A Guide to the Different Types of HVAC Systems

Learn about the common types of HVAC systems and how they work, including split systems, furnaces, boilers and more. Find out which is best for your home, whether or not you can retrofit AC to an old system and how much you can expect to pay.

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When it comes to replacing or upgrading heating and cooling equipment, homeowners have to navigate a myriad of confusing terms and understand how these magic metal boxes keep you comfortable. Explore your options to determine what is best for your home and climate.

Puron HVAC System

Types of HVAC Systems

 

Homeowners are usually interested in lowering their energy consumption, and with good reason. After the mortgage payment, utilities — gas, oil or electricity — are often the next sizable portion of the budget. Chances are even if sustainability isn’t top of mind, the comfort of your home is, and both roads lead to HVAC. If you’re thinking about upgrading your equipment because of age, high utility bills or you’re simply not comfortable, the good news is the options on the market are more diverse and efficient than ever.

The bad news is upgrading to better equipment, or replacing what you have with a more modern version is often a sizable investment. While you can, and should, research your options, working with the right HVAC contractor is vital. Even the most cutting-edge equipment — as a contractor will likely tell you — might not work as well as you expect without insulating and tightening up your home’s building envelope.

Efficiency Standards

From refrigerators to HVAC equipment, the US Department of Energy sets the minimum energy efficiency standard that manufacturers must follow and updates it periodically. So when you shop for a refrigerator at a home store you can feel confident knowing every model they sell meets that standard. However, when it comes to buying an HVAC unit, most homeowners are likely relying on a contractor to know the current energy efficiency standards. But keep in mind, if you are researching the cost of parts online, you should know that online retailers might be offering equipment that does not meet the efficiency standard where you live. To simplify things you can start your search by looking for Energy Star certification.

What are SEER Rating and AFUE?

It pays to familiarize yourself with these standards since Federal tax credits are available, along with any rebates your local utility provider offers for new equipment. Starting in January 2023 the newest standards changed the efficiency minimums for heating and cooling systems to reflect real-world conditions. Like a nutrition label on a box of cereal, HVAC equipment that relies on electricity — like air conditioning condensers and heat pumps — carries a new Season Energy Efficiency Rating (SEER) minimum. (Moving forward that rating will be known as SEER2.) While the minimum standards vary across the country, you’ll need to install a unit with a minimum of 13.4 SEER2 (which is equivalent to about 14 SEER in the older system) for an air conditioner in the north and even more efficient versions in the South where the cooling season is longer. Check out Trane's map that shows regional efficiencies for AC units across the country.

Practically speaking it’s difficult to find a new boiler or furnace that does not meet the minimum efficiency standard, though it’s always a good idea to get the most efficient equipment you can. Boiler efficiency starts at 84% annual fuel utilization efficiency (AFUE), but more efficient ones can reach 90% or more. Furnaces must reach at least 80% AFUE, though new regulations coming in 2028 will push that number to 95% minimum. Electric furnaces can be incredibly efficient, sometimes reaching 100%, but are too expensive to run as the main source of heat in many homes.

Types of Heating and Cooling Systems

How homes are heated and cooled, and the equipment you inherited with your house, varies across the country. “Our market has a lot of forced hot air heating, so we have a lot of ducting in the homes, but when they were installed 20 or 30 years ago no one had air conditioning,” says Craig Olson, vice president of Washington Energy Services, of the forced air furnaces his company modifies in the Seattle area. While it’s true that retrofitting a system that relies on ductwork to both heat and cool is common, adding air conditioning, which was often an afterthought in most of the country, is possible for those who heat their homes with water.

Here are the most popular methods to provide heat, air conditioning or, in some instances, both, along with upgrades you might want to consider.

Professional engineer doing a boiler inspection at home

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New tankless boilers have a couple of advantages over the traditional style. Because they're tankless, they hang on the wall, freeing up floor space. There are special versions of tankless units known as 'combis' that provide air heating and serve as a water heater.

Photo by: Stock-Asso

Stock-Asso

New tankless boilers have a couple of advantages over the traditional style. Because they're tankless, they hang on the wall, freeing up floor space. There are special versions of tankless units known as 'combis' that provide air heating and serve as a water heater.

Boiler (aka Hydronic)

Popular in colder, northern climates, a boiler in the basement burns fuel — usually gas or oil — to create hot water. A series of pumps push that heated water to the home through pipes to baseboard elements, installed on the wall just above the floor, or via PEX tubing to a radiant heat system in the subfloor. You might also hear this system described as hydronic because it relies on water to deliver energy and comfort, or ductless as it does not rely on a series of metal passageways to provide warmth. In some pockets of the northeast, steam boilers — and their hissing radiators — are still used and remain an efficient way to heat a home.

