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Old 01-01-2018, 05:45 PM  
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System Sizing


I did the online calculation to size my system and would appreciate any input to validate its accuracy. The house is a 1765 sq ft bi-level on the main floor with 750 sq ft finished below. The other half of the first level is where the garage is located. Thanks in advance.
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Old 01-01-2018, 06:31 PM  
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Personally I would suggest 4.5 to 5 ton for your square footage.. rule of thumb is a ton for every 500-600 sq ft.. I would find someone to do a heat load calculation.."manual J" so you could get a more accurate idea of your needs..
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Old 01-01-2018, 06:32 PM  
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What did your software suggest?
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Old 01-01-2018, 07:48 PM  
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Re: System Sizing


You can download hvac-calc for $50, it's a limited license. you can get the trial for free and the paid version lets you change the design temperatures.

There are also other calcs online which are probably better - https://www.coolcalc.com/

The A/C units are rated at 80F 60% indoor, 95F outdoor. So the actual delivered capacity is a little lower than rated for the typical user who may want 70 to 75. In the states, manual S is used to see what size you need adjusted for this.

If what you posted is accurate, would probably be looking at a 2-ton.

Looks like a semi-detached house.

The calculation says, air duct R-4 -> are your ducts in unconditioned attic or crawl space.


Have to look at ductwork and furnace too and see if it can handle the cfm the a/c requires.

Here's a good article on where most cooling loads fall: https://www.energyvanguard.com/blog/...thumb-must-die

I'm a bit north of you and the houses I've lived in have cooled fine with 1 ton per 800 sq ft to 1000+. Oversizing seems to be less rampant than in the states.

The smaller unit will do a better job of humidity removal.
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Last edited by user_12345a; 01-01-2018 at 07:54 PM.
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Old 01-01-2018, 07:49 PM  
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Re: System Sizing


Quote:
Originally Posted by Mikel7829 View Post
Personally I would suggest 4.5 to 5 ton for your square footage.. rule of thumb is a ton for every 500-600 sq ft.. I would find someone to do a heat load calculation.."manual J" so you could get a more accurate idea of your needs..
There is no rule of thumb.
Unless very poorly insulated, that would be a tremendously oversized system for the OPs space.
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Last edited by roughneck; 01-01-2018 at 07:52 PM.
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Old 01-01-2018, 07:53 PM  
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Re: System Sizing


OP, is the 750 sq ft lower area all semi-below grade, or is it a walkout at some point?
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Old 01-01-2018, 07:54 PM  
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For 2500 sq ft?
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Old 01-01-2018, 07:57 PM  
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Re: System Sizing


i thought he said it's 1765.

not clear on design of house -> one story with basement? two stories with basement and sq ft not listed.
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Old 01-01-2018, 08:00 PM  
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The way I was reading this was a 1765 sq ft area with a additional 750 sq ft finished basement to be supplied.I could be wrong though
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Old 01-01-2018, 08:34 PM  
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Re: System Sizing


The OP said this is a bi-level home. Which can be difficult to condition as the semi-below grade level has much different heat load characteristics then that of the main level. Not quite the difference as a fully below grade basement, but still enough to make a difference.
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Old 01-01-2018, 08:37 PM  
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Re: System Sizing


Quote:
Originally Posted by Mikel7829 View Post
For 2500 sq ft?
My home is a little over 3100 sq ft, with no shade in the mid Atlantic. I have a 5 ton unit and it’s oversized for this house.
As far as heat load, I’ve seen buildings with square foot per ton calculations as little as 200 sq ft per ton and as much as 1300 sq ft per ton.
As I said before, there is no rule of thumb.
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Old 01-02-2018, 06:46 AM  
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Re: System Sizing


Thanks for all the responses! The house is 1765 sq ft area upstairs/first level with an additional 750 sq ft finished basement. The other half of the basement/lower level is unconditioned garage. Half the basement/lower level is below grade. The house is on a slope with the front of the lower level being exposed. The ductwork is in between the two floors in conditioned space.
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Old 01-02-2018, 08:25 AM  
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Re: System Sizing


The cooling design temp looks a tad low. Double check your local historical temps. We use the highest temp that you'd see for 98% of the year.

Cheers!
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Old 01-02-2018, 08:32 AM  
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Re: System Sizing


The ductwork, does it currently run to both the upper and lower levels?
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Old 01-02-2018, 09:19 AM  
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Re: System Sizing


The ductwork supplies the upper and lower levels. Each branch has a damper if adjustment is needed. In the past few years I increased the attic insulation to R 49 and worked on sealing the attic penetrations. Thanks again!
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