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  1. #1
    Join Date
    Feb 2006
    Posts
    13

    Question

    I have a lennox OF23Q5 forced air furnace. I am trying to find out how many cfm of air does the blower move on Low/Medium/High setting.

    We will be installing a HEPA filter in the return duct and we need to make sure that the hepa filter motor is going to be programmed for the same CFM as the furnace motor so they do not fight. Can anyone help to find out what the numbers are? ...

    thx


  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,566
    Your contractor will be able to determine that by use of a flow hood, or hot anometer, or by measuring esp if he has the blower chart.
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  3. #3
    Join Date
    Feb 2006
    Posts
    13

    Question

    Isn’t there a simpler solution available? I am surprised the lennox does not have this kind of documentation on their website.

  4. #4
    Join Date
    Apr 2004
    Posts
    7,680
    It's in their spec sheets but unless you know the resistnace your ductwork has and any additonal items (such as your big filter) you cannot figure it out.

    Blowers have a curve, meaning that RPM, HP, and resistance all play into how much air a fan moves. Unless it is a constant CFM (ECM), you have to have the equipment and do the math to determine actual airflow.

  5. #5
    Join Date
    Jun 2004
    Location
    Howell, Michigan
    Posts
    16,181
    You have an oil fired lowboy furnace. The Q5 means you have a 5 ton blower, max cfm is 2000.

  6. #6
    Join Date
    Feb 2006
    Posts
    13

    Question

    What does usually a 5 ton furnace use for CFM during heating or cooling? I am going to have my furnace evaluated by I am just curious what the ballpark is.
    thx

  7. #7
    Join Date
    Jul 2000
    Location
    Louisiana , USA
    Posts
    3,280
    Originally posted by jantar
    What does usually a 5 ton furnace use for CFM during heating or cooling? I am going to have my furnace evaluated by I am just curious what the ballpark is.
    thx

    This is Turtle.

    400 cfm per ton of cooling and somewhat less for heating.

    now there can be about 500 different veriation to change these figure if things change to the system.

    TURTLE

  8. #8
    Join Date
    Feb 2006
    Posts
    13
    400 CFM does not look like a lot.

  9. #9
    Join Date
    Jan 2006
    Location
    Near Atlanta, GA.
    Posts
    14,586
    Originally posted by jantar
    400 CFM does not look like a lot.
    That's per ton,,,so a 5ton drive would be 5 x that or 2000 CFM. Now, that is a nominal figure, depending how your ductwork is designed it will in reality move less.

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