Furnaces and Home Heating Systems

Types of Heating Systems

A central home heating system provides the most important line of defense against the chill of winter, and homeowners can choose from a variety of options to heat their homes. While natural gas is by far the most common technology, homes can also be heated well, and sometimes more efficiently, with electric, geothermal, heat pump and boiler systems.

Heating is one of the most complex and important systems in your home, and can be dangerous when it fails. It's critical that homeowners understand the basics of their system, the types of maintenance they should perform, warning signs of impending problems, and when to call in an expert for help.

Heating is also one of the biggest energy consumers in your home, so homeowners who may be shopping for a new furnace should considering replacing it with a newer, more energy-efficient model to save money and help the environment. The average furnace lasts between 15 and 20 years, so you're making a considerable investment in your home. Spend wisely by learning as much as you can about available options. 

Measuring heat efficiency

It's important to understand how the numbers affect the cost of your furnace and its ongoing energy use. 

When comparing energy sources for home heating, the scientific unit of measurement is the annual fuel use efficiency rating. A furnace's AFUE rating, as it's commonly called, refers to the ratio of how much heat output a furnace system will produce compared to the amount of energy it consumes.

For example, if a system carries an 80 percent AFUE rating, that means 80 percent of the energy it uses translates directly to heat output, while the remaining 20 percent of energy is lost to inefficiencies, such as heat loss or escape.

Federal regulations now require manufacturers to include this efficiency indicator with every new furnace sold to help consumers compare energy efficiency.

Although they're more expensive than their non-label counterparts, Energy Star-certified heating products have achieved high energy efficiency standards, saving homeowners more money in utility bills in the long run.

Various regions and the federal government provide their own guidelines for HVAC efficiency. Find more details on HVAC standards here

Heater maintenance

No matter what kind of heating system you have, whether it's gas, oil or electric, regular maintenance can prolong its life and increase its efficiency.

When your HVAC professional tells you to change your filters regularly, they're not kidding. It's as crucial as a regular oil change in your car. A dirty filter forces the system to work harder, run longer, consume more energy and ultimately shorten its life through wear and tear. Furthermore, a fresh, clean filter more effectively traps contaminants and debris in the air. Energy Star recommends replacing your filter once every three months. During high usage months, check the filters at least monthly. 

Every year, as the cold season begins, you should hire a licensed, bonded and insured HVAC contractor to inspect your system, check for impending problems and give it a general tune-up.

You want to fully operate the system under the correct circumstances to see how it works, so it's best to schedule an inspection as the weather turns cold. The best time to schedule this is before the peak heating season — once winter sets in, HVAC professionals will be much busier, and the likelihood of catastrophic failure is higher during heavy usage periods. 

For a complete list of maintenance items you can do and the tasks you should expect an HVAC contractor to do, check out Angie's List's detailed HVAC Research Guide. 

However, even the best-maintained heater will eventually fail. HVAC professionals recommend following this basic rule when deciding whether it's worth investing in a repair: If the unit is more than 6 years old, and the repair will cost more than half the price of a new system, it's best to buy new. At the 15-year mark, it might be worth replacing even if it's still working — the system won't have many more years left in it, and it's likely to be using more energy than necessary. 

Natural Gas and Oil Heating Systems

The most common type of home heating system in the U.S. burns natural gas or propane to produce heat. With an average cost that ranges from $2,500 to $14,000 to install, they are not the least expensive option, but newer systems can be very energy efficient. According to the Department of Energy, older natural gas systems typically achieve a 68 to 72 percent AFUE, while newer, highly efficient natural gas furnaces can achieve AFUE ratings as high as 90 to 97 percent.

Oil heaters are less common now than natural gas, but they can be useful in more remote regions where utilities are harder to access, and in colder climates because it provides more heat per BTU than other solutions. The installation cost will be lower, but energy costs will be higher, as much as three times higher than gas or electric furnaces. They require a storage tank on the immediate property and more maintenance. Overall, they cost between $2,000 and $8,000 to install. Overall, they provide an AFUE rating of between 80 and 90 percent.

Natural gas heating systems work fairly simply

1. Fuel supply

Upon construction or installation of a new gas line, a home's permanent gas plumbing supplies natural gas to the furnace. Since natural gas is combustible and leaks in a gas pipe may result in a fire or explosion, this piping should only be repaired or replaced by a licensed, professional HVAC company or, in some areas, a licensed pipefitter or plumber.

2. Furnace startup and fuel ignition

When your home's thermostat falls below a certain preprogrammed temperature, it sends a signal to the furnace to switch on and begin supplying heat to the home. A permanently lit pilot light or an electronic ignition then ignites the natural gas burner. Lighting and combusting the natural gas at the burner is how heat is supplied to the rest of the home.

3. Heating the home

Once the furnace senses that the burner has reached a high enough temperature, a blower fan will begin to introduce air to a heat exchanger. The heat exchanger allows air to be heated without coming in contact with the actual flame or burner area. Once it reaches a sufficient temperature, the air warmed by the heat exchanger is then forced through the home's duct work, supplying warm air to individual bedrooms, living rooms and kitchens through the vents or registers.

4. Shutdown

When a thermostat senses that the home's temperature has reached the desired level, it sends a signal to the furnace to end the heating cycle. The gas valve that supplies heat to the burner shuts off, extinguishing the flames. The blower will likely continue to operate for a short time to ensure that all the available heat has been retrieved from the system.

Electric heat

In areas of the country where electricity rates are cheap, electrical resistance furnaces are common. Rather than moving air over a flame as with combustion-based, forced-air heating, air is moved over a hot electrical coil in the furnace.

Electric-based central heating can achieve 100 percent AFUE, since all the electrical power is converted directly to heat. However, because the supply of electricity is produced primarily by burning coal, natural gas or fossil fuels, an electric furnace isn't necessarily an environmentally friendly heating choice.

