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Replacing or Installing Central Air Units

While not a prime selling point for a home, not having central air will often be the primary cause of a hard pass for those seeking to buy a new home.

We have grown accustomed to having comfortable indoor climates in our homes and central air is the simplest way to achieve that goal.

If you don’t have a central air system in your home and want some of that comfort for yourself there are a number of factors that you need to consider.

If you have central air but your system is aging, replacing it includes going over the same process as a new installation.

Due to the advancements in air conditioning technology and tightening energy regulations, the following facts and considerations apply to either new or replacement systems.

Considering the Costs

A new central air system comes with costs beyond the simple purchase price of the system.

You need to contend with load testing, installation costs, permitting, and the potential need to improve your home’s insulation.

On the happier side, the EnergyStar tax credit program has recently been extended until 12/31/2021.

Average Installation Costs

The cost to install a new central air system, including purchase, ranges from $3,811 to $7,475 for a standard home.

For larger homes and more complicated systems the cost can rise past $10,000. For a smaller home, at 1,200sq ft, the cost is between $3,000 to $4,000. Factors that can affect your installation cost include:

  • Condition of your ductwork
  • Complexity of your AC system (single or multi-zoned)
  • Restricted spaces
  • Home size
  • Need for other upgrades (venting, insulation, new cement pad)
  • Regional pricing (can vary widely)

This calculator will give you an idea of installation costs in your area. It is not exact but allows to develop a generalized budget for the work.

Rebates and Incentives

The federal government is invested in making our climate control systems more efficient. In aid of that, they offer tax credits to reward homeowners who spend extra to install high efficiency systems.

You will also want to look for State and local level tax credit programs to help defer the expense of your new central air system.

This handy site helps you find Federal credit, loan and grant programs for high efficiency efforts.

There are a number of avenues for helping you afford a more efficient system such as:

  • Federal loans, grants and tax credits
  • State and local incentive programs
  • Manufacturer incentive rebates
  • “Green” loans from traditional lenders

The “Off-Season” Myth

Run a search on Google asking which season is best for buying a central air system and you will get every possible answer except summer.

For the most part, AC units cost what they cost regardless of the season. You may wish to avoid making a summer purchase because your choices may be limited as demand outstrips production but that’s as far as we are willing to go.

Installation, however, is a different story. The slow seasons for the HVAC service world are fall and spring when temperatures are generally mild and HVAC systems aren’t being stressed.

The honest installers don’t adjust their labor rates seasonally, but it wouldn’t hurt to have them installing your new equipment when they aren’t racing to keep up with demand.

Purchasing Your Central Air System

Choosing Your Brand

There are dozens of AC manufacturers to choose from, many of which are regional or discount brands for the big-name companies.

Consumer Reports has named their top five companies based on performance, reliability, customer support and overall quality:

  • Trane
  • Lennox
  • Bryant
  • American Standard
  • Carrier

If you pick any of these brands you can expect a well-made product, manufactured in the United States or North America, backed by superior customer service.

There are cheaper alternatives than these five but we wouldn’t recommend going cheap on something you expect to use for decades.

SEER Rating

The Seasonal Energy Efficiency Ratio (SEER) rating of a central air system is a measurement of cooling power vs required energy to achieve a set result. The higher the SEER rating the more efficient the unit.

SEER ratings were developed in the 70’s in a reaction to the energy crisis of the time. Minimum requirements were implemented in the 90’s and they have slowly tightened to the regulations we have since the last update in 2015. The latest change also divided the nation into regions.

These regions are based on Heating Degree Days (HDD) and this information was used to set the minimum SEER rating for each region based on expected annual use. You can view the regions in this document to see where your home falls and what the minimum SEER rating is for your home.

For practical purposes, the higher the SEER rating of the central air unit the lower your energy bills will be during warm weather.

There are no hard and fast numbers on how much you will save due to the many variables involved but you can expect around a 10% savings on your energy bills if you move up from the minimum SEER level.

Heat Load Calculation

Every home is different, especially when it comes to shedding or collecting ambient heat. To properly calculate the heat load of a given home you must consider and measure:

  • Position of home relative to sun travel
  • Amount of shade if any
  • Number of windows and thermal capacity of same
  • Average number of occupants
  • Amount of lighting in use
  • R value of home insulation
  • Quality of seals in exterior walls and openings
  • Region home is located
  • Local HDD
  • Average humidity levels


OR… you can use this calculator to get close enough to make an intelligent purchase. The choice, of course, is yours to make.

Load Calculation

Load calculation is the measurement of how much air a unit moves through your home, measured in tons. This is an essential number to have right because too much power will cause your thermostat to react before treated air gets a chance to circulate throughout your home.

If you guess low, treated air may never reach the furthest reaches of your home.

The most accurate means of arriving at this number is to hire an HVAC technician to load test your home with their specialized equipment.

If you are comfortable with an estimated number you can use this calculator (scroll to second chart) or review this brochure from the Department of Energy.

Whichever method you use, make sure your new central air unit is designed for your home’s load calculation.

Types of Central Air Systems

While most often working in conjunction with a forced air furnace, there are two main types of AC systems.

A split system has the condenser outside and the coils and blowers in separate units inside, with the refrigerant and communication lines passing through the walls.

A packaged system, usually used for commercial buildings or very large homes, has all the components in the same unit which is most often placed on the roof of the building.

We will be concerning ourselves with standard sized split residential systems only, of which there are still several types.

Standard Split Systems

These are what you see most often in our homes. A condenser unit sits outside on a cement slab with lines running through the wall and into your furnace space.

