New Condensing Gas Furnaces

The invention of the condensing gas furnace couldn't have come at a better time for American homeowners, gas users who have been watching the natural gas prices rise to heights that were once thought impossible. And any relief in the prices will only be short-lived because of the volatility of the fossil-fuel market.

In the colder areas of the country gas and oil are staples to provide heat for the home. In an effort to get relief from the fossil fuel crunch many homeowners are looking to various alternative methods like off-peak electric and solar hot water heat. However, these systems have very expensive start-up costs and, even with state and federal rebates, the costs can be double that of a gas-run furnace. The idea of a condensing gas furnace is to wring every last BTU of heat out of a unit of burnt gas.

Natural Gas Prices Are Sinking Gas Furnaces

Older gas furnaces waste a lot of energy. They are basically a metal box with a burner and blower apparatus The thermostat tells the furnace control that the house is cooling off and the burner is ignited. When the temperature inside the furnace header pipe, or plenum, reaches a certain point, the blower fan starts up and hot air is blown through the air ducts and into the rooms of the home.

The system works seems to work very efficiently but in actuality the reverse is true. Studies have shown that most of the gas furnaces over a ten years-old can only convert 55% of the natural gas burned into heat comfort for the home. The standard for measuring this efficiency is the AFUE, or Annual Fuel Utilization Efficiency.

Condensing Gas Furnaces Are Breaking the Ice

As the natural gas prices go up it doesn't mean that gas cannot be an economical way to heat the home. New technologies in all parts of the gas furnace have upped the efficiency of the units to an AFUE mark of 97 as compared to 55 for the old furnaces. These modern inventions include dual heat exchanging systems, more efficient gas valves, redesigned fan blowers and electronic motor technology. The new condensing gas furnaces combine all these new innovations into one energy-efficient package.

The Parts of the Condensing Gas Furnace

A traditional gas furnace heats a home by the combustion of the gas under a heat exchanging plate. The more heat that can be transferred to the heat exchanger is less heat that is allowed to go up the chimney. The ability to squeeze 25% to 45% more heat from a unit of gas than the old-style furnaces makes the condensing gas furnace a more energy-efficient source of heat production.

1. The Secondary Heat Exchanger: Old furnace technology required one heat exchanger and this meant that any heat that was not absorbed either went up the chimney or into the basement or crawlspace. The idea behind condensing gas furnaces is that the primary exchanger draws off heat and then the still-heated air is circulated through a secondary heat exchanger. In the second process the exhausting gases cool and condense into liquid form. The moisture is then drawn off into the home's drain system. This added time in a second heat exchanger allows more heat to be released and this is usable heat that can be ducted into the home.

2. The Modulating Gas Valve: Furnaces, like automobiles, need control devices to maintain an even flow of fuel. In a car, it's a carburetor, and in a condensing gas furnace it is the modulating gas valve, and this device regulates the gas flow to the furnace as per the demands of the thermostat. These new-style valves allow furnaces to modulate fuel consumption from 40% to 100% of allowed capacity. During warmer spells the furnace will automatically adjust to a thinner ration of gas.

3. The Variable-Speed Fan Blower: In all forced-air furnaces heat is distributed through the home ductwork with a blower. The blower controls are in tandem with the ones that control the modulating gas valve and the blower speed modulates with the demand for heat in the home. This coordinated control system eliminates the hot-and-cold cycles of old, conventional furnaces.

4. ECM (Electronically-Commutated Motor)

For most of the past fifty years the standard furnace fan motor was the SPC, or split-capacitor, motor. Tough and reliable, these motors have been used in industrial applications for more than a few generations. The knock is that they are to new technology as the incandescent bulb is to lighting. In other words they consume huge amounts of power. This means, when used continuously, these motors can use as much electricity as a refrigerator. This is over 800 kilowatts per year.

New, high-efficiency furnaces are using ECM (Electronically-Commutated Motor) fan motors similar to those used to cool computers. ECM's use up to 75% less power than the SPC motors because they are powered by direct-current. The other prominent features include:

  • Continuous, maintenance-free operation
  • Lower heat generation by movement than older, PSC motors
  • Low motor noise

Upgrading is a Sensible Solution

For those who cannot afford to buy a new condensing gas furnace can look into buying an upgrade kit. This can be as little as 1/3 of the price of a new one and the present furnace can begin to give savings immediately.

For more information on replacing or upgrading your present gas furnace into a condensing gas furnace consult our Contractor Directory for a heating contractor or simply post your project online.

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