Does misting an AC condenser save energy?

Yes, a little, and how much depends almost entirely on how dry your air is. Misting the air going into an AC condenser lowers its temperature, the refrigerant condenses at a lower pressure, and the compressor does less work. Measured results range from 2.8% energy savings over eight months on supermarket condensers in Florida to 22% on a chiller fitted with a wetted media pad in dry inland California. Three hose-fed residential misting kits tested in a Southern California Edison lab cut condenser power by 1.9-5.8% at 105°F. The 20-40% savings some kit makers advertise sit at the far edge of what the physics allows, on the driest, hottest hours, with a better device than a ring of mist nozzles.

Why does cooler condenser air save energy?

An air conditioner dumps the heat it pulls from the house into outdoor air blown across the condenser coil. The hotter that air, the harder the compressor works. Evaporating water into the incoming air lowers its temperature toward the wet-bulb temperature, the same limit that governs any misting system (see how misting systems work). No air enters the house, so none of the added moisture reaches the rooms.

The size of the effect is visible in SCE's 2015 lab baseline, a 4-ton packaged rooftop unit tested without any pre-cooler:

Baseline 4-ton rooftop unit, measured by Southern California Edison (ET13SCE1020, Table 7), indoor air held at 80°F

Outdoor air at the condenser	Power (kW)	Cooling delivered (BTU/h)	COP
75°F	3.49	50,782	4.27
82°F	3.69	47,801	3.79
90°F	3.94	45,746	3.40
95°F	4.12	43,656	3.11
105°F	4.52	39,255	2.55
115°F	4.98	35,186	2.07

Hotter air costs twice: the unit draws more power and delivers less cooling, so it also runs longer. Between 95°F and 105°F, each degree removed from the condenser air cuts power by about 1% and electricity per unit of cooling by about 1.8%.

How much does it save in your climate?

Two numbers decide it: the wet-bulb depression of your afternoon air (how far evaporation could cool it) and the effectiveness of the device (what share of that it achieves). SCE measured 8-25% effectiveness for three residential misting kits in 2012, and 20-80% for five commercial pre-coolers in 2015, with the best designs clustering at 60-75%.

Less electricity per unit of cooling, at the hottest hour, by climate and pre-cooler effectiveness (MistGuide calculation)

Afternoon air	Wet-bulb	25% effective (typical hose-fed kit)	50% effective	75% effective (best measured)
Phoenix, 108°F, 12% RH	69°F	98°F inlet, 18% less	89°F, 31% less	79°F, 40% less
Las Vegas, 105°F, 10% RH	66°F	95°F, 18% less	85°F, 30% less	76°F, 40% less
Sacramento, 100°F, 20% RH	70°F	93°F, 13% less	85°F, 22% less	78°F, 31% less
Dallas, 98°F, 40% RH	79°F	93°F, 9% less	88°F, 16% less	83°F, 21% less
Houston, 95°F, 55% RH	82°F	92°F, 6% less	88°F, 11% less	85°F, 15% less
Miami, 91°F, 65% RH	81°F	89°F, 4% less	86°F, 7% less	84°F, 10% less

How the numbers are built: the afternoons are the climate examples used across this site, with wet-bulb temperatures from the Stull formula. The inlet temperature is the dry-bulb minus effectiveness times the wet-bulb depression. The saving is 1 minus the ratio of COP at the outdoor temperature to COP at the cooled inlet temperature, read by straight-line interpolation from SCE's baseline table above. Check your own afternoon's wet-bulb in the cooling potential calculator.

Read this table as the best hour of the year, not the season. SCE's modeling across Southern California climate zones put season-long savings at 3-25% of energy for an 80% effective pre-cooler, and about 8-10% in its climate zone 10 example at 50-70% effectiveness, with peak-demand savings roughly twice the energy savings.

Is it "save 20-40%" or "barely 3%"?

The gap is climate, hour and hardware, and the 3% is the one measured where most homeowners asking live. Florida Solar Energy Center measured 2.8% energy savings and 3.2% peak demand reduction from air misting products on supermarket condensing units over eight months in hot, humid Florida. The report says hot and humid climates "can expect much lower savings compared to hot and arid climates," and names wind as a significant cause of diminished savings.

The large figures need everything to line up at once. The 22% at Beale Air Force Base came from a commercial media-pad pre-cooler on a 50-ton chiller in dry inland California, monitored from August 2 to September 9, 2012. It used about 0.9 gallon per day per ton. The 20-40% figure was a kit maker's claim quoted in a 2015 Green Building Advisor review, which found that the kit did not sense humidity at all.

