Forced hot air furnaces are one of the most common methods of heating a home. They circulate warm air through ducts to vents installed in your floor, walls, or ceiling. The furnace uses several different fuel types to produce this heat - oil, gas, propane, or electricity. Each unit type has its own attributes and cost structure, which impacts the cost of your installation.
The average range for installing a new furnace in your home is between $2,000 and $11,000, with most people paying around $5,935 for a 100,000 BTU gas furnace replacement for a 2,000 sq.ft. home with no significant modifications. This project’s low cost is $1,000 for an electric furnace replacement in a 1,000 sq.ft. home with no modifications. The high cost is $12,579 to fully install a 150,000 BTU replacement gas furnace for a 3,000 sq.ft. home with new ducts and a central humidifier.
|Furnace Installation Costs|
|National average cost||$5,935|
The cost to install a furnace is largely determined by the unit type, with electric units costing relatively less than others like propane, oil or gas. Gas units are particularly popular in areas where the unit will need to be run over long periods and produce relatively large amounts of heat efficiently. On the other hand, electric units may be best suited for warmer climates where less heating power is needed, because they are cheapest to install and efficiently produce smaller amounts of heat. Ductwork repair or other modifications will also be important factors to estimate furnace replacement cost. This cost calculator will tailor the price based on your location and other specifications.
Size, efficiency, location, and install type dictate your unit's price. The unit is one of the biggest driving factors in the total price. They can be powered by gas, oil, propane, or electricity. Each has prices for the unit and installation. Below are the average prices for each type for the unit and installed prices. The costs below do not reflect ductwork installation or significant modifications.
|Type||Average Cost Range (Unit Only)||Total Cost Range (Labor Included)|
|Electric||$700 - $1,100||$900 - $2,000|
|Propane||$600 - $3,600||$3,000 - $6,000|
|Natural Gas||$500 - $3,500||$4,000 - $8,000|
|Oil||$1,700 - $5,000||$5,000 - $9,000|
Electric furnaces average $700 to $1,100 for the unit. The installed costs range from $1,600 to $3,200. Electric units cost the least to install, but this is slightly misleading. They are only rated for homes in heating zones 1 to 3, which is the southernmost part of the country. The units are smaller and produce less heat. While electric units are very efficient at converting energy to heat, they are expensive to run, with prices based on the price of electricity in your area. They make good supplemental heaters for northern climates. Keep in mind they are smaller than other furnaces. While they cost less to purchase and install, they are unlikely to heat larger homes in cold climates.
The price of a propane 1 furnace is $600 to $3,600 for the unit and $3,000 to $6,000 installed. If natural gas is not an option, a propane unit is the recommended choice. Propane is very efficient and releases fewer particulates into the air than oil. They are also easier to clean and maintain than oil furnaces, which release a lot of soot. Propane is less expensive than oil and electricity, but costs fluctuate. Propane can cost dramatically more than natural gas if it is an option. Make sure propane delivery is available in your area before selecting this option.
The price of a natural gas furnace is $500 to $3,500, and installed costs range from $4,000 to $8,000. This unit is the most popular and often recommended if you have access to a natural gas line. The gas cost is a fraction of what you pay to heat your home with other fuels. While the unit and its installation may be slightly more expensive, you save a lot of money on your heating bills each winter. Many natural gas units are very efficient, reaching efficiencies of more than 98%. Natural gas is not often available in rural areas, so propane or oil are used alternatively.
The price of an oil furnace ranges from $1,700 to $5,000, with total costs for an installed unit averaging $5,000 to $9,000. Oil is another option if natural gas is unavailable. Oil units burn less fuel than other units because oil burns hotter, producing more BTUs. However, oil units are dirty and expensive to run. They are a good choice for northern climates where gas is unavailable but are less common than gas or propane due to the high costs of heating oil. You need to factor in higher maintenance prices because oil units produce a lot of soot, which must be cleaned.
To get a general idea of the furnace size you need, consider your home size and climate zone. Climate zones are one way to get a basic idea of the unit type and size you need.
Climate zones range from 1 - 5, with one being the hottest parts of the country, such as Florida and parts of Texas, and 5 being the coldest parts like Minnesota, New Hampshire, and Maine. Each zone has a base number of BTUs or British Thermal Units that you need to heat a square foot. A British Thermal Unit is a unit of measurement for how much energy is required to raise one cup of water one degree. Consult the U.S. Energy Information Administration’s climate zone map or the map below to determine your zone number.
