Disadvantages of High-Efficiency Furnaces

Heating is expensive. According to the American Gas Association, the average American household spends $661/year on average on home heating. This translates to about $55/month from January to December or over $165/month for the four winter months from December to April. 

For this reason, many homeowners invest in a high-efficiency furnace to reduce their energy bills. Indeed, some manufacturers say that you can save up to 45% of annual heating costs with their high-efficiency furnaces. 

This isn’t entirely untrue. Homeowners who’ve installed high-efficiency furnaces report significant energy savings, thus lower heating bills. But, unfortunately, it comes at a cost. Read on to find out why high-efficiency furnaces aren’t fault-free and learn valuable tips to help you make the right decision. 

What is a High-Efficiency Furnace?

A high-efficiency furnace is any furnace with an AFUE efficiency rating higher than 90%. This effectively means that the furnace converts into useful heat energy at least 90% of the chemical energy in the fuel it burns.

 Are you feeling lost? Don’t be. All you need to understand is that furnaces burn fuel, typically natural gas, propane, or heating oil, to generate the heat necessary to warm your rooms. However, since furnaces aren’t perfect, not all the gas is successfully converted to heat. 

Some of the gas, for instance, ends up as carbon dioxide and carbon dioxide. Moreover, the furnace’s internal components may absorb some of the heat. As a result, some heat is also lost alongside combustion gases. 

A high-efficiency furnace incorporates advanced technologies to keep these losses to a minimum. Thus, they can convert 90% or more of the fuel’s chemical energy into useful heat that eventually enters your rooms. 

The efficiency with which a furnace utilizes fuel is known as the Annual Fuel Utilization Efficiency (AFUE). Thus, the higher the AFUE value, the more energy-efficient the furnace. 

How Does a High-Efficiency Furnace Work?

Typically, high-efficiency furnaces utilize a second heat exchanger to heat air from condensed exhaust gases to prevent heat losses. 

You see, every furnace has at least one (primary) heat exchanger where heat from the gas burner is transferred to the circulating air before the now-warm air is discharged via the supply air plenum into your ductwork and ultimately into your home. 

In a traditional (low-efficiency) furnace, with just the primary heat exchanger, the hot exhaust gases from the combustion chamber go directly into a metal flue and are vented out of the furnace with the help of the exhaust fan. This means that all the heat in the exhaust gases (including carbon dioxide, carbon monoxide, and water vapor) is lost. Research shows that furnaces lose up to 10% of heat this way. 

High-efficiency furnaces introduce a secondary heat exchanger to limit the heat losses from exhaust gases. 

The secondary heat exchanger is strategically positioned to extract as much heat from exhaust gases, which it redirects to the supply plenum for increased heat output. 

High-Efficiency Furnaces vs. Standard Furnaces

The main differences between high-efficiency furnaces and traditional low-efficiency furnaces are as follows;

  • Two vs. one heat exchanger: This is the primary design difference. Whereas traditional furnaces only have one heat exchanger, high-efficiency models have two. 
  • Sealed vs. open combustion: High-efficiency furnaces typically use an air-intake pipe to bring combustion air outside the house. This is unlike the traditional furnace that uses the warm air inside your home for combustion. 
  • Plastic vs. metal exhaust flue: All traditional furnaces have metal (usually stainless steel) exhaust flues due to the extremely hot exhaust gases. Meanwhile, many high-efficiency models have plastic flues as the exhaust gases are very cold in the end. 
  • High vs. moderate efficiency levels: Above all, high-efficiency furnaces are very efficient, typically above 90% AFUE. Meanwhile, traditional furnace efficiencies vary wildly, from below 60% to the high 80s.

Advantages of High-Efficiency Furnaces

Consumers have in recent times fallen in love with high-efficiency furnaces, and for a good reason.

