Mini split head – mounting location considerations
I’m interested in feedback on what must be a common dilemma with mini splits – where to place the indoor head unit when the best location for aesthetics, function, proximity to the outdoor condenser unit, and gravity condensate draining are often in conflict with each other.
I’m most interested in opinions about how much weight to put on a location that will not require a condensate pump – what are the issues there – but decided to open up the question further as these various considerations are probably a source of struggle to many people.
Thanks in advance for what I have no doubt will be quality answers from some very dedicated people.
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Replies
David,
This question comes up about once a month here on GBA. Most people who ask the question post a floor plan. If you can do that, it makes it easier for readers to provide advice.
Thanks for the quick reply, Martin. I am actually considering a mini-split installation for my own home but, as a contractor and owner of several properties, was answering the question generically. I realize that aesthetics vs function are factors that only the homeowner can place a value on. I was mostly curious about opinions about how big a deal it is to not have gravity condensate draining as that opens up several times the number of mounting options for people.
David,
I imagine that some GBA readers will post their opinions on condensate drains. In the meantime, these two articles include relevant information:
Net-Zero Homes Show Signs of Convergent Evolution
Rules of Thumb for Ductless Minisplits
Some people have reported having problems with temperature settings. It seems like units mounted too close (less than a foot or so) to the ceiling have trouble maintaining the temperature set on the remote. They end up installing a wall-mounted thermostat.
My inside units are mounted about 18" from the ceilings, but I have the advantage of high ceilings. IIRC, Fujitsu says you need 4" of clearance, but I think that's too close. The warm air pools near the unit and may screw up the temperature control.
Lots of people recommend placing the units close to the floor, but that can conflict with furniture placement sometimes.
In heating dominated climates it's worth considering the floor mount heads as opposed to the traditional air conditioning wall coils. With floor units there is a heating season efficiency & capacity advantage of pulling the coolest air from near the floor into the head instead of the stratified warmer air near the ceiling. This of course flips in cooling dominated climates, where it's better off pulling in the warmer ceiling air during the cooling season. The floor units tend to be thinner profile than wall heads too, and are low enough to place below windows, etc.
In cooling dominated climates, the best the place to attach the indoor "head" of a mini-split heat pump system is in a mechanical closet, connected to ductwork. That is to say, I think it's a BAD idea to use ductless mini-splits for a whole-house application in a cooling dominated climate.
Dear Friends at GBA,
Thanks again, you have helped me so much in the green journey! So I went ahead and went against orders- I am putting 5 mini splits in my 4000 sf 2-level 1900 vintage home in Maryland, which for my purposes, is moderate-cooling dominated. I did so despite having natural gas, because our ducts were so messed up by previous owners' contractors and the local HVAC company (sad to say they came out and claimed it was their work and wanted more $$$ to fix it!!!). It looks like the monthly bill is much cheaper (around $150, less than half the cost) than gas with bad ducts. But I can't say what it would be like compared to a properly designed home with proper ducts. I do have solar which increases the potential as well. And we have FAA's new NextGen airplane pollution, so I'm glad not to be putting negative pressure from badly designed duct systems to draw in more ultrafine particles in my home through all the leaks in the ducts and shell. It has a pretty bad stack effect which I will be working on next, and it seemed that the duct system was actually causing it because you can feel cool air coming through the basement returns like an air conditioner.
But I do have a question for the expert mini-split designer. My installer is a Mitsubishi diamond and put the split head in the middle of the kitchen (see attached) facing the short length of the room. But it seems to me like the warm air carries across and gets stuck on one side of a large kitchen countertop, whereas in other rooms where the head facing with the long axis of the room, it seems like there is much better warm air distribution across the room. I was wondering if it would make a big difference for my contractor to switch the location of the split head from A to B (see attached) which is centered at the end of the room blowing across the long distance? Now is the time to make the change if needed, while they are still doing the install!
Thanks,
Ken Phillips
Columbia, MD
Is this a multi-split, or 5 separate single zone mini-splits?
What size head are they calling out for the kitchen?
What are the design heat/cooling loads for the kitchen?
Is a ceiling cassette an option?
This is an 18,000 BTU size head with the hyper heat. It is also connected to another 12k upstairs above it. there are three doorways at the far right side of the room, two of which go to other rooms with the units in them ,another which is the entry hallway, which goes to the stairs, so there is some loss through there. I think they estimated with the manual J calculation something less than the 18k BTU like around 15 or 16, but the room has a 10.5 foot ceiling and quite a few windows on one end. Are you thinking to run two ceiling casettes, one for each side of the area that is divided by the countertop in the middle? That would seem to give the most even distribution in my mind. But then ductwork through the ceiling would create a lot of extra labor?
To be clear, are you saying that two indoor units are connected to one outdoor unit?