To determine the size you need, calculate your home’s square footage, and then multiply it by the range in your zone. Measure the length and depth of each heated room in your home and multiply these together to get your square footage. Add up all the rooms to get your total heated square footage.
|Zone||BTUs per Square Foot|
|Zone 1||30 - 35|
|Zone 2||35 - 40|
|Zone 3||40 - 45|
|Zone 4||45 - 50|
|Zone 5||50 - 60|
Stay within 10% to 20% of the number of BTUs you determine in this calculation. If you are between two sizes, round up to the next nearest, but try not to go over 20% because this yields a furnace that is too large for your home. Furnaces that are too large cost more upfront, cost more to run, and often wear out more quickly.
Keep in mind that electric units are only recommended for zones 1 and 2 and partial use in zone 3. Oil and propane are most commonly found in the Northeast and Midwest, where natural gas is unavailable. Before deciding which one to use, find out which fuels are available in your area and compare their average monthly costs to determine the best fit.
Below is a list of the average BTUs needed for homes located in zone 4 based on size.
|Square Footage||BTUs per Hour|
|500 sq.ft.||22,500 - 25,000|
|800 sq.ft.||36,000 - 40,000|
|1,000 sq.ft.||45,000 - 50,000|
|1,500 sq.ft.||67,500 - 75,000|
|1,700 sq.ft.||76,500 - 85,000|
|2,000 sq.ft.||90,000 - 100,000|
|2,500 sq.ft.||112,500 - 125,000|
A large part of your furnace’s price is dictated by size. The larger your home, the larger the unit you likely need to heat it. Bigger is not always better when it comes to HVAC equipment. A unit that is too large works harder than necessary, uses more fuel, and wears out faster than one that is properly sized to your home.
Below are the average prices for furnaces based on home sizes. Cost ranges on the low end include electric units for homes in zone 2, and cost ranges on the higher end include oil, natural gas, and propane units for homes in zone 4. All prices are for the unit without installation or new ducts.
|House Size||Average Costs (Unit Only)|
|900 sq.ft.||$600 - $1,900|
|1,000 sq.ft.||$600 - $1,900|
|1,200 sq.ft.||$700 - $2,200|
|2,000 sq.ft.||$900 - $2,600|
|3,000 sq.ft.||$1,200 - $5,600|
The price of a furnace for a 900 sq.ft. home ranges from $600 to $1,900. This assumes an electric unit in zone 2 or another type in zone 4. Homes of 900 sq.ft. do not often need to heat the entire area, making the heated space usually 800 sq.ft. or smaller. In this case, you need a unit between 36,000 and 40,000 BTUs. Your unit may be slightly larger or smaller than this based on other factors like insulation, layout, and age. Always have your unit size calculated by a professional to find the best fit for your home.
The price of a furnace for a 1,000 sq.ft. home averages $600 to $1,900. This assumes an electric unit in zone 2 or another type in zone 4. Homes of this size fall roughly into the same size category as 900 sq.ft. homes. This means you likely want a unit between 36,000 and 40,000 BTUs. Your unit may need to be larger or smaller than this, however. Factors like insulation and layout can impact your unit’s size. For this reason, you need your unit size calculated by a professional for the best size fit.
The price of a furnace for a 1,200 sq.ft. home is between $700 and $2,200. This assumes you are using an electric unit in zone 2 or another type in zone 4. Having a home in a warmer or colder climate could impact the unit size. Homes of this size need a minimum of 40,000 BTUs and frequently need slightly more. Several factors affect your unit’s size, such as insulation, home layout, and the age of your ducts. For this reason, have your unit sized by a professional.
The price of a furnace for a 2,000 sq.ft. home averages $900 to $2,600, assuming an electric unit in zone 2 or another type in zone 4. If you live in a warmer or colder climate, you may need a different sized unit. Most homes in this size range require 80,000 BTU furnaces. However, several factors impact the unit size needed. Insulation, home layout, and the age of your ducts impact the size you need. Always have your unit sized by a professional to find the correct fit.
