Originally Posted by wenflo1
I have a lennox cbx27uh-036 air handler and a 13hpx-030-230 heat pump. I have to install it mayself because I can't afford someone else to do it. however I thought there would be some kind of direction in the box and there isn't. How big do I need to make the plenum and can it be made out of duct board since that is what I am running. Also how long should I make the trunk line stay as big as the plenum before I can do a reduction?
This calc. is more complicated than figuring current flow in electrical circuitry but not as complicated as figuring out drain sizes for landscaping runoff. The problem is that all the variables of interest are interdependent.
See if you can peek at some ASHRAE books in a votech or university library. ASHRAE does not like to lend their books to public libraries.
The ACCA publishes simplified versions of the ASHRAE basic research. The complicated formulas are solved graphically.
Here's what you're up against.
You'll also need some instruments to check your installation, and to troubleshoot your installation you'll need HVAC and electrical skills.
Unless you like high-stakes gambling, if the price of an emergency room visit in your area is anywhere near the price of having this professionally installed, I'd have it installed by a pro.