Over sized units!

[an3745]

A 3800 sqft house has 2-5 ton units installed by the builder in 1999. I think I can get by with 2-3 ton units.

[moideen]

A 3800 sqft house has 2-5 ton units installed by the builder in 1999. I think I can get by with 2-3 ton units.
hi an welcome to re.you mean 2.5 or 2+5=7.unit capacity will be governed by ambient temperature,internal load,heat transmission...........etc.

[an3745]

Total installed was 10 tons(5 tons +5 tons) and I want to install (3 tons + 3 tons) for a total of (6 tons)!

[install monkey]

best to oversize to allow for those extreme weather days, no point fitting a 3 ton unit that's gonna flog its nuts off trying to reach setpoint

[an3745]

I used Manual J to calculate the heat gain and it came out 45,462 BTUH. Therefore a total 6 ton of cooling is enough for the whole house.

[monkey spanners]

It would be wise to get a Manual J (or whatever its called) done to check the sizing needed, depending on where you are in the States, going oversized could lead to a cold clammy house as it meets the set point before it has dried the air enough, going indersized could mean it will never reach the desired temp.
Best get the advice of an experienced tech or company.

[dougheret0]

Monkey Spanner is correct, oversizing can cause moisture problems. Understand that the bulk of residential load is sensible, and ac units generally only deliver about 70% of their capacity as sensible, (assuming no outdoor air being induced directly into the unit). So six tons is still a little oversized. A trick to avoid moisture problems is to run your units at minimum air flow - 300 to 325 cfm per ton, or 900 to 1000 cfm for each unit. If you find you're not holding space temperature on the hottest days, you can always increase the air flow on either or both units, but I doubt you'll have that problem.