Dual Fuel Heat Pump and Gas Furnace in Monmouth County NJ

A dual fuel system is a heat pump and a gas furnace sharing one set of ducts. The heat pump carries the mild majority of the heating season on electricity, and the furnace takes over when it gets cold enough that gas is the better deal. Our guide on whether a heat pump is worth it in NJ covers why this is the answer we give most often to a homeowner with a good gas furnace.

What that guide does not get into, and what almost nobody explains at the kitchen table, is the one setting the entire system turns on: the changeover temperature. Get it wrong and you own two heating systems that argue with each other. This is how to find yours, check it, and know whether it is set where it should be.

Changeover is an economics setting, not a comfort setting

The changeover point, sometimes called the balance point or the switchover, is the outdoor temperature where the control hands heating from the heat pump to the furnace. People assume it is set where the heat pump stops being able to keep up. That is not it. On a typical winter day both machines can heat the house. The question is which one does it for less money per unit of heat delivered.

That answer depends on three things: what your electricity costs, what your gas costs, and how efficiently the heat pump is running at that outdoor temperature. A heat pump's efficiency falls as it gets colder, so at some temperature the cost lines cross. Above the crossing, electricity wins. Below it, gas wins.

Two consequences follow, and both matter. First, there is no universal right number, so any contractor who gives you one without asking what you pay for energy is guessing. Second, the correct setting moves when utility rates move. A changeover set at install and never revisited is running on whatever the rates were the year it was installed.

Find your own two numbers

You cannot judge the setting without knowing what you pay, and both numbers are printed on bills already in your house.

• On the gas bill, find the price per therm. It is usually broken into a delivery charge and a supply charge, and you want the total of the two, not just the supply line.
• On the electric bill, find the price per kilowatt hour, again totaling delivery and supply.
• Write both on the inside of the furnace closet door with the date. When you get a rate change notice, you will know whether it is worth revisiting the changeover.

You do not have to do the arithmetic yourself. You do have to walk into the conversation with the two numbers, because they are the inputs, and a proposal that never asked for them was not designed around your house.

Find out where yours is actually set

Most homeowners have never been told their changeover temperature, and plenty of systems are not set where the paperwork says. Three ways to check, in order of effort.

• Watch it happen. On a cold day, with the house calling for heat, go look at the outdoor unit. If the fan is turning, the heat pump is doing the work. If it is completely still while the house is warming up, the furnace has taken over. Note the outdoor temperature. Do that on a few days at different temperatures and you will bracket where the changeover actually falls, without opening a single menu.
• Look for the outdoor sensor. A dual fuel control needs to know the outdoor temperature to decide anything. Some systems use a small sensor wired outside. Others take the temperature from the thermostat's internet connection, which is fine right up until the connection is not. Ask which yours uses, because a system that has lost its outdoor reading is deciding blind.
• Check the thermostat's installer settings. The changeover or auxiliary lockout usually lives in a configuration menu rather than the everyday screen. Look before you change anything, and write down what it says now.

One thing to listen for. On a dual fuel system the furnace should take over from the heat pump, not run alongside it. If you can hear the furnace firing while the outdoor unit is still running, that is worth asking about rather than accepting.

What it costs

Dual fuel is usually cheaper than people assume, because the furnace half of it is already in the basement. These are our installed ranges for a 1,800 to 2,600 square foot house.

• Adding a heat pump and keeping your existing furnace: $9,500 to $11,400 to start, $11,100 to $13,300 at the top of the range. This is the common dual fuel project.
• Heat pump plus a new furnace: $13,100 to $14,500 to start, $14,800 to $16,400 at the top. This is the one to price when the furnace is near the end of its life anyway.
• For comparison, replacing the furnace alone and keeping the AC: $5,300 to $6,300.

The reason the first option is the interesting one: if you are already replacing central AC, the heat pump version of the same job is a smaller step than it looks. An AC replacement keeping the furnace runs $9,000 to $10,900 at that tier, against $9,500 to $11,400 for the heat pump. That gap holds steady, roughly $500, whether you compare the entry tier or the premium tier, so ask for both priced at the same tier rather than comparing a base AC quote to a premium heat pump quote. Either way, the furnace you already own becomes the backup, and you end up with dual fuel on a job you were doing anyway.

