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Community and Q&A

Maintenance for ducted minisplit heads

maxwell_mcgee | Posted in Mechanicals on

Designing a new house in Southern Ontario (Zone 6a).

We’re thinking through HVAC design for the home, and we’re inclined towards a multi-split system to provide for both heating and cooling. 

We’re considering the Mitsubishi “Zuba” (which I think is just the HyperHeat branding in Canada) system multi-split system, with low- or medium-static in-ceiling ducted units with ducts to the rooms. 

We want to achieve some zoning, and want to split the upstairs (~2000 sq. ft) into a minimum of two zones (North-facing bedrooms in one zone, south-facing bedrooms in another zone). Right now the thinking is that we have one in-ceiling unit for each side. We’ll also be adding zones to the lower level so likely multiple medium-static heads downstairs also. 

I’ve read about the maintenance demands of the wall-mounted minisplit heads which seem quite intense due to build up of dirt and mold (!) — but tearing down and cleaning the fan coils every 6 months sounds exactly like something I’ll never end up doing. 

What are the maintenance demands like for these in-ceiling units? Are they the same or different than the wall-mounted heads?

I don’t mind changing filters every few months. But tearing apart and cleaning fan coils is a serious turn-off and would push me towards using a larger single centralized air-handler system. At least then i only have to perform maintenance on one indoor unit instead of 4-5. 

In terms of my priorities, I would rank them as (1) comfort (2) ease of maintenance (3) efficiency. 

Any thoughts or lived experience would be helpful!

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Replies

  1. mgensler | | #1

    We have the Fujitsu ducted and ductless mini-splits. They have been installed for a year and so far it's just changing the filters on the ducted and cleaning the filters on the ductless indoor units. I think the whole breaking down the indoor ductless might be a bit over stated. I see these things running in all kinds of dirty places, half hanging off the walls, and covered in dirt and grease. Unless you are in a very dusty or dirty place I wouldn't sweat it.

    The outdoor units on these do require periodic cleaning which requires some of the sheet metal panels removed and coil cleaner sprayed in them then hoses out.

  2. user-5946022 | | #2

    Interesting question. I have never seen this discussed on GBA. I've read through the manual on my Mitsubishi ducted and don't see anything about this. An estimate on cleaning the fan coils of my ducted units was over $1k for three units. NO WAY am I doing that annually. I change the filters religiously, and tape the edges with blue tape as recommended by Allison Bailes. Would be happy to do any other basic PM such as that if I knew what it was...

    So what is the recommended maintenance? I'd love to learn more about this outside unit maintenance.
    1. What are others with ducted mini's doing for maintenance of the indoor units?
    2. What is everyone with any type of mini doing for maintenance of the outdoor unit?

    1. STEPHEN SHEEHY | | #3

      We have the installer clean the indoor and outdoor units of our ductless minisplits every two years. It's around $200 per split, including replacing the inside filters.

  3. ohioandy | | #4

    Maxwell, in my home I have a Fujitsu ceiling cassette and a Fujitsu mini-ducted mounted up by the ceiling. The former is primary heat and cool, the latter is upstairs and used only sporadically. Both are using ONLY the onboard filters, which must be cleaned every couple months at least. I cleaned the coils last year, finally, after about six years. They were both kinda gunked; still probably with 80% of airflow but these units are gentle brainy things and it seems a shame to let them get hobbled like that. Cleaning every year would be overkill, but probably don't let it go more than four. All depending on your environment, of course. And incorporating a second filter would be a great way to reduce--not avoid--the problem.

    I've never cleaned a wall-mount, but I assume these units aren't any harder. In both of mine, all access is from the bottom. Pop out a few screws and the housing comes off, then the rigid foam drip pan can be wiggled out which exposes the coils.

    Of course the fins are too delicate to do any scrubbing. There are expensive foaming products specially marketed for this, but the big box stores sell inexpensive versions. The idea is to get it in an aerosol or spray bottle so you just spray on and let it do the work. Have something below for the filthy suds to drip into. Repeat if necessary, then spray with rinse water. After the initial learning curve, I can't imagine the whole process taking more than an hour per unit. I sure wouldn't pay someone $200 each, but we all have our tolerances.

  4. maxwell_mcgee | | #5

    Thanks -- super helpful responses.

    I think cleaning these things out once every ~4 years feels reasonable. Annually or 2x per year feels ridiculous.

