how bad is my ducted minisplit plan?

https://i.imgur.com/UbFITa5.png
red is the proposed airhandler, the green box is my current wall mounted minisplit that i would be getting rid of and that room is the bedroom i sleep in. i’ve never heard a concealed duct minisplit but they can’t be any louder than a cheap 12 seer single stage central ac, right? 🙂
dimensions are pretty accurate. room 2 is a bathroom, room 1 is an office room. the 21×21′ is the rest of the house, excluding a 6′ wall dividing .
https://i.imgur.com/p958z2b.jpeg
is the proposed location. i don’t mind sacrificing half of the cabinet, which is 24″ deep and 60″ wide in total. if i place it on the right side, i could also add 16″ of depth by stealing space from the reach in closet inside of the office room.
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in my head , i would do a vertical installation and have a single return in the hallway. the purple squares are the duct locations. room 1, 2, unmarked bedroom have 8′ ceilings and the 21×21′ room has 10′ ceilings.
it would be easy to do a drywall soffit above the door in the bathroom, that way the ducts for all 3 rooms + the return would be in conditioned space.
the duct that is in the 11′ room would have to go into an unconditioned attic and through the 8–>10′ ceiling height transition kneewall, but it would be less than 4′ and could easily be covered in insulation. 4′ doesn’t seem too unreasonable.
how crappy is this idea? think it would be possible to keep it between 30 and 36″ of overall width? that way i could place either a 24″ or 30″ RTA pantry to the left of it.
the condensate will have to be pumped into the attic and to where the old central AC drained to.
thanks in advance.
(akos, i need your big brain)
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Replies
First, what you have shown with the purple boxes are supply registers. There is no duct design here. There is however, a ducting strategy.
Do you have a basement or crawl space? If so, consider air sealing that space and putting the ducted mini and it's ducts there. If you don't, then consider a variation on your strategy
- Frame out a space in the attic that is essentiall over your hallway, but about 1' further north and 1' further south, and covering the bath entrance. Frame it to the same height as the big room, and put sealed drywall on the top and the plan north, west and south sides. The east side is already there at your ceiling height change. Insulate around this - you can displace the horizontal insulation over it now and put it over this pop up. Then you need to insulate the vertical sides. This area becomes part of the conditioned space and you install your ducted mini in it.
- Supply to serve big room needs to be at least two sidewalls, as far apart as possible
- Supply to serve Room 1 is ceiling mounted over the door or where you show
- Supply to serve the bath is ceiling mounted about where you show
- Supply to serve the current bedroom is ceiling mounted about where you show
You might need to do some reframing to get a large enough hatch to place the AHU. If you don't want to reframe for an access hatch, then build the pop up anyway and install only the ducts per the plan above, and install AHU where you show it.
Regarding the noise level of a ducted AHU, if the duct is properly designed and the thing is balanced, you should not have any issue - it should actually be much quieter than a wall head. However, it MUST be properly designed and the install must follow the design, and the unit adjusted accordingly. Consider hiring Energy Vanguard to do the duct design. They will calculate and spec length, size, turning radius, size of supply and cfm at each supply, size of returns, etc all as needed to fit your parameter
sorry, i 110% meant register locations.
i realize that actual duct design will be slightly complex, but for the most part i don't think it would make or break the space constraints -- of course i could very very easily be wrong. which is why i didn't bother trying to get too detailed about the ducting itself.
am on a slab, sadly. just an attic insulated with about 2.5' of cellulose.
https://i.imgur.com/Y0rZnmS.png
the green box would be the return grate, the purple would be duct going to the bathroom and other rooms. 8' ceiling, with an 80" pantry to the left of the air handler would leave about 12" of space for some ducts.
https://i.imgur.com/Nqi54X7.jpeg
the space i could steal from the reach in closet.
" - Frame out a space in the attic that is essentiall over your hallway, but about 1' further north and 1' further south, and covering the bath entrance. Frame it to the same height as the big room, and put sealed drywall on the top and the plan north, west and south sides. The east side is already there at your ceiling height change. Insulate around this - you can displace the horizontal insulation over it now and put it over this pop up. Then you need to insulate the vertical sides. This area becomes part of the conditioned space and you install your ducted mini in it."
that was also already a consideration. plenty of easy access. this might make you laugh. https://i.imgur.com/1ggIelP.png i used to have central AC, but for many reasons i got rid of the ducts. i don't regret it one bit, but i never patched over the opening for the old return.
it seems like the ducting would be a million times easier if the air handler is in the attic, and i'd get to retain the entire pantry. i have spent way too much of my life in my attic, lol. i'd almost sacrifice the pantry to not go back up there to re-frame the ceiling :(
thank you for the response :)
If you are in warmer climate, supply register locations are not as critical. Generally, for better winter comfort you do want the registers by the outside walls and preferably with decent throw to get air down to the floor.
An up flow ducted unit in the back of the closer as you show should work. Since there is a bath near by, I would do a gravity drain to the tailstock under the sink. Condensate pumps can work but I have much more faith in gravity.
The mini attic room suggested above can also work if you have the space. I like the closet better as it makes servicing a breeze.
A small run of duct into the attic is not an issue as long as you air seal properly. Make sure to encase the ceiling register boot in spray foam both to air seal and to keep it from sweating.
In the photo you posted of the old return you never patched, based on the walls on both sides, it looks like that area might be the small hall area? If so you have PLENTY of space there for both a mini split and it's ducts and you don't need to build an enclosure in the attic.
I'd put an up flow AHU in the closet cabinet, slid in like a book, with an oversize return (so things are quieter), and the ducts below the ceiling you show in the last photo so that everything is in the conditioned space, and then frame a ceiling below the ducts and be done...