The price of a unit for a 3,000 sq.ft. home is $1,200 to $5,600. These prices assume you are using an electric unit in zone 2 or another type in zone 4. If your home is in another climate, this may change your unit’s size and price. Most homes of this size need furnaces roughly 150,000 BTUs in size. Homes of this size do not need special heating requirements. However, to ensure your system works optimally, make sure your ducts have enough returns to circulate properly. Larger homes need more returns than smaller ones, so ask your contractor to ensure your furnace is adequately serviced for the best results.
Efficiency refers to how much energy is converted to heat. In many units, the more efficient it is, the less fuel it uses, and the more money you save on your bills. The most efficient units get close to 100% efficiency, meaning they use nearly all the energy to produce heat.
Each type has a range of efficiencies. Electric units are generally considered the most efficient from this standpoint. They use nearly 100% of the energy generated to produce heat. Keep in mind the source of your electricity impacts how efficient this system is. Solar energy means having an extremely efficient system, while using electricity generated by coal may make the system only 40% efficient overall.
Other furnaces have two efficiency levels. Standard efficiency is currently considered to be anything between 80% and 89% efficient. High efficiency is considered above 90%, with many gas and propane units achieving efficiencies above 98%. Oil units are difficult to find in efficiency ratings above 90%. There are a few brands that make more efficient models - up to 95% - but your costs for these units are much higher than those with standard efficiency.
Below are the average prices for standard and high-efficiency units. While high-efficiency furnaces cost more upfront, they save money each month. In general, homes in very cold climates see the biggest rate of return on high-efficiency HVAC systems, while homes in warmer and more moderate climates may be better off with a standard-efficiency system.
|Efficiency||Average Costs (Unit Only)|
|80% - 89%||$500 - $2,500|
|90% - 98%||$700 - $5,000|
Many good brands manufacture furnaces. Not every brand makes units for every fuel type, so double check when choosing your unit. Some brands may specialize in certain attributes like energy efficiency, making one a better fit for your home. Below are the average prices for popular brands without installation.
|Brand||Average Costs per Unit (Materials Only)|
|Goodman||$800 - $1,900|
|Amana||$800 - $2,500|
|Bryant||$800 - $2,500|
|Carrier||$1,000 - $2,500|
|American Standard||$1,200 - $3,600|
|Trane||$1,300 - $3,600|
|Lennox||$1,300 - $4,100|
The price of a Goodman furnace is $800 to $1,900. Goodman is made by the same manufacturer as Amana, and Amana is a subsidiary of the Goodman brand. This is a good, dependable line of budget furnaces. They make propane, natural gas, and electric units. The company does not produce oil units at this time. Goodman is often considered the preferred brand by builders, who frequently choose Goodman when building on spec.
The price of an Amana unit averages $800 to $2,500. Amana is a subsidiary of the Goodman brand. They use many of the same parts, casings, and packaging. Many of the lower-price units are identical between the two brands. Amana has a few more choices for higher-end units than Goodman. Like Goodman, Amana makes electric, gas, and propane units. They do not produce oil units.
The price of Bryant furnaces ranges from $800 to $2,500. Bryant is owned by the same company as Carrier. Both brands are made with the same parts and casings and are often marketed the same. Bryant is considered the line’s budget brand. Bryant makes a range of oil, propane, and natural gas units. They do not produce electric units.
The price of Carrier furnaces averages $1,000 to $2,500. Carrier is owned by the same parent company as Bryant. Both brands share many of the same parts, casings, and marketing. Carrier is sometimes considered to be a slightly higher-quality brand than Bryant. The company makes a range of oil, propane, and natural gas units. They do not produce electric units.
The price of American Standard furnaces is $1,200 to $3,600. American Standard is the owner of the Lennox brand. American Standard is considered the company’s budget or standard brand. American Standard produces oil, natural gas, and propane units. They do not carry electric units. American Standard is considered a dependable and long-lasting budget brand.
The price of Trane furnaces ranges from $1,300 to $3,600. Trane makes a wide selection of luxury and high-performance furnaces. They produce oil, natural gas, and propane units. They do not currently make electric units. Trane is well known for their energy efficiency. Their units can achieve efficiencies of more than 98% and are considered quiet.
The price of a Lennox unit is $1,300 to $4,100. Lennox is the flagship and luxury brand of American Standard. They produce high-efficiency, high-quality units designed to last. Lennox units are available in oil, gas, and propane. They do not produce electric units. Lennox furnaces are considered quiet and highly efficient, reaching 98% or higher in several models.
