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    wildstarrman's Avatar
    wildstarrman Posts: 7, Reputation: 1
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    #1

    Nov 4, 2009, 08:31 AM
    How do you know if your Forced Air Furnace is BIG enough?
    We purchased a 10 year old home last fall. Since it was build, the lower level was finished off, and two years ago the two-car garage was turned into a mother in law appointment with two rooms, a bathroom, and a kitchen.

    It doesn't seem like the existing furnace is forcing enough air out of the vents, and it only come out at about 80 degrees?

    How can I tell if the furnace is big enough for the whole house and the addition?

    Should the air be coming out at a higher temperature when heating?

    Thanks for the help!
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #2

    Nov 4, 2009, 10:06 AM
    The only TRUE way to tell if the equipment has the capacity to heat your home is to do a manual J to size the home.
    wildstarrman's Avatar
    wildstarrman Posts: 7, Reputation: 1
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    #3

    Nov 4, 2009, 10:18 AM

    Hvac1000, you Rock! Again, your are on top of these questions, thanks for your help! However, as you probably expected, I have no idea what a Manual J is. Any way for the Average Joe to accomplish this?

    I see you are from Ohio, are you located any where near Perfect North Slopes Winter Recreation Area? Its in the SE Corner of IN.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #4

    Nov 4, 2009, 10:48 AM
    Kevin I usually have a problem posting the guessing game figures because it contains about 50% human error. LOL I hope no one uses this to try and calculate a exact figure. This is used in class actually as a demo to prove how wrong improper calculations can be but for the sake of argument I am posting the one sheet here. There are 6 of them in total but the others do not have heat calculations you could use. I have a second home (camp) in Indiana and my daughter goes to Northern Slopes for fun once in a while.
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    dac122's Avatar
    dac122 Posts: 463, Reputation: 17
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    #5

    Nov 4, 2009, 10:57 AM

    A Manual J is an intricate calculation that tells you how big a furnace you need. Unlike the "rule of thumb" hvac is posting a Manual J goes into detail about insulation values, door and window counts and types, living volume, etc. - you get the picture.

    But once you have a rough number or an exact from Manual J the next issue is whether your ductwork is up to the task of deliver it as needed. A Manual D will determine that.

    Since you've had a great deal of remodeling done it might be worth your time to pay to have both done. Otherwise you're just guessing.
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