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

Maybe I’ll try asking a similar question in a different way. I currently have a 3-ton system in my house from 1999 (only giving about 20k BTUs of cooling according to measure quick). I was thinking that i would gain far more energy savings by going with a 2 stage 4-ton unit so i would not have to run it all day while everyone is gone but it could cool the house down pretty quick since it would be oversized for my 1400 sq ft house. It would probably be running on the first stage almost the whole time once the house is cooled preventing short cycling issues.

Is this flawed thinking? Am i missing something?

Rookie Answered on May 30, 2018.
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