October 17, 2024

Hybrid heating systems combine a heat pump and a furnace. The furnace may be fuel-burning or electric. When the furnace is gas-powered, these hybrid systems are also referred to as dual-fuel. The heat pump component of this system is nearly always electric. It is the main heating and cooling component of the system, while the furnace provides an auxiliary boost on cold days. Let’s explore dual-fuel technologies in greater detail and why hybrid heating may be the right choice for your next HVAC system.
Heat Pumps and Transferring Heat
Heat pumps don’t generate heat. They use the process of compressing and expanding refrigerant to transfer it from one medium to another. This process is also used in refrigerators and air conditioners. A reversing valve allows the heat pump to choose to transfer heat into or out of the home.
Heat pumps are most efficient in temperate climates where there is enough heat in the ambient air to transfer. As temperatures drop, this becomes more difficult to do efficiently. Warming your home on the coldest days with just a heat pump can be slow and may require a heat pump to run consistently. When this happens, a dual-fuel system will activate the furnace to help get your home to the desired temperature more quickly and maintain it when necessary.
Furnaces and Generating Heat
Gas furnaces generate heat by way of combustion. Fans then blow it into ductwork where it flows into the home via forced air vents. Furnaces are less efficient than heat pumps, but they can warm things to hotter temperatures and provide heat very quickly to a cold home. This reduces the overall running time of the system during the winter.
Air-Source and Geothermal Heat Pumps
The most common heat pump is an air-source heat pump. Air source means that the heat pump transfers heat energy to and from the ambient air. The downside to this approach is that the ambient air has a limited amount of heat energy during winter.
Geothermal heat pumps are ground- and water-source systems that transfer heat energy to and from the earth or a large body of water. The ground provides more abundant and consistent heat energy during winter. Geothermal hybrid systems are less likely to rely on the furnace component during cold days.
Energy Efficiency
When assessing the efficiency of a dual-fuel heat pump, you have to consider both components. The Department of Energy (DOE) measures furnace efficiency differently than it does heat pump efficiency.
AFUE
The DOE uses annual fuel utilization efficiency (AFUE) to rate fuel-burning furnaces. The value indicates how efficiently the system burns fuel. An 80 AFUE furnace converts 80% of the fuel it burns into heat and loses the other 20%. The higher the AFUE rating, the more affordable the furnace will be to operate. Mid-efficiency furnaces range up into the high 80s while high-efficiency furnaces range up into the high 90s.
HSPF and HSPF2
Heating seasonal performance factor (HSPF) measures heat pump heating efficiency over an entire winter. The higher the number, the more efficient the heat pump is. HSPF2 is a new version of the rating system. It also accounts for ductwork. In the future, HSPF2 will supplant HSPF, and the DOE will drop the number. The current DOE minimums are 7.5 HSPF2 and 8.8 HSPF.
Note that you can’t compare AFUE to HSPF. To compare furnaces and heat pumps, you can use the data from the EnergyGuide label to calculate your estimated annual costs.
SEER and SEER2
Seasonal energy efficiency ratio (SEER) is similar to HSPF but measures cooling efficiency over an entire summer. Use it to compare the cooling performance of air conditioners and heat pumps. The higher the value, the more efficient and affordable the cooling will be.
ENERGY STAR
The Environmental Protection Agency (EPA) sets its own standards for energy efficiency. Furnaces and heat pumps that achieve those standards through independent testing receive ENERGY STAR certification. The ENERGY STAR gives you confidence that the system you choose is highly efficient.
Purchasing HVAC equipment with the ENERGY STAR label may also make you eligible for rebates and tax credits. You can claim rebates for both the heat pump and furnace. This is true of tax credits as well, such as the Energy Efficient Home Improvement Credit.
Is a High-Efficiency Furnace Worth It for Dual-fuel Setups?
Efficient appliances often come with a higher initial cost. Because the furnace operates only on the coldest days, not all installers will recommend that you purchase the most efficient model. However, combustion furnaces also require a consistent source of natural gas or propane. If you live in an area where you must have your fuel delivered, there is peace of mind in knowing that you have enough fuel to run your furnace after a big winter storm. This is especially true if the roads are closed at the time. Prices of natural gas and propane also rise in the winter with increased demand. This can lead to a creeping increase in cost year over year that may make an efficient furnace more worthwhile over its lifetime.
Dual-Fuel Systems and Backup Generators
If you live in an area prone to storms, you may wish to invest in a backup generator. Both the heat pump and the fan component of the furnace run on electricity, so neither unit can operate without power. While a heat pump is very efficient, the electrical startup load can be high, The unit also requires a 240V circuit. Fans on furnaces run on the more common 110V circuits. The best way to ensure that your system is properly set up and can be accessed during a power outage is to work with an electrician and your HVAC professional.
Dual-Fuel System Maintenance
Most HVAC warranties require seasonal maintenance. We also recommend seasonal maintenance because it increases efficiency and lowers operating costs. Regular tune-ups help avoid repairs in summer and winter, extend equipment lifespan, and help systems age more gracefully. You’ll need to schedule a cooling tune-up in the spring for the heat pump. You should schedule a heating tune-up in the fall for the heat pump and furnace.
Maintenance plans come with additional advantages. You are often given discounts on repairs during any year that a tune-up is performed. Also, a professional who looks at your system every year can tell you when you may want to begin looking for a replacement. If you have this information early enough, it gives you time to research, budget and shop around.
Are You Interested in a Dual-Fuel System in St. Louis?
Scott-Lee Heating Company is a family-owned and -operated HVAC with decades of experience serving St. Louis, MO and the surrounding areas. Our NATE-certified technicians install, maintain, and repair dual-fuel HVAC systems. We also specialize in gas and electric furnaces, air-source and geothermal heat pumps, air conditioners, and ductless mini-splits. Our team installs and services HVAC zoning systems, air scrubbers, humidifiers, and dehumidifiers. Call today or contact us online to learn more about these products and services or to schedule an appointment.