The federal tax credit is not what it was

Check this before you let a proposal subtract anything. The federal energy efficiency credits, including 30 percent of the cost of a qualifying heat pump up to $2,000, were available through the end of 2025 and ended December 31, 2025. Any quote still showing that credit on the bottom line needs a conversation. State and utility programs run on their own schedules and are worth asking about separately.

Why this is the Freehold answer specifically

About 77 percent of households in the 07728 area heat with natural gas. That single number is why dual fuel comes up here more than a full heat pump conversion: most of these houses already own half the system, and the half they own is the cheap fuel on the coldest nights.

The rest of the local picture shapes it too. We are in climate zone 4A with a winter design temperature around 13 degrees, cold enough that the coldest stretch of the year is genuinely worth having a furnace for, and mild enough the rest of the season that a heat pump does most of the work. Basements are common, which is where the air handler and the furnace usually sit, and Monmouth County is EPA Radon Zone 1, so basement air sealing and duct work should be coordinated with radon control rather than done separately.

The Township's housing generations land differently. Systems installed around 2004 to 2010, including Freehold Pointe and the age-restricted communities, are at first-wave replacement age now, which is when the heat pump half gets added instead of a same-size swap. The mid-1960s split-levels and raised ranches around Stonehurst, and the late-1960s Levitt homes in Monmouth Heights, have a different problem first: original ductwork now roughly 55 to 60 years old, leaky and often undersized for modern loads.

What has to be right for it to pay off

Both halves share one duct system, and the heat pump half is the fussier tenant. It moves more air at a lower temperature than the furnace does, so ductwork the furnace never complained about can hold the heat pump back.

On a Manalapan replacement, testing before the swap measured total external static pressure at 0.933 in. w.c., against a normal range of about 0.2 to 0.7, with airflow very low for the equipment at about 313 SCFM per ton. The existing equipment was correctly sized for the home's load. The ducts were the limit. Every other company quoting that job proposed a straight equipment swap, and none offered a Manual J, a blower door test or a static pressure test.

On a job in Freehold, a homeowner called about AC that was not working right after several companies had been out and charged him without finding the cause. Testing found static pressure a little high, a unit leaking air all around its cabinet, leaky supply ductwork, and the unit installed right next to the water heater pulling air from around it, which raises the risk of back-drafting the water heater. A blower door test read about 3,100 CFM50 on a house of roughly 2,600 square feet, and a Manual J confirmed the existing 3 ton size was correct. Since the system was being replaced anyway, it was worth asking about inverter technology and a heat pump rather than straight single-stage cooling, because the added cost over cooling-only was small next to the rest of the job.

When it makes sense to call someone

The moment to price dual fuel is when you are replacing something anyway, the AC or the furnace. The order that saves money is a Manual J load calculation and a static pressure reading first, a blower door test if the house has never been measured, and equipment chosen after, which is how we work on every job. That sequence is the whole difference between a heat pump installation that performs like the brochure and one that spends its life leaning on the furnace.

FAQ

What temperature should a dual fuel system switch to the furnace?
There is no single right answer, because it depends on what you pay per therm of gas and per kilowatt hour of electricity, and on how efficient your heat pump is at that outdoor temperature. Anyone who names a number without asking about your rates is guessing. The setting should also be revisited when rates change.

Do I have to replace my furnace to add a heat pump?
No. Keeping the existing furnace as the backup is the common version of this project and the cheaper one. The furnace does need to be in good enough shape to be worth keeping, and the two have to be properly controlled as one system rather than installed as two.

Can I tell whether my heat pump or my furnace is running right now?
Yes, and it takes ten seconds. Go outside while the house is calling for heat. Outdoor fan turning means the heat pump. Outdoor unit silent while warm air is coming from the vents means the furnace has taken over.

If you want the changeover set from your actual rates rather than a default, that is the visit to book. Reach us through the contact page or call Novus Mechanical at (848) 288-1133.