Furnace and Boiler Energy Efficiency

gas-flameEnergy efficiency, it’s a term with a lot of meaning behind it and a lot of nuances. You’ll probably hear it a lot when you’re shopping for your next Austin heating system but without a firm grasp of what it means and how it is calculated, it can be hard to know what you’re getting and how the energy efficiency of your new boiler or furnace will translate into your day to day life.

Heating in Austin is usually provided by one of three types of heating systems. Most homes have a boiler, a furnace, or a heat pump. Heat pumps run on electricity like air conditioners and as such they use the same energy efficiency rating system, the SEER rating. But boilers and furnaces are different beasts. They both run on typically fuel, although you can get an electric furnace. Today’s tip however will be all about these fuel-burning heaters and everything you might need to know to navigate their energy efficiency levels, how they are rated, why a higher energy efficiency rating is better, how to shop for the right heater for your house. Read on to learn about energy efficiency when it comes to fuel-burning heating systems like boilers and furnaces.


This is the acronym for the rating system that fuel-burning heaters use to describe their energy efficiency levels. It stands for annual fuel utilization efficiency. It’s all about thermal efficiency, how efficiently a device heats water or the air. It was invented as a way to provide a look at how much efficiency you’ll be getting out of heater over a season and as such doesn’t actually represent a steady-state, peak measure of conversion efficiency, but instead attempts to represent the actual, season-long, average efficiency of that piece of equipment. So it isn’t as accurate as a measure of the energy efficiency at one specific moment but it is more useful because it can be used to judge how much you’ll be spending on utilities to run the device over the course of the year.

One handy thing about AFUE is that it doesn’t use units, and instead is expressed as a percentage. This makes it easy for the layman to read and understand without any deeper understanding of the units or unit conversions involved in thermal devices. It’s a measure of the ratio useful energy output to the energy input over a year expressed as a percentage. For example, a 90% AFUE for a gas furnace means it outputs 90 BTUs of useful heating for every 100 BTUs of natural gas input (where the rest may be wasted heat in the exhaust). A higher AFUE means higher efficiency.

Typical Average AFUE

While it is true that AFUEs can vary wildly from brand to brand, price point to price point, and depending on the age and type of heater you’re looking at, there are useful averages for the different types of heaters. These numbers can be helpful to look at to get a baseline idea of what one might see out there when shopping for new heater and what one can expect. By knowing the averages, you can know when you’re looking at a heater that is better or worse than average when it comes to measures of energy efficiency.

The biggest factor that is going to determine the average AFUEs for a type of heater is going to be the type of fuel it runs on. Heating oil tends to lend itself to lower AFUEs than other types of fuel and isn’t used as commonly anymore. The average cast-iron furnace or boiler built before the 1970s is probably going to run on heating oil and is going to have an AFUE of around 60%. A retention head burner boiler or furnace that runs on heating oil will likely have an AFUE of between 70% and 78%. In contrast, you might be able to get an AFUE of anywhere from 83% to 89% out of a mid-efficiency boiler or furnace that uses heating oil.

Natural gas is the most common source of fuel nowadays for furnaces and boilers. With a standard efficiency furnace or boiler you can expect to get on average anywhere from 78% to 84% AFUE. For a more advanced condensing heater this goes up to 90% to 97%. Propane as a fuel has similar levels of energy efficiency. Your standard propane burning heater will likely have an AFUE of somewhere between 78% and 84% whereas a condensing heater running on propane will be anywhere from 88% to 95%.

Firewood is interesting as a heater fuel source because there has actually been a lot of progress made in the design of firewood burning heaters. So the amount of energy efficiency you’re going to get out of a firewood boiler or furnace is going to depend heavily on how advanced and modern the design is. A conventional wood burning heater is going to have an AFUE of somewhere between 45% and 55%, not very impressive. An advanced firewood fuel heater will be somewhere around 55% and 65%. But with a state-of-the-art firewood boiler or furnace, you’re looking at anywhere from 75% to 90% AFUE.

AFUE Requirements

Just like with air conditioners and SEER ratings, requirements for minimum levels of energy efficiency have been put into place over the years. Non-condensing furnaces are required to be 78% efficient, except for units designed for mobile home use. Mobile home units are required to have an AFUE of 75%. In June 2011, the Department of Energy raised the efficiency requirements for many furnace styles. The requirements were set to go into effect in May 1, 2013 and January 1, 2015. Following a January 11, 2013, court ruling, the DOE put the increase in requirements on hold pending the lawsuit's outcome.

Some of those requirements include that non-weatherized gas furnaces must be 80 percent efficient, non-weatherized mobile home furnaces must be 80 percent efficient, non-weatherized oil furnaces must be 83 percent efficient, and all gas furnaces installed in the northern states, about 30 in total, must be 90 percent efficient.

Why Consider a More Efficient Heater

The question of whether it is time to get a new heater is big one. There are a lot of factors involved and it is usually a somewhat costly investment. One of the biggest factors worth your consideration is the energy efficiency of your current boiler or furnace and the efficiency of a potential new heater and what that could mean for you going forward. If your old furnace has stopped working entirely, it’s definitely time for a new, high-efficiency furnace. But, even if your old furnace seems to work okay, it might be time to consider replacing it with a more efficient model to save money over the long run and enjoy more comfort and quiet now.

Why is energy efficiency a big deal? Sky-high energy bills, diminishing resources, and environmental concerns have brought a great deal of attention to the topic of home energy efficiency in recent years especially when it comes to heating. People are struggling to spend less, use less, and pollute less without giving up the warmth and comfort they’ve come to cherish. So the race to make higher and higher efficiency machines for less money is on. That’s good news for all who are in the market for a new heater.

Really it all comes down to your bills. The efficiency of your furnace can make a major difference in your energy bills. According to the U.S. Department of Energy, heating and cooling account for approximately 56 percent of the energy used in a typical U.S. home (the portion for heating is about 30 percent). Obviously, if you can squeeze more efficiency out of your heating and cooling equipment, you can make a major dent in your monthly energy bills. If you intend to stay in your home for a few years, upgrading from an old, inefficient furnace to a new, high-efficiency model can pay for itself and improve your comfort.

Another way to think about this is to consider that 98.2 cents out of every dollar spent for energy to heat your home is converted to heat. With a lower performing model, 20 cents or more of every dollar is wasted. Those dollars can add up in a hurry at today’s energy prices.

Heater Efficiency and Heating Repair in Austin

When it comes down to it, eventually you’re going to have a choice. Do you keep your current furnace or boiler or do you replace it with a newer and higher efficiency model? This question will become most pertinent the next time your furnace or boiler needs a repair of some kind. As heaters get older, not only do they lose efficiency and become outdated by newer technology and more energy efficient models, they become more and more likely to breakdown. A heater breakdown is a terrible thing especially in the middle of winter, but with it comes a choice. Is it worth the cost of the repair to get your current heater back to working order or are you going to be better suited by buying a new model?

The answer to that question is going to rely on a number of factors, including your budget for new heater, the age of your current heater, and how well it has worked for you in the past. It will also depend on how long you intend to stay at your current residence. Either way, you’ll want to have experienced professionals on your decide when you make this decision. The technicians at AC Express are all well versed in heaters of all kinds and all levels of efficiency. We can help you make the right choice and pick the best heater for your situation. We can repair any model or install any brand. AC Express is an Austin heater repair company that operates anywhere from Cedar Park and Manor to Pflugerville and Leander. If you need heater repair in Austin, call today!