Gas furnace vs ductless mini-split

A gas furnace heats a whole house through ducts for $3,000 to $8,000 installed. A ductless mini-split costs $3,000 to $5,500 for one zone, so a whole-house system is usually more expensive than a furnace replacement. What a mini-split buys instead is no ductwork, room-by-room control, and air conditioning from the same unit. Neither is universally better.

What each system is

A gas furnace is a central forced-air appliance. One unit heats air and a blower distributes it through ducts to every room.

A ductless mini-split is a split heat pump with an outdoor condenser and one or more indoor heads, each serving a single room or open area. There is no ductwork; refrigerant lines connect the head to the outdoor unit.

One system conditions the whole house at once. The other conditions specific rooms.

Cost compared

The comparison that matters is whole-house against whole-house. A three-zone mini-split at $5,500 per zone is $16,500, against a furnace at $5,500 plus a central air conditioner at $4,000 for $9,500. On a like-for-like basis, ducts usually win on price when they already exist.

Where the mini-split wins

• No existing ductwork. A house with radiators, baseboard heat, or no central system at all.
• Additions and converted garages, where extending ducts is expensive or impossible.
• Zoned comfort. Heating one occupied room instead of the whole house.
• Cooling as well as heating from one unit.
• Quiet operation, with no blower or duct noise.
• No duct losses, which in a vented attic can be significant.

Where the furnace wins

• Whole-house heating at the lowest installed cost, where ducts exist.
• Cold climates, where a single central system with high output is simpler.
• Filtration and humidity control through the duct system.
• Fewer wall penetrations and outdoor units.
• Simpler maintenance, with one appliance rather than several.

Running cost, with the arithmetic

Assume a house needing 60 million Btu of delivered heat.

Gas furnace at 90 AFUE, $1.20 per therm:

• 60 ÷ 0.90 = 66.7 million Btu input
• 667 therms × $1.20 = $800

Mini-split at an average COP of 2.5, $0.16 per kWh:

• 60 ÷ 2.5 = 24 million Btu of electricity
• 7,030 kWh × $0.16 = $1,125

The furnace is cheaper on those assumptions by $325. At a COP of 3.0 the mini-split costs $938, and at $0.12 per kWh it costs $844, which beats the furnace.

The mini-split’s real running-cost advantage is not the fuel arithmetic — it is zoning. Heating two rooms instead of six can cut consumption by more than any efficiency difference, because you are not conditioning space nobody is using.

Zoning, the actual argument

A ducted system heats the whole house to one setpoint. A mini-split system heats the rooms that are occupied.

For a retired couple using two rooms in the evening, a zoned system can use far less energy than a central furnace heating an empty upstairs. For a family using every room, the advantage disappears.

That is why the honest answer to “which is cheaper to run” is: it depends on how much of the house you actually heat. The equipment efficiency is secondary.

Maintenance and repair

A mini-split needs its indoor filter rinsed monthly and its outdoor unit kept clear. The heads are also visible on the wall, which is a design consideration in a living room.

A multi-zone system multiplies the service cost: one outdoor unit with four heads still needs the heads checked, and each is a potential leak point at the flare connections.

The furnace side is priced in how much furnace repair costs, and the mini-split side in ductless mini-split cost.

What to ask before choosing

1. Is there existing ductwork, and what condition is it in?
2. How many rooms are actually occupied at the same time?
3. What is the design temperature, and does the chosen model hold capacity there?
4. How many outdoor units will the design need, and where will they sit?
5. Is cooling needed, and is there an existing air conditioner?
6. What is the total installed cost for the whole house, not per head?

Question three decides cold-climate viability. A model rated at 80 percent capacity at 5°F is a different proposition from one that drops to 50 percent.

Question four matters for appearance and for maintenance. Four outdoor units on a wall is a different installation from one.

The related comparisons are heat pump vs ductless mini-split and boiler vs ductless mini-split.

A mini-split is the right answer when there are no ducts, when only part of the house needs conditioning, or when cooling is wanted without a duct system. A furnace is the right answer when ducts exist and the whole house needs heat.

The purchase price comparison favours the furnace on a whole-house basis. The running-cost comparison favours whichever system heats less space. A note on appearance, since it is part of the decision: a ducted system hides its work behind registers, while a mini-split puts a head on the wall of every conditioned room. In a living room with a clear wall, that is a design choice rather than a technical one, and it is worth deciding before the equipment is ordered rather than after. Some households accept the heads for the zoning and cooling; others prefer the invisibility of ducts and pay for it in running cost.