Thread: Manual J Calculation

I know the term Manual J calc comes up a lot, especially when sizing AC units. Have any of you physically done one? And if so, what program did you use if it was on a computer? I'm having trouble finding one that will allow for more than basic insulation levels. I see that the WrightSoft program comes in at about $300, which is not a big deal if you design systems, but pricey for a one off design of my house. I know I can probably get it done at the plumbing supply house, but I'd like to do one on my own first to cross check their numbers to determine my boiler size.

Kind of funny how much it is focused on AC size, since we won't have any cooling in the house.

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If you are not cooling the house (which is a mistake in my opinion, to not installing cooling), you should not need to do a manual j. There are base guidelines for how many btu's per floor the house will require with insulation values.

With the world of variable speed furnaces, you can overestimate slightly and not have any negative affects with "heating too quickly".

If you are using a boiler system, there should be methods of restricting the amount of hot water sent to each room as well.

These people offer a free trial which might just meet your needs for a one off. PE1950 HVAC Software, Air Conditioning Software "The Easy Way to Manual-J" - hvac software for load calculations HVAC Software, airconditioning software, air conditioning software, heat loads, heating loads, cooling loads, manual-j calculations

HVAC Load Calculation - Maunualj - Whole House Loadcalc