A high-efficiency, also termed a condensing furnace, converts 90% or more of its fuel (typically gas) into heat that can be used to heat the home , resulting in lower energy consumption and heating costs.
AFUE (Annual Fuel Utilization Efficiency) is a rating system for furnaces (and other appliances, like tankless water heaters) that lets homeowners compare the efficiency of different models.
Furnaces with an AFUE of 90% or higher are considered high efficiency, condensing furnaces. Standard efficiency furnaces typically have an AFUE around 80%.
If you’re not sure whether you have a high-efficiency furnace, look for the AFUE rating on the yellow EnergyGuide sticker on the outside of the furnace. You can also tell by the venting material: a standard efficiency furnace will use a metal pipe (or chimney flue), but a high-efficiency furnace will have a PVC vent pipe. This is because high-efficiency furnaces extract more heat from the combustion process that is used to heat your home minimizing heat loss through the vent/exhaust pipe thereby lowering the exhaust gas temperatures allowing for the use of specialized PVC vent piping. High efficiency furnaces also allow for combustion air (air used to burn gas) to be pulled in from outside the home. So many times a high-efficiency furnace will have two PVC connections. One that brings in combustion air the other to exhaust the combustion gasses.
How High Efficiency Furnaces Work
High efficiency furnaces have three key features that make them more efficient.
- Condensing technology: A stainless steel second heat exchanger captures heat from exhaust gases, which would otherwise be lost. Because they extract more heat from combustion gases, it causes those gases to cool down enough for water vapor to condense into liquid creating what is commonly referred to as condensate.
- Flexible venting: Because of the lower exhaust temperatures of a high-efficiency furnace, it can be vented with specialized high temperature plastic vent pipe. This is typically a smaller diameter than standard efficiency furnaces and can be run in lengths significantly longer than a standard efficiency furnace. This provides more flexibility on installation, more options to install the furnace where you want to, and vent the product in a desired location, whether through a sidewall or a roof penetration.
- Sealed combustion: High-efficiency models can also have a sealed combustion chamber that allows combustion air to be drawn from outside the home instead of using the air in the home that you just heated to burn the gas then exhaust it outside the home. This improves indoor air quality by minimizing infiltration and maximizing efficiency.
High-efficiency furnaces reduce your home’s environmental impact and lower heating bills. Learn about even more benefits of variable capacity furnaces.
Do All High Efficiency Furnaces Use Variable Speed Motors?
No, high efficiency furnaces are available with two different types of blower motors:
Standard ECM
Standard ECM (Electronically Commutated Motors) are similar to the PSC (Permanent Split Capacitor) motors used in the past, except they are based on a high-efficiency ECM platform. Electronically commutated motors are also referred to as constant torque motors.
ECMs will adjust their operation to maintain a pre-programmed torque level that is associated with a pre-identified CFM (cubic feet per minute). ECM are not variable speed. Standard ECM furnaces typically offer five blower speeds or taps.
Variable Speed
Variable speed (also referred to as constant CFM) blower motors are based on a high-efficiency ECM platform, and provide the advantage of constant CFM (cubic feet/minute). This means the variable speed motor is constantly monitoring its operating conditions and adjusting to maintain the CFM the unit was set for, while automatically accounting for marginal ductwork or dirty filters within the ability of the motor.
High-efficiency, constant CFM furnaces are available on premium, featured comfort products, such as the Navien NPF Hydro-Furnace, providing better airflow and comfort throughout a home using minimal energy.
For high-efficiency furnaces in general, increased runtime does not mean higher energy costs. Because they run longer at a lower speed (or at modulating speeds, if variable capacity), they maintain a consistent indoor temperature while using less energy.
Will My Thermostat Work with a High Efficiency Furnace?
Not all high-efficiency furnaces (or thermostats!) are the same. Most high-efficiency furnaces are compatible with conventional 24VAC thermostats as well as the latest smart thermostats. Some manufacturers use proprietary communicating thermostats that will only work with their equipment. It’s important to know exactly which pairing of high-efficiency furnace and thermostat you are considering, and check with the manufacturers.
Navien’s high-efficiency NPF hydro-furnace is compatible with conventional single or two-stage thermostats. It also integrates seamlessly with the latest thermostat and Indoor Air Quality (IAQ) technology.
You can maximize efficiency by using a newer programmable or adaptive learning thermostats.
Smart thermostats can help you reduce heating costs by optimizing energy usage based on your home and away patterns, and minimizing power consumption during peak usage times when electricity is more expensive.
How Long Does a High Efficiency Furnace Last?
High efficiency furnaces have a lifespan of around 15-20 years, with proper maintenance. Keeping up with regular maintenance is also important to protect your furnace warranty.
Rebates for High Efficiency Furnaces
There are often rebates for high efficiency furnaces - it can vary by location. In addition to Federal Tax Credits, a high efficiency furnace may be eligible for rebates or instant discounts through state programs.
Just search “NPF” in our rebate center and enter your ZIP code to see residential rebate programs in your area.
NPF Hydro-Furnace
Navien’s NPF hydro-furnace is a high-efficiency residential heating innovation. In addition to all the high-efficiency furnace features listed above, it has a unique design and hydronic coil. The NPF uses hot water to heat the airstream, rather than having the heat exchanger located in the conditioned airstream the NPF burns gas to heat water in a separate compartment isolated from the airstream minimizing sound as well as the impact on the homes humidity level.
NPF efficiency features include:
- 97% AFUE
- Sealed & isolated combustion compartment
- Variable speed (constant CFM) blower
- Industry-leading variable capacity operation from 15% to 100%
- User-friendly unit mounted controls
