Homes in the Flint area with central air conditioners often have gas furnaces for heat.

In this Flint HVAC guide we look at how furnaces work, why the correct size is important, factors related to cost, and tips for finding the right contractor.

How A Home Gas Furnaces Works

Here’s an overview of how a gas furnace heats your home.  You’ll be able to discuss any potential issues with a contractor when you know how they function.

When your thermostat calls for heat, you’ll hear a motor start. This is a draft inducer fan that blows air through the vent system to make sure that the vent is open allowing exhaust gases containing deadly carbon monoxide to escape. It also supplies air for combustion. When it is determined that the vent flue is open, the gas valve opens to allow gas into the burner. The burner is similar to the burner in a gas grill or a gas oven, but much larger. Gas is ignited by one of several types of igniter electric spark, glow plug, hot surface. When the burner fires, it begins to heat air. This takes place in a sealed combustion chamber with air that never interacts with air that travels into your home. The heated air travels through an important component known as a heat exchanger which is made from metal that transfers heat very effectively. The furnace blower fan moves air over the heat exchanger, heating the air in the process. The heated air is pushed into your home through the supply ductwork while cold air is drawn into the system through the return ductwork.

The exhaust gas is vented from the furnace after it leaves the heat exchanger. Furnaces that are very efficient employ a second heat exchanger to transfer even more heat out of the exhaust before it leaves the house. This entire process continues until the air temperature in your home matches the temperature called for on the thermostat. The burner shuts off and the blower continues to run for a few seconds to remove heat from the furnace.

The Right Size Furnace is Important

Gas furnaces for residential use are made in sizes from about 40,000 Btu to about 150,000 Btu. Most manufacturers make them in 10,000 to 20,000 Btu increments. If the furnace is too small for your home, it won’t adequately heat it. If it is too large, the heating of the home will be imbalanced. For example, the area near the thermostat might heat up so quickly that rooms in the remotest part of the house don’t get adequately warmed. If the thermostat is some distance from the furnace, some rooms closer to the furnace may become too hot before the room with the thermostat gets warmed.

To ensure the right size furnace, an HVAC contractor will do a load calculation to determine the heat loss of your home. If your home didn’t lose any heat, the furnace would never have to run. But homes lose heat through windows and doors, the walls and roof, etc. A load calculation takes the Flint climate, the size of your home, plus factors like the quality of the windows and the amount of insulation you have to determine the right size furnace for your home.

Factors Affecting Furnace Costs in Flint

  • Size/Capacity: The more Btus the furnace makes, the more it will cost, all else being equal.
  • Efficiency: Standard efficiency furnaces use 80% of the created heat while 20% is lost out the flue. Furnaces with efficiency levels between 90% and 97% are available too, many of them using a second heat exchanger. Efficiency affects prices sometimes more than size does.
  • Performance features: Some furnaces are equipped with 2-stage gas valves and variable-speed blowers that help to balance the heating and improve air filtration. These gas furnaces cost more than those with single-stage gas and a single-speed blower.
  • Installation Issues: Some installations are more complex (attic installation, for example) or require more materials. These will cost more.

For more info, Call Us At (810) 653-4328.

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