A furnace, also known as a heater, is a device that generates heat in a controlled manner through the combustion of a fuel source to produce thermal energy. This thermal energy is used to heat places such as rooms, buildings, or other structures. In addition, some furnaces are used in industrial and commercial settings to process certain materials. Furnaces are mostly used as major components of central heating systems, providing heat to interior spaces through intermediate fluid movement, which may be air, steam, or hot water. Electric resistance heating is used in some areas, especially where electricity costs are low or the primary purpose is for air conditioning. Modern furnaces can be up to 98% efficient and operate without a chimney, while a typical gas furnace is about 80% efficient.
Let’s delve into how a furnace works. A typical furnace consists of six main components:
- Thermostat: The thermostat activates the furnace when the temperature setting drops below a specified level.
- Gas Valve: When the gas valve is turned on, it delivers gas to the burner.
- Burner: The burner ignites the gas, leading to air combustion. The air is ignited by the gas fuel supplied through a valve, producing heat.
- Heat Exchanger: The heat exchanger converts the gas fuel into heat. This heat is then distributed through air ducts in your home.
- Blower: The blower forces the heated air into the ductwork, distributing it throughout the house.
- Air Ducts: Ductwork connects the furnace to each room, allowing hot air to reach its destinations.
Here’s how the process works:
- The thermostat sets a base temperature that needs to be maintained.
- When the actual temperature drops below the designated level, the thermostat sends a signal to the control board.
- The control board activates various components, including the gas valve and blower fan.
- The gas valves release more fuel, which ignites in the burner.
- The heat exchanger converts the gas fuel into heat.
- The blower fan pushes warm air through the ductwork, while cooler air is pulled in to be heated.
- This cycle continues until the desired temperature is reached, as established by the thermostat.
- Any excess combustible gases are discharged through the flue, ensuring safety for the occupants of the property.
Furnaces come in various types, including natural gas, oil, electric, propane, and wood-burning furnaces. Each type has its own working principles and applications.
Furnaces rely on a combustion source that can vary with each furnace. The most common fuel types are: Propane furnaces: Propane is just one of several natural gas sources used to fuel a furnace. This fuel source is usually contained in tanks on a property that need to be refilled. The fuel tanks come in different sizes but are commonly found outside of a home or business and are not connected to a city’s infrastructure. Natural Gas Furnaces: Natural gas is another gas source used to fuel combustion. This source is usually connected to gas lines that are connected to a gas main that are connected to a city’s infrastructure and do not need to be refilled like propane. Oil Furnaces: This natural fuel source is usually pulled from an oil tank using a fuel pump because it comes in liquid form. This liquid oil is then compressed and dispersed in a fine mist which is sprayed into a combustion chamber connected to a burner. This heats the combustion chamber which then allows heat to be distributed. Electrical Furnaces: This furnace type does not require a fuel source for combustion as it relies on the heat generated through electrical resistance to heat up the surrounding air before being distributed by the blower. Electric vs Gas Furnaces The most common dispute between fuel sources is choosing either a gas or electric furnace. Each fuel source has their distinct benefits and downfalls. Determining if a gas vs electric heater is right for you requires an individual to evaluate their specific needs. Gas burning furnaces tend to more cost effective in operation because gas tends to be cheaper than electricity, but they also require a city gas main connection to function. Gas heaters are also capable of producing more heat in a shorter time frame which means that the same sized space will be heated faster by a gas fueled heater.
Natural gas fueled furnaces tend to last between 15 – 20 years when maintained properly. That being said, gas heaters generally require more maintenance and upkeep which can add additional costs. They also introduce hazards like gas leaks and the potential release of carbon emissions. Electric heaters, on the other hand, last longer with less maintenance. A typical electric heater can last between 20 – 30 years with much less upkeep. They typically cost more to operate due to electricity costing more. That said, they can have increased efficiency because newer units come with smart controls that allow heat to be dispersed where it needs to be. They are quiet and do not release harmful emissions. Different Types of Furnaces Most furnaces are categorized into one of four categories: Natural Draft: These furnace types are usually dated models that don’t use a blower fan to distribute air. Their efficiencies are some of the lowest at 65%- 70%, as there is nothing to propel heated air through the system. Forced Air: Newer forced air systems utilize a blower fan to draw and push air through the system. These are more common and have a slightly higher efficiency level. Induced Air: Induced air models are similar to forced air units but with an additional fan that draws air into the unit to help supply the furnace with cool air to warm while also expelling wasted gas. This relieves pressure on the blower fan, so it is not responsible for the draw and push of air flow which increases efficiencies. Condensing: Condensing furnaces are highly efficient furnace units that use a secondary heat exchanger to draw additional heat from exhaust gasses before they are expelled via the flue. This condensed heat is added to the heat that is already being dispersed which can reach efficiency levels of 98%. Different Furnace Fan Types
Fuel Types for Furnaces
Propane Furnaces:
- Propane is one of several natural gas sources used to fuel furnaces.
- Propane fuel is typically stored in tanks on a property and needs periodic refilling.
- These tanks are commonly located outside homes or businesses and are not connected to a city’s infrastructure.
Natural Gas Furnaces:
- Natural gas is another common fuel source for combustion in furnaces.
- Natural gas is connected to gas lines, which are in turn linked to a gas main within a city’s infrastructure.
- Unlike propane, natural gas furnaces do not require manual refilling.
Oil Furnaces:
- Oil furnaces use liquid fuel extracted from oil tanks.
- A fuel pump pulls the liquid oil, compresses it, and disperses it as a fine mist into a combustion chamber connected to a burner.
- The heated combustion chamber then distributes the heat.
Electrical Furnaces:
- Electrical furnaces do not rely on a fuel source for combustion.
- Instead, they generate heat through electrical resistance.
- The surrounding air is heated before being distributed by the blower.
Electric vs. Gas Furnaces
Choosing between electric and gas furnaces involves considering specific needs:
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Gas Furnaces:
- Cost-Effective Operation: Gas heaters tend to be more cost-effective due to the lower cost of natural gas compared to electricity.
- Faster Heating: Gas heaters can produce more heat in a shorter time, heating a space faster.
- Maintenance and Hazards: Gas furnaces require maintenance and upkeep, including potential hazards like gas leaks and carbon emissions.
- Lifespan: Natural gas furnaces typically last 15–20 years when well-maintained.
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Electric Furnaces:
- Longevity: Electric heaters last longer (20–30 years) with less maintenance.
- Operating Costs: Electricity costs more, but newer electric units with smart controls can disperse heat efficiently.
- Quiet and Clean: Electric heaters are quiet and do not release harmful emissions.
Different Furnace Fan Types
Furnaces fall into several categories based on their fan systems:
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Natural Draft:
- Older models without blower fans.
- Efficiency: 65%–70% (lower due to lack of forced air distribution).
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Forced Air:
- Newer systems with blower fans.
- Common and slightly more efficient.
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Induced Air:
- Similar to forced air units but with an additional fan.
- Draws air into the unit to supply cool air for heating while expelling wasted gas.
- Increases efficiency by relieving pressure on the blower fan.
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Condensing:
- Highly efficient units.
- Use a secondary heat exchanger to extract additional heat from exhaust gases.
- Efficiency levels can reach up to 98%.