Quick guide to oil, natural gas and propane furnaces - efficiency ratings and other specifications

Furnaces: A Quick and Easy Guide

This quick guide to furnaces will help you choose the ideal model for your home and your budget.

Written by
Kate Webb
May 11, 2021

Whether you’re looking to upgrade your existing furnace or to install a new one, you have more options than ever. This quick guide to furnaces will help you choose the ideal model for your home and your budget.

Different types of furnaces

Oil furnaces

Oil furnaces heat your home by burning heating oil, which is stored in a tank on your home’s property. Your monthly expenses will rise and fall depending on the price of oil. However, some models are able to burn a blend of heating oil and biodiesel, which is cleaner than pure heating oil. Because biodiesel also lubricates your oil furnace system, a biodiesel furnace may have lower service costs.

Gas furnaces

A gas furnace heats your home by burning natural gas or propane. The flames heat up a metal heat exchanger, which transfers its heat to incoming air. The gas furnace’s blower forces the heated air into your home’s ductwork and distributes it throughout your home. As the warm air fills your home, cooler air is drawn back into the gas furnace via return ducts, and the process begins again.

Is there a difference between natural gas and propane furnaces?

Natural gas furnaces and propane furnaces are comparable in terms of efficiency, safety, and environmental footprint. Unit for unit, propane is twice as efficient as natural gas—this means you can use half as much propane to do the same job as natural gas. That being said, the cost of a propane furnace is slightly higher than a natural gas furnace. The decision really depends on your personal preference.

What size furnace is right for my home?

It depends on how much space you need to heat. A furnace that’s too small won’t keep your house comfortable in extremely cold weather, and a furnace that’s too large will cycle on and off more frequently. This causes wear and tear, uncomfortable temperature variation, and unnecessary noise—not to mention, it wastes a lot of energy. It’s best to work with an expert to determine the ideal furnace for your home.

What do furnace efficiency ratings mean?

Furnaces are rated with an annual fuel-utilization-efficiency (AFUE) score, which tells you how well your furnace converts energy into usable heat. New furnaces are required to have an AFUE rating of at least 78%—and if you splurge on an ultra high-efficiency furnace, your furnace can be up to 97% efficient. If you have a furnace with a 90% AFUE rating, there is just 10% heat loss through the vents, chimney, open windows or doors, and other sources.

What kind of features should I look for in a new furnace?

Variable-Speed Blowers-
When less heat is needed, variable-speed blowers deliver air slower and make less noise. Furnaces with this feature produce fewer drafts and uncomfortable temperature fluctuations.

Variable Heat Output- This feature automatically varies the amount of heat the furnace delivers, greatly increasing its efficiency and your home’s comfort. 

Air Filtration- A high-quality filter will reduce the amount of airborne particles in your home. Consider an electrostatic filter, which uses an electrical charge to help trap particles, or a HEPA  filter, which can significantly reduce the amount of dust blown through your heating system.  

‍Dual Heat Exchanger- Heat exchangers draw heat from the fuel your furnace burns. High-efficiency furnaces often employ two heat exchangers to draw as much heat as possible. Furnaces with high efficiency ratings typically have dual heat exchangers.

Ignition System- Newer high-efficiency furnaces employ intermittent, direct spark, or hot-surface ignition, which do not require a constant flame (like a pilot light.) Furnaces with ignition systems are more efficient and have higher AFUE ratings.

What are the basic parts of a furnace?

- The thermostat uses a sensor to monitor the temperature of your home. It switches your furnace on and off as needed to maintain your home’s target temperature.

Filter - The filter traps dust and dirt in your HVAC system, improving indoor air quality and preventing damage to your HVAC components.

Hot surface igniter - An electrical current creates heat in the ignitor. This heat starts combustion when it meets the gas supply. Newer furnaces have igniters instead of pilot lights.

Flame sensor- This is a safety device that detects heat from the hot surface ignitor. If no heat is detected, the flame sensor turns off the gas supply.

Shut-off valve - This valve stops the flow of gas, oil, or other fuel to your furnace so you can safely repair, or inspect your furnace.

Burners - The burners in your furnace mix gas and hot air to make a flame. This flame is the furnace’s heat source.

Heat exchanger - Air is warmed as it passes over the hot surface of the heat exchanger. This component also prevents toxic combustion gasses from mixing with the air you breathe.

Blower- This component blows warm air through your ducting system and into your home. 

Limit switch - The limit switch monitors temperatures within the furnace. If the furnace is too hot, the limit switch turns off the gas to prevent safety issues.

Still have questions?

Tetra’s experts are ready to talk you through your options and help you choose the best furnace for your home. Get an instant quote today.

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