That's a lot of firepower for one room. Counter intuitively a smaller unit may actually make the room more even by lengthening run times. I think Dana was wondering if it was a single or multi head, because single heads (1:1) modulate over a fairly broad range, but multi heads tend to cycle on/off at close to their rated capacity, so oversizing a head is worse on a multi head system.
It's concerning you mention a manual J calculation was done and then go on to give some reasons to ignore it (big windows high ceilings), a properly done manual J calculation accounts for those things, so it shouldn't be necessary to oversize (there is built in oversizing already in the calculation factors).
The vanes do have directional options, and there is a setting to tell the unit if it's biased right or left on a wall. Don't leave the fan on low, put it on auto or high.
In multizone applications the indoor heads perform almost 1 size about their rating:
the 15,000 btu head is actually rated for 18,000btu heat
http://meus1.mylinkdrive.com/files/MSZ-FH15NA_For_MXZ_MULTI-ZONE_SYSTEMS_ProductDataSheet.pdf
the 18,000 btu is rated for 20,300 btu
http://meus1.mylinkdrive.com/files/MSZ-FH18NA_For_MXZ_MULTI-ZONE_SYSTEMS_Submittal.pdf
12,000 head is 13,600
http://meus1.mylinkdrive.com/files/MSZ-FH12NA_For_MXZ_MULTI-ZONE_SYSTEMS_ProductDataSheet.pdf
Josh has it right- a 1.5 ton head for a single room is overkill, and a real problem if it's on a multi-split compressor where the head itself doesn't really modulate. With big archways to the other rooms and mounted so that it directs air to those other rooms it might work. But seriously, did they even run a Manual-J? (And if yes, did they show it to you?) If the project hasn't been started you might put it on hold and get a third party Manual-J as a sanity check. That would be a lot cheaper than swapping out heads later to bring comfort levels in line.
A ceiling cassette blows in four directions, taking it's return air up from the center, which can make for more even temperatures across the room at low cfm. But the "throw" and cfm of a 1.5 ton head is substantial at anything but the lowest blower speed- you won't have an issues with uneven heating within the same room with just one head no matter what direction it's pointing. I have a relative who heats her whole house with a single FE18 head, and even around corners into the hall it stays pretty comfortable, but it can't quite cover the loads of the bedroom at the far end of the hall 40' away on the coldest days. But it probably would if it were directed down the hall and didn't have to turn the corner.
But make sure it really needs the 1.5 ton head before going there.
Both of the diamond contractors who came out recommended 18k units for this room. The room is about 25 x 20 feet (the drawing is not exactly to scale). I can say that its definitely not enough for the whole first floor except when it ramps up to really high blowing noise for a really long time (like hours). When it comes down real quiet on slow, it barely warms the area in front of it and everything else feels cold. And we are not even into the really cold part of winter yet. The home has a field stone basement with two crawlspaces and none of it has been sealed or insulated yet except the floor under the far side of the kitchen. So I've got a lot to address. It is also a fairly large home with 4,000 square feet and we are not heating the upstairs much past 64 degrees at any time, so a lot of it is probably going to heat the upstairs because of the inability to "zone" it out from the first floor. Once the other units are in, I hope that it will be more balanced. I wish I had hired a contractor and built my own, I'm sure the 18k unit would have done the whole house! But we did like the charm of the old house which is difficult or impossible to find in newer ones around here. It sound like there a lot of excellent green renovators up further north, but down in our area I've had a hard time finding people who really know what they are doing- most of them don't know anything at all, or just make up something convenient with a big price tag attached.
So is it heating the whole first floor or just the kitchen area? If there is no heat in adjacent rooms then yes, you have to factor in some of that load as well.
Sounds like an air sealing and insulation project would be worthwhile.
Do you have any pictures? or a floorplan?
Just because two separate contractors proposed the largest single head compatible with the multi-zone compressor doesn't mean either of them have it right. The nominal output of an FH18 head is over 20,000 BTU/hr, which for 500 square feet of space is a ratio over 40 BTU/hr per square foot. That's a really high ratio even for an uninsulated house with 10' ceilings. Most uninsulated houses would have load ratios under 30BTU/hr per square foot, many will be under 25 BTU/hr per square foot.
But every room and house is different, which is why there's no substitute for a third party Manual-J.
Yes, good point. Is there an inexpensive third party source for manual J? My contractor is claiming to have a proprietary calculator through a website called ductless america which is used by Mitsubishi.
>" My contractor is claiming to have a proprietary calculator through a website called ductless america which is used by Mitsubishi."
And he won't/can't share hard-copy of the report?
The public website page discussing load calculations isn't very confidence inspiring:
https://ductlessamerica.com/blog/choose-right-size-hvac-unit/