The Hidden Cost of Owning Ductless Mini-Splits
Last week the condensate line on the wall-mounted ductless mini-split in my sunroom clogged. It didn’t take long to discover the problem because I saw water on the floor below the unit. Since that happened on a Monday, I turned the unit off for a few days so I could tackle clearing the line on the weekend. And, as almost always happens, this project turned into a bigger one…and it emphasized in my mind the hidden cost of owning ductless mini-splits that most people aren’t aware of.
What moisture does to ductless mini-splits
The reason it turned into a bigger project is obvious in the three photos below. Two years ago I wrote an article and made a video about my first time cleaning out this same ductless unit after four years of operation. It was foul! Watch that video, and you’ll see that it was far worse than this time. But it still needed cleaning again, so I couldn’t just clear the condensate line and turn it back on.
The two photos above and below show the condition of the blower wheel and plastic shroud. It may not have been as bad as last time, but it was still worse than I should have let it get.
But the photo of the drain pan (below) was gruesome. Look closely and you’ll see some nasty frass in there. The biggest pile of it is right at the opening that connects to the condensate line (red arrow). Maybe that’s part of the reason it got clogged.
I used the word “frass” above to ease you into the fact that it’s really roach poop. But you probably figured it out when you saw the roach leg. (See it?) We rarely see roaches in our house, but that doesn’t mean they’re not here. And the reason they hang out in the drain pan is because insects need water.
So, yeah, ductless mini-splits get nasty inside. I thought it was just dirt and microbial growth, but now I’ve discovered that it makes a nice little roach oasis, too.
How often do they need to be cleaned?
I found out two years ago that four years was too long to let them go. Clearly, letting it go for two years was still too long. Now I’m going to start doing it annually…but twice this year. Here’s why.
Since we don’t have to run it in cooling mode in our Atlanta winters, I’m going to clean it once more this fall. Mid to late October is generally when we stop cooling, so I’ll open it up again after the cooling season ends. That will be a good prep for winter, too, especially now that I know about how nasty the drain pan gets. I don’t really want to be breathing baked frass all winter.
Those of you in hot, humid climates (e.g., Chauvin, LA, Sopchoppy, FL, Corpus Christi, TX) probably ought to plan on twice a year minimum. The longer cooling season and the higher humidity levels mean there will be more water inside the ductless unit.
Method #1 to clean ductless mini-splits
Before I get into describing how to clean a ductless unit, read this:
A word of caution: I cleaned mine myself, and it worked out fine. But that doesn’t mean it’s a job for everyone. These units pack electrical components and circuit boards close to the coil, and water in the wrong place can fry them instead of cleaning them. Spray with too much pressure or at the wrong angle and you can bend the coil fins, damage the blower wheel, or even crack a refrigerant line. If you don’t have the right tools—and the patience to go slowly—this is a job better left to a professional who does it for a living.
In addition to the caution above, let me emphasize that step number one is to turn off the power to the unit if you’re going to do it yourself. Beyond that, there aren’t a lot of specifics in what I say below. If you really want to try this yourself, a good starting place with more details is the HVAC School page on cleaning a ductless unit blower wheel.
Now, let’s get started with method 1. In my 2024 article, I showed you how to clean a wall-mounted ductless unit with a special HVAC pressure washer (photo below). I don’t know that it’s easier than what I did, but if you’re going to clean the coil, too, you probably need a pressure washer. You also need a bib like the one in the photo below to catch the dirty water.
With this method, you don’t have to do a full disassembly. But if you don’t take the drain pan down and the blower wheel out, how will you know if you removed those dead animals or the glowing biofilms hidden within?
Method #2 to clean ductless mini-splits
Method 2 is what I did this year. I took off the vanes and the various covers. I let the drain pan down. Then I removed the blower wheel. That took a while. You’ve got to know which screws to remove and where the tabs are that hold some parts in place.
Once I got the blower wheel out, I took it into the backyard and gave it a good washing with the garden hose. That got nearly all the dirt off of it, but then I did a second round of spraying and brushing all the surfaces I could reach. As you can see below, it looks like new.
Before I could put it back into the unit, though, I had to clean all the filth—dirt, microbial growth, roach poop and parts, and biofilms—from the other reachable parts within. For that, I used a sponge and a bucket of water. You can see the drain pan below is now, if not sanitized, at least a lot more sanitary than it was.
Of course, the reason I opened the unit up to begin with was because of the clogged condensate line. To fix that, I got out my compressor and blasted air down the vinyl tubing a few times. A lot of crud shot out the end. (Helpful hint: It’s best to do that after cleaning all the crap out of the drain pan. Ask me how I know.)
