@Jon, not sure where your
@Jon, not sure where your quote came from (not from this article), but the issue you refer to is real, and it’s not necessarily a thermostat/control problem. There are two issues at play… First, the air handler simply may not be able to modulate low enough to provide adequate latent capacity regardless of whose control is used. This is especially true for multi-splits, where there’s an inherent imbalance between blower capacity during single zone calls and minimum compressor capacity.

Not being familiar with the Cielo thermostat and controller, I took a quick look and it apparently mimics the IR commands produced by an OEM hand-held remote, so in that regard, it can’t fix a problem that’s inherent with the equipment.

BTW, other third-party thermostats typically rely on 24VAC relay control as opposed to the proprietary digital controllers sold with mini-splits (and virtually all other variable capacity systems). Relay-based thermostats should not be used to control variable capacity equipment as this forfeits the ability to track room temperature (google PID temperature control). At least the proprietary controller can operate the blower over its full range, whereas all a relay can do is turn the blower on and off.

The most extreme system we have done was a 5500 sq.ft. passive house conditioned with a single 2-ton air handler. Very pretty and worked just fine. That was the only time we’ve had the county inspector ask to see our loads!

Dave, as David Butler already

Dave, as David Butler already pointed out, I was wrong about the pressure drop across the coil and have revised the text above.  The system we’re using, though, is by Mitsubishi:

Outdoor unit:     MXZ-3C24NAHZ2

Air handler 1:     SEZ-KD18NA4

Air handler 2:     SEZ-KD09NA4

You can read more about it in the article I wrote about the load calculation and equipment sizing:

My Undersized Ducted Mini-Split Heat Pump

Richard, no, I haven’t had

Richard, no, I haven’t had that problem.  We went through the whole winter this year and the heating worked fine.  Maybe our ceilings (8 feet high) are lower than yours?

David, you must have missed

David, you must have missed the last paragraph.  That’s where I wrote about our living experience.  I probably will add dehu at some point but I want to see how well the system does without it this summer.

D’oh!  That slipped right by

D’oh!  That slipped right by me when I wrote the article.  Yesterday, though, it did occur to me that I’d made that mistake but I didn’t get back here to fix it.  I’ll do so now.