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Central Heating & Cooling: Guide to Installing a Central A/C

by Stewart Unsdorfer

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This guide has everything you need to know about installing a central air conditioner.

It will walk you through the process and terminology as you plan to have your central A/C installed.

If you want to alleviate the problem of which air conditioning system is right for you, how they work, sizing, installation and what to expect when your technicians get started, you're in the right place.

Bonus Offer: Download our Guide to Installing a Central A/C as a PDF for free. Easily save it or print for reference anytime.

Chapter 1

Frequently Asked Questions - Central Heat and Air

Let's face it...

When adding to an existing central heating & cooling system, central air for a 2,000 square foot home roughly costs $3,500 to $4,000. If ducts need to be added the cost will increase. The final cost will depend on the system, additional items added and the technician's installation rates.

And whether or not you've got ductwork, adding central air is more affordable and less disruptive than you might imagine.

But you probably have a bunch of questions before you get started...

10 Common Questions to Installing a Central A/C

1. What actually is a central air conditoner?

The central air conditioning system found in most homes are a "split system". This typically means there is a compressor unit (outside) and an indoor coil, installed on your furnace inside the home.

2. How does a central A/C system work?

Central heating and cooling systems are separate things, but they are matched to work together. Here's what Trane and "How Stuff Works"  have to say how central cooling and heating works:

How Does a Central Heating and Cooling System Work

Heating and Cooling System Basics

3. What does the term HVAC stand for?

HVAC (Heating, ventilation and air conditioning) is the technology of indoor and vehicular environmental comfort. It's goal is to provide thermal comfort and acceptable indoor air quality.

4. How often should I replace my filters? And why do I need to change my filter regularly?

Changing your furnace filter is one of the least expensive maintenance items for your home with one of the greatest benefits. They should be changed regularly to improve air quality, increase the efficiency of your furnace and extend the life of your HVAC system.

Never Forget to Replace Your Air Filter Again

How to Replace Furnace & AC Filters

5. How often should I have maintenance done on my unit?

Keeping your AC system running smoothly depends on proper maintenance and service needs.

Air Conditioning Maintenance - The Ultimate Guide

The Importance of Annual HVAC System Maintenance is Greater Than You Think

6. What size central air conditioner should I have?

Too big? It will not be energy efficient. Most will turn on quickly, cool your house, then turn off. Then repeat the same cycle.

Too small? Your A/C will constantly run trying to cool your home. This will increase the wear and tear on the unit.

Just right? a properly sized central A/C will run through the required amount of cycles to keep your house comfortable, but will not run inefficiently. 

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ASM (All Systems Mechanical), created a short but thorough guide on:

What Size Central Air Conditioner Do I Need for My House?

Simply put, size matters...

Go to Chapter 5 for more on sizing.

7. Should I close the registers and doors to areas of the home that I do not use on a regular basis?

The short answer - closed vents increase pressure.

Here's an excerpt from Energy Vanguard, "When you start closing vents in unused rooms, you make the duct system more restrictive. The pressure increases, and that means an ECM blower will ramp up to keep air flow up whereas a PSC blower will move less air. Most homes don't have sealed ducts either, so the higher pressure in the duct system will mean more duct leakage."

They summarize 9 unintended consequences of closing vents.

8. What is the SEER rating? 

SEER stands for Seasonal Energy Efficiency Ratio. It is the ratio of the amount of cooling produced (BTU) divided by the amount of electricity (watts) used.

The ratings measure an A/C unit's energy efficiency. The higher the rating, the most efficient.

The ever-present federal EnergyGuide label can help you determine a unit's SEER rating at a glance.

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(photo credit: Energy Star)

The label helps identify high-efficiency A/C units. 

9. Should a thermostat be set to "auto" or "on"?

There are pros and cons of both:

Should I Use My Thermostat's Fan "On" or "Auto" Setting

When Setting Your Thermostat, Should You Use Fan On or Auto?

Why "On" Isn't always the best choice.

What are the Advantages and Disadvantages of the settings?

