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The following features should be considered when selecting a furnace:

Energy efficiency

Today's high efficient furnaces can reach 95% AFUE or more in their efficiency rating. What this means is that 95% of the fuel received by the burner is actually burnt in the heating cycle and that there is only a nominal loss of 5% (in this example) lost. Compare that to a standard efficient furnace that is typically 55 - 60% efficient and loses as much as 45% of the gas it receives!

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Two stage design

A two stage furnace is one that is equipped with a gas valve that has two burn positions. The first position is full-fire maximum performance while the second position is 30% less and therefore burns less gas. The purpose and utility of a 70% of performance position is that furnaces operate efficiently when they are working at 70% or greater and, once your home has been warmed up, furnaces can maintain the set temperature with less energy than they need when starting from the "off" position. In fact, studies show that in Winnipeg most homes equipped with two stage furnaces, use the "low-fire" position 80% of the time.

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Variable speed motors

Some high efficient furnaces are equipped with ECM or DC motors as they are sometimes referred to. These motors actually "ramp up or down" based on the readings received from the thermostat and the air temperatures measured in the return air. The electricity received by your home from Manitoba Hydro is AC power. These furnaces convert that power through the operation of their circuit board and these specialized fans to run as DC power, which is approximately 80% per cent cheaper.

Gas Furnaces

High efficient furnaces draw air from the outside down a plastic pipe made of CPVC636 materials. This pipe is called a ‘combustion air intake’ and is attached directly to the ‘burner box’ of the furnace. (Note: Manufacturers also allow this pipe to be open to the interior of the home/building rather than just from the outside however the overall efficiency of such installation is compromised if this style of installation is employed).

During the ‘burning cycle’ gas is directed horizontally across the igniter and into the chambers of the heat exchanger. The heat exchanger is warmed during the process and when a design temperature is achieved, the blower is engaged and blows air across the outside of the heat exchanger, and into the plenum and duct work system of the house. Older furnaces heated their exchanger from the outside, usually from the bottom similar to a-pot-on-the-stove and as a result they took much longer to achieve the design temperature and burned more fuel in the process.

Flue gases accumulating in the heat exchanger are pulled through the heat exchanger by the ‘vent blower motor’ and pushed out through a second CPVC636 plastic pipe, called the vent pipe or chimney. The vent blower motor is audible when running and will be a new sound in the home. It is not oppressive and usually any sound it makes is drowned out by the operation of the main blower fan during the heating cycle.

Lastly, as the heat exchanger is warmed up quite quickly and achieves a temperature much in excess of the surrounding air, and then it is cooled quite rapidly as the blower pushes air through the furnace, condensation naturally occurs on the outside of the primary heat exchanger. This hot fluid is collected and directed into a device called a secondary heat exchanger. When the blower stops, the secondary heat exchanger radiates its heat until the fluid cools and is discharged through a drain tube to the sewer. The result of this operation is that the duct work and more importantly, the air in the duct work, stays relatively warm. When the thermostat starts the next heating cycle, the air is already warmer and therefore it takes less time and less gas, to re-heat and reach the thermostat's set point.

Features have now been added to enhance the furnace efficiency

The first step was the advent of two stage gas valves. These valves have the traditional on / off positions but they also have a 70% of capacity position which is normally employed 80% of the time. Reducing the burn by 30% reduces gas consumption. The second step was to add a Direct Current fan to the furnace. These blowers dramatically reduce electrical consumption, enhance the heating and cooling performance of the equipment, and provide a very even temperature through out the home. They are also exceptionally quiet.

The latest enhancement to gas furnaces is a completely variable system. These furnaces have variable speed direct current blower motors, variable speed vent blower motors, and variable position gas valves that all work in unison. They usually require more expensive digital thermostats to employ all of their features however, so the cost of the control should always be factored into the price of this system.

Electric Furnaces

Electric furnaces are forced air furnaces, but instead of a heat exchanger, a series of coils, is employed. These coils typically are 5 kilowatts each and they are employed in series as the heating demands increase. Current utility costs for operating an electric furnace rival the costs of operating a mid-efficient gas furnace, and therefore many customers are considering these furnaces when they review replacement options.

In most cases, a minimum of 200 amp electrical service is required to operate an electric furnace. The costs of upgrading an electrical service are substantial and should be carefully reviewed in advance of this investment.


Visit the Reliance Superior Heating office for more information on our full line of products.