After all the cleaning, I put it back together and turned it on. It’s been humming softly and keeping us cool for three days now with nary a problem. And yes, the condensate line is indeed draining again.
The cost of regular maintenance
If you can—and are willing to—do this yourself, you can save a bunch of money. I’ve done some research on this, and here are the fees I’ve found for two levels of service.
- Basic cleaning – filters, light coil rinse, condensate flush: lower end, $100–$200
- Deep cleaning – blower wheel removal, chemical treatment, antimicrobial sanitization, full disassembly: $200–$400 per head
What I did both in 2024 and this year would fall into the second tier. I didn’t do the chemical treatment and antimicrobial sanitization, but it was definitely a deep cleaning. Maybe I’ll add those things in the fall.
Ductless units come with an obligation—and a cost
If you’re thinking that ductless mini-splits are the answer to all your problems, you need to know about this extra maintenance required of them. If you have several of them, you might get a volume discount on the fees, but it’s still going to be a significant cost. Plan for it. And save for it, too.
Afterword: When we work with our HVAC design clients at Energy Vanguard, we often try to convince clients not to put ductless units in each bedroom because they’ll be oversized. We suggest going with ducted systems first and using ductless mini-splits only in places where it’s difficult to use a ducted system. We do a lot of ductless and ducted mini-splits in our HVAC design work at Energy Vanguard, so let us know if you’d like help with getting a great HVAC design for your home.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel.
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This is the hidden secret of mini split ownership and maintenance. They work great, but the ongoing cleaning is complicated and costly and needs to be done.
Yup. Important, expensive, and easily overlooked.
I suspect the roaches are climbing up the condensate drain to get into your home. I have had the same problem with critters getting into the condensate lines and clogging them. To address this, I use a shop vac at the outside to pull it clean at least once a year. I also put a touch of algaecide in the drain pan once or twice a year.
As far as cleaning, I have one unit I run in drying mode during the summer to act as a dehumidifier. It works great, but it also means the blower wheel is turning very slowly, making dust accumulation more likely. I had it cleaned earlier this year as part of a coil replacement (material warranty covered, thankfully, but not the labor). I need to do this more often .
I am also thinking of an insect guard to go over the outside lines.
Norman: I suppose that’s possible, but they’d have to be small roaches. I don’t think the large ones could fit in that vinyl tubing. But maybe I’m wrong.
TOTALLY agree with using a shop vac, wet/dry preferably, to clean out from the outside. Pour in water as needed from the top. If several units are attached to one outlet, one may have to block at the unit and open one at a time. Alison, putting pressurized water at the top may result in a flood in the water pan of a unit on a lower level, similar to a blocked sewer line event. Unfortunately some HVAC installers do not take basic plumbing lessons.
John: I didn’t use pressurized water. It was an air compressor, so it I just blasted some air down the condensate line.
Good morning,
Do you have geckos. Looks like gecko waste. my electric panels fill up with it.
All the best,
Louis Shiell
Louis: No, we have no geckos in our house…that I know of anyway. But we don’t have them outdoors either.
Allison – Would love to see you do a review of one of the new ductless units that claim easy cleaning (Bosch & Daiken Oterra series). Do the blower wheels and coils really snap out in under a minute in those units, and do those units make it possible for a regular homeowner to do their own maintenance?
The same can be said for window units. The new inverter models are great, but they require upkeep as does anything.
Were you able to verify if the line set hole through your drywall was effectively sealed and therefore not an insect highway? As in insulation contractor we recently inadvertently “dense packed” an inside high mount wall unit while insulating the empty wall cavity behind where the installer failed on this critical air sealing detail despite it being a program requirement for our state-wide efficiency program. Another critical detail for all installers that is perhaps frequently missed.
I’m also thinking that a small mesh screen at the outside end of your condensate drain line would prevent any ‘visitors’ from climbing up inside it. Also, a larger diameter drain line might help drain the condensate more efficiently. I use a small UV-C bulb and power supply in my cat fountain to kill algae and any microorganisms in the water; it’s designed for use in aquariums to kill algae. The bulb is waterproof and they cost about $20 on Amazon; they usually include a timer of some sort to control the bulb’s on and off time. Something like this in the condensate drip pan might help cut down on microbial growth in there.