10. What's the difference between a split and a package unit?

which leads us to the next chapter...

Chapter 2

Types of Central Air Conditioners

Whether you are a homeowner looking to upgrade your system, a homeowner looking for available options, or a business adding A/C, there are a variety of central air conditioners on the market.

1. Split System

The most common or popular is the split systems. Simply put, the split system has it's cooling parts of the unit inside the home, and it's heating parts outside of the home. With a split system, the condenser and compressor are housed outside.

An indoor cabinet has the evaporator coil. There is also an air handler that is usually part of the furnace. This handler sends the warm or cool air through the ductwork. The most important aspect of this particular combination is matching both parts for maximum efficiency.

2. Package System

The package system is self contained - not split up - and the entire unit is installed outside at ground level, or on top of the roof.

Here's a recent photo of a "package rooftop unit" we installed for a church.

central heating and cooling

A package unit is a completely self contained heating/cooling unit that has the blower, coil and condenser all built into one unit. Fully self-contained air conditioners are ready with refrigerant and can be used on a rooftop like in this case or ground mount. It is imperative that the unit be level for your HVAC system to operate properly and efficiently.

The older system was loud and there was no way to get a new indoor unit into the attic. The access was not big enough. 

Sitting on the roof as an option will air condition the space below and fit (unlike the constricted space in the attic). It was the solution for an easy-to-install outdoor unit.
 
We figured out a way of routing the ducts from the unit into the attic and connecting to the existing duct system.
 

central heat and air

3. Mini-Split System

Like a split system, the mini-split system uses an outdoor compressor/condenser linked to the indoor air-handling unit.

The advantage of the mini-split system is that the indoor units are small and can be used to cool rooms, or zones. Also, a professional installer can create these "zones" and can hook up multiple units to one outdoor unit.  

Exclusive Blog Post Bonus: Download Our 11 Key Benefits to Fujitsu Mini-Split Systems. Easily save it to your computer or print it for reference. 

The Fujitsu Mini Split system is the perfect solution for homeowners who have boiler systems, and requires the minimum amount of disruption to your home.

It offers both a central heating & cooling system that is perfect for seasonal transitions, although you can use it year round.  

4. Heat Pump

Installation for this type system typically consists of two parts: an indoor unit called an air handler and an outdoor unit similar to a central air conditioner, but referred to as a heat pump. As part of a central heating and cooling system, it uses the outside air to both heat a home in winter and cool it in summer.

A central air conditioner is really either a split-system or packaged unit. Choosing the right A/C system for your home is a decision you have to live with. You want to guarantee your comfort, cost-savings and optimum performance.

Chapter 3

Adding Central Air - Choosing, Upgrading or Replacing

Today's best air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20% to 40% of your cooling energy costs by replacing it with a newer, more efficient model. (more on energy efficiency in Chapter 6.)

"If you’re thinking about adding central air conditioning to an existing house, statistics show you’ve got a lot of company. In fact, while air conditioning was installed in just over 60 percent of homes as recently as the early 1990s, today about 87 percent of existing U.S. residences now enjoy some form of A/C."

Griffith Energy Services reiterates ...

What's Involved When Adding Central Air Conditioning to Your Home?

Time agrees central air conditioning will change your life.

"No more sweaty nights tossing and turning because you haven’t installed the window units yet. For that matter, no more installing the window units—or bashing your knuckles carrying them up and down the basement stairs each spring and fall."

And it lets you understand the ...

5 Things to Know Before You Add Central Air Conditioning

What if you're on the fence as to whether you should upgrade?

Answer these questions provided by HGTV:

  • Is your heating or air conditioning system more than 10 years old or not keeping you comfortable?
  • Is your air conditioner, furnace or boiler running a lot?
  • Are you paying more than you think you should in energy bills?

Before spending money on a new HVAC system, it's wise to check for costly air leaks. According to Energy.gov reducing air leakage can "significantly reduce heating and cooling costs, improve building durability, and create a healthier indoor environment."

