If you’re shopping for a new furnace, the first big choice is whether to go with a high efficiency or standard efficiency model.
- High-efficiency furnaces use two heat exchangers to get more heat out of the same amount of fuel. They cost more up front, but save money on energy bills in the long run, and are better for the environment.
- Standard Efficiency furnaces only use one heat exchanger and are typically faster to install, but waste more fuel and have higher energy costs.
The main takeaway: high efficiency = higher efficiency and lower energy bills. Standard efficiency = lower upfront cost but higher operating cost.
Here’s a closer look at how high efficiency and standard efficiency furnace features compare:
| Feature | High Efficiency Furnace | Standard Efficiency Furnace |
| Efficiency | ~97% AFUE (almost all fuel becomes heat) |
~80% AFUE (20% of fuel wasted)
|
| Venting | PVC venting (flexible, lower cost) | Metal venting (more restrictive, higher cost) |
| Drain | Yes – condensate drain needed | No drain needed |
| Initial cost | Higher, but may be offset by rebates/tax credits | Lower |
| Long-term cost | Lower monthly bills | Higher monthly bills |
| Environmental impact | Lower (burns less fuel) | Higher (wastes more fuel) |
When to choose a high-efficiency furnace
Choose a high-efficiency furnace if…
- You plan to stay in your home for at least 5+ years.
- Lower energy bills are a priority for your household budget.
- You want to reduce your home’s carbon footprint.
- You may qualify for rebates or tax credits.
When to choose a standard-efficiency furnace
Choose a standard efficiency furnace if…
- You need the lowest upfront cost, even if it means higher energy bills.
- You expect to move soon and won’t recoup efficiency savings.
- You have unique space limitations for installation or a complex venting setup incompatible with a condensate drain or sealed venting system.
High-Efficiency vs Standard Efficiency furnace FAQ
Find answers to some of the most common questions homeowners ask when weighing High-Efficiency vs. Standard Efficiency furnaces.
Do high-efficiency furnaces really save money?
Yes. A high-efficiency furnace is up to 99% efficient, which means you’re losing almost nothing as waste. Over time, the lower energy bills often make up for the higher upfront cost. You can calculate your estimated AFUE savings here.
What’s a heat exchanger, and why do high-efficiency furnaces have two?
A heat exchanger is the part of your furnace that transfers heat from the burning gas into the air that’s blown through your home. Standard-efficiency furnaces only have one heat exchanger, which means roughly 20% of the heat generated escapes with the exhaust gases. High-efficiency furnaces have a second heat exchanger that reclaims additional heat from the exhaust before it leaves the house. That’s how they reach efficiency ratings of 97% or higher.
What about the Navien hydronic heat exchanger? Navien’s NPF hydro furnace uses an innovative stainless steel combustion heat exchanger located outside the airstream, paired with a hydronic coil that transfers heat from the hot water into the air — delivering consistent, efficient warmth. If you’re curious, you can learn more about how a hydro-furnace works.
Besides heat exchangers, what else affects furnace efficiency?
A lot of it depends on how the furnace adjusts to your home’s heating needs. Standard-efficiency furnaces are either single-stage or two-stage. They’re either on or off, with the ability to match only two different comfort points. More advanced models, like Navien’s NPF hydro furnace, use variable-capacity operation. That means the furnace can automatically adjust to deliver just the right amount of heat, which improves efficiency and comfort.
Are high efficiency furnaces louder than standard efficiency ones?
Both types use blowers and fans, so neither is silent. However, Variable capacity furnaces like the Navien NPF can adjust down to an industry-leading low capacity of 15% whereas most competitors can only adjust down to 35-50%. This allows the NPF to operate at lower capacities when it is not needed, reducing cycling, power consumption, and sound. That means instead of the loud blasts you may be used to with older staged heating systems.
Why do High-Efficiency furnaces “condense”? Where does the water come from?
