Article Summary

Any HVAC unit, be it Trane, Carrier, Lennox, etc. can have its performance compromised by poor installation. Installation problems plague the HVAC industry. Proper sizing of the equipment, duct design, correct airflow and refrigerant charge are all key elements in the installation process that can’t be shortcut, if you are going to achieve the benefits of the new equipment you are investing in. The quality of your new system “installation” will have more bearing on the performance of your new HVAC system than the equipment itself.

Another dimension of this problem is that this new equipment gets installed in a house and if the house has problems with the thermal and pressure envelope the comfort and efficiency gains are not going to be realized. Many homes have poor duct design, undersized returns, duct restrictions, duct leakage, air barrier issues, insulation defects and inadequate solar control. There HVAC salesman who ignore these issues still call themselves “comfort consultants,” which is an obvious misnomer.

Although we primarily focus on equipment installation issues in this article, you will quickly see that it is impossible to ignore the whole house in this process if we are going to do a proper load calculation or deliver the correct amount of air to a room to satisfy the load calculation. When performing load calculations we must make determinations about the house’s R-values, infiltration, duct leakage…. At Advantage Home Performance we are expanding the definition of a quality installation.

There is a major quality control problem in HVAC industry

Many, if not most, homeowners who buy new high efficiency heating and cooling equipment don’t get what they pay for. They often see minimal utility bill savings and small or negligible gains in comfort. This can be traced back to the lack of professionalism in the quality of the unit installation. There is substantial body of research that indicates that the HVAC industry has a major quality control problem.

An EPA-sponsored report titled, National Energy Savings Potential from Addressing Residential HVAC, reviewed many individual studies of installation flaws and provided the following summary.”

Installation – Related Problem % of homes Savings Potential
Duct air leakage (Avg. 270 CFM 25) 70% 17% Avg.
Inadequate air flow 70% 7% Avg.
Incorrect Charge 74% 12% Avg.
Oversized by more than 50% 47% 2-10%

Saturn Energy Auditor Field Guide, ©2009 p.201

This table highlights the fact that most HVAC companies don’t have high standards when it comes to equipment installation. Based on these statistics your brand new HVAC system will most likely have at least three of the following problems: duct leakage, inadequate air flow, incorrect refrigerant charge or an oversized unit.

Why so many HVAC installation problems?

For many HVAC companies doing a quality installation is at odds with their business model. As far as these companies are concerned, making duct modifications, duct sealing, repairing the air barrier and adding insulation complicates a job and does not generate the profit that the sale of a unit does. They also lack the knowledge to properly assess and repair these problems. These HVAC companies basically pay lip service to comfort and energy savings.

Another explanation for HVAC installation problems is that many contractors only sell on the virtue of having the lowest price. These contractors squeeze as much quality out of the installation process as they possible can. They don’t do a proper load calculation, do not commission their work and skip duct sealing and modifications. Many of these companies pay their installers a flat rate which rewards quantity and not quality. The faster the installer gets off a job the greater their hourly rate is.

The company’s culture is also reflected in their lack of attention to detail during the sales process. These company’s sales people often don’t even inspect the attic insulation and duct work because it slows up the sales process. When they do inspect an attic it is often a cursory inspection done from the top of a ladder. These types of sales people are often very polished and work hard to make a favorable impression, however if they don’t inspect your ductwork and attic insulation, they are looking out for their self-interest and not yours. It is as simple as that.

Lifespan of an air Conditioning system

The lifespan of a central air conditioner is typically about 15 to 20 years. If your unit is approaching 20 years old it will eventually fail and you should begin to think about replacing it. When it actually fails depends on a lot of factors such as severity of climate, level of maintenance and quality of unit. As a home owner you have a choice, the reactive or proactive path to replacement. The path you will select will have a large impact on the quality of the installation.

Two paths to HVAC equipment replacement and a quality installation

There are two paths to HVAC equipment replacement. One path is the “emergency” replacement” and the other is the “performance path.” The emergency path is when your equipment finally quits and can’t be repaired at a reasonable cost and thus replacement is the only choice. The performance path is one in which you plan to replace your older equipment before it fails. If you are concerned about getting a quality installation be proactive and don’t wait unit the weather is extreme and your system fails.

Emergency HVAC equipment replacement

The first path to replacement is the emergency path. The emergency replacement is usually stressful. Don’t wait until your air conditioning system stops working on a day that the outdoor temperature is 108°F or 20°F. Your house is either uncomfortably hot or freezing and now you have a crisis. Aside from the fact that it is stressful, it is simply not the right time to purchase a new HVAC system. Almost every reputable HVAC company is busy when the weather is extreme. Most companies will understandably be in the “crisis mode” focused on getting their customers up and running and too busy to make fundamental changes to your home to improve the comfort and efficiency of your home.