Once you decide you're ready to replace your system, the question of cost will be next on your list.

Furnace Compare recently updated their article on central air conditioner pricing. It isn't about the average price of central air conditioners but the result of a series of interviews with contractors and distributors about how they set their prices.

A few of the questions they answered...

  1. Does the equipment affect the cost of installation?
  2. Should I bypass the contractor to purchase equipment?
  3. Will the price increase based on the value of my home?
  4. How common is it to revise a bid?

Their best advice: "periodically consider the age of your system and ask a technician during regular maintenance how the system looks."

Download our free PDF version of the Ultimate Guide to Air Conditioning Maintenacne

Basically don't get caught in an emergency situation where you are desperate for A/C.

"The fact is that it takes time to do your research to find contractors to request bids from, research their bids and learn all that you need to know about AC system replacements."

Chapter 4

Installation and Location

75 percent of air conditioning problems can be resolved by the correct method of installation in combination with the right-sized air conditioning unit.

Installation Details 

Electrical Requirements to Install Your A/C

Your electrical must be able to handle the additional demand of the A/C unit. An older circuit breaker panel may need to be upgraded to supply higher amperage.

Modern homes may have a panel that has the ability to add additional circuit breakers. Discuss the possible upgrades with your contractor in advance of beginning work. A reputable contractor can recommend a licensed electrician that is familiar with upgrading electric service.

Space Requirements for Your Air Conditioner

The central A/C unit will have a condenser unit outside that will need space and the blower and connections inside your utility room. An independent electrical outlet hookup may be necessary with wiring to your main panel.

All the required space should be planned out in advance. Your contractor can help to plan the details. Any construction necessary should be figured into the total cost of installation.

Thermostat Replacement - Options to Fit Your Lifestyle

This would be a good time to replace an older dial-type thermostat with a new programmable model. Modern programmable thermostats can save you significantly on monthly utility expenses. Available options are 5 or 7 day models with several different settings for each day.

Several are capable of wireless control by your smartphone or other communication device from anywhere the internet is available. You can be notified when a filter change is necessary, time for regular maintenance, or if there is a problem with the system.

Sign up for our FREE Air Filter Replacement Reminder

Chapter 5

A/C Sizing & Cost

Choosing an air conditioner size that is too large forces your unit to run constantly in short bursts, which can cause the unit to burn out faster. Furthermore, if your unit is running in short busts, it allows heat and humidity to creep back into the house, which can cause damage over time.

Now that you know the importance of properly sizing your air conditioning unit, you need to know how to figure out the correct size.

Do you know how the size of air conditioning units is measured?

Central air conditioning units are measured in tons. This measurement is based on the unit's ability to cool your home. For example, a 1 ton unit will cool 12,000 BTUs (British Thermal Units) per hour. With every 1 increase in tons, the BTUs increase by 12,000. This means a 4.5 ton unit will cool 54,000 BTUs. If you aren't familiar with the term BTU, it means the amount of energy needed to cool or heat a pound of water by one degree F°.

To calculate the size of the unit your home will need, you can use one of two methods. The first is to take the square footage of your home and multiply it by 25. Then take that number and divide it by 12,000 and subtract .05

Calculation: ((sq feet x25)/12,000)-.05= AC ton needed)

The other method is to use the Air Conditioning Square Footage Range by Climate Zone chart

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Start by finding your location on the map of the US, which has been divided into five zones. Once you know your zone color, locate your home's square footage, and then you will find the proper air conditioning unit size.

A HVAC professional can also conduct a load calculation to properly size your system. Load calculation is the process of determining the proper size of a furnace and /or air conditioner for a home.

7 Tips for Accurate HVAC Load Calculations

Make sure the equipment is properly sized, using accurate load calculations. The proper way to calculate the required size for your central air conditioner is by running a load calculation known in the HVAC industry as a “Manual-J.”

Introduction to the “Manual-J” – The Proper Way to Calculate the Right Sized Central Air Conditioner for your Home.

