Heat Pumps vs Gas: Which Is The Best Way To Heat An ADU In Massachusetts?

By Buz Artiano, BuildX | January 2026

Choosing the right heating system for your ADU is a big deal. It determines how comfortable you are and affects how much your utility bills are. If you pick the wrong system you can have uncomfortable temperature swings in the home plus high utility bills and equipment that just can't keep up with the New England cold.

At BuildX, we've installed countless heating systems in custom ADUs in Massachusetts. We work with HVAC professionals who have 20 years or more of hands-on experience with these systems in our specific Massachusetts climate. So we can tell you what works, what fails, and what people wish they had known before choosing a heating system.

Why Are Heat Pumps the Default Choice for New ADUs?

The cheapest way to heat and cool a new ADU with high-quality equipment is a ducted heat pump system, all electric. Heat pumps work by moving heat around rather than creating it. The way they work is actually very interesting. Even cold air contains heat energy, so in winter the system extracts heat from outside air and transfers it inside. In summer, it simply reverses that process and works as an air conditioner.

Massachusetts energy codes have now made this decision even easier. New construction, including ADUs, have to meet the new strict energy efficiency codes. Heat pumps combined with good insulation and tightly sealed structures give you 250% to 350% energy efficiency. What that means is that for every unit of electricity you use, you get two and a half to three and a half units of heat. Just for comparison, a gas furnace only runs at about 80% to 95% efficiency.

That's why heat pumps are the standard in new ADU construction across the state. They're not some kind of new or experimental technology. The technology has been around for over 20 years, and the newer cold-climate models you get nowadays work much more efficiently than the earlier generations.

What Type of Heat Pump System Works Best in an ADU?

At BuildX, we recommend ducted heat pump systems for most ADUs. A ducted system uses a central air handler that goes in the attic or crawl space, pushes temperature controlled air through ductwork and out of the ceiling or floor vents throughout the home. An outdoor unit called a condenser handles the heat exchange.

You may be familiar with wall-mounted mini-splits, which use the same heat pump technology. We prefer the ducted approach for several reasons:

• No wall units. You don't have those bulky heads mounted on your walls. The whole system hides in the attic or crawl space, with only small vents that are visible.
• Better air filtration. Ducted systems use real home-grade filters. Wall-mounted mini-splits have small, basic filters that you have to clean all the time and they're just not as effective.
• More even temperature. Ductwork distributes air evenly throughout the entire ADU so you don't end up with hot and cold spots.

The air handler can be placed in the attic or crawl space depending on the layout. We will talk to you and make that decision based on what works best for each specific project.

Do Heat Pumps Actually Work in Massachusetts Winters?

People ask us this all the time, and yes they absolutely do. The heat pump systems we install are rated for -15 to -20 degrees Fahrenheit. They also include electric backup heating just in case the equipment fails. That way you won't lose heat entirely even when it gets down below zero.

The reason heat pumps work so well in such cold temperatures is the way they work. A gas furnace blasts 140-degree air and then shuts off, but heat pumps run low and slow. The fan is almost always on, running at low speeds, which maintains a steady, even temperature in the home. For a lot of people this is different than what they are used to, but it is actually more comfortable, especially once you understand how the system works.

New ADUs are built with quality insulation and air sealing, which means it will hold temperature extremely well. The house is not cooling off while the system cycles. Once it reaches temperature, it stays there.

How Should You Operate a Heat Pump for Best Results?

If you want your heat pump to work at its absolute best capacity and efficiency, all you have to do is set the temperature and leave it alone.

Heat pumps run their best at a consistent temperature. Turning the thermostat down to 55 degrees when you leave and then cranking it back up when you get back is the worst thing you can do. Unlike a gas furnace, a heat pump doesn't just blast a ton of hot air to catch up from being turned down. It can take several hours to bring the temperature back up, and while it's doing that, it's running at higher rate and costing you more on your electric bill.

We've had customers call us saying their system takes forever to heat the house. The first thing we do is ask them if they turned it down when they left the house. They almost always say yes. If you need to adjust the temperature we suggest that you keep changes to four degrees or less. If you only live in your ADU part of the time, it's best to turn the thermostat to the right temperature a couple days before you get there.