When the second heat exchanger reclaims extra heat out of the exhaust gas, the gas cools down enough for the water vapor inside it to turn into liquid. That’s the condensate. It’s basically distilled water with a little bit of acidity from the combustion process. This is why high-efficiency furnaces need a small drain line to carry the condensate liquid away.
What is sealed combustion, and why do high-efficiency furnaces offer it?
Standard-efficiency furnaces pull the air they need for combustion from inside your home, typically where the furnace is installed. That means they’re taking the air you’ve already paid to heat and condition, using that to burn gas and then exhausting it out of the home.
High-efficiency furnaces can solve this issue by allowing sealed combustion. They bring in fresh air from outside through a sealed pipe to use for combustion, not affecting the building envelope (conditioned air inside the home).
The benefits are big:
- Your indoor air is cleaner, minimizing the potential for infiltration.
- You’re not wasting pre-warmed air, which improves efficiency.
In short, sealed combustion improves efficiency and comfort.
Is installation more complicated for high efficiency furnaces?
Not necessarily, it’s just different. High efficiency furnaces need a small condensate drain and PVC venting, while standard efficiency furnaces require metal venting but no drain. In many homes, PVC venting is actually easier and less expensive to install compared to long runs of metal pipe. A good installer will recommend the best setup for your space, but in most cases, high-efficiency installation isn’t harder (and sometimes it’s simpler).
Is PVC venting safe?
Yes. Because of the efficiency, the exhaust from high-efficiency furnaces is much cooler, which is why specialty plastic venting works safely.
Can the drain on a high-efficiency furnace cause problems?
High-efficiency furnaces produce condensate water as a byproduct of their high efficiency. It drains away through a simple plastic line. The condensate is slightly acidic (typically similar to that of pine needles) certain markets may require a neutralizer to be installed in the drain line. In practice, it’s very low-maintenance:
- Drain setup is a standard part of installation.
- The line flows to a drain or sump.
- During annual service, your HVAC tech will check and clear the line as part of routine maintenance.
Worried about clogs or freezing? Installers have solutions like routing the line indoors to a floor drain or using insulation and a neutralizer kit if it needs to exit outside.
As long as the furnace is installed correctly, the drain line isn’t a weak point. In fact, high-efficiency furnaces are built to shut down safely if the line should ever back up, to protect against leaks or unsafe operating conditions.
How long does a high-efficiency furnace last?
Similar to standard efficiency, usually 15–20 years with proper maintenance.
Is maintenance different for high-efficiency and standard-efficiency furnaces?
Overall, both types of furnaces need the same regular preventive maintenance: filter changes, annual inspections, and cleaning. One difference is that high-efficiency furnaces have a condensate drain line, which should be kept clear so water can flow out. It’s a small task your HVAC technician will handle during routine maintenance.
If I won’t be in my home long-term, is a high-efficiency furnace still worth it?
Yes. Even if you don’t stay long enough to see the full return via energy savings, a new high-efficiency condensing furnace is a major selling point. Home inspectors and savvy buyers notice the difference, and a “97% AFUE high-efficiency system” can make your home more attractive on the market.
Why high-efficiency furnaces make sense today
High-efficiency furnaces used to be a premium choice. Today, models like the Navien NPF Hydro Furnace make condensing technology more accessible than ever — with quiet operation, 97% AFUE efficiency, variable-capacity operation, flexible installation, and compact design.
Imagine a family that upgraded to the NPF hydro furnace last winter: Instead of rooms that ran hot and cold, the variable-capacity operation kept their whole home consistently comfortable, even on the coldest nights. They loved the simple, modern control panel that let them fine-tune settings without confusion. A rebate helped offset the upfront cost, and lower monthly bills were icing on the cake. Best of all, winter felt less like a season to “get through” and more like a season to enjoy.
Learn more about how variable-capacity furnaces stack up against single-stage and two-stage models, or make your home more comfortable this winter by finding a Navien installer near you.
