Duct Dynasty: When Diagnosing Comfort Problems, Look at the Big Picture
If you’re not measuring, you’re guessing
Every season, homeowners across the country search for solutions to their comfort problems. Many don’t know where to turn for answers and will talk with everyone from relatives to industry outsiders to get opinions on what to do.
The big issue with this is none of those consulted are in the comfort business, and virtually none of their opinions are based on tests or diagnostics. Comfort problems are best reserved for those with the specialized skills to diagnose them.
So, where do you start when diagnosing a comfort complaint, and what steps need to be taken in the process of elimination?
ASK SMART QUESTIONS
One of the most important steps when diagnosing a comfort problem is the customer interview. Sadly, this part of the diagnosis is often skipped over. By slowing down and asking the right questions, a customer can give you valuable information about their comfort problems that may lead you to a quicker diagnosis and modify how you approach the situation.
Sample questions to ask include:
• When did you first notice this problem?
• What time of day does this problem occur?
• Is the problem more prevalent in cooling or heating mode?
• Is this problem isolated to a particular room or does it affect the entire house?
• Did anything change in your home when this problem first appeared?
These are just a few questions that might get you started in the right direction. Be sure to listen and take notes. Listen twice as much as you talk. This is a simple rule to follow and goes a long way toward figuring out what’s going on.
BEWARE OF SILVER BULLETS
Many comfort solutions are often weighted toward a particular product or “silver bullet” that supposedly will magically solve all issues. One contractor might recommend air sealing or spray-foam insulation as a silver bullet for a comfort problem, while another might recommend upgrading the HVAC equipment to a larger size and higher efficiency rating. One contractor may focus on the building, while another suggests changing the equipment altogether. Who’s on the right track?
Progressive contractors understand that one side just doesn’t seem to work well without the other, yet they’re often viewed separately from each other. The HVAC system and the building enclosure have to be examined together because they work with or against each other. When these parts of the total system are considered together, uncovering the root cause of a comfort problem becomes much easier through the process of elimination.
Instead of guessing at a silver-bullet solution, try following these three steps to uncover comfort issues that others said were unsolvable or just didn’t exist.
• Step One: Determine HVAC Equipment Performance — Start out by measuring how the HVAC equipment is truly performing in the field. There are several performance measurements that need to be gathered in this step, including static pressures, fan airflow, temperatures, refrigerant charge, and combustion readings, just to name a few. These readings need to be correctly analyzed to determine if the HVAC equipment is operating at rated capacity in the field. Yellow tags on the door of the equipment and a load calculation simply won’t cut it when doing this. Performance must be measured live in the field — not assumed. If the equipment’s performance is as it should be, then you eliminated one potential piece of the problem. If its performance turns out to be lower than it’s designed for, then you know more investigation is required before proceeding to the second step.
• Step Two: Determine Duct System Performance — Next, you must consider how the duct system is performing. Ducts are often assumed to work properly, even though most are never tested. Once proper airflow delivery, duct leakage, and duct temperatures are analyzed, the duct system’s performance can be accurately evaluated. Progressive HVAC professionals capitalize on these issues. It’s common for duct systems in an attic environment to lose 50 percent of the equipment’s capacity through radiant gains alone. For homeowners who think the answer is to install bigger equipment, the true solution could be repairs to the duct system or to redefine the building enclosure.
If the duct system is delivering the right amount of airflow and temperature, then you’ve eliminated another piece of the problem. If duct system performance turns out to be lower than what it should be, then you have more investigation to perform.
• Step Three: Verify Building Enclosure Performance — The third step is to verify the performance of the building enclosure. If everything checks out properly with the HVAC equipment and duct system (which it rarely does), move to checking the building enclosure for defects. This step is another one of those areas where assumptions are made but real measurement needs to be done. It’s hard to condition a room that is more connected to an attic than it is to the inside of the home. Air leakage, proper insulation levels, and proper installation need to be verified through various testing methods.
If the proper amounts of heating and cooling are being delivered to a space and there’s still a comfort problem, you can bet the issue is the performance of the building enclosure. This is one reason it’s so important for HVAC industry members to understand the load they’re trying to condition. Comfort issues are created due to thermal bypasses, and their impact on mean radiant temperature must be understood to truly solve comfort problems.
DON’T ASSUME — TEST TO VERIFY
There will be some of you who won’t agree with this diagnostic approach based on your experience, and that’s fine. You may contend that I should have started with the building enclosure as the first step, and that’s fine, too.
Ultimately, the key to success is having a process in place that verifies instead of assuming. Ensure you have a process that allows you to eliminate potential issues that create comfort problems instead of jumping around and guessing. Testing is the foundation for knowing what will really work to solve a problem.
It’s dangerous to assume the performance of an HVAC system due to a duct-leakage test, yellow tag on the equipment, or load calculation. Start testing the right way and make sure you have a complete list of possibilities. Otherwise, you’re guessing at the solution and possibly creating more problems. Remember: if you don’t measure, you’re guessing.
Publication date: 11/30/2015