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  1. #1

    Duct and Vent sizing for 125,000 BTU Heil 92%er

    Hello everyone, I have a qusetion for ya and this is after hours of searching for the info myself online with no luck. I have a brand new Heil ultra high effecient DC90 furnace ,that I snagged for $100 still crated its rated at 125,000 btus which is going to be a little bigger than I need but for the $100 I am going to use it as I am in a very rural town a 100 miles away from any HVAC store... sooo, I need to know how many sq. inches of return air grill to install and how many sq inches or vents to install and sizing of the ducts. I want to get this correct as undersizing will cause stress on the blower motor and heat exchanger and cause them to be short lived. if I had to guess I would say my house is just shy of 1000 sq feet with 9 foot celings, I know I know kinda small for the btu but I believe I can make it work with the right duct system and the unit will probably only run for short intravals at a time. I have 2 bedrooms, one bath, one living room, one kitchen, and one dining room I planned on a tottal of 7 vents so I might need them to be larger to let the unit breath.... if you can help or point me in the right direction that would be great thanks.

    blower motor specs are 3/4 horse 1075RPMS
    Also house has no exsiting duct system so all will be from scratch.

    Mike.

  2. #2
    Join Date
    Feb 2006
    Location
    Taylors, SC
    Posts
    403
    Sorry, but this is not a DIY site. The best advice I can give you is to not attempt to install your discount unit yourself, and unless you have a load cal saying you need that much heat, I wouldnt let anyone else install it.
    Poor planning on your part doesn’t necessarily constitute an emergency on my part.

  3. #3
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,903
    A 125k furnace will shortcycle like crazy in your house, unless you don't have any insulation. (Not to mention most likely overheat and trip the high limit switch on the existing duct system)

    Don't be cheap - contact an HVAC contractor and get it done right.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  4. #4
    Join Date
    Jul 2002
    Location
    Zelienople, Pa
    Posts
    2,965
    Hope you can find a deal like that on cemetary plots and funeral arrangements for your family when you kill them.
    How tall are you Private???!!!!

  5. #5
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
    Posts
    1,051
    Wow. I can't even believe you would think of using a furnace of that size for a 1000 sq ft house. Don't do it and be cheap with your families safety. Get a properly sized furnace installed by a pro.
    Its a good Life!

  6. #6
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,743
    how close is your neighbors house?



    if its the same size as yours you could probably run some ducts over for him.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,081
    Hey. Whats wrong with using a furnace that 4 to 5 times the size you need.

    Apparently. Giving you this info would be useless. As you have a problem reading and following instructions.

    Since you asked for DIY instructions, on a NO DIY site.


    Is this a troll.
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    How many times must one fix something before it is fixed?

  8. #8
    thats weird, I worked on an airforce base for 2 years as a HVAC tech, Mountain Home Idaho to be exact and although I never installed a system from scratch I did install many many units out there over them 2 years and I saw their homes were 1500 sq feet and they had the same 125,000 BTU rating. I figured I could make it work in a 1000sq foot home with proper breathing ducts....

    I know it can work safely with the right duct runs, I'll continue my search elsewhere...

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,081
    They ran. They most likely did not work right.

    For your 125,000 90% to maintain a 55° temp rise. You wqill need to move 1890 CFM.
    Thats enough air that it will exchange all the air in teh house in lees then 5 minutes.
    As an average, your 7 vents will have to move 270 CFM each.

    If you don't move enough air, it will short cycle, and use a lot more gas.


    PS: Did you derate those furnaces. Mountain Home Idaho has an elevation of 3146 foot.
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