NCI Article Library

High-Performance HVAC Resources

Current Category: Airflow

Gas Pressure Adjustments Done Right

Whether starting up new equipment or servicing existing equipment you should never assume that the recommended gas pressure of an appliance will assure safe or adequate operation. Performance cannot be determined until combustion testing has been completed. There are...

Fresh Air for Ventilation and Building Pressurization

by Rob "Doc" Falke

Adding fresh air to a heating or cooling system accomplishes two primary indoor air quality goals: It helps control building pressures and improves indoor air quality by diluting polluted or stale indoor air. Outside air enters the system through a roof or sidewall...

Flow Hood Calibration Quick Check

by National Comfort Institute, Inc.

From time to time you may question whether your flow hood is reading accurately. Most of the time, when you're using a quality hood like the TSI 8371, you'll find that even though you might be getting a questionable reading, the problem is not the hood, but the outlet...

Five Airflow Rules You Need to Know

by David Richardson

Five Airflow Rules You Need to Know Troubleshooting the airside of an HVAC system can be one of the most frustrating, yet rewarding challenges you'll have in this industry. Airflow is at the core of what we do -- yet it's one of the most misunderstood aspects of an...

Interior Doors and Intermittent HVAC Comfort Problems

by David Richardson

Interior Doors and Intermittent HVAC Comfort Problems by David Richardson This cooling season, HVAC professionals across the country will be called upon to solve intermittent comfort problems they can't recreate. These frustrating and random problems often involve...

IAQ/Mold: No Silver Bullet – Just Get Bullet-Proof

by Dominick Guarino

It's amazing how many contractors are still looking for a "Silver Bullet" solution to mold. Ideally we would have some magical pixie dust you sprinkle on a home or building to make it mold-proof, or better yet, to cure all existing mold issues forever. In this attempt...

How to Use Fan Performance Data in Your Diagnostics

by National Comfort Institute, Inc.

Almost every day we receive requests for additional generic fan performance tables other than .50" table we published previously. Well, you asked for it, you got it. We've just introduced two new generic tables, one for constant speed blowers with up to .80" ESP and...

How to Use Air Density Correction Factors

by Rob "Doc" Falke

Air density correction factors have been a part of our air balancing curriculum since the early 1990's. NCI published a small table years ago and encouraged you to make corrections for air density when measuring airflow at higher altitudes. But the accuracy you are...

How to Size a New Fan Belt

by Rob "Doc" Falke

When you spin an adjustable pulley and increase its diameter to squeeze a little more air out of a belt-drive fan, there are times you'll find the old belt no longer fits. The first fix is to loosen the bolts on the motor mount and slide the motor as close to the fan...

How to Redesign an HVAC System – Part I

by Rob "Doc" Falke

We've looked, but can't find it. There are mountains of information about how to design a new HVAC system, but nothing much that addresses how to redesign an HVAC system. It would take hundreds of pages to completely detail the process, but let's take a stab at the...