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HVAC -Manual J load calculation

Jon Fitzgerald
May 25, 2019


My builder has computed Manual J for HVAC load.I have a couple of questions.

1.In the attachment HVAC-01,if I add upstairs and downstairs cooling load it totals to 49056 btuh but the AH1 only uses 43282 btuh? Why is builder using lower btuh?

2.The cooling CFM upstairs and downstairs adds up to 2028 but builder using 1800.Why builder is using the lower cfm(1800)?

Attachment HVAC_03 has manual D calculations.


Comment (1)

  • sktn77a

    Kinda hard to read the small print but your heating load looks like its 59000 BTU and he's specified 90,000 BTU 80% furnace (which will give you about a 71000 BTU heat output). Your cooling load is 54000 BTU (4.5 tons) and he's specified a 5 ton condenser/coil. 1800 CFM is about right for the cooling, a little high for the heating. This may be adjustable in the furnace (not too familiar with that model furnace).

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