Coils are placed in the outflow path of your furnace to cool the air as it passes and moves through a network of ducting and vents.


  • Relatively inexpensive
  • Simple installation
  • Works in any location
  • Zoning is inexpensive
  • High reliability


  • Low efficiency
  • Doesn’t draw in fresh air
  • Uses refrigerant
  • For cooling only

Geothermal Split Systems

Arranged in the same manner of a standard split system the geothermal system uses long curving pipe systems buried deep underground to draw geothermal energy from the earth.

This system also requires extensive ducting and venting configurations.


  • Environmentally friendly
  • Works for heating and cooling
  • Highly efficient
  • Zoning is inexpensive
  • No refrigerant needed


  • Requires open land
  • High installation costs
  • High unit costs
  • Extremely noisy

Ductless Mini Split Systems

The ductless mini split system is growing in popularity. It consists of an outdoor condenser and multiple air handlers inside with the refrigerant and communication lines snaking through your walls.

The requirement for ducting is eliminated with this system making it ideal for replacing baseboard heating systems or adapting to unducted home additions.


  • Can be used to cool and heat
  • Quiet operation
  • Always draws in fresh air
  • Customizable
  • Efficient


  • Difficult installation
  • Potential for hiding structural problems
  • High system cost
  • Some indoor units highly visible


Manufacturer warranties are quite limited in nature, covering only defective parts and errors in manufacturing.

Purchasing an extension to these warranties is not recommended as these types of problems will generally show themselves within the first 90 days.

Some big box stores offer decent coverage plans that are worth the price, but read the fine print to make sure they cover parts AND labor and that the deductibles are reasonable before adding one to your purchase.

With major systems like these, home system protection plans are your best bet for peace of mind.


Ducting Considerations

The ducting for your forced air HVAC system can make or break the efficiency levels of your system as a whole. As much as 20% of your thermal energy can be lost through your ducting.

Oversights and poor planning can raise that number dramatically. Keep in mind the following rules as your inspect/design your system ducting:


  • Pick your duct material carefully – many options exist from heavily insulated to sheet metal
  • Run it through interior walls whenever possible
  • Use appropriately sized ducting
  • Make your runs as short as possible
  • Use soft angles or curved architecture in your design
  • Seal each seam with mastic tape or UL listed aluminum tape
  • Include plenty of air returns for pressure stability
  • Use plenty of structural supports
  • Use noise dampeners when appropriate


  • Use the cheapest material available
  • Use narrow ducting to save money – you won’t in the end
  • Run it through uninsulated attic space or crawl spaces
  • Include sharp angles – they cause cavitation and energy loss
  • Use “duct” tape – the name is a lie
  • Use insulated ducting in the basement – your water pipes need the heat in winter

Cutting corners will, quite literally, end up costing you extra money in lost efficiency and increased energy bills. A well planned and properly installed duct system will serve you for decades to come.

The DIY Question

It can be tempting, considering the cost of professional installation, to try to install your new central air system on your own.

Other than installing your ducting, we strongly recommend that you fight the urge. The simplest argument against self installation is that it is ILLEGAL, from local to federal laws, to handle refrigerant unless you possess proper and up to date licensing.

You may want to consider the following as well:

  • Release of refrigerants, accidental or otherwise, is a $10,000 fine per day per item (consider the cost of an unnoticed slow leak dating back to your installation)
  • It is illegal to buy, sell or possess refrigerants without a proper license
  • The reward for turning in someone who buys, sells, or possesses refrigerants without a license or who releases refrigerant is $10,000
  • Improper installation of certain systems can damage your home’s structural integrity
  • All warranties are null and void – including most home warranties
  • Home insurance won’t cover damages from a self installed system

Installation Concerns

While we argue against installing the actual units yourself, we encourage you to verify your installer is doing a proper job for a fair price.


There are certain conditions that will increase your installation costs. Some will vary in cost depending on whether an installer can handle the task or needs to subcontract the work.

These factors include:

  • Ductwork replacement or installation
  • System size
  • Difficulty of installation
  • System type – geothermal requires extensive digging
  • Number of zones

Processes to Check

Certain aspects of installation are more essential than others. Be certain to verify these areas haven’t been overlooked or had corners cut by your installer:

  • Outdoor unit placed on a cement pad with a rubber pad underneath
  • Outdoor unit placed where it will get good airflow
  • Outdoor unit placed where noise has least chance of annoying you or neighbors
  • Grommets and insulator used where lines pass through walls
  • Access panel, with proper seal, in place for servicing coils within output duct at furnace
  • For Mini Split systems – ensure refrigerant and drain lines aren’t crimped or at poor angles
  • For Mini Split systems – ensure communication lines are the proper gauge, use grommets at pass throughs and aren’t stressed in any way
  • For Mini Split systems – ensure air handlers are installed securely

Options To Consider

There are ways to improve on your new central air system to increase comfort, efficiency and your indoor air quality.

You may want to consider any of the following:

  • Smart Thermostat – controls your system with precision and allows add-on services and controls
  • Zoning – allows you to shut off unused spaces to save on energy costs and the setting of occupant preferences in each area
  • Whole House Humidifier – controls moisture content in your home aiding in indoor air quality and extending the life of wood flooring, fixtures and furniture
  • Active Air Cleaners – use high end filtration and active functions to remove particulates and kill microorganisms in your home’s air

Whicher way you decide to go, replacing your old central air system with a new system will decrease your energy bills and increase your family’s comfort. Good luck!

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