  1. Energy-saving: Research shows that high-efficiency furnaces utilize up to 15% more heat than traditional furnaces. Improved energy utilization means lower bills and a reduced environmental impact. 
  2. Sealed combustion: The main advantage of sealed combustion is that the furnace doesn’t deplete the oxygen in your home. This is especially valuable in closed-out environments such as a basement with few or no windows. 
  3. Tend to last longer: High-efficiency furnaces generally require fewer repairs over their lifetimes and also last longer. The longer life is mainly attributed to reduced internal heating as they extract heat better. 
  4. Tax credits: Finally, many states, as well as the federal government, offer tax credits for high-efficiency furnace installations. For instance, the federal government offers up to $500 in tax credits for new high-efficiency furnace installations. 

Disadvantages of High-Efficiency Furnaces

Unfortunately, high-efficiency furnaces aren’t without fault. The following are seven critical drawbacks of high-efficiency furnaces to keep in mind as you go shopping. 

More expensive 

The first thing you need to know about high-efficiency furnaces is that they’re significantly more expensive than traditional furnaces. Although the exact prices vary depending on size and brand, you’re guaranteed to pay 50% to 100% on a high-efficiency furnace than a comparable standard model.

For instance, according to the Home Advisor, the average cost of a new standard natural gas furnace rated 80% to 85% AFUE is $2,100. Generally, the prices range from $700 to $3,500. Less efficient models are even less expensive. 

However, the cost shoots significantly for high-efficiency models rated 90% AFUE or higher. On average, a new high-efficiency natural gas furnace costs a staggering $5,500. 

Of course, the prices vary from one unit to the next. Generally, though, high-efficiency furnace prices start at around $3,000 for tiny units from Trane, and American Standard rated 40,000 BTUs and below. On the other extreme, the highest-priced units, typically extra-large units rated up to 120,000 BTUs from luxury brands such as Carrier and Lennox, cost up to $13,000. 

Higher installation costs 

The other issue is the complexity and cost of installation. You’ve probably heard a few people talk about DIY-installing their furnace to cut costs. For instance, some DIYers save up to 70% of standard installation costs to install their furnaces. 

The first thing you must know about high-efficiency furnace installation is it’s strictly a professional job. The law prohibits DIY-installing a high-efficiency furnace. You risk hefty fines and potential jail time if you attempt to install a high-efficiency furnace without a proper license. 

It gets worse – high-efficiency furnace installation is not cheap. Standard labor charges for furnace installation range from $50/hour to $150/hour, depending on the type of furnace and your geographic location, among other factors. High-efficiency models are the most expensive to install. 

Given that high-efficiency furnaces also take the longest to install because of complex design, you can see why the total cost can be very high. Typically, it takes 10-15 hours to install a high-efficiency furnace. But, again, it depends on the size and model. 

Thus, in total, you can expect to pay up to $150/hour x 15 hours = 2,250 for labor alone, assuming that it’s a new install. 

The costs are slightly higher if replacing an old furnace with a high-efficiency model. Converting from an oil heater to a high-efficiency natural gas heater is the most expensive process, costing $6,500. 

Then you also need to factor in building permits. Although traditional furnace permits cost about $350 to $500, depending on complexity and your jurisdiction, high-efficiency model permits can cost as much as $1,800. An inspection alone can cost you over $500. 

So, as you can see, you may need up to $4,000 for a new installation and at least $2,500 more to replace your old furnace with a new high-efficiency model – before you even purchase the new furnace. 

Venting challenges 

Finally, switching to a high-efficiency furnace comes with fresh operational challenges that may negate some efficiency gains. Specifically, venting problems on high-efficiency furnaces are well-known issues that you must beware of as you go shopping. 

The following are some of the most common venting challenges on high-efficiency furnaces and how they can impact overall convenience. 

  • Obstructed air intake vents

The most common venting challenge is obstructed air intake vents. As we mentioned earlier, most high-efficiency furnaces are sealed combustion systems that draw combustion air from outside the house. They have a special pipe that brings in fresh air from outdoors. 