Pros + Cons: While a boiler can last up to 15 years, it needs regular service to keep it running efficiently. As with any HVAC system, poor insulation can sap your level of comfort, though a hydronic system is not prone to efficiency loss through leaky ductwork, which can be a major issue with a forced air system.

Cost: Start at about $1,200 for parts, not including installation.

Boiler Upgrade: Some manufacturers offer a tankless boiler with a couple of advantages over the traditional style. Because it’s tankless, it hangs on the wall, freeing up floor space. Sometimes called a combi unit, this special version of a tankless unit provides heating and cooling. It can also serve as a water heater.

Gas furnace

Gas furnace

Retrofitting air conditioning is possible in an older forced air heating system, and you can likely use the same ductwork.

©Trane

Trane

Retrofitting air conditioning is possible in an older forced air heating system, and you can likely use the same ductwork.

Furnace (aka Forced Hot Air)

A furnace uses a burner and a fan to make, and then push, hot air into the home. In this system a fan, usually in the basement or attic, blows ambient air across a heat exchanger, which relies on gas but sometimes oil or electricity to provide the desired temperature. As the air passes through, it picks up heat, and then is pushed throughout the home through a series of ducts, usually installed lower on the wall or in the floor. Somewhere in the home, a big gate covers a section of duct that returns the air to the furnace so the cycle can start again.

Pros + Cons: While it can be common to add air conditioning (see below) to a furnace, a major downside to a forced air system is the efficiency loss through the ducts, which can leak air or be uninsulated.

Cost: Starts at around $4,700 for parts, not including installation.

Furnace Upgrade: In an older forced air heating system you can add cooling that uses the same ductwork. Typically a contractor adds an air conditioner evaporator coil to dehumidify the air and a dedicated blower inside the house, though it can also be attached to a compatible hot air furnace. This is often described as central air conditioning as it tends to reach all parts of the house. Copper tubing passes refrigerant from that indoor unit to the condenser outside where a fan expels the warm air. While reusing existing ductwork sounds like an easy win, in older homes initially designed for forced hot air, the ducts will enter the room lower on the walls because heat rises. That’s not the most efficient means to cool a house because cold air wants to fall down into a room.

Duct sizing can be an issue, too. “Having the right amount of air moving is critical if you’re going to add air conditioning, and if the house was designed for heat, that ductwork can be pretty small,” says Olson who said replacing the ductwork on a house can add at least 20% to the project. When both of these elements are installed, usually at the same time, combining forced hot air with air conditioning is often referred to as a split system.

Heat Pump Unit

Heat Pump Unit

The most popular heat pump scenario extracts heat from the ambient temperature in the air outside, and transfers it to the furnace inside — sometimes called an air handler system.

©Trane

Trane

The most popular heat pump scenario extracts heat from the ambient temperature in the air outside, and transfers it to the furnace inside — sometimes called an air handler system.

Heat Pump

Furnaces and boilers burn a fuel source to create warmth, but a heat pump uses refrigerant to move heat from indoors to outside or vice versa, depending on the season. In the winter, these electrically powered devices extract heat from the air outdoors and bring it inside, as forced air or hydronic. Come summer, the system’s reversing valve operates backward, removing heat and humidity from indoor air, venting it outside, and blowing dryer air into the home. Like any air conditioning system, a heat pump doesn’t make cold air, it removes heat and humidity and returns it as cooler, dryer air.

Homes heated with existing ductwork or hydronic can use a heat pump. There are generally four main categories of heat pumps. Geothermal drilling is a main component of two styles, where the heat in the Earth is pulled into the house to warm a hydronic system, like baseboard heating or radiant floors, or to warm the air coming from the furnace. The two more common forms of heat pumps don’t require expensive geothermal drilling. The most popular heat pump scenario extracts heat from the ambient temperature in the air outside and transfers it to the furnace inside — sometimes called an air handler system. Lastly, there are heat pumps that put that same temperature from the air outside and use it to heat hydronic for domestic hot water as well as heating.

Cost: Starting at about $7,000 for parts, not including installation.

Air Conditioning and Heating Vent

Climate Control

Homeowners don’t often love seeing the massive, surface-mounted ductless systems on the wall so manufacturers have moved to offering more discrete ceiling-mounted options.

Photo by: Christopher Shane

Christopher Shane

Homeowners don’t often love seeing the massive, surface-mounted ductless systems on the wall so manufacturers have moved to offering more discrete ceiling-mounted options.

