What “Sensible Heat Ratio (SHR)” Really Means
Think of your AC doing two jobs at once: (1) lowering temperature (sensible cooling) and (2) removing moisture (latent cooling). SHR = sensible cooling ÷ total cooling. An SHR of 0.75 means 75% of the unit’s capacity goes to temperature drop and 25% to moisture removal. Lower SHR = more dehumidification. Many homes run into humidity trouble when their equipment has a high SHR (great at dropping temperature) but the house has a high latent load (showers, cooking, people, and fresh air). If your space gets cool but still feels sticky, the SHR isn’t working in your favor. Matching equipment and settings to your home’s actual mix of heat and moisture is the key to steady, comfortable humidity.
Latent Capacity: The Part That Dries the Air
Latent capacity is the horsepower your system has for removing water vapor. It’s measured in BTU/h or by how many liters per hour of water the system can pull from the air. Typical central ACs remove around 2–6 L/h, depending on size and conditions. Here’s what shifts that number: warmer, wetter air = more moisture removal; cooler, drier air = less. Long, steady run times help because the coil stays wet and keeps draining. Short cycling does the opposite—water re-evaporates off the coil during off cycles, and humidity creeps back up. If you consistently see high indoor RH even with a cold house, your system’s latent capacity is either too small for your load or it’s being underused due to setup and controls.
Typical SHR Ranges by System Type
Most central systems land somewhere between 0.65 and 0.89 SHR. Standard split systems and other unitary gear commonly sit in the 0.65–0.80 band, which gives decent moisture removal at normal settings. High-efficiency systems often show 0.75–0.85 SHR at their rated point, prioritizing temperature control. That isn’t “bad”—it just means you’ll want variable speed and smart airflow control to keep run times up and humidity down. VRF/variable refrigerant systems are flexible and can swing wide in how much latent they’ll handle depending on setup. The takeaway: don’t chase the highest SEER alone. Look at SHR and confirm the system can slow down and run longer when humidity is the problem, not just temperature.
Helpful resource: See our Sizing Guide for a right-fit starting point.
How Much Moisture Should You Expect It to Remove?
In real homes, you’ll usually see 20–35% of a central AC’s capacity going to moisture removal. On a muggy day, that can translate to 2–6 liters of water per hour going down the drain line. But that number isn’t fixed. If the entering air is cooler and drier than the rating point (say, rainy but mild weather), dehumidification can drop by ~21–25%. Likewise, if the system is oversized and short cycles, condensed water on the coil re-evaporates when the blower stops, raising indoor RH. Want better real-world results? Aim for longer, slower cycles, coil temperatures below the dew point, and ductwork that delivers the right airflow—not just “max airflow.”
If your condensate line barely drips on humid days, your system isn’t doing much latent work.
Why Modern Homes Still Feel Humid
Tighter, energy-efficient homes reduce sensible heat gains (great for bills), but moisture still comes from people, pets, cooking, showers, plants, and ventilation air. It’s common to see buildings with a load SHR around 0.50–0.60 meaning they need a big chunk of latent control served by equipment operating at 0.75–0.80. That mismatch causes the classic “cold but clammy” complaint. Outdoor air requirements for fresh ventilation can also add moisture that a high-SHR system won’t keep up with during mild weather. The fix isn’t to overcool the house (that just drives bills up). It’s to select equipment and controls that can hold ~45–55% RH under typical conditions without dropping the thermostat to sweater weather.
Comfort, Health, and Equipment Risks
High indoor humidity makes 78°F feel like 82–84°F, so you keep lowering the thermostat. That means more runtime, higher bills, and still-meh comfort. Worse, sustained indoor RH above ~60–65% invites mold, musty odors, dust-mite growth, and swollen wood. Electronics, flooring, and trim don’t like that either. On the flip side, getting humidity right helps your AC work at a reasonable setpoint, stabilizes room temps (less overshoot), and extends equipment life by avoiding aggressive short cycling. If your hygrometer regularly reads over 55–60% RH when the AC is on, treat that as a real problem to solve—not a quirk. A small airflow or controls tweak can make a big difference before you consider new equipment.
