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Old 03-31-2009, 05:30 PM   #1
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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?

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Old 03-31-2009, 05:46 PM   #2
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Need to know how many CFM each section of duct work needs to carry, to determine when to reduce trunk size.

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Old 03-31-2009, 05:47 PM   #3
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Originally Posted by wenflo1 View Post
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.
http://www.engineeringtoolbox.com/

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.

Last edited by Yoyizit; 03-31-2009 at 06:02 PM.
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Old 03-31-2009, 05:47 PM   #4
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where do I find that information
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Old 03-31-2009, 06:07 PM   #5
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Many libraries will have copies of Manul J, and Manual D.

You determine the load, heat loss, gain, and CFM with J, and design and size duct with D.
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Old 03-31-2009, 06:09 PM   #6
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I appologise I am blonde.....lol I took a panel off and found the booklet inside It says 400 cfm per nominal ton at .4 satic I have a 2.5 ton heat pump if that helps you too help me.
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Old 03-31-2009, 06:13 PM   #7
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thank you beenthere I will hit the library tomorrow
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Old 03-31-2009, 10:52 PM   #8
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Is this something that you have done B-4 ?? Where will you get all the install equipment ?

Last edited by kenmac; 03-31-2009 at 11:43 PM.
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Old 03-31-2009, 11:03 PM   #9
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Sure is sad what the economy has become.

Just my .02

With the cost of buying or renting snips, vac pump, manometer, gauges and installing duct Whew

and then,

when the system does not work right and you have to call out the guy who says that the duct is all wrong and needs to be torn out and redone and when you smoked the txv bulb because it overheated from connecting the line set

It might just be cheaper to pay for a pro...

Don't get me wrong you may be just fine but, What IF

Again Just my $.02
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Old 04-01-2009, 01:32 AM   #10
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No I haven't but my Step Dad and Twin brother have. If I had the money to hire a pro I would but 10,000 dollars is nowhere close to my budget. I have all the tools I need to do the duct board and the company that sold me the lennox will come out and set the copper from the heat pum to the air handler. And charge it after they inspect it. I just need to know how far I should make the truck off of the plenum. I am mechanical inclined but never messed with a heat pump and duck work. I can fix cars , do minor electrical work ,minor plumbing ect. I grew up with 7 brothers and was raised that you do it yourself. I do appriciate all the feed back.
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Old 04-01-2009, 01:25 PM   #11
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Originally Posted by wenflo1 View Post
my Step Dad and Twin brother have.
I have all the tools I need to do the duct board and the company that sold me the lennox will come out and set the copper from the heat pum to the air handler. And charge it after they inspect it. I just need to know how far I should make the truck off of the plenum. I am mechanical inclined but never messed with a heat pump and duck work. I can fix cars , do minor electrical work ,minor plumbing ect. I grew up with 7 brothers and was raised that you do it yourself.
Your odds of success are increasing.
Post photos along the way.
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Old 04-01-2009, 01:27 PM   #12
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I will post photos for you guys

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