RE: Is Manual J worth it?

I have been learning more and more about “proper” system design because the way i was taught was almost all rule of thumb stuff. I do mostly service and haven’t really done any full system designs. I recognize some short comings in some of the things i was shown and started looking into things like manual j and how to properly size a system if/when i need to do that.

The main point i am wondering about is for your average or even above average single family home, how much larger or smaller can you determine is needed from all the load calculations in manual j versus a simple equation or 1 ton of a/c per 500 square feet. If i oversize a unit by half a ton is that really going to make a noticable difference? 

Im asking this in hopes that i learn something, not so i can argue that the way i learned is better.

Andrew Souza Rookie Asked on May 17, 2018 in Design.
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3 Answers

I know the humidity and short cycling stuff.

I guess what i’d like to know is if anyone has gone from a more simple/old school way of sizing units (volume of conditioned space and general “tightness”) to full manual j load calculations and seen a big difference. Im not denying that it would be good to have a very detailed and accurate load calculation, but someone has to pay for it.

Rookie Answered on June 23, 2018.
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