I’m a broker and have a client with a mix of seven ductless and cassette-style Mitsubishi units throughout his 3,800 sq ft multilevel home. These systems were installed around 2013 as part of a major remodel and expansion of the house. He had moved to a new house and was in the process of leasing the home. One of the make-ready items was calling in his HVAC company to clean the systems, which he does annually. IIRC, the cost was something north of $1,000, and I was there for the cleaning. The ductless units require extra care to avoid making a mess while rinsing, as you show. A couple of these were located in the main living areas, and it was difficult enough to do this in a vacant home. I can only imagine the headache when furnishings must be moved and/or protected. I had considered the cassettes for my own upcoming remodel, but witnessing this convinced me to install Mitsubishi ducted systems (I have two).
Thank you for this!! It’s something I’ve been telling people a long time. I love my mini-split — maybe the best purchase I’ve ever made now that Seattle summers are actually summers lol — but it’s more than just vacuuming or rinsing out the filters once a month. I’ve cleaned it myself, but this year decided to have it done by the company that installed it because I wasn’t finding time. It was $900 for one indoor and one outdoor unit! (This is Seattle we’re talking about, so I’m sure prices are lower elsewhere.) We (I work for a utility) do a lot of work promoting this technology and looking for ways to make it accessible to people, but we’re still not addressing the ongoing costs. Thank you for doing just that!
Katie: It’s nice to find someone else who does their own cleaning. Seattle is a dry climate for cooling, but that doesn’t mean no condensate forms on the coil and drains into the pan. How dirty does your ductless unit get?
This article and these comments bring up another question: Other than changing filters regularly, what, if any, is the recommended maintenance for mini split ducted units? Certainly blowing out the condensate line so it does not clog, but anything else?
cal: The great thing about ducted units, whether they’re mini-splits or not, is that if it’s designed and installed properly, you should never have to clean the ducts or the coil. To get there, you have to have airtight ducts, especially the return side, and high-efficiency filtration with no bypass. A system like that doesn’t let dirt get in.
Thank you for the clarification!
I have never seen a unit that nasty that wasn’t an ice machine. FYI those get incredibly nasty and you really don’t want to know what’s inside the ones in restaurants. And yeah there isn’t much holding that drain hose on in any brand. Some imports now glue them to the pan. If yours isn’t glued at install I would glue it with Gorilla snot AKA 3m weatherstrip adhesive.
I’ll have to take pics of my 2 year old unit that has never been cleaned and there is no way it’s anything like that and it’s in a very dusty workshop. As for the drain hose. Depending on the install you can use Pex B for the drain line and a rubber coupling to clamp it on but only if it lines up nicely with your brand and install as it doesn’t bend. You can also use Pex B to extend a drain as it will fit tightly inside the drain hose. Not that leaky Pex A Uponor stuff that’s ruining houses.
The real hidden cost of minisplits is board replacements. They are often half the price of the unit if you can get them. I have found the best way to go is to buy certain cheap brands with an extended warranty. Some you can get parts for but the issue is that the unit costs as much as a typical service call with light repairs so they really aren’t worth repairing after warranty just swap it out and go on. Spending more on brands like Mitsubishi etc are not a cost effective way about doing it.
Our Mitsubishi is doing the same, I can’t figure out how to clean it. I did the shop vac suctioning from the outside, but that didn’t clear the clog and it’s only a nuisance drip at the moment. Probably gonna have to take apart the inside unit as shown in your pics and several online videos.
Thanks for that! I should have a look at ours with an endoscope attached to my phone.
Algicide tablets in the drain pan.
Ultraviolet light for the coil and drain pan.
Regular housing with self washing coil cleaner.
Since there is virtually no real filtration on most ductless units (despite the marketing), I have always believed that a separate, stand-alone air filtration system would be essential. My personal choice would be a variable speed blower powered, ducted system with near HEPA filters. Or, even better, the proven filtration-assisting COSATRON brand equipment.
Can you provide some brand options for this that might be more attractive than the box fan ones common during Covid? Something I could place near the head would be great.
My three ducted Fujitsu heads were nearly pristine after four years of operation in the Chicago suburbs. I have MERV 13 filters (with 1/4″ charcoal impregnated pre-filters) at the return air grilles with sealed ducts. I had been considering ductless minis at the lake house (double wide) when the 25 year old R22 unit dies but after seeing this article I am convinced to figure out how to install ducted units.
After thinking about it more I suspect your drain gunk issue has to be environmental. There has to be a large source of mold etc spores in thee structure etc that are being caught and flourishing in the drain pan. the older minisplit in my shop is near new looking and it has water pouring out of it like a fountain. It’s impressive how much moisture a minisplit can remove from the air. It also has allot more dust etc to deal with than one in a house.