Tons per sq ft?

[Farmerstu]

How do I calculate how many tons of AC per sq ft I need?

[Hube]

You don't ...The tonnage (BTU's) required is derived from a cooling Gain/Loss calculation.(Manual J, etc.) Hube

[imeduc]

Get 3 bids for the job. Make sure they run a heat and AC load and loss for you .

ED

My mistakes dont define me they inform me.

[LazyPup]

As was stated by Hube, you cannot compute AC tonage by square feet. When a proper heat loss study is conducted they begin by taking each room one at a time beginning with square footage, then factor in the length of exterior walls and the type of wall constuction, frame & siding, masonary block, brick face etc.Type and quality of insulation in the walls, type of siding etc. Then you have to factor in the size of windows and doors, type of glass, type of doors, whether or not there are storm doors etc. next you consider what is under the floor? Another level of environmentally controlled space, basement with limited enviroment control, slab, raised foundation, etc, etc..The you examine the ceiling. Is there another floor of environmentally controlled space or simply an attic. If it is an attic you have to consider the type and amount of insulation, pitch of the roof and even the type and color of the roofing material. When one room is finished you move on to the next until you have computed the BTU requirment for the structure. Then you have to examine the terrain and landscaping. Is the house in the open or shaded by big trees? If in the open you have to allow for wind load based upon weather statistics for your region.

While many people guess at their tonnage based upon what the neighbor may have with a similar house, if a finite heat loss study is performed you would see that ten homes, all built from the same blueprint, by the same builder, in the same neighborhood could end up with totally differnet BTU requirements simply because one is out in the open, another under trees, one painted white and the other brown, etc etc.