Sizing & Load Matching That Actually Works
Start with a Manual J load that separates sensible and latent needs. If your house’s latent fraction is high, don’t pick a unit that only shines on sensible. Consider smaller, variable-speed equipment that can run longer at low capacity. Target 350–400 CFM per ton as a baseline, then fine-tune. In muggy climates, slightly lower airflow (closer to 325–350 CFM/ton) often improves moisture removal by cooling the coil more deeply—as long as static pressure and coil performance remain healthy. Avoid oversizing “for safety.” That’s how you get short cycles, poor dehumidification, and comfort issues. If the load math says you’ll still be short on latent, plan on supplemental dehumidification from the start.
Ready to scope options? Visit our Design Center.
Equipment Choices That Dehumidify Better
Variable-speed (inverter) systems shine at humidity control because they can slow down and stretch run times. Match them with communicating air handlers and smart thermostats that support dehumidify-by-overcool (typically 1–2°F) when RH rises. Where ducting is tricky or zones vary, ductless mini-splits can help since they modulate deeply and run long, steady cycles. For packaged needs, look for units that support variable indoor fan and low-stage cooling. If you need an equipment refresh, consider modern R-32 systems with advanced controls. See Residential Packaged Systems (R-32)
Settings & Airflow Tweaks for More Moisture Removal
You don’t always need new gear to fix humidity. Try these pro-level adjustments first:
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Lower fan speed slightly (within manufacturer limits) to drop CFM/ton and cool the coil more.
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Enable dehumidify-by-overcool on compatible controls (usually 1°F).
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Use continuous fan = OFF in humid weather; it can re-evaporate moisture.
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Keep return leaks sealed; pulling humid attic/crawl air kills latent performance.
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Stage ventilation (or add ERV control) so you’re not dumping moisture during peak RH.
If you’re pairing new indoor equipment, check coil matchups and consider TXV/EEV metering for better low-load control. Need help? Our Help Center and HVAC Tips blog cover common settings.
Maintenance That Directly Impacts Dehumidification
Moisture control depends on airflow, coil temperature, and charge all maintenance items. Keep filters clean (check monthly in summer). Dirty evaporator coils act like a blanket, warming the coil surface and reducing dehumidification. A low or high refrigerant charge pushes coil temperature the wrong way; a quick check keeps the sweet spot. Make sure the condensate drain is clear if the pan floods, water can re-evaporate. Inspect ductwork for leaks and crushed flex that change airflow balance. Finally, confirm your line set insulation is intact so you’re not sweating refrigerant lines in humid spaces.
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Stock up on Accessories & Filters
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Need new piping? See Line Sets
When to Add Dedicated Dehumidification
If you’ve right-sized equipment, tuned airflow, and optimized controls but indoor RH still floats above 55–60% add dedicated dehumidification. Options include whole-home dehumidifiers tied into the return, reheat coils that let you dehumidify without overcooling, or desiccant systems in special cases (high outdoor moisture or ventilation-heavy buildings). This is common in coastal, mixed-humid, and basements where loads swing with the weather. In light-commercial or hospitality spaces, PTACs and VTACs with proper sizing and control settings can also improve latent performance.
Considering window or room units for spot control? Browse Window Units and Room AC
FAQs: Central AC & Dehumidification
What SHR should I target for a humid climate?
Aim for equipment and setup that deliver an effective 0.65–0.75 SHR under typical operation, plus variable speed for longer runtimes.
Why is my house cold but still sticky?
Likely oversized equipment, high airflow, or short cycling. The AC cools fast but doesn’t run long enough to remove moisture.
Is lowering fan speed safe?
Yes—when done within manufacturer specs. Slightly lowering CFM/ton deepens coil cooling and boosts latent, but watch static pressure and coil icing.
Does continuous fan help dehumidification?
Usually no in humid weather. It can re-evaporate water off the coil and raise indoor RH.
What indoor humidity should I aim for?
Keep 45–55% RH most of the time. Try not to exceed 60% for long periods.
Do mini-splits dehumidify better?
Often yes. Their deep turndown lets them run long and steady, which is great for latent control. See Ductless Mini-Splits.
Can high-efficiency units be worse at dehumidifying?
They can show higher SHR at rating, but with variable speed and the right settings, they usually control moisture well.
When should I add a dehumidifier?
If RH stays over 55–60% after proper sizing and setup, add whole-home dehumidification. Ask our Design Center for options.
