replacing a 3 ton airconditioner

It would not be a bad idea to have it recalculated. I think I would have it done if you are not sure it was done before, however it is not likely to have changed, UNLESS you have added insulation or made other changes.

The Manual J calculations are very precise, but ultimately it comes down to a very unprecise choice of 3 tons versus 4 tons. It is always a big, rough compromise.

On the other hand, you may feel the old size cooled well, but you may not be properly critical. I would spend, say, $100 if I knew I was getting a correct analysis.

I would demand that it be calculated. While Richard is correct that there are only incremental sizes available, there is a 3 1/2 Ton unit in-between. Your unit does more than control air temperature, thus the term air conditioner vs. air cooler/heater. Any good company will change the unit ONLY after running the calculation since your comfort and satisfaction with the new unit should be a top priority.

- Robert

If a load calculation showed that the unit was oversized which could be the case with a unit that has cooled well, downsizing would have benefits. A smaller unit would run longer pulling more humidity and costing less to operate because of fewer starts. The higher efficiency units (above 12 seer) are dual speed or variable speed compressors to provide for a almost constant running of the unit. Where electricity rates are high the most efficient unit while costing more to install, save more than enough in energy to pay back the difference in a few seasons dependent mostly on the rate per Kw. With a heat pump your savings could be even more dependent on your heating requirements. Your local electric provider may be a source of lots of information on the best options for your area. It is always a good idea to confirm that equipment is properly sized and even more important when increasing efficiency.

Jolt