Ductless (aka Mini-Split)

Usually mounted on the exterior wall of a house, a ductless mini-split system relies on an air handler inside blowing either hot or cold air into a room, connected to a correlating condenser, usually mounted on the exterior of the house. Mini-splits rely on electricity and refrigerant lines to connect the interior and exterior parts in a closed loop that pulls cold or heat from the house, expelling it outside. The benefit here is controlling only the temperature in the rooms you’re occupying through a remote or a thermostat, and one outdoor condenser can often power several indoor units. A mini-split is a form of heat pump.

Pros + Cons: Homeowners don’t often love seeing the massive, surface-mounted air handlers on the wall so manufacturers have moved to offering more discrete ceiling-mounted options that are easier to hide in joist bays. The term ductless is a catch-all that can refer to hydronic heat, and niche products like a portable air conditioner that wheels into rooms and dumps hot air out a window through a duct, or a portable heat pump that can heat or cool a room in the same way.

Cost: Starting at about $1,200 for parts, not including installation.

Two Trane heat pumps installed outside of a multi-family home.

Trane Residential Heat Pumps

A geothermal system typically includes drilling a narrow well, about 4 inches wide, in the home’s yard to a depth between 100 and 400 feet. The heat from the earth is then transferred into the house, usually via a heat pump.

Photo by: Trane

Trane

A geothermal system typically includes drilling a narrow well, about 4 inches wide, in the home’s yard to a depth between 100 and 400 feet. The heat from the earth is then transferred into the house, usually via a heat pump.

Geothermal

The most expensive residential HVAC system on the market, geothermal is a renewable energy source in the form of the constant temperature in the Earth ranging from 45 to 75 degrees Fahrenheit. Since about the 1940s, a geothermal system typically includes drilling a narrow well, about 4 inches wide in the home’s yard to a depth between 100 and 400 feet. Filled with a loop, grout and refrigerant, the heat from the Earth transfers into the house, usually to a heat pump. In the summer, the system dumps the home’s heat into the Earth, returning cooler so the air handler inside doesn’t have to use as much energy to bring it to a comfortable 68 degrees Fahrenheit inside the home. In the winter it reverses, pulling heat from the Earth and bringing it into the home where it only might need some supplemental heating to bring the home to 70 degrees Fahrenheit.

Pros + Cons: “I think what’s on the forefront, what I’m most excited about and what’s going to get better in the very near future, are geothermal heat pumps,” says Bill Ronayne, owner of Brandywine Valley Heatin & Air Conditioning, in West Chester, Pennsylvania, and a board member of the Air Conditioning Contractors Association of Pennsylvania. Ronayne’s seen geothermal installations make up about 30% of his annual business and considers it a selling point for a home. A geothermal system can be a significant upfront cost for most homeowners and the drilling labor usually starts at about $10,000 or 25% of the total installation.

Cost: About $18,000 including the heat pump for parts. Installation can cost another $10,000.

Worker installing new wooden laminate over underfloor heating system, closeup

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Radiant heat warms floors and walls via PEX tubing that circulates hot water underneath the floor or inside the walls. This is considered one of the most energy-efficient ways to heat a home. And because there is no air being blown around, there's a lot less dust in the air, making this a great option for allergy sufferers.

Photo by: New Africa

New Africa

Radiant heat warms floors and walls via PEX tubing that circulates hot water underneath the floor or inside the walls. This is considered one of the most energy-efficient ways to heat a home. And because there is no air being blown around, there's a lot less dust in the air, making this a great option for allergy sufferers.

Radiant Heating

A warm floor is not exactly a new idea — the Romans used a hypocaust system to keep their feet toasty. To many, it represents the most comfortable way to warm a home. A radiant system is a form of hydronic heating under the floor where a series of PEX tubing creates a loop that runs back to a manifold that controls the flow of hot water, usually from a boiler or a heat pump. “Because water in a radiant system has the capacity to transfer energy 3,500 times greater than air, a hydronic radiant system is significantly more energy-efficient compared with a traditional forced-air heating system,” says Hailey Mick, engineering business development manager for Uponor North America. This system keeps the surface at a constant and comfortable temperature. In bathrooms it’s common, when you’re replacing the tile floor, to add electric cables to take the chill out of the tile — another form of radiant. If you’re replacing the tile in a bathroom, the wire mesh mat is easy to install in the thinset bed under the tiles. An electrician would then wire it to a controller on the wall.

Pros + Cons: The floor warms without blowing hot air, so there is less dust being kicked up with radiant heat. Because the heat is fed with PEX tubing, it can snake up walls to, for example, make the shower wall on the exterior of a house warmer or make a stairway landing more comfortable. In a retrofit application, conductive aluminum can warm the floor from below after a contractor attaches them under the subfloor in the joist bay. Typically you'd see these in the basement ceiling of a home to warm the floor above. The downside of a radiant floor system is it can be difficult to retrofit an entire house with it without ripping up the subfloors.

