Interesting that you did a comparison. I think you put in your heating multiplier numbers in reverse order though. Best factor should be 1.7 and poor should be 3.7, correct? What area are you from doing this comparison?
After going thru huge a stack of Manual J Load Calculations here is something I developed to get close to a load on a residence. This was developed from loads I have done in my area. After I get the job I do run a Manual J Load Calculation on the home.
Cooling Load
Best Construction - 700 Square Feet Per Ton.
Average Construction - 600 Square Feet Per Ton.
Poor Construction - 340 Feet Per Ton.
Heating Load.....Square Feet Of Residence x Height Of Ceiling X Factor.
Best Factor - 3.7
Average - 3.0
Poor - 1.7
I use my experience along with this.
This is not "Fool Proof" and again I do believe in doing Manual J Load Calculations on each job.
Interesting that you did a comparison. I think you put in your heating multiplier numbers in reverse order though. Best factor should be 1.7 and poor should be 3.7, correct? What area are you from doing this comparison?
Admirable but to many variables to ever do rule of thumb....duct location, orientation , widow type etc....what we see in my desert climate...the worst of homes are still 500 square to the ton, average 700...best homes 1000...your effort is awesome though
The only thing we do 400 sq ft per ton is trailers. 600 is a good guess on modern homes with insulation.
It's kinda funny how we act like its so detail oriented, then the units come in increments of 6000-12000 BTUS, which is a pretty big spread.
After doing a couple thousand, you know a home with modern construction 1500 sq ft will be 2.5 ton, unless it is ridiculous insulated as mine is, then barely a 2 ton.
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If you used Manual S and expanded ratings , adjust your airflow you will see there are no 6000 to 12000 btus increments ...no 3 ton air-conditioner does 360000 btus ...the overlap in unit capacities is actually quite close ...run a 3 ton at 450 CFM per ton or a 3.5 at 350...very close in capacity
This is true, but around here, not applicable. 450 CFM would never be used in a green grass state(by design)
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We had a month of 85-90 with low humidity, it is amazing how comfortable that really is.
Now the humidity is here, and the days become increasingly grueling.
You envy the increased revenue tho I'm sure
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