    I'm planning on installing a Zehnder Q ERV with HEPA filtration for ventilation air, so am hoping the dust levels in the house will generally be kept under control through that. But maybe will also ask my engineer to design the return ducts for these in-ceiling units to include some type of ~MERV-8 pre-filters that can be easily changed out to keep some of the bigger dust/dirt particles from getting into the duct network and hitting the interior units in the first place.

    Welcome thoughts -- especially on the pre-filter idea. Any unforeseen ramifications I'm not thinking of?

    1. user-5946022 | | #6

      I'd be concerned about the static pressure. I'm no expert but I think these things are very sensitive and probably not made to operate forever with 2 filters. I guess it would also depend upon how big your prefilter is.

      Mine operate only on a filter at the return duct (at least I think they do - the entire box of the ducted mini is sealed up with white duct seal, so no metal piece to remove to change a second filter). The advantage of this is it is much easier to access.

  5. Expert Member
    AKOS TOTH | | #7

    The maintenance on a ducted mini split with a decent return air filter, not just the mesh that comes with a unit, would be no different than a standard furnace. In most cases it means the coil never gets cleaned unless the coil plugs up. Making sure the return is tight, that means no panned returns, installing an oversized Merv 8 or higher filter should make it maintaince free.

    I have a bunch of wall mounts used for cooling only in rental units, some now coming up to near a decade old. They only needed service when the drain got clogged, this seems to happen about 4 to 5 years. A ceiling mount unit has a similar intake filter, so I would expect it to be similar issues. Yearly cleaning is not needed, but I would budget every 5 years or so.

    The one issue that a lot of people might run into is the typical oversized multi split install. These inevitably end up with a lot of on/off cycling on the indoor units which means re-evaporation of condensate on the indoor coil. If the coil is dirty, this can start to smell pretty quickly and be quite noticeable. In that case, the units might need frequent cleaning well before they clog up.

    For a house, you want no more than two ducted units, these should be installed with well sealed returns and quality filters. I would avoid any additional wall/ceiling mounts, maybe only for that don't get a lot of use. Fewer units, fewer headaches.

    1. maxwell_mcgee | | #8

      Thanks, Akos.

      This makes sense to me, and the idea of only using two ducted units each with its own dedicated outdoor unit seems to get around a lot of the issues associated with these multi-split systems.

      The problem I have then though is how do you achieve any type of zone differentiation? E.g., upstairs we'll have bedrooms facing North and others facing South. I expect the south facing rooms will have pretty different heating/cooling demands than the North facing ones. Not to mention different temperature preferences for the occupants of each bedroom. If I use a single ducted unit for the upper floor where the bedrooms are, what happens?

      I remember reading about issues with the Mitsubishi and AirZone duct dampening system working well together ( https://www.greenbuildingadvisor.com/question/a-warning-and-a-question-about-mitsubishi-zuba-zoning ) and I learned from my HVAC engineer that Mitsubishi no longer supports that system in Canada. So if i can't do automated duct dampening, then do I just resort to a smart vent cover system like Flair to achieve the zoning I want?

      And also what is the general consensus on what to do about basements? Do people just not bother to cool them and then run space heaters as needed down there in the winter? Or does installing a dedicated split system for the basement still make some sense?

  6. user-5946022 | | #9

    I too have areas facing both north and south served by the same ducted minisplit unit. It seems to work well for me, which I attribute to a professional HVAC design that took room size, quantity of windows, wall orientation, etc into consideration. ie - everything that would impact the load on the HVAC system was taken into consideration when sizing the ducts and determining the cfm of conditioned air to feed to each room at the diffusers. Very comfortable and no zoning needed.

    I'll note this only works well if you air seal well. Any leak will significantly impact comfort.

  7. joshdurston | | #10

    My Mits Wall mount is gross after two years (should've cleaned it last year). I'm waiting a couple week until cooling season is over to clean it. It's tolerably while running in cooling, but if it cycles off to fan only it smells something like dirty socks.
    The combination of the fan after the coil, and poor basically mesh filtration on wall mounts is a double whammy that doesn't apply to ducted units.
    In the future I think I'm going to put a some filter media on the air inlet and see if that helps.
    I'm also advising friends and family to avoid ductless heads wherever possible. Not just for cleaning, but for proper air distribution. My ductless head heats fine but on really cold days (below -15C) a point source of heat that moves air can't compete with ductwork for comfort.
    The cleaning wouldn't be a big deal if they units were designed for disassembly, but to take them apart feels like taking apart a cheap kids toy made of flimsy plastic. Not sure why these things are made to be services by the homeowner (the fan should just pop up for a cleaning IMHO).

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