Cost: Starts at about $1,700 for parts, not including installation.

Best Options for Retrofitting AC

In a home with existing ductwork that provides forced hot air, there are many routes to adding air conditioning. The least expensive upfront cost is adding a condensing unit outside and a cooling coil inside to the air handler. However, if you were planning on replacing the furnace at the same time, a heat pump could be a more economical option in the long run with a lower cost of ownership.

If the home has hydronic heating, adding air conditioning can be a bit more expensive as you’d need to add new ductwork. Those ducts can be supplied with cool air by a condensing coil and air handler, though you might have a challenging time finding space for all this new equipment. In some homes, where space is tight and you don’t have a lot of room in walls to hide big main trucks, a version of air conditioning called small-duct, high-velocity (SDHV) replaces big square duct lines with 2-inch wide flexible round ducts that are easier to hide.

These systems can deliver both heat and cooling, running off an electric furnace or cooling coil. A high-velocity system replaces the volume of air a standard system would deliver with a more forceful stream of air that blends the temperature in the room so it varies very little from top to bottom. Homeowners appreciate the quieter operation that comes from the insulated duct lines and the small openings in each room that replace the larger square grates associated with more traditional air conditioning.

For those with the budget, a heat pump is a good solution for a retrofit because it can work with any existing setup the home already has, from heating with air or hydronic. Heat pumps are unique in that they can provide heating and cooling with minimal equipment outside of the house.

Zoning

Zoned HVAC systems can heat or cool individual areas of your home, which is more efficient since they can conserve energy by focusing on the most popular rooms in a house. Typically a hydronic system uses valves to control the flow of water that heats a zone or room, and when air is used, dampers inside the vents or ductwork work selectively to block the flow of air.

Humidity Control

If you live in a very dry or humid climate, humidifiers and dehumidifiers are options that can help you reach the ideal of 50% relative humidity. With these systems, you can automatically control the humidity levels in a home as you heat and cool, though this is not available through hydronic heating systems. The big drawback of a forced air system is the humidity can only be adjusted when the equipment is running. Beyond that, separate portable humidifiers or dehumidifiers can help that space feel more comfortable when the HVAC equipment isn’t running.

Energy Efficiency Audit

Whenever possible, have an energy audit performed first. That evaluation will determine how leaky your home is and where there are gaps in the thermal shell that need more or better insulation. These audits can usually be done in a day and can cost between $100 and $2,000, though many utility companies offer to cover some of the cost. While installing HVAC equipment isn’t a DIY job, the air sealing and insulation upgrades that can tighten up a home are. That’s a homeowner-friendly job that can save you up to about 20% on your energy bill, according to the Energy Department.

Leaky Air Ducts

When it comes to cooling, nearly every home in the country relies on ducts, and many need those same sheet metal trunk lines for heating, too. Leaky ductwork can sap up to more than 30% of a system’s efficiency, meaning you’re literally paying to condition unoccupied living space. This is one area of HVAC that a DIYer can have a big impact on, and while finding leaks can be tricky — an energy audit will help — you can seal ducts with paintable mastic and foil-backed tape.

Maintenance

Modern HVAC components are sophisticated pieces of equipment that should be evaluated, ideally annually, by an experienced contractor. If there is a major issue — the boiler isn’t firing properly or a hydronic system is leaking — there isn’t much DIYers can do. But you can help your system run more efficiently and see less wear by replacing air filters according to the manufacturer’s directions or about every one to three months for disposable filters.

Keep outside equipment free of leaves and prune shrubs so there are at least two feet of clear space to ensure proper airflow. Consult with your manufacturer’s instruction manual about cleaning the outer equipment. In winter, consider covering an air conditioning unit to prevent weathering.

Inside, avoid closing vents altogether. It might seem like an easy way to customize the airflow, but closing the vents throws the system’s balance off causing the blowers to work harder. If you routinely feel uncomfortable in a room, have a contractor evaluate it and adjust a damper on the branch feeding that room. If you have access to the condensate line, check it for clogs and remove any with a utility vacuum. You can make your home more comfortable with ceiling fans but understanding their rotation is critical. In summer, set the fans to rotate counterclockwise to create a breeze, and reverse it in winter to circulate warm air more effectively.

Easy Steps to Keep Your Air-Conditioning Unit Running Smoothly

Regular cleaning and maintenance will save you money and extend the life of your heat pump or HVAC unit.

Next Up

Heat Pump Options and Uses

Heat pumps can be great add-ons to existing systems or can be used as standalone appliances.

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Buying Guide: HVAC

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