Now, imagine if the air inlet pipe is blocked, perhaps from birds’ droppings or small insects within the pipe. It can cause serious heating challenges. It often results in a fragile flame that hampers heating output and causes the furnace to run longer than necessary. Or, the flame may go out altogether. 

  • Improper exhaust gas recirculation 

This problem is most common if the air intake and exhaust vents aren’t installed properly. For instance, if the installer mixed up the two vents, exhaust air may flow back into the combustion air intake pipe, creating a dangerous situation. 

Alternatively, maybe the two vents are too close together such that the exhaust gases are easily drawn into the air intake vents. Or maybe the air intake pipe is leaking, thus allowing exhaust gases to mix with in-bound fresh air. 

Whichever the case, it can cause a severe shortage of oxygen-rich combustion air, resulting in a weak flame or causing the furnace to off. Indeed, this is one of the biggest causes of short-cycling in high-efficiency furnaces.  

  • Obstructed exhaust flue issues

Finally, high-efficiency furnaces can also malfunction due to exhaust flue obstruction. If you understand their working mechanism, you’ll know furnaces have a pressure switch. The pressure switch closely monitors the exhaust process to prevent toxic combustion gases from entering your home via the supply air plenum. 

It tracks the negative pressure generated as exhaust gases are removed from the house and trips and consequently shuts down the furnace as soon as it senses insufficient negative pressure. 

A common cause of insufficient negative pressure in high-efficiency furnaces is a blocked exhaust vent. A blocked exhaust flue means that exhaust gases cannot exit the furnace, meaning the pressure will be relatively high in the pressure switch zone. Thus, the switch will open and consequently shut down the furnace. 

Here are symptoms of a bad furnace pressure switch that you should look out for.

What are Some of the Best High-Efficiency Furnaces Brands?

The best high-efficiency furnace brands are the same companies that make traditional furnaces. Top of the list are;

  1. Lennox
  2. Carrier
  3. Frigidaire 
  4. Maytag 
  5. Rheem 

How Do you Tell if your Furnace is Venting Properly?

The easiest way to tell that your high-efficiency furnace is venting well is to look at the color of the flame. The system is venting correctly if the flame is completely blue and cone-shaped with no smoke/soot. 

FAQ About High-Efficiency Furnaces

Is a high-efficiency furnace worth it? 

Yes. Although the higher initial costs can be off-putting, high-efficiency furnaces guarantee a cleaner, healthier home and significant energy and cost savings in the long term. 

Should I upgrade to a high-efficiency furnace?

Yes, you should strongly consider upgrading. Although they cost more to purchase and install, high-efficiency furnaces can save you up to 45% of your energy bills yearly. 

How much money do you save with a high-efficiency furnace?

According to the Department of Energy (DOE), you can save up to 50% of your utility bills by upgrading to a high-efficiency furnace. This translates to $330 in savings per year, given that the average US home spends $660/year on heating.  

Do high-efficiency furnaces pay for themselves?

Yes, high-efficiency furnaces can pay for themselves over the appliance’s life. However, you must be patient as the appliance can take several years to repay the initial investment. 

How long does it take for a high-efficiency furnace to pay for itself?

A high-efficiency furnace may take up to 10 years or more to pay for itself. Of course, the duration varies depending on the actual investment and the furnace’s efficiency level. A more affordable, more efficient unit takes shorter to repay the initial investment. 

Does a high-efficiency furnace need a drain?

Yes, high-efficiency furnaces need a drain, also known as condensing furnaces. The reason is that the secondary heat exchanger removes nearly all the heat from exhaust water vapor, resulting in liquid water. Therefore, a floor drain is necessary to remove the water from the furnace. 


High-efficiency furnaces are in high demand today and for a good reason. They significantly cut heating expenses, sometimes by as much as 45%. Additionally, high-efficiency furnaces ensure a cleaner, healthier home and last longer.

However, don’t be blind to the drawbacks. Despite the cost savings, high-efficiency furnaces cost up to 100% more upfront and are also more complex and costly to install, among other challenges. So, if you’re buying one, you must be prepared accordingly.