A furnace that’s been running reliably for 18 years has a way of choosing the worst possible moment to quit. If you’re reading this in late September or October with a heating system on its last legs, the decision in front of you isn’t just about replacing what you had. It’s about whether a heat pump makes more sense for your home than another gas furnace. That question comes with a lot of conflicting information, some of it genuinely outdated, and getting it wrong is an expensive mistake. We’ve been helping St. Louis homeowners work through this exact decision for over 70 years, and the answer is rarely as simple as either system’s advocates suggest.
St. Louis sits in a climate that gives HVAC systems a genuine workout. Summers are humid and hot, winters bring real cold snaps, and the shoulder seasons are mild enough that a well-chosen system can handle a wide range of conditions efficiently. That range is exactly why the furnace-versus-heat-pump question deserves a more careful answer than a generic pros and cons list can provide.
How Heat Pumps & Furnaces Actually Heat Your Home
The core difference between these two systems is generation versus transfer. A furnace generates heat by burning fuel. Most commonly, that fuel is natural gas delivered through the local Spire network. It converts that combustion energy into warm air. Its efficiency is measured by AFUE, annual fuel utilization efficiency, which tells you what percentage of the fuel you buy actually becomes heat in your living space. A 96% AFUE furnace wastes only 4 cents of every dollar spent on gas.
A heat pump doesn’t burn anything. It uses electricity to move refrigerant through a cycle that extracts heat from outdoor air (even cold outdoor air) and delivers it inside. In summer, the cycle reverses and it becomes an air conditioner. Because it’s moving heat rather than creating it, a heat pump can deliver more heating energy than the electrical energy it consumes, which is what makes it efficient. Heat pump performance uses two separate ratings: SEER2 for cooling efficiency and HSPF2, the heating seasonal performance factor, for heating efficiency. One unit handles what a furnace and a separate air conditioner would otherwise split between them.
Will a Heat Pump Keep Up During a St. Louis Winter?
The most persistent myth about heat pumps is that they stop working in cold weather. Older equipment struggled below 35 to 40 degrees Fahrenheit, and that reputation stuck. Modern cold-climate heat pump models are designed differently. They can maintain a meaningful portion of their rated heating capacity at temperatures well below that threshold, though output and efficiency do decline as temperatures drop. That’s not a flaw unique to heat pumps. A furnace also works harder and consumes more fuel as the outdoor temperature falls.
The concept that matters here is the balance point. Every heat pump has one: it’s the outdoor temperature below which the system can no longer meet the full heating load on its own and needs supplemental heat to close the gap. That supplemental heat comes from either electric resistance strips built into the air handler or a paired gas furnace.
A dual fuel system (sometimes called a hybrid heating system) pairs a heat pump with an existing gas furnace. The two work together: the heat pump handles heating during mild and moderately cold weather, where it’s most efficient, and the furnace takes over automatically when temperatures fall below the balance point. For a market where natural gas is widely available through Spire and where the coldest temperatures arrive in short stretches rather than month-long deep freezes, this configuration captures the efficiency advantages of a heat pump during the long shoulder seasons while keeping the reliability of gas heat for the worst winter days. It’s not a compromise. For many St. Louis homes, it’s the most practical configuration available.
What Does It Actually Cost to Run Each System?
A heat pump typically costs more upfront than a furnace alone, but that comparison is incomplete because a furnace only heats. A homeowner who installs a furnace still needs a separate air conditioner for summer cooling, and that combined cost often closes much of the gap. Monthly operating costs shift by season: because natural gas has historically priced lower per unit of delivered heat than electricity in this region, a high-efficiency gas furnace tends to be cheaper to run during sustained cold snaps when a heat pump is working hardest. During mild fall and spring months, a heat pump running at its most efficient range typically costs less than burning gas. A dual fuel system lets you take advantage of both economics. It runs on electricity when it’s cost-effective and switches to gas when it’s not.
Installation cost also depends heavily on what’s already in place. Homes with working ductwork and an existing gas line avoid added infrastructure expense either way. Homes without ductwork, or with ductwork in poor condition, face additional costs regardless of which system they choose. In those situations, a ductless mini-split heat pump may be worth evaluating as an alternative.
Matching the Right System to Your Home
There isn’t a single right answer that applies to every home in St. Louis. The decision depends on what’s already in your house and how those factors interact with each option.
- Existing Furnace & Ductwork
If your furnace is aging but your ductwork is in good shape, adding a heat pump as a dual fuel upgrade is often the most practical path. You keep the gas furnace for backup and get the efficiency and cooling benefits of a heat pump without replacing an entire system at once. - No Existing Ductwork
Homes without ductwork (or spaces like additions where extending ducts is impractical) are strong candidates for a ductless mini-split heat pump. Mini-splits deliver both heating and cooling to individual zones without requiring any duct infrastructure. - Full System Replacement
When a furnace fails completely and a home needs everything replaced, a cold-climate heat pump paired with a gas furnace as a dual fuel system (or a standalone high-efficiency furnace with a new air conditioner) are both worth evaluating based on the home’s insulation, square footage, and energy use.
Insulation quality, ductwork condition, the age of existing equipment, the home’s orientation and square footage, and how the homeowner uses the space all factor into which system performs best over the long run. A duct system that works fine with a furnace may need rebalancing when a heat pump takes over, because heat pumps deliver lower-temperature air more continuously rather than in the short, high-heat bursts a furnace produces. Getting this right means looking at the actual home before recommending a system. We offer free in-home consultations, and our licensed technicians can assess your ductwork, current equipment, and insulation before making a recommendation built around your specific situation. Call us at (314) 408-6068 or reach out online to schedule.