of speeds. The speed of the fan varies depending on the heat demand. Temperature swings, as well as uncomfortable hot and cold drafts, are eliminated. Less power is used to run the fan over single- and two-speed types, which means a reduction in electricity costs. Variable speed motors are more efficient because they are DC (Direct Current). A DC motor is more expensive to purchase but it uses about one-third the energy of a typical single-speed or two-speed AC motor.
There is a wide range of furnace efficiencies, although the conventional, standard-efficiency gas furnaces can no longer be sold in Canada. In addition, all indoor gas-furnaces manufactured after December 31, 2009 will have to meet a minimum performance level of 90% Annual Fuel Utilization Efficiency (AFUE).
High-Efficiency Condensing Furnace: Condensing gas furnaces are the most energy-efficient furnaces available, with seasonal efficiencies between 90 and 97 percent. Most have burners similar to conventional furnaces, with draft supplied by an induced draft fan. They have additional heat exchange surfaces made of corrosion-resistant materials (usually stainless steel) that extract most of the heat remaining in the combustion by-products before they are exhausted. In this condensing heat exchange section, the combustion gases are cooled to a point where the water vapour condenses, thus releasing additional heat into the home. The condensate is piped to a floor drain.
Because the flue gas temperature is low, a chimney is not needed; the gases are vented through a PVC or ABS plastic pipe out the side wall of the house. Depending on the AFUE of your old furnace compared to your new model, fuel savings of up to 30 percent can be achieved. Furthermore, polluting emissions released into the environment are also reduced.
Mid-Efficiency Furnace: Mid-efficiency gas furnaces mainly use a naturally aspirating burner and usually do not have a continuously lit pilot light. They are equipped with a powered exhaust (a built-in induced draft fan), and they do not have a draft hood. With a larger heat exchanger, no dilution air, and high resistance to flow during the off cycle, seasonal efficiency is much higher for mid-efficiency gas furnaces than for conventional furnaces. A mid-efficiency furnace has an Annual Fuel Utilization Efficiency (AFUE) of 78-83%.
Contrary to conventional and mid-efficiency furnaces, where efficiency decreases with furnace over-sizing, a new condensing furnace that is sized slightly larger than the house heat demand will not suffer an “efficiency penalty.”
Annual Fuel Utilization Efficiency (AFUE)
The AFUE is the most widely used measure of a furnace’s heating efficiency. It measures the amount of heat actually delivered to your house compared to the amount of fuel that you must supply to the furnace. As an example, a 97% efficient furnace means that for every dollar you spend on energy, 97 cents is used to heat the home.
Based on current building codes, outside combustion air is required for new furnace installation.