Furnace replacements have a similar range of costs to a new installation. When the unit needs replacing, the ducts may also need repair or replacement, or you may choose to upgrade to a new high-efficiency unit. This may require modifications, such as a drain line 2 for condensation or a new vent.
However, expect lower prices if you replace a unit with no new modifications and no new ductwork. The average price ranges for a replacement are similar to a new unit because of the many changes these systems undergo when moving to a new model. Below are the average replacement costs for each type based on the fuel source. These prices assume you are replacing a furnace with the same fuel type - not converting to a new one. They also include the costs for the labor ranging from no modifications necessary to moderate modifications. Prices do not include new fuel lines or ducts, which may be necessary in some installations. In most instances, companies remove and dispose of the old unit at no cost, but some may charge an additional $50 to $200 for this. Always speak to your contractor if this is the case for your project.
|Fuel Source||Average Labor Costs||Total Average Costs|
|Electric||$300 - $600||$900 - $2,000|
|Propane||$200 - $1,200||$3,000 - $6,000|
|Natural Gas||$500 - $3,000||$4,000 - $8,000|
|Oil||$3,000 - $3,500||$5,000 - $9,000|
Most units last 10 to 15 years, and some may last up to 25 years with good maintenance. However, if your unit is suddenly using more fuel, blowing cold air, or over 10 years old and you want to upgrade to a more-efficient model, it may be time to replace it.
Many issues are repairable, particularly if your unit is under 10 years old. Furnace repairs cost between $250 and $1,500, but if the repair price approaches $1,000 and the unit is more than 8 years old, replacing it might be the better choice because newer models are more efficient and save money. If your unit is under 8 years old, it is usually worth repairing, even at occasional high repair rates, because it still has many years left.
Several things impact the price of a new furnace installation, such as if you already have ducts, your ducts need replacing, or you are changing fuel types. If you previously had oil heat and a gas line was run to your neighborhood, a new gas unit installation requires a gas line to be run from the main gas line to your home, increasing the installation price. If you are getting propane for the first time and the company you contract with does not provide the tanks for free, factor in the cost of a propane tank and installation.
HVAC technicians charge between $50 and $100 an hour for their services, and a new unit installation takes 2 to 3 hours for the installation. Installing a gas line, new vent, new ductwork, or a drain for high-efficiency models takes longer and increases the installation cost. This makes a wide range of costs for a new unit.
|Fuel Source||Average Labor Costs||Total Average Costs|
|Electric||$1,000 - $1,500||$1,600 - $3,200|
|Propane||$200 - $1,200||$3,000 - $6,000|
|Natural Gas||$1,500 - $2,000||$4,000 - $8,000|
|Oil||$3,000 - $3,500||$5,000 - $9,000|
Prices do depend on the home and what exists at the time of the new furnace installation.
The price of your unit installation varies based on several factors. These include the unit brand, age and condition of your ducts, unit size, location, and whether you have the plumbing in place for the fuel and exhaust vent.
Oil, gas, and propane units need a line installed to fuel the furnace. Sometimes, this is done by the fuel company, while you are responsible for it at other times. If the location is difficult to reach, a new fuel line is needed, or you are upgrading to a high-efficiency unit that requires a drain, your installation costs more than in other scenarios.
Always have your entire system inspected before purchasing a new unit to determine what upgrades or modifications might be required to determine your final cost.
If you are installing forced hot air for the first time or your system is older, you need to install or replace your ductwork as well. Ductwork prices vary depending on how many feet, insulation, and materials. The average price to install ductwork is between $1,900 and $6,000 in addition to your other furnace installation costs. Adding ducts to an existing home can be more expensive than installing them in a home being built. This is because the ducts may need to be run through closets and crawl spaces if they do not have enough space. The type, size, and style of ducts you use impact costs.
While furnaces are not the greenest method of heating your home, a few options make them a little greener and less expensive to run.
The first is a furnace/heat pump hybrid. This system determines the temperature of the air outdoors, and when it is cool, but not cold, it uses the heat pump to pull heat from the air rather than using gas. When the weather turns colder, it switches to the traditional furnace. This can be a good solution for people who live in colder climates and run their systems for 6 months of the year or more. You likely only need the furnace portion for 3 to 4 months, allowing the heat pump to save you money the rest of the time.
