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sbauer7609 · Jul 1, 2009, 12:02 PM

My house that I just bought is a C.P. Morgan that has bad air flow and not to mention a very hot upstairs. The furnace is a Bryant 383KAV and I'm not sure where I can find out the tonnage and CFM rating of my unit. All I know is that I did some research online and downloaded a trial software of HVAC calc residential 4.0 and did the program to the best of my knowledge of how the house was built. The ducts in every room seem to be sized wrong with the downstairs using really large sizes and the upstairs using very small. The ductwork is all ran up in the attic using non-metallic flex ranging from 4 to 9 inches. There are (4) 8 inch, (4) 6 inch, (1) 5 inch and (2) 4 inch lines coming out of the supply with only (1) 7 inch and (1) 8 inch duct as well as a main return located on the wall opposite the furnace room. My master bedroom is over my garage and was very hot. I changed the single 7 inch line out to an 8 inch and split off to (2) 6 inch ducts and now is much better. I would like to redo every room so that the climate is very livable but want to make sure that I'm doing it correctly. Also, I've been doing research on flex duct and it seems to be very ineffficient when comparing to solid metal duct. I don't want to put a lot of money into this project and am wondering if any of you experts have any suggestions. I'm in construction myself so if you want to use specific terms I'll understand them. Thanks!

hvac1000 · Jul 1, 2009, 03:26 PM

You already made the first step. Now all you have to do is follow your calculations and finish the job. If you are unsure of your calculations then I suggest you seek the services of a ON SITE professional in your area to go over them with you until you are satisfied. Trying to figure exactly what you have and exactly what you need in a venue like this is just about impossible from past experience. There are just to many twists and turns in a duct system.

You said you do not want to put a lot of money into the project and I understand that but to have perfection/liveable air flow it will cost some $$$ to get it correct. Lack of money is the reason that it was not done correctly the first time since builders always cheat on the HVAC system to start with. My suggestion is to spend whatever it takes to do the job correctly or you will be unhappy living there.

dac122 · Jul 2, 2009, 05:56 AM

You're on the right track, and have discovered some changes that go in the right direction. Likewise, it is impossible to recommend specific changes, but instead point you to resources. Start by getting a copy of Manual D and read it cover to cover. Next search for ways to design ductwork and measure airflow such as here.

Be prepared for your entire system to be wrong sized, including your supply and return trunks and blower fan. But knowing that, you might be able to slowly optimize your system.

hvac1000 · Jul 2, 2009, 06:15 AM

HAHAHA Love the garbage bag tool. No everyone that looks at this post will be doing the garbage bag rag. LOL

dac122 · Jul 2, 2009, 06:24 AM

Yes. I thought twice about posting that. I will add the caveat that the garbage bag is to be used as a ROM to find gross problems in your system. Can't find it right now but there was a University lab study that actually compared that to other more sophisticated measurement tools and found it reasonable.

hvac1000 · Jul 2, 2009, 06:55 AM

Dang I was just going to toss my velocity/pressure meter setup since a plastic garbage bag will fit into my tool bag easier. I could just see the customer reaction when you ask them for a garbage bag for testing purposes. LOL