home with questions inside

Diagnostic Questions to Ask on an HVAC Maintenance Visit

May 3, 2018
Consider these four questions to help discover your customer’s hidden comfort and efficiency issues.

It’s spring tune-up season. In addition to completing your normal checklist, consider these four questions to help discover your customer’s hidden comfort and efficiency issues. Let’s take a look at how their answers can lead you to solutions beyond your typical maintenance agreement. The result will be more work for your company and a delighted customer.

Beyond the Box Questions

Customers are increasingly inquisitive about their cooling systems. A few appropriate questions can identify comfort and efficiency issues never-before addressed.

One of the primary reasons customers buy a maintenance agreement is the hope for optimum comfort, safety, and efficiency.

Most maintenance checklists only include the equipment and fail to consider the whole system. The following questions will take you to solutions outside of the box as you address problems your customers have been suffering with for years.

Question One: If you could have another thermostat in your home, where would you want it and why?
This question draws attention away from the equipment and often uncovers specific hard-to-detect comfort issues. The answer usually identifies the least comfortable room in the home. These comfort issues are commonly caused by inadequate airflow from defective or undersized ducts, additional heat load in the room, or a lack of insulation.

Whatever the problem, the solution can be solved by upgrading the duct system, adding a zoning system to redirect cooling capacity, or reducing the heat load. This produces the results your customer desires and additional sales and work for you. Both parties win.

Remember, this opportunity is missed if your attention is focused only on the equipment.

Question Two: How much lower do you think your utility bill could be if your cooling system operated efficiently?
No one likes paying unnecessary money to a utility company. In your customer’s eyes, this is wasted money, sucked into a black hole, never to be seen gain. On the other hand, everyone likes to be comfortable.

When a customer pays more than they should, it gnaws on them month after month. They feel like they are a hostage to this unnecessary penalty, especially when utility programs and multiple HVAC companies failed to provide relief in the past.

Many find that installing high efficiency equipment also failed to solve the problem. High efficiency equipment performance is controlled by the efficiency of the duct system. How many of your maintenance agreements include the duct system?

The answer is to investigate duct system performance. This means taking airflow and temperature measurements. See the end of this article to receive free information on these simple diagnostic tests. They will help you find and reduce causes beyond the equipment for excessive utility bills.

Question Three: If you could change the size of your cooling equipment, what are the reasons you would want to larger or smaller?
Your customer’s answer may take you down a few different paths. This question can lead to more questions and answers to find solutions for customer problems.

The unit may be sized correctly and run continuously on extremely hot days. In this case, there is no problem at all. With a little education for your customer, new understanding will ease their concerns.

 Short of a load calculation, here are some simple rules for your technician to follow when talking about equipment sizing during a maintenance visit. These rules are based on average square feet per ton, depending on the age and features of the home.

 This information was derived from thousands of ACCA Manual J Load Calculations from around the country. Recognize that a home built in the 1970s may have been upgraded with features described in a 2010ss era home. 

  •  In a 1970-era home – the rule is 500 square feet per ton. Features of home include R-11 insulation in the walls, R-19 attic insulation, single-pane windows, and minimal weather stripping.

  • 1980s-era home – the rule is 600 square feet per ton. This type of home usually has R-30 attic insulation, storm windows with caulking, and increased weather stripping.  
  • 1990s-era home – The rule is 650 square feet per ton. Upgrades during this period include sealed attic penetrations, solar screens on south and west windows, and gaskets in electrical outlets.
  • 2000s-era home – The rule is 750 square feet per ton. Changes qualifying a house for this smaller size air conditioning system are air infiltration reduced to .35 natural air changes per hour, a sealed attic system, and a radiant barrier.
  • 2010s-era home – The rule is 800-1000 square feet per ton. Added improvements supporting this sized air conditioning system include spray foam insulation and low-e windows. Better, newly-constructed homes today fall into this range if the improvements function as the manufacturer’s claim.

  • Today’s best homes – The rule now is from 1000 to 1500 square feet per ton or more by verified installation of top-performing HVAC systems, significantly reduced infiltration rates below .18 natural air changes per hour, and high performing spray foam insulation.

Question Four: In the summer, when do you find that your cooling system no longer keeps the house cool?
During spring service, the system may adequately cool the home, but as your customers think about last summer, they may remember their cooling system failing on the hottest day. Cooling system performance varies as the temperature increases. 

Loss of cooling through the duct system in the attic is usually one hidden culprit of this customer complaint. Duct loss is quantified by measuring the supply air temperature a few feet after air leaves the equipment and then measuring the air temperature at the farthest register from the equipment. Subtract the two temperatures to find the difference. Ideally this temperature change should not exceed 1 degree in mild weather and 2 degrees in hot weather.

Many contractors often interpret the issue as undersized equipment that doesn’t have the capacity to cool the home on hotter days. However, equipment sizing may not be the problem. The ductwork could be. Duct temperature testing helps answer that question.

Question Your Way to Diagnostic Solutions
More comfort solutions may be found beyond the equipment than you think. Well planned questions allow your customers to help with your diagnostics by providing answers that guide you. Their experience living in the home qualifies them to help you with your diagnostics.

Rob “Doc” Falke serves the industry as president of National Comfort Institute, Inc., an HVAC-based training company and membership organization. If you're an HVAC contractor or technician interested in a free test procedure describing simple airflow and temperature testing you can do on a maintenance visit, contact Doc at [email protected] or call him at 800-633-7058. Go to NCI’s website at for free information, articles, and downloads.

About the Author

Rob 'Doc' Falke | President

Rob “Doc” Falke serves the industry as president of National Comfort Institute an HVAC-based training company and membership organization. If you're an HVAC contractor or technician  interested in a building pressure measurement procedure, contact Doc at [email protected]  or call him at 800-633-7058. Go to NCI’s website at for free information, articles and downloads.