Ventilation efficiency fallacies

By Glenn Mellors

As residential replacement furnace and air conditioner companies, we have become prone to using the term system loosely, no pun intended. We tend to go about our business convincing consumers that our system is the most efficient system on the market. We throw around acronyms like AFUE and SEER as if they mean something that delivers optimum savings to the home, when in fact, those ratings should be referred to as potential AFUE or potential SEER. Now I am not looking for a fight, but rather reminding us that a system doesn’t stop at the plenum.

If we were to use the human body as an analogy of a system and compare it to a home comfort system, we would find several similarities, such as the heart with a furnace; air conditioner or heat pump with the lungs/air filtration; purification with the liver or kidneys; supply run with the arteries; return air with the veins; and lastly, the intake and exhaust with the mouth.

We are all aware that a healthy, happy body requires all parts to function harmoniously. The heart alone is only one part of the system, and a 100 per cent efficient heart isn’t enough to properly sustain a healthy body. Our focus in this article will be on the arteries and the veins.

Fallacy No. 01: Energy rating

While most contractors measure in AFUE or SEER, National Comfort Institute (NCI) certified professionals use what they call either a heating system efficiency rating (HSER) or a cooling system efficiency rating (CSER). Both are the efficiency rating of your installed system, including the effects of the ducting and the construction of your home.

Typically installed equipment operates at 55 per cent to 70 per cent of rated capacity. An NCI-trained and certified contractor will field measure the installed efficiency of the current system. As a contractor, you should recommend improvements while installing the new equipment, such as duct sealing and insulation where possible. Once completed, you should test again and prove the value with actual energy savings.

Fallacy No. 02: Air leakage

“It doesn’t matter if we have air leakage, all the ductwork is inside the home, so why should I worry about it?” Have you ever had a homeowner ask you this? These leakages cause an imbalance in airflow and create hot and cold spots throughout the home, making it very uncomfortable.

A way to test this would be with a simple pocket thermometer. While the system is running, insert the thermometer into the plenum above the furnace and record the temperature, then, insert your pocket thermometer into the supply air grill and record the temperature. Now divide the latter temperature by the plenum temperature and you will see the energy loss percentage.

For example, 26c divided by 49c is 53 per cent of energy making it to the register. If you were to do every register in the home, the average may be somewhere around 60 per cent. The HSER would be equal to a 59 per cent efficient furnace, or conversely, our potential energy savings opportunity could be over 40 per cent!

You can use this formula to calculate energy-saving opportunities for central air conditioning as well. NCI reports that it is not uncommon to find 14 SEER air conditioners acting and performing equal to that of a seven SEER.

Fallacy No. 03:Duct sealing

While duct sealing is part of the solution, it can also be part of the problem. Before doing any sort of duct sealing, we need to search for damaged ducts, inspect pipes that might be flattened in joist spaces, locate fittings that have come apart, and determine if ducts have been sized correctly. Is there enough return air? Without remediating these items first, you will not get the benefit of sealing.

Fallacy No. 04: High wall returns
Typically, we look for high wall returns in each room, especially on the second floor. This is one of the easiest fixes and can usually be accomplished by another return with a damper directly above the existing sidewall and replacing the current grille with one that has a damper.

If it already has an existing floor return against a wall, sometimes, by gently removing the baseboard and cutting out the base two-by-four, it can create a cavity to supply the high wall return, utilizing dampers.

Food for thought

Dislodged fittings can be a bit tricky. However, with the use of rope and two people (and a little bit of patience), it can be pulled back together. By feeding the rope through the duct and having one person on each end working the rope back and forth while pushing or twisting, the pipe can get the fitting back in place. Another option is to run a bypass around the problem area and create a drywall chase if it can’t be done out of sight.

Another use for a rope and thimble is for crushed pipe. Pull the thimble through the damaged area to improve airflow. Plan B is the bypass option, which was also used for dislodged fittings.
When wanting to add additional return air, simply think of the common rule of thumb — what goes in must come out. Adding returns to areas of concern can be a simple solution by using joist spaces and closets to get the returns where needed. Take advantage of turning vanes wherever possible. Not only does this improve airflow but it also improves coverage of an air filter.

When it comes to too small of a supply, it often is easiest to run a new run and, where possible, use ceiling chases to hide the run. Another alternative is to provide an extra run to the room to provide the proper CFM.

Dips and dives

Check for the proper suspension of the duct. The perimeter pipe should create a smooth flow, shorten runs whenever possible. You are now ready to seal the system. We want the air, or rather the blood in our analogy, to stay inside the airway and all the return air coming in from the proper location. Once completed, test the system and congratulate yourself on a job well done. And most importantly, share the new results with the homeowner. Even a 20 per cent increase in energy savings is something to brag about.