Electric furnace heating also tends to be more expensive to operate compared to other electric resistance systems because some of the warm airs leaks through the ducts or loses heat to the duct's interior surface.

Electric baseboards offer an alternative option, with individual heaters in each room providing heat through metal pipes that contain heating elements. Each operates independently within its own room, which allows considerable zone control.

Baseboard heating offers several advantages. The modular design means that the system has fewer moving parts, requiring less maintenance and repair. Individual rooms can be serviced without having to address the entire system. Furthermore, they cost about $100 or $150 per room for installation. 

However, quality can vary widely, so choose carefully and look for labels from Underwriter's Laboratories or the National Electrical Manufacturer's Association.

Radiant heating is another option, driven either by electric or hydronic power. It's not for everyone, but it has its advantages.

Radiant heating involves installing coils or pipes in the floor, providing heat from below and moving upward. It presents an even, overall heat temperature throughout the room. With no moving parts, it's very quiet and comfortable, and it doesn't stir up as much dust and allergens, as compared to forced-air systems. It also doesn't create any drafts, and eliminating the need to blow air makes it more energy efficient.

However, radiant heating tends to be more expensive to install, especially when retrofitting it into a home. Electrical heat is also more expensive to operate and it's used more often as a supplemental heat source or in small areas, such as a bathroom or kitchen.

When installing radiant heating, you should give serious thought to the type of floor covering in the home. Ceramic tile works well because it conducts and stores heat. Wood, vinyl and linoleum are less efficient, but work reasonably well. Carpeting will directly insulate the floor from the room, decreasing efficiency, so if you want to install carpet in a radiant-heated room, use a thin carpet with dense padding.

Geothermal explainer graphic

Geothermal pipes were traditionally laid horizontally (C), but recent innovations allow them to be installed diagonally (A) or vertically (B), requiring less real estate.

Geothermal heat pumps

geothermal heat pump is one of the most energy efficient methods of heating or cooling a home. Relying on a series of liquid-filled pipes, a home can be heated in cooler months by transferring and condensing energy from the 50- to 60-degree temperatures found just a few feet below ground. In the summer months, the process reverses, thereby cooling a home by removing heat. Underground temperature remains constant no matter the climate, so geothermal systems provide consistent and reliable heating and cooling.

Geothermal offers maximum efficiency while costing less to operate and lasting longer. Upfront installation costs are high, ranging from $10,000 to $30,000, depending on the site conditions, but some of these costs may be recouped through local, state or federal tax incentives.

Installation involves digging long trenches or deep holes to install the pipes, so it's labor-intensive on the front end. However, you'll save money over the long term because of the lower energy costs. Also, a geothermal system tends to last about twice as long as conventional air-source units. The lack of moving parts means you're less likely to spend big on repairs down the line. The buried loop system can be expected to last for 50 years. They're significantly more efficient then even the highest-efficiency air source units. 

Until recent years, geothermal systems required significant real estate to lay the pipes, but recent innovations in boring and drilling straight down or at an angle make geothermal systems plausible even for homes with very small yards. 

Don't underestimate those federal tax incentives, either. For systems installed through Dec. 31, 2016, homeowners can receive a 30 percent tax credit, so that $20,000 geothermal system translates to $6,000 on your next tax return. Various state incentives can offer even more immediate recoups of the investment. 

Boilers and combination boilers

Many options exist for choosing a heating system for your home, including boilers and combination boilers.


More common in relatively older homes, a boiler-based heating system uses gas, oil or electricity to heat water and produce steam that moves through pipes to heat radiators in individual rooms. All-electric boilers can achieve up to 95 to 100 percent AFUE, according to the DOE. Newer gas boilers must achieve 80 percent AFUE and newer fossil-fueled boilers must achieve a 75 percent AFUE.

Steam-based systems tend to be older, and were very popular in the first half of the 20th century, especially in commercial buildings, apartment buildings and very large residences. Many steam and radiator boiler systems installed more than 50 years ago remain operable, because the lack of moving parts makes them less prone to wear and tear. A steam boiler replacement costs between $4,000 and $30,000, depending on boiler size.


Combination boilers, which heat water for both bathing and home heating, have been popular in Europe for more than a decade but are only recently beginning to take hold in the United States.

Combination boilers can work with radiant systems, hydronic furnaces or traditional steam radiators. They burn natural gas to heat air and water, and one major system has an AFUE rating of 93.5.

However, they are best suited for smaller residences, and finding an installer qualified to repair them can be difficult. A new system tends to cost between $2,000 and $4,000 to purchase and about $7,500 to install.

Air-source heat pumps

If your home relies on cheap electricity rates, a high-efficiency heat pump may be a better choice. Used for both heating and cooling, an air-source heat pump condenses warm air and moves it either indoors or outdoors. Air-source heat pumps also tend to last longer, with average lifespans between 20 and 25 years.

In warm weather, it condenses and extracts heat from inside, cooling a home, and in cool weather, it condenses and extracts heat from outdoor air, heating a home.

According to the Department of Energy, the heating efficiency of an air-source heat pump is determined by its heating season performance factor, or HSPF. It's a measure of the total space heating required during the heating season, expressed in BTUs, divided by the total electrical energy consumed during the same season, expressed in watt-hours.

Overall, they tend to require less energy than other kinds of heating, and they're relatively comfortable, not hitting you with a sudden surge of heat. They tend to cost about $6,000 to install in the average home. Because many air-source heat pumps have difficulty working in extremely cold temperatures, they're best suited for temperate climates, and will usually require an alternate backup heater. 

Are you ready to hire a qualified heating or cooling expert? Check your local Angie's List of HVAC Companies here to find three qualified pros to contact for quotes.

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