<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Miles:
It could be the changes in EPA regs different coolants being used. I think the 13K units are marginal at best in any unit now. </div></BLOCKQUOTE>
The units still produce the same capacity....13,500 BTUH is still 13,500 BTUH. Back when people were converting, from R-12 to R-134a, you did see some loss of capacity due to the inefficient design for the newer refrigerant.
Roof top units are still R-22 for now. Manufacturers have tightened the margins of error on the units and build them to produce the capacity as noted and no more. I believe the unit are certified to ARI standards, so they have to make the rated capacity at the rated conditions within +/- 5%. Since this is a competitive market, they are going to push them toward the -5% side as it will save some money n the manufacturing process.
I do know for a fact that some manufacturers design and submit for ratings and then they catalog a rating that is +3% over actual. This still leaves them a margin of 2% error and still meets specs. The 5% number has been around a long time and I feel it should be tightened up a bit since we are capable of rating and designing to a much tighter tolerance.
So your 13,500 BTUH could actually be as low as 12,825 BTUH and still meet the rating requirements. Much like the truck tow ratings, it is a numbers game for the A/C market.
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