The constant low fan you hear is the system working exactly how it's supposed to. The fan running at low speed is how heat pumps keep temperatures even and give you good air quality by continuously filtering the air.

What Are the Tips for Heat Pump Success in Your ADU?

"Set It and Forget It"

Unlike a gas furnace, where you might turn down the thermostat when leaving for work, you don't want to do this with a heat pump system. Heat pumps work best at a consistent temperature. So just set your desired temperature and leave it. If you turn it down 10 degrees while away for the weekend, it takes so long to recover that it's not energy efficient at all. Experts recommend adjusting no more than 4 degrees at a time and to try to keep it as consistent as possible.

Common misconception: We get calls all the time from homeowners who think something is wrong because the fan never shuts off on the ducted system. The fan is not going to shut off. It is constantly moving that air at slow speed, and then it determines from the return air when to turn the condenser on to either add heat or AC. This constant, gentle air movement is what it's supposed to do. It keeps temperatures even throughout your ADU and improves air quality by continuously filtering the air.

"Invest in Quality Ductwork"

If you are going with a ducted system, the quality of the ductwork you choose matters enormously. We work with contractors who custom-design the ductwork for each and every project, using special interior-insulated ducts that are quieter and more efficient. This gets rid of the expansion noises and sweating that you get with standard ductwork.

Why Does Heat Pump Brand Quality Matter?

Not all heat pump systems are the same. You don't want to skimp on the heat pump or cut any corners because it will absolutely cost you more in the long run. We only install name-brand equipment like LG and Mitsubishi. They are rated to work in extreme cold, they have long lasting parts and great service networks in the United States, and their installers are factory-trained and certified.

The two biggest problems with off-brand or discount heat pumps are performance in cold weather and trying to find parts for them if they break. Usually these off-brand units people find can't maintain temperature below 5 or 10 degrees, which is a real problem in Massachusetts. When they fail, and they will, you can't find the parts because the manufacturer has gone out of business or doesn't stock replacements.

That's important to know because the outdoor condenser and the indoor air handler cannot be separated. If the outdoor unit fails and you can't get parts, you have to rip out and replace everything, the indoor and the outdoor equipment. The $2,000 to $3,000 you saved on cheaper equipment ends up forcing you to pay for a second entirely new system.

With a name-brand system, we call tech support, scan the error code, and they ship the replacement part overnight making it a simple fix that doesn't leave you without heat for long periods of time. You don't get that kind of support with cheap off-brand equipment.

When Is a Gas or Propane System the Better Choice?

Yes, we recommend and install heat pumps for most of our ADU builds, but heat pumps are not right for every situation.

Gas or propane systems make sense in a few specific scenarios:

• Radiant floor heating. A lot of people love the idea of warm floors in winter. Radiant heat requires hot water, and the most practical way to do that in an ADU is with a small gas-fired or propane combi boiler. A combi boiler is a unit that handles your normal hot water and your hydronic heating. The current Massachusetts code says that ADUs can use mixed-fuel systems, so you can use a heat pump for your main heating and cooling and still have a gas boiler for your radiant floors.
• Strong fuel preference. Some homeowners are adamant about having gas heat. If gas or propane is available on your property and you prefer that option, a combi boiler paired with a hydroair system (hot water running through a coil in the air handler) provides both heat and hot water.
• Faster heat recovery. Gas-fired systems deliver higher-temperature air and heat spaces faster than heat pumps. For homeowners who prefer that immediate warmth, gas is the only way to accomplish that.

But know that there are downsides to installing gas. Switching from a heat pump to a gas-fired combi boiler adds $8,000 to $9,000 to the cost, including the boiler, gas piping, and installation. Gas systems also don't give you air conditioning, so you need a separate cooling system on top of that. Also gas furnaces make the air in the home extremely dry, which can be very uncomfortable.

Why Is Electric Resistance Heat a Poor Primary Choice?

