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National Comfort Institute's Knowledge Base

National Comfort Institute's Knowledge Base is a collection of questions and answers to help NCI members and industry professionals. The knowledge base is open to both NCI members and NCI Online users.

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Each question has an Access Level, NCI Member Only and NCI Online User. NCI Members can view all questions and answers in the knowledge base. NCI Online Users can read NCI Member Only questions but cannot access the answer. NCI Online users can only access NCI Online User level questions. Both NCI Members and NCI Online Users can ask knowledge base questions.

Asking a Question
Even though Knowledge Base questions are answered by both National Comfort Institute and trusted Industry Professionals, all questions and answers must be approved by National comfort Institute.

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Question Category: Air Balancing

NCI Member Only

Question: During the Performaxx university you gave us the formulas for figuring filter static. But I am hoping you can analyze. And create some of your really cool charts for us to design proper filtration using the popular filters out there. IE: electronic, Media filters like abatement cap100, space guard, Honeywell f100, and some Hepa's like the abatement cap 600/1200, April air and others I can not think of. And of course the 1" standard and pleated filters. If this chart had some basics like tonnage or cfm to determine how many tons per filter we need. - To view, please click on the question.
Asked Date: 08/30/2007

Question Category: Carbon Monoxide Safety

NCI Member Only

Question: I have a different quandary. This is associated with our latest weather disaster in the Chicago area. Generators in a garage or vented crawl space. In driving around I noticed quite a few generators running in a garage with the doors open. Then as I am cleaning up branches in my own yard. I noticed the neighbor two doors away had a generator in the crawl space of a 100 year old home. This crawl had a window they open during operation. It was about 150 degrees F and wreaked of combustion products. I didn't have my co meter with me so I couldn't check the readings. I told the mom (old lady living there) How dangerous it is and called her son that lives in a different home. He basically told me to shove off. I called the Police they came out and talked to her. He did finally move it.

I am wondering if there are any calculations that show how fast and how much CO can build up in a garage or crawl. Or if there is any printed materials that I can use in situations like this. - To view, please click on the question.
Asked Date: 08/27/2007

Question Category: Static pressure

NCI Member Only

Question: I have tried checking static pressure useing a "needle" on the end of my hose instead of a static pressure tip. The "needle is one that is used for blowing up air in a basketball, football etc.. The pressure's seem fine when I compare the two tips readings. I do this because many times all I need to do is remove a screw and no holes are drilled, or I simply shoot a screw then remove it to test. Is this okay? Or is there an issue I don't know of? - To view, please click on the question.
Asked Date: 08/22/2007

Question Category: Air Balancing	NCI Member Only
Question: Do you have a fan table for .50" variable speed ? - To view, please click on the question. Asked Date: 08/07/2007

Question Category: HeatMaxx & CoolMaxx

NCI Member Only

Question: In running our Cool Max tests. I have found that we need really high Delta T to achieve hi efficiency.

Example: 3Ton, 1202 measured air flow, 15 td = 54%.

I ran it out and finally at 27degrees we were at rated air flow. What is a person to do? Should I slow the blower down? less air higher td. I have found this several times where I have good air flow but poor performance. - To view, please click on the question.
Asked Date: 07/30/2007

Question Category: Duct Work

NCI Member Only

Question: When doing a duct traverse, it is almost impossible to find a duct length that meets the traverse rules (8 duct diameters down stream or the 80/20 rule) that does not have a take off etc. involved in it. If I traverse a duct drop at the furnace is there a rule of thumb that will get me close to the amount of air going the through the drop? - To view, please click on the question.
Asked Date: 06/14/2007

Question Category: Heating	NCI Online User
Question: Do you have anything in writing I can share with my customer about High Low fire or staged equipment? - To view, please click on the question. Asked Date: 06/12/2007

