Thoughts on sizing for humidity vs. raw cooling speed?

I went thru this exact same thing when we moved into our place in Georgia. My brother-in-law convinced me to install a 4-ton Goodman unit beacuse he thougth more power was better for the humidity. It was a nightmare. The house woud hit 72 degrees in ten minutes, but the humidity sensor on my thermostat stayed stuck at 68%. I spent the whole summer feeling like I was living in a cold, wet basement because the compressor would shut off before it actualy dried the air.

Last year, I finally swapped it for a 3-ton Carrier with a variable speed blower. The difference is night and day. On those 95-degree days, the system runs for forty minutes at a time on a lower stage. Because the coils stay cold longer without the compressor constantly cycling off, it actually pulls out gallons of condensate. My indoor humidity now stays right around 45-50%, wich feels way cooler than a chilled room that's still soggy. Stick with the Manual J calculation and ignore your neighbor's bigger is better advice.

I acutally disagree that staying strictly with the "correct" size is always the win, expecially if your current unit is already struggling with that afternoon sun. I had a contractor do a Manual J on my house in Houston, and he insisted a 2.5-ton was plenty. But when we hit those brutal August heatwaves, the temp inside woud creep up to 78 degrees by 4 PM and stay there until sunset. The unit ran 24/7 and still couldn't maintain a comfortable environment.

Instead of just going bigger and dealing with the short-cycling clamminess mentioned earlier, I ended up installing a 3.5-ton Trane variable speed unit. Since it can ramp down to 25% capacity, it runs those long, slow cycles you want for dehumidification during the morning, but it has the extra overhead to handle the massive heat load when the sun is hitting the back windows hard in the afternoon. If you stick with a single-stage unit that is exactly "on paper" right for your square footage, you will likely be miserable on the hottest days of the year. Getting a slightly oversized unit with variable technology gives you the best of both worlds without the mold risk or the damp feeling.

I learned the hard way that windows are usually the real culprit, not the tonnage. My old unit was short-cycling like crazy but the living room stayed a furnace because of two west-facing sliders. Instead of upsizing the AC, I spent a weekend installing some high-quality ceramic window film and upgraded my attic insulation to R-49. Total game changer. Now my 'undersized' unit keeps the house at a rock-solid 73 degrees even in July, and the air feels crisp because it actually runs long enough to drain the condensate pan. Check your seals and insulation before you let a contractor sell you a bigger compressor.

Have you ruled out your ductwork capacity before you commit to a size change? Everyone fixates on tonnage, but I’m wondering if your current unit 'struggling' is acutally an airflow issue. If your ducts can't handle the CFM of a larger unit, you’re just going to end up with a noisy system that still doesn't cool those back rooms. Have you checked if your blower speed is actually set correctly for your climate? Sometimes a simple adjustment to the fan speed can fix that clammy feeling without needing a whole new machine.

Everyone overlooks the nuances of the sensible heat ratio, which essentially dictates the proportion of energy used to lower the dry-bulb temperature versus the energy required for dehumidification. If you install an oversized unit as your neighbor suggests, the evaporator coil will likely satisfy the sensible load far too rapidly, preventing the system from ever reaching the steady-state operation neccessary to drop the coil temperature below the ambient dew point for sustained latent heat removal. You’ll end up with a high-cycling compressor that leaves the indoor environment feeling like a cold sauna becasue the moisture never actually makes it to the primary condensate drain.

This is all way more complicated than I thought. I'm a total newbie here, so forgive me if this is a dumb question, but what exactly is a 'Manual J calculation'? Is that something I can do myself with a tape measure, or do I have to pay a pro to run the numbers? I'm also really curious about that variable speed thing. Does that mean the AC has like a 'low' and 'high' setting instead of just being totally on or off? If it runs for forty minutes at a time like you mentioned, does that make the electric bill go through the roof or is it actualy saving money because it's not working as hard?