Long-term solution for a humidity issue?
I am trying to identify a long-term solution to address high humidities in a recently purchased house. The circa 2015 house is almost 1900 ft2, including finished first and second stories and a walkout basement of which ~40% is finished. The basement was poured using ICFs (2.5” foam insulation on either side of the concrete walls) and has 2” of foam under the slab. The framed portion of the walkout basement was built using 2x8s and insulated with R-30 roxul between the studs. The walls on the first and second floors use 2×6 framing and include R-23 roxul between the studs. Currently, somewhere between R30 and R40 worth of blown in fiberglass exists in the attic, increasing this by topping things off with blown in cellulose is in the plan. The house is heated with a direct-vent propane heater, hot water is supplied using an electric water heater. I recently had a blower door test conducted and found an ACH of ~1.4. The house is located along the coast in Lubec Maine, zone 6.
RH readings in the house are oftentimes 20 points higher than outdoor readings, I don’t recall indoor readings less than 60% since last June or so (when I started taking some measurements using a $10 Acurite meter). Sources of moisture include two adults, showers taken with exhaust fans on, a couple plants, a gas stove/range (with no ventilation), and the great outdoors.
Three strategies have been identified/discussed to help reduce moisture levels including (1) run exhaust fans in one or both bathrooms 24/7, (2) run a dehumidifier 24/7, or (3) install a mini-split as the primary source of heat and rely on its capabilities to reduce the humidity. The bathroom fan approach relies on air being sucked in from leaks in the house and exhausts heated air. Given that it would be difficult to retrofit a full ERV/HRV, options like the Lunos products might be a useful refinement on this idea. I have seen mention on GBA of the Nexxt unit that ventilates at rates as great as ~50 cfm. Given the moderate to good tightness of the house the ventilation aspect would probably be a good thing. Therefore, perhaps 1-2 units of this type make sense.
Running a dehumidifier 24/7 doesn’t appeal to me and does nothing in terms of ventilation.
Heating the house with a mini split on the first floor would result in lower heating bills. Things I have read at GBA and elsewhere (some possibly outdated) discuss a dry mode that would help me deal with humidity in the summer (the mini split is likely to see little or (more likely) no cooling duties). I’ve seen mention (in a ~2015 post) of a Daikin unit that can help from a dehumidification standpoint during heating and cooling seasons, I don’t know if other units are on the market now. This approach doesn’t do anything in terms of ventilation.
So, that is my understanding of the pros and cons, please correct me where I am misinformed. Input about the best path forward would be greatly appreciated.
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