Ventilating dehumidifier to complement mini splits?
After getting a trio of single-zone Mitsubishi mini splits last summer we’ve had a tough time controlling humidity in our 1200 sqft home. Total cooling BTU is 24k – a 6k and two 9k; We sized above the roughly 18k BTU cooling the Manual J called for to account for additional winter heating load.
With a summer and a half of testing, it seems like there are a specific set of climate conditions that overwhelm the Mitsubishis: cool-to-moderate (75-85ºF outdoors), cloudy, and damp. Unfortunately these conditions make up a fair chunk of our summer weather in southern Ohio, with our county on the boundary between Zones 4 and 5.
In these conditions neither “cool” nor “dry” modes make much of a dent in indoor relative humidity, which can stray as high as 70% and routinely sits in the 60-65% range. I’d like it to stay pegged around 50% if possible. I’ve reduced fan speed and tried turning off a unit to test for it being an oversizing issue, but these tweaks haven’t made any difference.
The house is a relatively recent build – late 90s on the original structure, mid-2010s on an addition. In spite of this the older part of the house is quite leaky: 2×4 stud walls with fiberglass, no crack sealing, no house wrap. The addition is much tighter, but connected to the old structure on an open floor plan. We’re under a lot of tree cover, and three stories with a shed roof probably leads to strong stack effect. I realize that better windows, insulation, and sealing in the old house are probably the long-term solution, but these improvements aren’t in the cards for at least a couple more years.
At the moment, my idea is to connect a ventilating dehumidifier with a fresh air inlet to an existing duct system that used to do distribution for a gas furnace – the house could also use more positive fresh air ventilation than it currently gets. I’ve looked at the Santa Fe Ultra70 and the AprilAire E070 or E080.
My questions are: is the above a smart strategy, or are there other, better approaches? And if a ventilating dehumidifier is the ticket, would one of the models I note or a different one be a good choice?
Thanks in advance for your help and advice.
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