Replacing like for like

We get it. After 15 to 20 years you are not thinking about your old dependable HVAC system and when it does fail it catches you off guard. We routinely replace existing equipment “like for like.” Meaning if you have three ton system on the house and it was working for you we simply will replace it with a new three ton system. If we see duct leakage or insulation issues we will bring them to your attention, but our focus during an emergency installation is to get you up and running as quickly as possible. In an emergency replacement we don’t follow the steps we would normally take in a quality installation because the goal is simply to get a new unit up and running as quickly as possible.

The performance path to unit replacement

This second path to equipment replacement is more proactive and information based. Home owners on the performance path don’t wait for their system to fail. They recognize that the unit is past its useful service life and operating on borrowed time. They begin to plan for replacement. They also develop criteria for how they want their home to perform in terms of performance, i.e. comfort and efficiency. This is one of the reasons we call this the performance path.

The goal on the performance path is to improve the comfort, efficiency and indoor air quality of your home when you replace the unit. For a variety of reasons home owners who opt into the performance path get superior value. Not only do they get a new system, but often a system that achieves the goals set forth in the beginning of the project. We also think they benefit from the quality of the work we perform in their home when they go to sell their homes. Home inspectors are impressed with our work. Issues with a poorly installed HVAC system can become a bargaining chip when you go to sell your home.

A quality installation starts with a thorough home assessment

A quality installation starts before any actual work commences. You can’t address problems in a home if you don’t know they exist. A quality installation starts with a thorough inspection of the house and attic, load calculations and assessment of current duct design. A thorough assessment means the salesman goes through the attic to inspect the duct system, insulation and air barrier. You can’t do a legitimate load calculation if you don’t inspect the whole house.

Manual J Load calculations

A very important part of the HVAC installation is installing a properly sized piece of equipment. HVAC equipment performs more efficiently and lasts longer if it is properly sized and your home will be more comfortable. Unfortunately we routinely see systems that are as much as twice the size they need to be, which as we will explain in a moment, creates comfort and efficiency problems.

At Advantage Home Performance we use an engineering software program to perform the Manual J load calculation to properly size heating and cooling systems. To determine the proper size of your HVAC system – we enter all the parameters of the house into the design software. It requires areas and R-values of all walls floor and ceilings, U-vales and shading coefficients of windows, overhang projections over windows, infiltration values, etc. In existing homes this means going into the attic and confirming R-values of insulation in the attic, R-value of duct work, quality of air barrier etc. When done correctly, performing a load calculation is a fairly involved process.

According the ENERGY STAR Guide to Energy Efficient Heating and Cooling, “Installing the right size equipment for the home is essential to getting the best performance and comfort. Many homeowners believe that bigger is always better when buying new heating and cooling equipment. In reality, a system that’s too large will not keep your home comfortable because of frequent ‘on/off’ cycling. Incorrect sizing can also put stress on system components and shorten the equipment’s life.

In Phoenix we are required by code to size an AC system in the summer at a design temperature of 108˚F and in the Prescott Tri-city area at 94˚F. We size AC systems for extreme weather. In Phoenix the outdoor temperature goes over 108 ˚F only 1% of the time. This is important to note because we are required to size equipment for extreme weather conditions. When done correctly the load calculations are very accurate and reliable.

It is imperative to evaluate the duct system

The duct system is the most neglected part of your HVAC system. The quality of that duct system has a tremendous bearing on the performance of your new comfort system. According to the Air Conditioning Contractors of America Manual D: Residential Duct Systems, “residential duct systems have a direct effect on equipment performance, equipment size, equipment efficiency, equipment malfunctions, indoor air quality, occupant comfort and owner satisfaction. Therefore the duct system must be carefully designed and properly installed.”

It stands to reason that if you put any “top of the line” piece of equipment on a duct system that is not properly designed, restricted and leaks, you will experience mediocre comfort, compromised energy efficiency and poor indoor air quality. The duct system is part of your HVAC system. The HVAC equipment itself does not make the system; it is part of the bigger system.

Duct modifications & Duct Sealing

Duct modifications and duct sealing should be part of every HVAC quote. Our experience informs us that at least 70% of residential homes need both duct modifications and duct sealing. We must make sure the existing duct system is correctly sized. Parts of the existing system will often need modifications, repairs and duct sealing, in order for your new equipment to perform the way the manufacturer intended it to.

Duct modifications are often the key to making a system work. We find situations where ducts are incorrectly sized and or duct runs that are so long with so many connections they can’t possibly deliver the proper air flow. We often enlarge or add a return duct. We reconfigure duct work for homes that have comfort problems. Our goal is to make only essential modifications and not to do full duct system replacements. In other words we take what you have and with an eye on budget constraints make the necessary corrections to the air distribution system.