Electric resistance heaters, which include baseboard heaters, wall heaters, and electric furnaces, convert electricity directly into heat. The technology is simple and the installation cost is low, typically $3,000 to $6,000.

The problem is how much they cost to operate. Electric resistance heating runs at 100% efficiency, meaning you get exactly one unit of heat for every unit of electricity it uses. Remember that heat pumps give you 250% to 350%. To put it simply, your monthly heating bills with electric resistance will be two to three times higher than with a heat pump.

Electric resistance heating can make sense as supplemental heating in a bathroom (small electric floor mats), in a garage or workshop used occasionally, or as emergency backup. But as the main heat source in your home, it's very inefficient and will end up costing you up to 3 times what a heat pump would cost to run. So the cheaper installation costs are not worth it.

How Do ADU Heating Systems Compare Side by Side?

Here is a chart to compare heating types for a typical 900-square-foot ADU in Massachusetts with quality insulation and air sealing. The heat pump installation cost is for a ducted system. The gas/propane cost includes a combi boiler, hydroair system, gas piping, and a separate cooling system.

*Estimated winter month costs. Actual costs vary based on insulation quality, usage patterns, and current energy prices.

Why Does Insulation Quality Affect Your Heating Decision?

Your heating system is only as good as the building. Even a perfectly sized, brand-new heat pump will struggle to keep up in a leaky, poorly insulated building. A well-insulated ADU needs a smaller, less expensive heating system to maintain a consistent temperature, and it's cheaper on a monthly basis.

Some people think that proper insulation is just about how much actual material you add and how thick it is. But it's not, it's about doing everything right from the start. The insulation and air sealing in your ADU will hold your heat and your air conditioning in the house for its entire life. You can change the paint, flooring, and fixtures, but replacing insulation means you have to tear everything apart. That's why we invest in the best quality insulation and air sealing on every ADU we build, because it saves you money every single month on your bill forever and it keeps your home comfortable.

What Do Massachusetts Energy Codes Require for ADU Heating?

Massachusetts has some of the strictest energy codes in the country. Every new ADU now has to meet some pretty demanding energy efficiency standards, including blower door test results that verify the building is properly air-sealed. These codes are making heat pumps more and more common because they simply perform best in tightly built structures.

Under current codes, ADUs are permitted to use mixed-fuel systems. That means you can use a heat pump for the main heating and cooling, and then use a gas or propane boiler for radiant floors or domestic hot water. This is really the best way to go if you want high efficiency with a heat pump, but still have nice warm floors in the winter.

According to the code, every ADU also requires what's called an energy recovery ventilator (ERV). What that does is exchanges stale indoor air for fresh outdoor air while recovering heat energy. We install Panasonic ERV units in our builds to meet this requirement. For more details on Massachusetts ADU regulations, visit mass.gov/info-details/accessory-dwelling-units.

Can You Build a Net Zero ADU?

For homeowners who are interested in maximizing efficiency and having a minimal impact on the environment, net zero ADUs are now achievable using today's technology. The combination of an air tight building, efficient heat pump, and rooftop solar can give you an ADU that produces as much energy as it consumes over the course of a year.

Net zero does not need to be this big, fancy, expensive architectural beauty that matches the landscape perfectly. It does not. It can be a small, regular building. You do not even have to know it is net zero. Our technology is there. There is no reason why any home needs a boiler of any sort burning fossil fuel anymore. Net zero ADU designers tell us that naturally energy-efficient homes are actually very simple, rectangular shapes with thoughtful window placement that New Englanders have been building for hundreds of years.

Massachusetts actively supports ADU development as part of its housing strategy. Learn more about state ADU guidelines and regulations at mass.gov/info-details/accessory-dwelling-units.

Frequently Asked Questions

Which Heating System Will Keep Your ADU Comfortable Year-Round?

For most new Massachusetts ADUs, heat pumps offer the best combination of efficiency, comfort, and value. They heat and cool from one system, they are quiet, cheaper to run, and they work perfectly with the well-insulated structures that are required by current building codes. If radiant floor heating or a strong gas preference is part of your plan, a combi boiler system is the way to go.