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furnace sizing

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  • #16
    Re: furnace sizing

    Originally posted by MoJourneyman View Post
    Silly question, but is there a relatively cheep software for that? or possibly a formula to use on it?

    I barely do any hvac work, almost all service, just a handful of replacements.

    I certainly have more options than an 80 or 105, those are just the closest to the existing furnace in the brand that my preferred supplier sells.

    Here's the cheapest way to go. ACCA Manual J and a good calculator. I've been using the ACCA manuals since 96.



    • #17
      Re: furnace sizing

      Originally posted by OkieBill View Post
      I have been using and am very happy with it My area now requires an approved load calc before a changeout or new install...

      No simple formula unfortunately though we have all beeen told them at one time or another...

      400 CFM Per Ton of Cooling
      500 SQFT Per Ton of cooling

      The rules of thumb may work 75% of the time but that will make you wrong the other 25%. Completly throw standardization out the window (no pun intended) when it comes to loading new construction...
      New residential rule of thumb we use 400cfm, & 600 sq' per ton.

      Last edited by James P; 10-21-2010, 04:47 PM.


      • #18
        Re: furnace sizing

        Arn't furnace/boiler heat calcs done for coldest degree days, like maybe 2% of the year. Should'nt a furnace run steady when producing heat for those coldest days, I think thats when you get the full 80 or 90%. Most of the year a furnace is oversized. Anything mechanical does not like to cycle.