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  1. #1
    Join Date
    Nov 2019
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    Supply plenum and duct questions

    I'm getting ready to replace the HVAC system in my modular home. It is 1500 sq ft on a basement. The air handler is currently on main floor but I will be installing the new one in the basement. I have no problem with the electrical and refrigerant parts of the install but not sure about ducting. The current supply duct is a 10" round duct. It is the normal mobile home open return. I'm installing a 3 ton heat pump with a 15kw heat strip. The manual says for 15kw heat strip I need to have a minimum of 1345 cfm. I found a calculator on line that shows that a 10" round duct with 1345 cfm is 2466 ft/min velocity. Is it going to be OK to use my 10" round supply duct?

    Do I need a plenum box of a certain size before hooking to the 10" duct or can I just make a short plenum and hook it up? Thanks for your help. I appreciate it.

  2. #2
    Join Date
    Nov 2019
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    Thread Starter
    After I posted this I seen the "not for DIY" information. Now I can't see how to delete my post. I'm probably considered a DIYer even though I have repaired several HVAC systems as I have an appliance repair business and I have a refrigerant handling license. I have never installed an HVAC system before. I am not HVAC licensed as that's not required in Kansas. Moderator: I understand if you need to delete my post. Sorry I posted before I read what I should have read. Thanks.

  3. #3
    Join Date
    Jan 2004
    Location
    PA
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    Is this heat pump and air handler approved for mobile home use.

    How much air did the old unit move, and did it also have 15 KW of electric aux heat in it.

    You won't get the help you want here. But maybe a few point outs of the perils.
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    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Nov 2019
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    Thread Starter
    Thanks for the reply.

    I wouldn't know why it would need to be approved for mobile home use. It still has the original furnace from 1985. It does not have a heat strip. I believe it's putting out around 1025 cfm although I changed the fan motor several years ago and I don't know if it was an exact replacement. I understand with the much higher velocity that I may have unwanted noise but I just wanted to make sure it wouldn't put too much strain on the blower motor of the new unit. Thanks again.

  5. #5
    Join Date
    Jan 2004
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    PA
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    Post model number of old furnace.

    Your home is most likely under HUD rules.
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    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    Nov 2019
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    Thread Starter
    7680c846

    I don't know that our home is under HUD rules. We bought this house new and a few years later moved it onto our basement. Thanks.

  7. #7
    Join Date
    Jun 2014
    Location
    Dover, DE
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    I believe HUD still applies to the original structure.
    Yes, the duct needs to be sized properly for the equipment size.
    The equipment also needs to be commissioned once the installation is done.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

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  8. #8
    Join Date
    Nov 2019
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    Thread Starter
    Commissioned?

  9. #9
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    Nov 2019
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    Thread Starter
    Nevermind that. I just looked it up. Thanks for your replies. I appreciate them! Have a great weekend.

  10. #10
    Join Date
    Jun 2014
    Location
    Dover, DE
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    Yup, after you flip the switch there’s a multitude of adjustments and checks to do.
    HVAC is far from plug and play.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  11. #11
    Join Date
    Nov 2019
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    Thread Starter
    I wasn't expecting plug and play. I just want to do it right. Thanks.

  12. #12
    Join Date
    Oct 2011
    Location
    Gladstone, Oregon (Portland)
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    15kw is too much for your home.

  13. #13
    Join Date
    Nov 2019
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    Thread Starter
    Quote Originally Posted by Adlerberts-Protege View Post
    15kw is too much for your home.
    Interesting. My local pro said I needed 20kw but I don't have enough power for that. You think I'd be fine with 10kw? That would alleviate my duct concern. It will also trim some cost off the project. Thanks!

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