Question Category: System Efficiency	NCI Member Only
Question: We calculate efficiencies on all of our AC tuneups. We are running into a problem with older condensing units. We do not always know what the rated BTU output of the unit is. We would like to be as accurate as possible for our customers. If there are any good ways to get this information it would really help us out. - To view, please click on the question. Asked Date: 05/24/2007

Question Category: Air Balancing	NCI Member Only
Question: I had someone helping me balance a system. How can I tell if he did it right? - To view, please click on the question. Asked Date: 04/12/2007

Question Category: Test Instruments

NCI Online User

Question: I'm thinking of buying a TSI flow hood. It seems that it will read up to 2000 cfm, but I will be reading values much lower than this that may total 2000 cfm. How accurate is it when reading individual 4" to 9" supply ducts that are no where near the high range? Is it more accurate as the volume of air increases or is uniform accuracy across all volumes? I have read where some lose accuracy at low volume levels. I just want to trust my measurements if I fork out that kind of dough. - To view, please click on the question.
Asked Date: 02/25/2007

Question Category: IAQ

NCI Member Only

Question: The practice of building tighter homes is becoming more common today. All "Green" certification programs require ventilation and most codes recommend it. One of the least costly solutions is to add a 6" fresh air intake to the return side of an HVAC system. What does that do to the sizing for heating and cooling. Does it add a 1/2 ton cooling and 6000 BTU requirement to heating? What is the impact? - To view, please click on the question.
Asked Date: 02/22/2007

Question Category: Static pressure	NCI Member Only
Question: A while back I emailed about the possibility of a chart for .8 and 1.0 static fan chart for variable speed blowers. I received an email stating you were working on it. Any results yet? - To view, please click on the question. Asked Date: 02/12/2007

Question Category: Static pressure	NCI Member Only
Question: In reading several articles about static pressure most refer to the fact that this is an important factor with AC systems but not as important for a furnace alone is this so? - To view, please click on the question. Asked Date: 11/06/2006

Question Category: Technical	NCI Member Only
Question: Do you have any info on performing a heatexchanger test by watching the o2 on blower sartup. I was told by a certain manufacture that no heat exchanger will hold water therefore air from the blower can enter and show change on your meter. - To view, please click on the question. Asked Date: 11/04/2006

Question Category: Air Flow

NCI Online User

Question: I recently finished servicing a montgomery ward furnace model # SRM54-4345B 80 BTU. The blower had not been cleaned ever. My before static pressure readings were return .016 supply .041 after cleaning the S.P. were return .042, supply .095. here is my question. The before and after delta T remained at 70 degrees. I expected the temp. difference to drop by some amount say 5 degrees? If I'm moving more air across the heat exchanger why did the temp. reading stay the same? Is this usually the case? - To view, please click on the question.
Asked Date: 10/06/2006

Question Category: Air Diagnostic	NCI Member Only
Question: Is all btu gain/loss on the the supply side of the duct system sensible btus or can there be latent btu gain/loss as well? Assuming no other components installed in the duct system? Will cfm leakage(supply) have an effect on air temperature on the supply side of the duct system? - To view, please click on the question. Asked Date: 10/04/2006

Question Category: CO AND COMBUSTION	NCI Member Only
Question: Is it ok to drill pvc pipe on a 90% furnace to check the CO levels? - To view, please click on the question. Asked Date: 10/03/2006

Question Category: Technical	NCI Member Only
Question: Which Residential Load Software, Duct Sizing Software do you recommend? - To view, please click on the question. Asked Date: 09/23/2006

Question Category: Air Diagnostic	NCI Member Only
Question: Im looking for a Universal External Static Pressur Chart , is there such athing and where can i get it? - To view, please click on the question. Asked Date: 09/21/2006

Question Category: Carbon Monoxide Safety	NCI Member Only
Question: I have 3 NSI 3000 CO Monitors in this one building where there's a dentist's office and they always read 5-9ppm. I have checked and there is no CO anywhere. Are the Monitors defective? - To view, please click on the question. Asked Date: 08/11/2006

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