This is part of our Designing with ICF: A Technical Guide for Architects & Engineers.
Direct Answer: ICF homes are "Coolers." They hold temperature exceptionally well. If you size the HVAC system using standard wood-frame logic (500 sq ft per ton), the unit will "short cycle," satisfying the thermostat in minutes without removing humidity. This leads to mold growth and uncomfortable "clammy" air.
The Physics of the "Cooler Effect"
In a leaky wood house, the AC is constantly fighting heat gain and infiltration.
In an ICF house:
1. Conduction is negligible: The R-23+ mass wall stops heat transfer.
2. Infiltration is near zero: The concrete core stops air leaks.
The Result: The "Sensible Load" (temperature) drops by 60%. But the "Latent Load" (moisture) remains the same (cooking, showers, breathing).
The Engineering Challenge: You need a system that can run at low speed for a long time to extract moisture, without turning the house into a meat locker.
Equipment Selection: Inverter is King
Do not specify single-stage "on/off" compressors.
The Spec: Variable Speed (Inverter) Heat Pumps.
* Why: They can ramp down to 20% capacity, running continuously to scrub moisture from the air while maintaining a precise temperature.
* Brands: Mitsubishi Hyper-Heat, Daikin VRV, Carrier Greenspeed.
The "Shoulder Season" Danger Zone
In May and October in New England, the outdoor temp is 70°F (no cooling load) but it's raining (100% humidity).
* The AC won't run: The thermostat is satisfied.
* Humidity rises: Indoor RH climbs to 70%+.
* The Solution: A stand-alone specialized whole-house dehumidifier (like Santa Fe or Aprilaire) integrated into the ductwork. It manages humidity independently of temperature.
Ventilation: Build Tight, Ventilate Right
An Element ICF home is a sealed vessel. You cannot rely on "accidental fresh air" through cracks.
Code Requirement: ASHRAE 62.2 mechanical ventilation.
Our Standard: Install an ERV (Energy Recovery Ventilator). It exchanges stale indoor air for fresh outdoor air while transferring the heat/cool energy, preserving your efficiency.
