Its Time to Redefine a Working System

Sept. 1, 2005
If a system , does that mean it ? With all the changes coming our way in the industry, it may be time to take another look and redefine what is and isn't

If a system runs, does that mean it works? With all the changes coming our way in the industry, it may be time to take another look and redefine what is and isn't a working system.

Let's take a look at the typical equipment startup. The thermostat is cranked up, the fan comes on, and there's hot or cold air delivered. Voila! The system is deemed to be working.

Is that good enough? Is has been for the majority of the industry, so let's rephrase the question: Is it good enough for you? I hope not. Because we've learned that the typical system around the country really isn't working the way we have assumed it should be. In order to move forward, let's take a look at an expanded definition of what constitutes a working system.

If we strip away all the efficiency hype and get back to the roots of our industry, we are simply providers of comfort. The best definition of a working comfort system is where the occupants are so comfortable that they are unaware of any need for heating, cooling, or ventilation. All their comfort needs are met, and the thought of whether or not the system is working properly never occurs to them.

That's our job. However, to be effective, we need to be able to define how we get to this ideal state, or at least something close to it.

Our job is to move around heat and provide adequate humidity control, ventilation, and a little filtration to help clean the air. In the summer months, we cause heat to be removed from the building. In wintertime, we add heat to the building.

Moving Heat Around

Let's start with the heat we move around. Let's take a look at the amount of heat our buildings need, and how we quantify if we have done that part of our job or not.

Last winter, a number of contractors participated in a project that measured the amount of Btus that systems actually delivered into the buildings. The results both frightened us and introduced us to some new opportunities.
First, we recorded on our test reports the amount of heat the furnaces were rated in the laboratory to deliver. This information is printed on the nameplate data of most furnaces as BTU Output.

Next, we measured the Btus being delivered by the system into the building. It's much simpler than you'd think. Basically, we measure airflow from each of the supply registers and add them together. Then we take the average temperatures in the supply registers and return grille, followed by about 30 seconds of simple math.

What we found sacred us because the average heating system was delivering only 50% to 60% of equipment rated Btus into the building. Yet the same facts excited us, because we saw an unlimited (and extremely profitable) opportunity to improve the performance of systems.

So, how much heat did that last furnace you serviced actually deliver into the home? Remember, it's not just the equipment that determines that; the duct system also makes a big difference. And it's not just tight ducts, but the ducts have to be sized right and installed right, or the static pressure the fan sees will limit the airflow to a point where a large percentage of the heat has to escape through the flue.

Even Temperatures

Is a system really working when there's a 10F difference between upstairs and downstairs. Perfection isn't necessary for most of our customers, but if your customers want improvement, you can give it to them.
Comfort balancing is achievable in most cases with a good quality air balancing hood and some simple duct modifications.


Ventilation is essential, even during winter months. Room-by-room the right amount of airflow is an essential element of whether or not a system is working. It's also an issue of air patterns, not just total airflow into a room. Consider discussing room-by-room airflow at startup or during a service call. In winter, a direct velocity of more than 100 fpm on a person can create discomfort.

Register replacement can be a valuable service above and beyond the call of duty.


Consumers are demanding cleaner and cleaner air. One way to fulfill their needs is to offer improved filtration systems. In many cases this can also improve the longevity of the equipment and improve the operation of the system.

However, use caution when selecting air filters. In many cases, technicians are selecting filters that the systems fans cannot afford. I believe filters are the number one cause of poor indoor air quality in certain parts of the country. Many technicians are proud of their pleated, electrostatic and 4-in. media filters. While there's nothing inherently wrong with these filters, many technicians have never stopped to consider if the fans in their systems could afford filters with such a high of restriction to airflow

Could the filters you install be the cause of your systems not working? For more information on this, click here to access my article, "Can Your Fan Afford That Filter."

Humidity Control

In summer months, the primary contributor to excess humidity can be duct leakage. Return duct leaks can pull in hot, humid air from attics and crawlspaces. A return duct leak of only 10% of system airflow can exceed the cooling coil's capacity to remove the added moisture to the building.

A supply duct leak outside the building envelope can cause a negative pressure in the building and pull hot humid air inside. The longer the fan runs, the greater the effects of duct leakage. Did you know a 5-ton fan can move 9,000 lbs of air in an hour? So what's the effect of a 20% return duct leak? Not too pretty.

So, if a system runs, does that mean it works? Maybe, maybe not. The final proof is delivered Btu. If the system can't deliver the Btus the equipment produces, one of the problems above needs attention, because the entire system, including refrigerant charge and combustion efficiency has to be right to deliver all the Btus. Whatever you do, don't worry about making every system perfect starting tomorrow. Pick your battles and improve your systems one at a time.

Rob "Doc" Falke serves the industry as president of National Comfort Institute. a training company specializing in measuring, rating, improving, and verifying HVAC system performance. If you're an HVAC contractor or technician interested in a no-cost, one-page Heating BTU Measurement Procedure, contact Doc at [email protected] or call him at 800-633-7058.