Heat Pump Basics

What’s the deal with heat pumps?

The trouble with heating that relies on fossil fuels, including the most advanced natural gas furnaces, is that their efficiency peaks around 99%. But, what if you could buy a furnace that’s 300% efficient? What if that furnace was also an air conditioner?

That’s what’s up with heat pumps. They’re far more efficient because instead of creating heat out of nothing, they just move heat from one place to another. And that’s why they began outselling natural gas furnaces nationwide in 2023.

There are two reasons why heat pumps aren’t more common in Wisconsin:

1. We have very low natural gas prices. That means that the operating costs of air source heat pumps can be higher than natural gas.
2. Our cold climate can be a barrier. While there have been many advances in cold climate heat pumps when the daily low is below 5 degrees, they’re going to need a boost. The technology has also improved substantially in the last few years, so many HVAC contractors are not yet comfortable with the technology.

Dual fuel systems, ones that use BOTH an air source heat pump and natural gas furnace in tandem, are the way to go for most people in Wisconsin in 2026.

How do heat pumps work?

Heat pumps work by moving, or ‘pumping,’ heat energy from inside to outside or the reverse. In summer, they pump the heat out like an air conditioner. In winter, the valve is flipped into reverse to move the heat energy from outside to the inside. This is done using by taking advantage of the phase changes between liquid and gas caused by condensation and evaporation. This is basically the same compressor technology you have in your refrigerator or air conditioner. it just goes in both directions.

If you, like me, are still a little hazy on what this means, Undecided’s Matt Ferrell and Jon Okun have an excellent explainer of heat pump basics here (or below).

Air Source vs. Ground Source

Heat energy needs to be transferred to or from a source. Air source heat pumps are the most common, but ground source systems are also very effective. They tend to be more expensive than ASHPs, especially since they require excavation. But once they are in place they can last a long time, possibly a century or more. They can use horizontal or vertical wells.

One homeowner has a ground source system in downtown Green Bay that uses six 300′ deep wells in their side yard! You’ve likely driven past and not noticed. It has recently returned its investment and now provides most of their heat (they supplement with wood fire when needed), all of their cooling, hot water, and radiant floor heating at no further cost (except occasional maintenance).

Are Heat Pumps For You?

Air Source Heat Pump System

An air source heat pump, by itself, will increase your utility bills over the winter and decrease them in summer. Overall, you can expect to pay about $1,000 more per year for an average home. If the climate is your chief concern and you can afford it, this may be something you would consider.

Here are some things to consider when weighing the choice of whether or not to upgrade to a heat pump:

• If you are motivated primarily by your concern about climate change, the increased cost may be one you find acceptable.
• If you have a home that is partially or fully powered by solar PV, that may offset the higher cost of heating with heat pumps.
• If you are able to qualify for significant rebates for an air source heat pump, that may partially offset the higher costs.
• Most people find that homes heated and cooled by heat pump systems are more comfortable. They tend to maintain consistent temperatures rather than bouncing between set points.

Dual Fuel (Hybrid) System, a better choice?

If a full heat pump system isn’t right for you, a dual fuel system may be a better choice.

A dual fuel system is one in which the air source heat pump essentially replaces your AC unit and functions alongside your natural gas furnace. It cools your home during the summer and heats it until the temperature outdoors drops to a certain point (typically 20-30 degrees F). Dual fuel systems have operational costs similar to natural gas and AC systems, but they will decrease your carbon emissions and increase your comfort. And with instant rebates (see below), they may even be cheaper than conventional systems!

Heat Pump Typology

What types of heat pumps are there?

There are many different types of systems because different spaces have different heating and cooling needs and design requirements. So, choosing a heat pump system is something best explored with a qualified HVAC contractor who can create a system for your specific needs. Here are some of the choices you will need to make:

• Ground Source vs Air Source Heat pumps: Heat pump systems make use of heat differences between the inside of a building and the outside. Some systems are designed to pull heat from the air, others from the ground. Ground source systems are more efficient and to last longer, but they are more expensive.
• Ductless vs. Ducted: These can be single or multiple zone, ducted or ductless, mini-split or multi-split. This is where it gets complicated. It’s best to work with a qualified expert to fit your system to your home.
• Cold Climate Heat Pumps vs. Standard Heat Pumps: The requirements of a system designed to work in North Carolina are different than one made for Wisconsin. Cold climate heat pumps have only really been “good enough” for the past five years. So, if someone tells you that they don’t work in our climate, they’re just working off of old information.
• Air Source Heat Pumps vs. Dual Fuel (or ‘Hybrid’) Heat Pumps: Dual fuel heat pumps use heat pump technology until the outside air temperature reaches a set degree, then it flips to a natural gas furnace. This allows for a heat pump’s greater efficiency during the summer and “shoulder season” while maintaining a lower operating cost.
  
  As of 2025, cold climate systems are designed to work down to about 5 degrees Fahrenheit. In Green Bay, we have weeks where it’s much colder than that. There are multiple ways of boosting the temperature for those handful of extremely cold days, including hybrid systems and electrical strips.

For more information on heat pumps, check out Focus on Energy’s “Electric Heat Pump Customer Buying and Operation Guide”.

Online Resources

• Rewiring America’s Heat Pumps Page
• Focus on Energy HOMES rebates
• How do heat pumps work? (Undecided)
• “Electric Heat Pump Customer Buying and Operation Guide” (Focus on Energy)

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