AC Condenser Misting Systems

Has anyone tried misters near/around the condenser unit? I think the theory is that the misters lower the ambient air temp a few degrees and should help the efficiency. I’d be interested is hearing whether this works or not.

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There are good physical reasons why this will of course work but there are reasons beyond the physical to carefully consider:

  • Using potable water (that often takes considerable energy to deliver to you) to then “save energy” is questionable.

  • Trying to make less-than-optimally efficient air-sourced heat pumps more efficient using water seems questionable.

  • In areas where evaporative cooling is very efficient (i.e. hot dry environments) water is often scarce.

  • Water-sourced heat pumps are great in, say, marine environments or when you want to heat a swimming pool in summer.


We hit 123F last weekend in La Quinta…humidity was around 13%. It doesn’t make much sense but water and electricity are very cheap here, compared to my other house in San Diego.

I’m trying to extend the life of my 3 AC units an extra year or two and wuld only need this to run for a few weeks when the temperatures are extreme.

You might be better off doing some indoor evaporative cooling and so raise your indoor humidity to more comfortable levels … I assume they are very low. That’s something you could continue to use after your existing system dies.

“3 AC units” but 1 compressor? If you needed 3 separate misting systems the costs and complexity (they need to be fed water + electricity) might be a little overwhelming.

I assume your outdoor unit/s are protected from direct sun? That’s a real AC killer. A simple awning can make a huge difference.

And here’s an organic idea: Take the mist system money and buy a large number of big pot plants and put them around the outdoor unit. Keep them well watered and plant them in the ground if possible. Thoughts?

3 AC units and 3 outdoor compressors. 2 on one side of the house that are in the sun, after noon.

I get what you’re saying but has anyone tried this and have some real data?

I thought about buying couple Mistboxes a year or so ago, but the reviews on Amazon were mostly quite bad. Several people noted that that Amazon reviews were for the Rev 1 version and that they were now on Rev 2. But the rev 2 can only be bought direct, possibly to alleviate Amazon reviews and to present only positive outcomes. Seems like the big issue is limited benefit vs. possible damage to your compressor due to minerals/etc. in your tap water.

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These things are supposedly notorious for either caking your condenser coils up with mineral deposits, or causing them to rot out via corrosion. I’d pass.


Commercial patio misters in SoCal typically have filters on the supply line. I’m guessing so the nozzles don’t get blocked.

I’ve seen exactly what @pswired mentioned before in the community, @2uskiwis. I believe the feedback was given by someone here that is very familiar with HVAC’s, who also happens to be a Sense community member. I specifically remember the dangers of corrosion and a before/after photo that someone shared. I’ll take another look and see if i can dig that up…

+1 to this point… To me it’s both the added corrosion risk, as well as the condenser coil dirtying quicker (more dust and particulate matter sticking to the wet coil fins). A dirty condenser coil is obviously less efficient, which would mean it would need to be cleaned more regularly to maintain peak efficiency. I once tried to contact Mistbox about whether they considered this potential con or had tested in real environments, but didn’t receive a comment.

The numbers Mistbox advertises are likely on a brand-new system within a lab under ideal conditions. I also echo another point I saw… these systems likely aren’t as efficient in humid environments (humid environments may also be more prone to buildup on the coils since less of the mist is evaporating therefore more moisture is pulled into the condenser). There are a few things you should be doing regardless to help make your AC more efficient… ensure filters are replaced, ducts aren’t leaking, ducts insulated when outside the building envelope, good airflow around condenser, condenser fins are clean and straight, system is properly adjusted & maintained, etc. For me, most important of all these was cleaning the indoor evaporator coil(s). Check these things first. There’s no point in trying to make your condenser reject heat more efficiently if heat absorption in the evaporator coil isn’t optimal. I also insulated the portion of the suction pipe that runs outdoors to the condenser to help reduce unwanted superheat. Not sure how significant of an improvement this made, but it can’t hurt.

My understanding is that AC condenser devices like Mistbox do have the potential to improve the efficiency of a split AC system, although with many caveats. A while back while looking to understand the effect of shading a condenser, I came across an experiment that looked at both shading and evaporation cooling (i.e. misting systems). The misting system had far more of an impact than shading did. Main finding was that the temperature of the air being drawn into the condenser is a lot more critical than the sun exposure. As ixu pointed out, they do consume potable water. So if the desire for improved efficiency is to be environmentally conscious, this is somewhat hindered - especially if you live in an area where water is more ‘valuable’ than others. There seems to be agreement that these system could potentially shorten the life of the condenser. So if the desire is to save on costs, then one would have to consider whether the savings in utility bills offsets the equipment maintenance & replacement costs.

Overall point… a misting system may not be for everyone. I personally may give one a try next summer if our landlord doesn’t replace our systems over the winter. The system at my place is nearly 30 years old, with likely only a few years max of life left in it. Corrosion from the mist system therefore isn’t a concern, water is relatively available, and I’ve exhaust all other options I’m aware of. If I end up getting one I’ll try to quantify the improvement using Sense data.


I just finished installing a three ton, four head Mitsubishi in my house. I had a one ton window unit and a portable roll around unit.

I’m not allowed to share screenshots but my watts usage dropped by half when i switched over. When the outside temp is low the humidity is higher than I like, turned the fan speed down and it helped.

ROI is probably crazy but I didn’t have central air and now I do. And it’s properly zoned. Much better than trying to zone a standard split system.

Another fun device is the AcuRite weather station. Didn’t buy a real fancy one, just five outside sensors and the broadcaster hooked up the the modem. I have it set up to measure outside temp in the shade of the north side of my house. I have the rest in the occupied rooms. So I can now monitor energy usage and comfort of my home. No comfort control online so it’s not real smart, but smarter than the average home.

I have a single Mitsubishi mini-split unit, the MUZ-FH06, for a small apartment and after using it mid summer in high humidity when the indoor humidity was building I realized that they have mis-programed (IMHO) the system to allow high fan speeds in DRY mode. Other models I have used just set the fan low automatically and lock out fan speed control. I have an Awair and an iQAir AirVisual indoors (Purple outdoors) to verify the humidity and it wasn’t until I switched the fan to low or “quiet” in DRY mode that the humidity was brought down. Of course it doesn’t work as well as a dedicated dehumidifier but the efficiency of the small units is hard to beat.

I dedicated a Sense to just the mini-split from day one and it’s been quite something to watch the power ramping at high resolution and see stuff like the air vane control motors NOT showing any wattage change in the waveform. Capacitors! It all feels super-smooth and I think challenges Sense native detection even more than, say, an OLED TV!

Hence, mini-split gets it’s own Sense; OLED gets a smart plug.

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Green Building Advisor has a write-up about these. Basically, it could take up to 28 years to break even before you start saving money.

You can simulate a mister by turning off everything in the house except for on ac unit. Get a nozzle with a mist selection. Take a baseline power reading over several minutes with no mist. Next, turn on the mist and spray the air around the condensing unit for several minutes. If you see a noticeable decrease in energy consumption, you’ll then want to calculate how long it will take for it to pay you back for what you’ve spend on the mister, consumables, water, etc.