A 2025 study from Chennai, India reported a median 29% saving from mist alone on a 1-ton split unit, while reporting an average temperature reduction across the condenser unit of only 1.2°C (about 2.2°F). If that is the drop in the air reaching the coil, SCE's lab curve values it at about 4% less electricity per unit of cooling near 95°F. Ask any savings claim for the inlet temperature drop behind it. The same logic explains why misting in humid climates disappoints on patios too.

Which designs work, and which ones wet the coil?

SCE's two lab programs tested eight products between them:

Condenser pre-cooler designs tested by Southern California Edison, 2012 and 2015

Design	Water on the coil?	Measured result	Water problem reported
Nozzles spraying directly onto the coil, pulsed by a temperature controller	Yes, by design	25% effective, 7.89 gal/h, 20% of water used for pre-cooling (2012); 20-50% effective (2015)	Scale on the unit within about 10-15 hours of well water; needs softened or RO water for continuous use
Mist nozzles inside a fiberglass filter wrap	Filter wrap meant to catch the minerals	20% effective, 4.94 gal/h, 31% used	Small orifices clogged with well water; worst after overnight shutdown; filters replaced once or twice a year
Low-flow mist nozzles on hose pressure, valve opened by condenser exhaust	Not stated	8% effective, 1.21 gal/h, 51% used	Same nozzle type, expected to clog; uses a scale-inhibitor cartridge
Spray onto 1 in polyester media in front of the coil	No	20-50% effective	Dry media cut COP 10.5% at 75°F when the water was off
Recirculating media pad (cellulose or polyester)	No	60-75% effective, 80-100% of water used	Needs bleed water, 10-50% more depending on hardness
220 psi mist evaporating before the coil	Not intentionally	60-75% effective, 55-75% of water used	Maker recommends softening or RO to protect the coil and nozzles

The cheap hose-fed kits were the least effective products in both programs, and the designs that worked kept liquid water off the fins. A home mister built from patio parts resembles the first three rows; for the droplet sizes behind that, see high vs mid vs low pressure.

Does spraying water on the coil damage it?

It fouls it. Evaporating water leaves every dissolved mineral behind, as a crust on the fins the air must pass through. In SCE's 2012 lab work, the kit spraying straight onto the coil was run for roughly 10-15 hours on non-potable well water, and scale became evident on the outside of the unit. The report calls it "a significant and expected concern for a design that sprays directly onto the coil." The 2015 report says the coil-spray design "requires water treatment such as softening or osmosis for continuous use."

The Beale report makes the opposite point for media pads: because evaporation happens on the pad, the coil "will not corrode, and will not become fouled by mineral deposits."

If your water is above about 7 grains per gallon of hardness, do not let tap water reach the coil at all. Treatment options are in hard water and water treatment. Nozzles on any of these kits clog for the same reason patio nozzles do, and the fixes are in clogged misting nozzles.

How much water does misting a condenser use?

Cooling 1,000 CFM of air by 1°F evaporates about 0.12 gallon per hour, from the 0.24 BTU per pound per °F that air gives up and the roughly 1,050 BTU per pound water absorbs to evaporate.

The same article quotes an engineer's mass balance of about 32 gallons per hour for this case. Evaporating 32 gallons absorbs roughly 280,000 BTU per hour, around six times the heat a 3-ton condenser rejects, so that figure cannot be the water evaporated. The 6.6 gallons per hour above is the ceiling for this airflow and air.

In SCE's lab, the three residential kits used 1.21, 4.94 and 7.89 gallons per hour on a 3-ton unit, and only 20-51% of it went into pre-cooling the air. At 7.89 gallons an hour, 6 hours a day for a 120-day season (an assumption) comes to about 5,700 gallons. Price your own figure with the water use and cost calculator, and check the local rules in misting during drought restrictions.

If you do it, how should it be set up?

1. Only in dry heat. Run it above a temperature threshold and below a humidity limit, not whenever the AC runs. A plain timer cannot do this; a controller with a humidity input can, as described in controllers, timers and humidistats. Green Building Advisor quotes Southface Energy Institute removing its office misters because "we could never get the controls to work properly."
2. Keep water off the fins. Evaporate on a pad or in the air ahead of the coil, never directly on it unless the water is softened or RO treated.
3. Remove or bypass dry media in mild weather. One media design cost the unit 10.5% of its efficiency at 75°F with the water off.
4. Drain before freezing weather. Outdoor lines and pads must be shut off and drained, the same as any winterized misting system.

When does this answer stop applying?

• Commercial rooftop units and chillers. With long run hours, treated water and maintenance contracts, the economics differ, and the authors of SCE's 2015 report recommended including pre-coolers in utility rebate programs.
• Heat pumps in heating mode. Every figure here is for cooling. None of the reports tested a heat pump's outdoor coil in heating mode.

For the other ways misting gets sold as cooling, start at the misting systems section.