The HVAC quote says one number. Then an electrician arrives and there is a second conversation nobody warned you about. A heat pump conversion is a mechanical job with an electrical job attached to it, and the electrical job is frequently larger than the homeowner expects, because a gas furnace draws almost nothing and the thing replacing it does not.
This is the most common surprise we see on central Ohio homes moving off gas heat. It is entirely avoidable, and avoiding it takes one walkthrough before equipment is ordered.
What a heat pump conversion asks of your electrical system
A gas furnace needs one modest circuit to run a blower and a control board. That is it. The heat pump replacing it brings three separate electrical demands.
The outdoor unit. Its own dedicated circuit, sized from the nameplate rather than from the tonnage. The nameplate states a minimum circuit ampacity and a maximum overcurrent protection, and those two numbers, not a rule of thumb, decide the wire and the breaker. It also needs a disconnect within sight of the unit.
The indoor air handler. A blower motor, which is modest, plus whatever supplemental electric heat is specified. That element bank is the large one. Depending on the size it may need one circuit or two, and on a bigger bank the manufacturer’s own instructions call for a specific breaker arrangement.
The controls. A heat pump thermostat needs more conductors than a single stage gas furnace thermostat did, including a common wire for power. Existing thermostat cable in a 1980s house frequently has too few conductors, and the fix is either pulling new cable or fitting an adapter, neither of which is free and neither of which appears on a mechanical quote.
Add those together and the question becomes whether the panel and the service take them. Our electrical panel service answers that, and the full arithmetic is in our guide to panel capacity for electrification.
Supplemental heat is the load, and there is a way to shrink it
Electric resistance backup is the single biggest electrical load in most conversions. It exists to cover the coldest hours, when the outdoor unit alone cannot keep up, and to cover the defrost cycle.
The size of that bank is a design decision, not a fixed property of the equipment. It follows from the heat loss calculation for the house and from the balance point, which is the outdoor temperature at which the heat pump’s output stops matching what the house is losing. Below that temperature something has to make up the difference.
Two things shrink the bank honestly. A properly sized cold climate unit holds more of its capacity at low temperature, so the gap it has to cover is smaller. And a dual fuel arrangement keeps the existing gas furnace as the backup instead of electric elements, which removes the large electric load from the picture entirely. Dual fuel is often the right answer in central Ohio precisely because the gas line is already there, and it is what our hybrid system installation covers.
What you should refuse is a bank sized by habit. Ask what the balance point is, ask what the heat loss calculation says, and ask why that size was chosen.
The mechanical work that changes at the same time
The electrical side is not the only thing that shifts.
Airflow. A heat pump delivers heat at a lower supply temperature than a furnace does, so it moves more air for longer to deliver the same comfort. Duct systems built around a furnace’s short, hot cycles are often too restrictive. The symptom is a house that is comfortable in mild weather and disappointing in cold, plus a system that is louder than the one it replaced. Static pressure should be measured before the equipment is chosen, not diagnosed afterwards.
The refrigerant line set. Reusing existing line set is sometimes acceptable and sometimes not. It depends on the size, the condition and what refrigerant the old system used, because residue from an incompatible oil can damage the new compressor. A proposal should say explicitly whether the line set is being reused, flushed or replaced.
Condensate. A heat pump produces condensate in cooling, as any air conditioner does, and the outdoor unit sheds water during defrost in winter. Indoors that needs a proper drain with a trap. Outdoors it needs somewhere for the meltwater to go that is not a sheet of ice across a walkway in January.
What happens to the gas appliances you leave behind
This is the part that catches people, and it is a plumbing question arriving inside an HVAC job.
If the furnace shared a chimney with an atmospheric water heater, removing the furnace leaves the water heater alone on a flue sized for two appliances. Oversized flue, cool exhaust, condensation inside the chimney. That is a real deterioration mechanism, not a theoretical one, and the answer is usually to reline the flue or to change the water heater to a direct vent or electric unit at the same time. If a water heater replacement was on the horizon anyway, doing it in the same visit is much cheaper than doing it twice.
The gas piping to the furnace also gets capped properly rather than abandoned, and if a generator or a gas range is planned later, that capacity is worth thinking about now rather than after the pipe is gone.
What a good conversion proposal contains
It should name the outdoor unit and the air handler by model and state the nameplate minimum circuit ampacity and maximum overcurrent protection for each, because those numbers determine the electrical scope. It should state the size of the supplemental heat bank and the balance point it was chosen from. It should say whether the existing panel takes the new circuits or whether panel work is required, in writing rather than as an assumption. It should say what happens to the thermostat wiring. It should state whether the line set is reused or replaced. It should say what happens to the orphaned flue and to the capped gas line. And it should say who is doing the electrical work and whether it is included.
If you want that scoped in one visit rather than in three, start at the contact page. Our heat pump replacement team and the electrical department walk the job together, and the thermostat question gets settled in the same conversation.
Frequently asked questions
Does a heat pump conversion always need an electrical panel upgrade?
No, and assuming it does is as expensive as assuming it does not. Whether you need one depends on the supplemental heat bank, on what else in the house is electric, and on the size of your existing service. A dual fuel arrangement that keeps the gas furnace as backup removes the largest electrical load entirely and often means no panel work at all. Get the load calculation before you get the quote.
Will my existing thermostat work with a heat pump?
Frequently not, and the reason is wiring rather than the thermostat itself. Heat pump control needs more conductors than a single stage gas furnace did, including a common wire for power and additional conductors for the reversing valve and the supplemental heat stages. Older thermostat cable often has too few. Ask whether new cable is being pulled and whether it is in the quoted price.
Can I keep my gas furnace as backup instead of electric heat?
Yes, and in central Ohio it is often the better engineering. That arrangement is usually called dual fuel or a hybrid system. The heat pump runs whenever it is efficient to do so, and the gas furnace takes over below the changeover temperature. It removes the large electric resistance load from the electrical calculation, it uses gas piping you already have, and it means the coldest days are covered by equipment that does not care how cold it is.
Will my existing ductwork work with a heat pump?
Sometimes, and it should be measured rather than assumed. A heat pump supplies air at a lower temperature than a furnace, so it needs to move more of it for longer. Ducts sized for a furnace’s short hot cycles can be too restrictive, and the result is a system that disappoints in cold weather and runs louder than the one it replaced. Static pressure should be measured before the equipment is selected.
What happens to my water heater if I remove the gas furnace?
If the two shared a chimney, the water heater is now alone on a flue sized for both. The exhaust runs cooler than the flue was designed for, it condenses inside the chimney, and that damages the liner over time. The usual answers are relining the flue or changing the water heater to a direct vent or electric unit. Whichever it is, it belongs in the conversion proposal rather than being discovered a year later.