Advantages and disadvantages of high efficiency furnaces

Furnaces form an integral part of our home’s HVAC system, and like everything mechanical, they come with a shelf life. If you’re in the market for a new furnace, it is likely that you have heard about high-efficiency furnaces. And it wouldn’t be surprising if you’re seriously considering investing in one.

After all, who wouldn’t want an appliance that is more efficient than its predecessor? But is a high-efficiency furnace all that it made out to be? What makes it more efficient? Will it save you money? 

Well, there is only one real way to answer these questions, and that is by doing a comparative analysis. Let’s take a look at the advantages and disadvantages before you decide to install a high-efficiency furnace in your home.

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Know the difference

Furnaces use either electricity or gas to heat up the air, and this warm air is then transported to your whole house via ducts. The Department of Energy measures the efficiency of these furnaces using what is known as Annual Fuel Utilization Efficiency (AFUE).

While really old furnaces had an AFUE rating of around 60%, it is commonplace now for most standard furnaces to have a rating of around 80%. That means around 80% of the air warms the house, while the rest of it passes through the exhaust vents.

High-efficiency furnaces, however, boast an efficiency rate of between 90% and 97%. This makes them, on paper, a lot more efficient than 80% of the furnaces available in the market. However, does a better AFUE rating make this type of furnace your best choice? 

Advantages of a high-efficiency furnace

Increased efficiency

Obviously, as the name suggests, high-efficiency furnaces are more efficient in comparison to what you probably have in your home currently. A furnace with an AFUE rating of 95% will be 15% more efficient than one with an 80% rating.

This will also mean your energy bills will reduce due to more efficient heating and cooling.

Another feature that makes these models more energy efficient is that a lot of them are condensing furnaces. What this means is that they have two heat exchangers instead of one. The additional heat exchanger captures heat from the venting gases as well, reducing wastage.

Designed for sealed combustion

A lot of homes have sealed-off attics and crawl spaces that are sealed off from the outside by spray foam insulation. Since high-efficiency furnaces are designed for sealed combustion, they are ideal to be installed in such areas.

Furnaces with an 80% AFUE rating use the air surrounding them as a part of the combustion process. This means they cannot work efficiently in a completely sealed-off attic or crawl space. 

However, if properly installed, high-efficiency furnaces have a dedicated pipe that draws in air from the outdoors for combustion, making them ideal for sealed-off spaces.

The reason this is an advantage is that with regular furnaces, if they do not have access to sufficient ambient air for combustion, it could lead to back-drafting, or simply put, introduce carbon monoxide into your living space.

This is a safety hazard since carbon monoxide can be lethal. However, high-efficiency furnaces do not depend on the air present in the room but source it from the outdoors for combustion.

Disadvantages of high-efficiency furnaces

Upfront cost 

The upfront cost of a high-efficiency furnace can be more than 40% higher than the cost of an 80% AFUE rating furnace.

For example, a moderate efficiency gas furnace costs between $1,000 and $3,000 on average. A high-efficiency furnace with an AFUE rating of more than 95% will cost between $2,000 and $6,000. 

Let’s not forget though that these models have lower energy consumption.

Furnace installation costs

High-efficiency models are also more expensive to install. And one of the reasons for this is that there are extra PVC pipes that the HVAC technician will need to install.

One pipe, which we have already spoken about, is to bring in fresh air for combustion. The second is a condensation drain pipe, often attached to a condensation pump, to send excess moisture from the furnace to the outdoors.

AFUE ratings don’t cover everything

While AFUE ratings may talk about energy efficiency, they do not cover all aspects of it. For example, a single-stage high-efficiency unit operates at full blast by default every time the thermostat dips lower than a specific temperature.

However, an 80% AFUE rating two-stage furnace will use its high stage only when the home needs to be heated up by several degrees over a short span of time. Otherwise, it will run on the lower stage at most times, which means lower energy consumption.

Modulating furnaces with variable speed blowers offer you the added advantage of controlling fan speed based on the heating needs, which also increases the energy efficiency of the stove. 

Deciding which furnace to buy

A high-efficiency furnace may be the right choice for your home if you need to use the furnace extensively during the year. However, if your usage of the furnace is going to be seasonal, as the usage of air conditioning is in a lot of places, consider this simple formula to help you decide.

Find out the cost of buying a new high-efficiency furnace and an 80% one, including installation. The average lifespan of a furnace is around 15 years or so. Review how much your energy bills have been over the last couple of years to arrive at an average. 

Then, compare it and see if the proposed savings of 15% or so covers up for the difference in cost you are going to incur over the next 15 years. If the numbers don’t add up, you probably do not need a high efficiency furnace. 

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Written by Narayan Shrouthy. September 23, 2022

Narayan is a content writer for Kukun. With experience in both content writing and editing, Narayan mixes his writing and love for reading with his passion for music. As an active musician, He aims to be a key player in Kukun's content experience.