NCI Article Library

High-Performance HVAC Resources

Current Category: Airflow

Design Vs. Redesign

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 one. It would take hundreds of pages to completely detail the process, but let’s take a stab at the basic ideas....

Dealing With Condensing Furnace Venting Issues

by Jim Davis

The winter of 2007 delivered several extremely cold blows across the country that was not only good for business, but made evident condensing equipment deficiencies that we don't see too often. Before winter slips away, it's a good time to identify and file away three...

Combustion Air – a Grimm Fairy Tale

by Jim Davis

Combustion Air - a Grimm Fairy Tale by Jim Davis When it comes to combustion air, safety truths created by someone's imagination -- based on little or no factual data whatsoever -- nothing but fairy tales. This article not only addresses the need to provide combustion...

CO and Combustion Diagnostics: Cause Versus Symptom

by Jim Davis

Jim Davis, Senior Instructor, National Comfort Institute When using the NCI Combustion Diagnostic Reports and Diagnostic Matrix, it is important to recognize the most likely defect/cause of the problem, versus a symptom that it creates. Specifically, a defect/cause is...

Changing Fan Speed with an Adjustable Pulley

by Rob "Doc" Falke

Changing Fan Speed with an Adjustable Pulley by Rob "Doc" Falke Adjustable pulleys are the most commonly used method for changing fan speed in commercial balancing. Let’s take a look at how adjustable pulleys work and learn how to adjust them. We’ll also learn how to...

Calculate CFM With the Air Changes Method

by National Comfort Institute, Inc.

Some rooms present a real challenge when it comes to determining how much air to deliver. The problem is that heating or cooling load airflow requirements are sometimes very different from ventilation airflow needs. When you find yourself wrestling with this scenario,...

Building Surface Temperature and Your Customer’s Comfort

by David Richardson

Building Surface Temperature and Your Customer's Comfort by David Richardson One of the primary goals of an HVAC professional is to ensure the comfort of their customers. Let's say that you have designed and installed an HVAC system that is absolutely perfect. The...

Building Air Leakage and Two-Story Cooling Problems

by David Richardson

A common complaint Performance-Based contractors across the country have to deal with during the summer is the large temperature differences in two story homes. The second floor is typically hot and burning up, while the first floor is extremely cold. It is common for...

Both Sides of the Fan are Equal

by National Comfort Institute, Inc.

One phrase we hear at nearly every seminar is something like "Airflow is low on the return side because of high suction pressure at the fan." Although it sounds good, and most of us may have believed it at one time, it's not accurate. In truth, airflow at the inlet of...

Balancing a Zoned System

by Rob "Doc" Falke

Balancing a zoned system requires a few more steps than balancing a typical constant volume system. Let's take a look at the zoned system balancing procedure and investigate the differences. The added work increases the labor about 25% on a project. The first step is...