The other option is to use a furnace with an adaptable or modulating system. These units use anywhere from 40% to 100% of their capacity, depending on the needs of the home. This is in contrast to traditional or single-stage furnaces that use 100% of their capacity all the time. By lowering the capacity, you reduce the amount of fuel used.
Hybrid heat systems range between $3,000 and $5,000 for the unit, while adaptable systems range between $1,200 to $3,500 for gas or propane systems - they are not available for oil or electricity. Installation is a separate cost and has similar labor prices to other furnaces of the same fuel type.
It is very common to install a new air conditioning system when you install your new furnace. Both systems use the same set of ducts to heat and cool your home. You have a few choices for installing both HVAC systems.
Many people keep the two systems separate. This means installing the furnace at an average price range of $2,000 to $11,000, depending on the type, and installing a new AC unit for $3,750 to $9,800. However, you can get a packaged HVAC system. This unit holds your furnace and AC for $10,000 to $14,000 installed. This can make the installation easier and save space but often means the system does not last as long as the individual components, requiring more maintenance and repair and a faster replacement.
The average AC installation ranges between $5,000 and $12,000 if you need ducts, plus the new furnace at $2,000 to $11,000. This makes your total price range $5,750 to $20,800 for a separate AC and furnace installed with existing ducts, $7,000 to $22,000 on average for a separate AC and furnace installed with new ducts, or $11,900 to $20,000 for a packaged HVAC unit with new ducts installed.
Furnaces are not the only heating systems available. There are also heat pumps, boilers, and different types of furnaces. If you choose, you can change your home’s heating system from one type to another. Unless you are changing from one furnace type to another, such as converting from an oil furnace to an electric unit, your system needs more than the installed furnace. You also need air ducts and vents for the system to work. Below are the average prices of converting some of the more popular types of heating systems to furnaces.
|Conversion||Average Cost (Labor Included)|
|Oil Furnace to Electric||$3,600 - $5,200|
|Boiler to Furnace||$4,200 - $17,000|
|Heat Pump to Gas Furnace||$4,400 - $19,000|
The cost to replace an oil unit with an electric furnace is $3,600 to $5,200. Because an oil unit already uses ducts, these costs do not include new ductwork. They include the cost to remove the oil tank and oil line and clean the existing ducts and surrounding area. Oil heat produces a lot of soot, which must be cleaned before a new furnace installation. Costs also include the new electric unit and installation. If you need a circuit upgrade to accommodate the new electric furnace, you have additional costs of $1,500 to $4,000.
The cost to replace a boiler with a furnace ranges from $4,200 to $17,000. Boilers heat water that is distributed through your home via pipes to radiators or radiant flooring. Furnaces heat air that is distributed through your home via ducts. Converting from a boiler to a furnace means installing ducts in the home, disconnecting the boiler, and capping off and disposing of the radiators. New ducts cost between $1,900 and $6,000 to install, plus the cost of the new furnace and its installation. Depending on what powers the furnace, you may have additional costs for an oil line, gas line, propane line, storage tanks, or circuit upgrade.
The cost to convert a heat pump 3 to a gas furnace averages $4,400 to $19,000. Heat pumps are frequently known as mini-splits or ductless heating systems. They take heat from another source, such as the air, and transfer it to your home. They use electricity for this process, even though the electricity is not needed to produce the heat. Converting a gas furnace means installing ducts and a gas line to the furnace and the unit. You also must dismantle, remove, and dispose of the components for the heat pump system. This may entail some repairs to the walls of the home where the system was installed.
The unit type you have impacts more than just the installation cost. Different furnace types have varying impacts on the cost to run, how difficult they are to install, maintenance, and how they impact the environment. Each fuel type can change the way a furnace behaves in certain areas. The comparisons below show you how they stack up to help you make the most informed decision.
All furnaces require some maintenance. This includes cleaning the unit, replacing worn parts, changing filters, and cleaning the ducts, vents, and pipes. The type of fuel you have directly impacts how much maintenance the unit requires. Electric units are very low in maintenance because they have fewer moving parts and do not burn fuel, which can produce soot and exhaust. They require regular cleaning, filter changes, and inspections. Oil units are the highest in maintenance because they produce a lot of soot, which gets into every part of the system. This means the furnace must be cleaned more regularly than the other types. Gas and propane units require regular cleaning, inspections, and filter changes to work their best.
|Type||Difficulty of Maintenance|
The fuel type your furnace uses also impacts its energy efficiency. Some units can be very efficient, while others may not use fuel as effectively. The unit’s efficiency impacts your monthly bills and the environment.
