Cold-Weather Heat Pumps... But What About Dehumidification

Setting the Stage: Historic Buildings, Modern Goals

In 2024, HVAC 2 Home Performance was selected to lead the HVAC design, load analysis, and electrification feasibility study for a portfolio of affordable multifamily buildings in Cincinnati’s historic Over-the-Rhine (OTR) district.

These are nineteenth-century, double-wythe red-brick row buildings on stacked-stone foundations—constructed long before insulation, ductwork, or vapor barriers existed. Our goal was to determine how these historic buildings could be electrified cost-effectively while maintaining comfort, durability, and humidity control in a mixed, heating-dominated climate.

The study indicates a critical insight: in mixed-climate electrification, the challenge will not end with heating performance—it will begin with humidity management.

Weatherization: The Prerequisite for Electrification

HVAC 2 Home Performance also developed the predicted weatherization scope, which will include R-49 attic insulation, R-30 floor insulation above unconditioned basements, and aggressive air sealing targeting up to an 80% blower-door leakage reduction.

Design target: reduce modeled heating loads to roughly 5 tons (60,000 BTU/h) per unit before electrification is considered feasible.

If implemented as designed, modeling predicts these envelope improvements will cut heating demand by roughly 40–60%, setting the stage for heat-pump viability. This same improvement is also expected to shrink cooling loads more dramatically, creating a new design challenge.

The Electrification Paradox

As modeled heating loads approach about 60,000 BTU/h (≈ 5 tons), the corresponding cooling loads are predicted to fall near 24,000 BTU/h (≈ 2 tons). That difference would require a system capable of serving both extremes—providing 5 tons of heating while throttling down to 2 tons or less for cooling and humidity control.

Most available cold-climate inverters cannot modulate low enough to handle both conditions. At full heating performance they meet the winter load, but during summer their minimum capacity would still be near 2 tons, effectively operating like single-stage systems for cooling. The result would be short runtimes and diminished latent removal unless controls are carefully managed.

Equipment Availability & Modulation Limits (The Reality Check)

Modeling showed that one manufacturer’s data could theoretically solve the range problem—an inverter capable of roughly 11,400–60,000 BTU/h. However, that range would only be attainable with a commercial-grade controller not supported in these residential applications.

Outside of that configuration, none of the readily available systems provided the necessary turndown. As a result, the design team selected a strategy that sizes to the cooling load (≈ 3 tons) and relies on outdoor-temperature-based lockout logic to extend heating performance before auxiliary heat engages.

Predicted Heating Performance of the Selected 3-Ton System

Using manufacturer data for the 3-ton 37MUHA class with a compatible AH, the outdoor unit is expected to deliver approximately 42 kBTU/h at 32°F ODT, ~39–40 kBTU/h around 17–22°F, and ~32–35 kBTU/h from −13°F to 0°F (70°F indoor DB, ~1050 CFM).

AUX heat expectation: With a 15°F design target, auxiliary heat would likely be required during typical cold snaps (low-20s °F and below). With a −13°F coverage target, auxiliary heat would likely appear only in the coldest hours.

Cooling Performance & Predicted Latent at Part Load

From the same 3-ton cooling tables, the sensible-to-total (S/T) ratio is expected to climb as the inverter ramps down to match the smaller post-weatherization loads. That means latent capacity will diminish at part load. Tim De Stasio’s publicly shared field snapshot (from a different building) illustrates this behavior and aligns with our modeling.

• Near peak: total 35–40 kBTU/h, S/T ≈ 0.70–0.80 → latent ≈ 7–12 kBTU/h (about 5–9 pints/hour).
• Part load (~20–24 kBTU/h): S/T ≈ 0.83–0.95 → latent ≈ 1–4 kBTU/h (about 1–3 pints/hour).

There are no ventilating dehumidifiers in scope. Basement dehumidifiers are planned only to keep the stacked-stone foundations dry. Apartment humidity control will rely on the heat pump’s latent capacity and the control strategy described below.

Control Strategy for Commissioning

Heating Priority Below Balance

• AUX enable (W1): outdoor temperature below ~25°F and space temperature error > 15 minutes.
• Full strips (W2): OAT below ~10–15°F or time-to-setpoint > 45 minutes.
• Ventilation damper lockout: OAT below ~10°F (IAQ exceptions only).

Humidity-Biased Cooling

• If indoor RH > 55–60%, use lower fan (≈ 300–325 cfm/ton) and a colder coil target (dehum mode).
• If RH is acceptable, use normal fan (≈ 350 cfm/ton).
• Avoid the deepest turndown when RH is high; allow slightly longer runtimes to preserve latent capacity.

Predicted Unit-Level Load Reductions

All unit identifiers are redacted. Values below reflect predicted targets for weatherization-driven reduction; installations are now moving into the field.

Economic Outlook

With A2L cold-climate heat pumps, cost modeling predicts electricity will remain roughly 20–50% more expensive than gas heating below freezing. Permanent load reduction and intelligent control will be essential for long-term economics.

Why It Matters

The OTR project demonstrates that electrification will work best, and sometimes only work when load reduction comes first; comfort will only last when humidity is controlled; and efficiency will only matter when systems fit the building.

Cold-climate heat pumps may solve most of the heating challenge. The next frontier is managing humidity and operating cost in high-mass, mixed-climate envelopes.