Airtight ductwork is one of the keys to a quality heating and cooling system. The duct system or air distribution system is a crucial part of your heating and cooling system. It is critical that is designed correctly and is tested to meet airtightness standards. Compared to a lot of energy conservation improvements, duct sealing is relatively inexpensive. An airtight duct system helps make a home healthier, more comfortable and more energy efficient. This issue is so significant and widespread we have dedicated a whole article to it (Duct Leakage & Repair).

Proper Air Flow

You’ll sometimes hear people refer to HVAC systems as forced air heating and cooling systems. This is because the air is the medium that provides the heating and cooling. If a system delivers too much or too little air, then there are comfort problems. During the duct design process it is determined how much air flow a room needs to be comfortable. The amount of air required is based on load calculation, which means the quality of the room’s windows; insulation and airtightness have a large bearing on the system size and amount of air flow required.

In our Energy Star new construction projects we are required to submit a balance report. We always measure air flow at each supply register with a flow hood (see picture below) to ensure the proper amount of air flow is being delivered to each room. We install balancing dampers to be able to make adjustments to air flow. In the Energy Star program we have tolerances that we are required to meet. Our experience of designing systems and commissioning them has yielded the insights that inform this website. In some existing homes we will perform full “air balancing” packages to help balance temperatures.


Proper airflow across the unit’s indoor air coil also has an impact on the refrigeration cycle. This is why we measure static pressure on all our HVAC installations. We measure static pressure to make sure the pressure is neither to high due to restricted ductwork or too low due to improperly sized duct work. If the air flow is too high or too low you will most likely experience comfort problems and high utility bills. We routinely see systems with high static pressure due to undersized returns and poorly designed duct systems. In some of the higher end equipment we install the equipment will provide us the static pressure and air flow in CFM (see photos below).


The irony of proper refrigerant charge is that you cannot measure it without proper airflow. The researchers tell us that incorrect refrigerant level can lower efficiency by 5 – 20 percent and can ultimately cause premature component failure, resulting in costly repairs. Our technicians use digital gauges to assure that we have achieved the proper refrigerant charge.

Pressure balancing bedrooms

Ideally every bedroom in your home has either a return register, a jump duct or transfer grille. Without one of these pressure relief measures, when bedroom doors are closed and the HVAC system is running the supply air that is being delivered to the room gets trapped. The supply air has no way to easily get back to the return grille in the hallway. Door closure issues often occur in bedrooms where there is more than one supply grille. What happens is that the air supplied to the bedroom can’t easily get back to the return duct when the bedroom door is closed. The result is that bedroom goes under a positive pressure and the main body of the house goes under a negative pressure, which dramatically increases infiltration. Pressure imbalances due to door closure can significantly increase infiltration rates, which in turn increases utility bills and compromise comfort.

To prevent room pressurization issues we recommend either a multi-return strategy, jump ducts or transfer grilles. In the low income weatherization programs we participate in, as well as Energy Star, we have to ensure that no bedroom exceed a room pressure standard of three pascals. This is one of many parameters we routinely test for.

Commissioning & performance testing

At Advantage Home Performance we take commissioning or performance testing seriously. On our new construction HVAC jobs we are required to submit load calculations and a duct design as part of the permit process. In our Energy Star projects we must submit a balance report and refrigerant charge to verify that the HVAC system is delivering enough conditioned air to meet load requirements. When we perform a HERS rating (Home Energy Rating System) it includes blower door test, room pressures and duct leakage numbers. On our gas furnace installations we check a half dozen parameters with state of the art combustion efficiency gauges. Advantage Home Performance is an Energy Star Certified HVAC contractor.

Envelope Issues

Envelope repairs can make a profound difference on how you feel in your home. Many of our customers who have major air barrier issues and insulation problems can literally feel the difference when we perform air sealing and insulate their homes. A great time to invest in envelope repairs is when you invest in a new HVAC system. The costs should be wrapped into your project.

Although we have several articles on these subjects on this website, here are a few quick dos and don’ts in regard to envelope issues. We never recommend radiant barriers or power vented attic fans. It is relatively inexpensive to have your attic insulation repaired. Solar control strategies like shade screens and reflective films are a great way to reduce your AC’s runtime. We are big supporters of unvented attics with cathedralized foam insulation. This strategy brings your duct system inside the thermal pressure envelope. Remember if you get the basics right, you are way ahead of the curve.

What third party standards do we recommend?

We encourage homeowners to do their own research. The more independent research homeowners do, the more aligned with national standards and best practices our recommendations become. There is great deal of information available if you know where to find it. We provided a few very home owner friendly links below.

  1. ACCA – The Indoor Environment & Energy Efficiency Association: The Air Conditioning Contractors Association of America has a series of short videos for home owners as well as ACCA Standard 5: HVAC Quality Installation Specification.
  2. Energy Star: A guide to Energy Efficient Heating & Cooling
  3. This is the American Council for Energy Efficient Economy: The Smarter House website is helpful.

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