Pairing a Heat Pump with Furnace: What to Know About Dual-Fuel Systems

Conventional heat pumps have been heating and cooling homes for decades. In fact, about one in three homes in the United States already uses one. However, heat pumps are mostly found in southern and southwest states because they don’t work efficiently in subfreezing temperatures. They work great in temperate climates but are notoriously inefficient and expensive to run in cold Northern winters.

However, if you pair a heat pump with a traditional furnace, they work together to cool a home in the summer and heat it even during bitterly cold winters.

Read on to learn more about this efficient heating and cooling system with insights from two heating, ventilation and air conditioning (HVAC) pros — Liam Hogan from Hogan Mechanical Incorporated and Alexander Siv from Amherst Heating and Plumbing.

What Is a Dual-Fuel Heat Pump HVAC System?

This type of HVAC system relies on a connected heat pump and furnace to meet a home’s heating and cooling needs. The heat pump provides heat during cooler seasons, like fall and spring, while the furnace provides heat in the winter. “Heat pumps are really efficient and limit gas usage, so are a nice alternative heat source in a home during cool, but not cold months,” Hogan says.

Additionally, in warmer summer months, a dual-fuel system also works like a high-efficiency central air conditioner. “It’s like the best of both worlds,” Siv says. “You get the efficiency of the heat pump for cooling in the summer and some heat in the spring and fall. Then, in the winter, you get the heating efficiency of a furnace.”

How Does a Heat Pump with Furnace System Work

Agrima Sharma/Family Handyman

A dual-fuel heat pump with a furnace system alternates between using electricity to power the heat pump and gas or oil to power the furnace. Outside temperatures are the catalyst for the change within the system.

Cold Weather Operation

As long as the temperature is above 35 degrees F or so, a heat pump can pull heat from the outside air. Under ideal conditions, it can transfer 300 percent more energy than it consumes. So, during cooler seasons like fall and spring, the heat pump handles the heating duties.

The dual-fuel system still incorporates the furnace but does not use burners, just its air distribution features. The heat pump sends hot “refrigerant” through the furnace’s air conditioning coil. The furnace fan draws air from the home’s cold-air returns, blows that air over the warm coil and then sends the warmed air throughout the house.

The furnace kicks in for only the coldest months. “In Massachusetts, your thermostat makes the switch to the furnace when it’s 32 degrees outside or colder,” Hogan says.

Warm Weather Operation

As shown in the photo above, an air-source heat pump is basically a hybrid air conditioner. Both have a compressor (a high-pressure pump) that circulates refrigerant (a volatile gas) through indoor and outdoor coils, a network of tubes designed to facilitate the capture and release of heat.

But while an air conditioner can move refrigerant in only one direction, a heat pump can force refrigerant in either direction, for heating one way and cooling the other. The pump does this by means of an extra diverting device called a switchover valve. In the summer, the heat pump reverses the refrigerant flow so cold liquid flows over the coil and cools your home just like a conventional air conditioner.

Will a Heat Pump with a Furnace System Work for Your House?

To figure out whether a heat pump is practical for your home, you’ll need to contact a heating contractor.

• Start with a heating and cooling load analysis. Don’t trust the label on the old furnace; ask your installer to measure and double-check the math. Home improvement projects (new insulation, new windows or an addition) can change your heating and cooling needs.
• Conduct a comparative cost analysis. If you live in an area with lower-priced natural gas and sky-high electrical rates, a heat pump will not pay itself off as quickly. Your installer can factor in local energy rates (including peak and off-peak electrical rates) to calculate your potential savings and payback.
• Ask about compatibility. Dual-fuel heat pumps are designed to be straightforward A/C replacements, but older furnaces probably won’t work with a new switch-hitting system. “It will need to be determined whether the current furnace can be controlled together with the new heat pump equipment,” Siv says.

How Much Does a Heat Pump with Furnace Cost?

A dual-fuel heat pump with a furnace will cost more than a furnace and A/C install. “A typical gas furnace with an air conditioner will be between $8,000 to $10,000,” Hogan says. “Expect to pay between $12,000 to $15,000 for a dual-fuel heat pump with furnace installation.”

What Tax Credits Are Available for Heat Pumps?

In addition to saving money in the long run, a dual-fuel heat pump might pay you back right away. This upgrade may qualify for an energy-savings tax credit plus rebates. Ask your utility company and HVAC installer about available incentives in your area.

FAQ

What are the downsides to a heat pump?

Heat pumps on their own are not effective in very cold temperatures. While more effective when paired with a furnace, Siv points out that the higher installation cost of a heat pump with furnace system is the main downside. “It’s a great system upgrade if you can afford it,” he says.

At what temperature do heat pumps become ineffective?

Generally, heat pumps are ineffective at 35 degrees F or colder.

Can heat pumps cool your house in 100-degree weather?

Most heat pump models can effectively cool your house in outside temperatures up to 115 degrees F.

What’s the “20 degree rule” for heat pumps?

Never set your thermostat for more than 20 degrees cooler than it is outside. So, if it’s 90 degrees F outside, the thermostat should not be set any lower than 70 degrees F.

About the Experts

• Alexander Siv owns Amherst Heating and Plumbing in Amherst, Massachusetts. He has a master plumber’s license in Massachusetts and more than 10 years of plumbing experience.
• Liam Hogan is the owner of Hogan Mechanical Incorporated a full-service residential and commercial plumbing and heating company in Springfield, Massachusetts. He has ten years of industry experience.