* Electric furnaces are considered efficient in that they convert nearly all the energy to heat. However, the source of where the electricity comes from can impact its efficiency. Solar-generated electricity means your furnace is very efficient. Coal-generated electricity, however, can drop the overall efficiency and have a bigger, more negative environmental impact.
Each furnace type has a level of difficulty for installation. Some units can be much easier to install than others. Total installation difficulty includes whether this is a replacement or a new installation, whether you have fuel lines in place, and where the unit is installed. Electric units are the fastest and easiest to install because they do not require a fuel line. They also have fewer moving parts and do not require the same exhaust vents and drains as other systems. Oil units rank the lowest in terms of installation, mostly because of how difficult they are to replace. The initial installation is slightly more difficult than gas or propane, mostly due to the extra need for exhaust. Oil furnaces can be very time-consuming to replace. The soot they produce gets everywhere in the system, including the exhaust, drains, and ducts. This means that in a replacement installation, everything must be cleaned, complicating the project. Below are the average difficulties of installing just the furnace in an easily accessible area.
|Type||Difficulty of Installation|
The cost to run each furnace is dictated by several things, including the cost of fuel in your area, how efficient your unit is, and how often it is used. Efficient units cost less to run than those that are less efficient. In addition, fuel costs may be higher or lower than in other areas. The comparisons below are based on high-efficiency furnaces when comparing costs on a national average. Your exact costs can vary, however.
|Type||Cost to Run|
Furnaces last between 10 and 15 years, but some electric units may last as long as 25 years. Multiple factors impact the length of time a unit lasts. Furnaces must be cleaned and have their filters changed regularly. Doing so keeps them from working harder than they should, extending their lifespan.
If your unit is too large or too small for your home, it also has a shorter lifespan. This is because an incorrectly sized unit works harder than it needs to, wearing it out faster. A properly sized and maintained unit has the best chance at reaching its full lifespan potential.
In some areas, you may need a permit to install a new furnace. This permit is pulled so that the unit can be inspected after installation to ensure it meets local fire and building codes. The permit’s cost varies by area, with most costing between $75 and $100. Your costs may be higher in some urban areas, and in some states, a permit may not be necessary, in which case you have no additional costs for the unit installation.
The cost to move a furnace generally falls between $2,000 and $3,000. The unit must be disconnected from its fuel source and the ducts. Once moved to its new location, it must be reinstalled, along with the fuel line and the ducts, which usually must be moved or extended. You may have higher costs if the new ducts need to be brought through a new wall or into a completely new area. This must be done carefully to avoid damaging the unit, which can take time.
Many HVAC companies remove your old unit at no cost. Others charge a fee of between $50 and $200 to remove and dispose of it. These fees are included in the average cost to replace a furnace, as outlined in the section above.
Installing a new furnace is a great time to also install either a HEPA air filter or a humidifier in your ductwork. The average cost for these is between $600 and $1,000. Both systems can make your home more comfortable. HEPA air cleaners remove allergens from the air, while humidifiers prevent dry air. While neither is required, both make your home healthier.
You may also want to upgrade to a programmable thermostat to save money on heating bills by turning off the furnace during times when you are away. The cost of a new thermostat is $145 - $230 installed.
The cost to clean a furnace varies depending on the type, age, and how well it is maintained. Cleaning costs typically start between $75 and $100 for most units. However, for oil units, you usually have higher cleaning costs because the soot can travel to more areas. This can lead to costs of $200 or more for oil unit cleanings.
The average cost to install a gas unit for this size home is around $5,935, but total costs range from $2,000 to $11,000.
Homeowners insurance does not typically cover furnace replacement unless the unit was damaged by something indicated in the policy.
The average furnace lasts 10 - 15 years. However, an electric unit may last up to 25 years. Making sure your unit is properly sized and maintained helps it reach its longest lifespan.
This depends on the climate zone you live in. The size furnace for a 1,500 sq.ft. home in zone 4 ranges between 67,500 - 75,000 BTUs.
The furnace installation alone takes 2 - 3 hours. It takes longer if you need modifications or new ductwork.
If it is nearing the end of its lifespan, begins making noise, blows cold air, or uses more fuel suddenly, it may need replacement.