"A Manual-J calculation is a detailed analysis of your home’s central air conditioning and heating needs. There are two types of Manual-J calculations: a whole house load calculation and a room-by-room load calculation."

If you aren't sure about air conditioner sizing for your home, you can always consult an air conditioning specialist. These specialists will analyze additional aspects of your home, including:

  • The size of the living space
  • When the home was built
  • If there is an existing ventilation and ductwork system, and how well it works
  • If your home has proper insulation
  • Which exterior and interior areas receive the most exposure to the sun
  • How much shade your home receives from trees and shrubs
  • How many windows your home has, which direction the windows face, as well as the age and condition of those windows 

ASM's revolutionary new online program, the HVAC Design & Consultation Program gives you the information you need to make the right decision on your HVAC project.

Air Conditioner Installation Cost Calculator

In addition...

11 Questions You Can Ask for Your Air Conditioning Estimate

Chapter 6

Energy Efficiency

After determining the size of the unit, your contractor should talk to you about efficiency, which is expressed by the seasonal energy-efficiency rating (SEER).

The SEER rates how many BTU an air conditioner will remove for each watt of electricity it consumes. The higher the SEER, the less it costs to operate.

Federal law requires that new A/C units have a SEER of at least 13. These units have lower operating costs, tend to be higher quality, have more safety features, better sound shields and lower voltage requirements. In general, the higher the SEER, the higher the initial cost for the unit.

Older air conditioning systems have a SEER rating of 10 or under. Today’s more efficient air conditioning systems have SEER ratings as high as 23.

The United States now requires that residential air conditioning systems manufactured after 2005 have a minimum SEER rating of 13 (window units are exempt from this law, so their SEERs are still around 10). The SEER rating is usually shown on a yellow and black EnergyGuide sticker attached to the outside unit of the air conditioner. (image displayed in Chapter 1)

Calculate How Much You Can Save by Upgrading to a New Energy-Efficient Cooling System

SEER ratings only represent the potential efficiency of the system under perfect conditions. Over half of the system’s efficiency depends on correct equipment sizing for your home and proper installation.

Energy.gov shares tips when your contractor installs a new central air conditioning system:

  • Allows adequate indoor space for the installation, maintenance, and repair of the new system, and installs an access door in the furnace or duct to provide a way to clean the evaporator coil
  • Uses a duct-sizing methodology such as the Air Conditioning Contractors of America (ACCA) Manual D (Manual D is the ACCA method used to determine the overall duct lay-out including the individual duct sizes. To design a duct system, the HVAC system designer must have completed a Room-by-Room Manual J load calculation.)
  • Ensures there are enough supply registers to deliver cool air and enough return air registers to carry warm house air back to the air conditioner
  • Installs duct work within the conditioned space, not in the attic, wherever possible
  • Seals all ducts with duct mastic and heavily insulates attic ducts
  • Locates the condensing unit where its noise will not keep you or your neighbors awake at night, if possible
  • Locates the condensing unit where no nearby objects will block airflow to it
  • Verifies that the newly installed air conditioner has the exact refrigerant charge and airflow rate specified by the manufacturer
  • Locates the thermostat away from heat sources, such as windows or supply registers.

Conclusion

Professional air conditioning installation is arguably one of the best ways to guarantee an efficient and smooth running air conditioner.

Unfortunately, most individuals for one reason or another make the wrong calls when installing new air conditioning systems. This not only compromises the system’s overall performance, but results in a home owner incurring unprecedented bills which could have been easily avoided.

How do you go about choosing, adding, replacing, upgrading or installing your central heating and cooling to meet your needs?

Easiest answer...

Seek a qualified HVAC professional. They will get all your questions answered.

There are many ways you can go about your search for an HVAC contractor.

  • Ask trusted friends or family for contractor recommendations.

Get the free PDF of our Guide to Installing Central A/C

 

blog author

Stewart Unsdorfer

Stewart has been in the HVAC business for more than 25 years. He is a state licensed heating and A/C contractor, as well as being certified in design, fabrication, layout and installation of forced air heating / cooling systems.

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