Need help with re-routing of HVAC trunk and ducts

Hey folks, So I have started the process of building my basement studio. For various reasons, it is imperative that I move main trunk line form one side of the heat pump HVAC system. What I need to do is create a 90 degree turn right at the point where is attaching to the main system, extend trunk 8' back to the back of the basement, turn another 90 degrees and then run parallel to the back wall. This will also include extending 6 "tubes" that go to the vents throughout the house. Site unseen I have had two completely different opinions by HVAC professionals. One stating that every 90 degree bend you put in a trunk line, you are in essence adding 50 feet to the length of the trunk and one person said that was nonsense and what I want to do is no problem. While I like the opinion that says go do what I want to do, common sense makes me believe there is probably something to the opinion that I will be drastically changing the air flow. I was hoping there is a HVAC professional out there that could chime in on this issue. My photos are posted and a rough design of what I need to do. Your help is greatly appreciated. Ross Hancock Millersville, Maryland

I've been in the HVAC business for a little over 8 years. Adding the 90 degree turns like you propose will increase your TEL (total equivalent length) of the ductwork like proposal 1 said. However, by implementing turning vanes in those turns, it will greatly reduce the effect of the 90s. Instead of 50 feet TEL for each turn, the turning vanes can bring that down to, say, 15 feet each turn. Is your home a single story or two story? With single story, you may not notice a huge difference with airflow. However, if that trunk feeds 2nd story rooms, you may see more airflow loss. Hope I've helped you out some. Let me know if you have more questions and I'll try my best to answer.

Thanks so much for the input. This heating/cooling system serves three total floors for about 3500sq.ft. total. Basement, First Floor, and Second Floor. I mean no disrespect to your craft when I say the installation of the new duct work does not appear to difficult with the right tools, etc. however I am more concerned about a correct "design" in order to eliminate or reduce the loss of heating and cooling. It appears I will be best served hiring a professional? Or...is there a DIY website that can provide step by step instructions on how to design this system. Ross

Ross H wrote:

Thanks so much for the input. This heating/cooling system serves three total floors for about 3500sq.ft. total. Basement, First Floor, and Second Floor. I mean no disrespect to your craft when I say the installation of the new duct work does not appear to difficult with the right tools, etc. however I am more concerned about a correct "design" in order to eliminate or reduce the loss of heating and cooling. It appears I will be best served hiring a professional? Or...is there a DIY website that can provide step by step instructions on how to design this system. Ross

Ross, the first thing begins with the manufacturer of the equipment...... Your air handler is designed with particular maximum static pressures in mind - and if your system is designed on the edge of those pressures as it is - then just adding more into the system would be problematic....... I have worked with a lot of equipment manufacturers who will not allow anything less than 6 times the duct width away from the duct before introducing a bend - and doing so would actually void the warranty on the gear........ If you have the paperwork on your air handler - you should be able to see what their requirements are...... Also - one way of overcoming problems like this is to add an inline booster fan to make up for the losses you incur upstream from your source.......... this would (of course) need to interlock with your air handler controls). you can use (and I always recommend) turning vanes as suggested above- you can also increase the duct size to decrease the static pressure - The bottom line is - first and formost - the guy who told you this was nonsense is full of bull - I certainly wouldn't deal with him on any of my projects......... Sincerely, Rod

Fellas, Great advice. I posted hoping to find the "voice of reason". My Dad always said..."never do another mans job". I'm hiring the professional. Thanks guys...I'll be back! Ross