Ducted minis are VERY small - mine are mounted horizontal but only about 8" tall. Look up the size of the indoor unit for the capacity you need. The ducts, if properly designed, are max 8" diameter; many of mine are much smaller.
Oh - patch the old return before you do all this to prevent air leaks into the attic
thank you both for the good ideas.
". Generally, for better winter comfort you do want the registers by the outside walls and preferably with decent throw to get air down to the floor."
ive lived with 2 wall mounted minisplits for a 1500 sqft house for almost 3 years, so i imagine that the winter comfort will only go up even if its not ideally installed.
i thought most of the concealed duct units were reversible -- horizontal or vertical, but that is not the case.
https://i.imgur.com/WhA1Pdq.png unfortunately the sink isn't in the right location for a 100% gravity fed solution :(
", based on the walls on both sides, it looks like that area might be the small hall area? If so you have PLENTY of space there for both a mini split and it's ducts and you don't need to build an enclosure in the attic."
yea, the gray cabinets and the unpatched ceiling are in the small hall area -- the gray cabinets are where the red box is on the drawing. the width of the hallway is 36".
https://imgur.com/a/B4UxIEc
after sleeping on it, seems i'd have two options for a horizontal installation without building out the ceiling in the attic.
option #1, mount the air handler to the hallway ceiling, have the return grill facing the floor from the ceiling. have the ducts go above the cabinets.
i'd get to keep my precious cabinet space, at the cost of losing about 12" of ceiling space for a small portion of the hallway.
option #2, mount the air handler directly above the cabinets, borrow some space from the offices reach in closet. i would not have to give up ceiling space in the hallway.
either of those two options would allow me to have minimal amounts of ducts in the attic.
even with those two options, i'd still prefer a vertical unit. but i am not finding any affordable options. theres a million options for 9-12k btu horizontal concealed duct units that heat down to -22f, for $1000-2000.
thanks again for the great ideas.
edit: yeaaa, im just lazy with the drywall. its actually airsealed pretty well from the attic. i had a blower door test done with that patch present and it was good.
There is never a perfect install option when doing a retrofit like this, sometimes you just need to pick one and roll with it. I would vote for a halway ceiling mount with a bottom return. This can feed into a trunk that you can run right along the bedroom walls to both ends of the house with a couple of takeoffs and maybe a longer run across the living space to feed all the rooms.
Midea/Carrier and Fujistu are the only slim ducted units I know that can be installed vertically. ie:
https://ashp.neep.org/#!/product/169564/7/25000/95/7500/0///0
I've installed the Midea ones, work very well. The only thing to keep in mind with those is the condensate pump is external and they don't show it on the drawing. Using the factory brackets it sticks out a fair bit on the side but can be rotated with a custom sheet metal bracket.
Find attached a pic of a hallway install. You can see the unit feeding into a box plenum with takeoffs to feed the rooms.
"There is never a perfect install option when doing a retrofit like this, sometimes you just need to pick one and roll with it"
yep, pick your poison etc..
probably going with a 9k or 12k senville unit -- rebranded mideas, but no vertical option.
https://ashp.neep.org/#!/product/62000/7/25000/95/7500/0///0
https://ashp.neep.org/#!/product/56519/7/25000/95/7500/0///0
only about $1000-1400, does -22f heating. the minimums are good enough.
i think no matter what brand/unit i go with or the installation location, that i'll end up with a slightly more comfortable home.
thanks for the install pic. i have a lot to read.
so while i havent really done any duct calculations yet , i am slowly getting the gist of it. seems like for a .20 wc air handler to work with 4 registers, there would be next to no margin for error and the return filter area would need to be pretty big.
am i understanding that correctly?
gree has a similarly priced unit that can do up to .6 wc -- has like 7 switches to change between .10 and .60, seems like the safe option given that this is my first attempt and my space is limited. but for noise reasons, it would still be best to design for the lowest wc possible, right?
These 0.1" units can be made to work but like you said, requires big ducts and filters.
I would go for the mid static unit but still design for low static pressure. Lower pressure means lower blower speed and much quieter ducts. Also bumps up the efficiency a bit as fan power is lower.
thanks again.
what about my thought process on this?
i sleep with the door closed with the wall minisplit, which screws up the house temps in winter and summer, since i also turn off the heat in the winter at night... as much as i need to sleep in a cold room, it sure sucks getting up and the house be way colder than it should.
the plan for this is to do a motorized damper for the bedroom, so that i can leave the heat on, but hopefully reduce most/all of the airflow to the bedroom with the door closed. then of course in the summer, i will leave the damper open.
when searching through minisplit posts on here, i've read that its good practice to install manual dampers for each duct, for fine tuning everything.
so in the case of me closing off one room entirely; should I do a motorized damper for two rooms? so that when bedroom damper is closed, open another damper to 100%, but if bedroom damper is open, maybe close damper #2 to 70% or something. placeholder numbers.
There is no issues with a damper on a room feed as long as you are not cutting off a large percentage of the total flow. This will slightly bump up the static pressure of the unit and will increase the flow on the remaining outlets. Most units have no issue modulating around this bit of flow change. No need for any secondary damper.
You also don't need to fully close the zone damper. These can be adjusted to be partially open which still allows a bit of flow. This is good if you are using the air handler to deliver fresh air to the rooms.
thanks again. at least that will save a little bit of money and wiring effort.
makes sense on adding at least some air circulation. i am getting pretty close to legitimately needing an ERV on top of everything :(
(thinking out loud for the most part)
above the cabinet is just a no go.
started to do some of the math(scary) and seems like i really need a 30x14x4" filter at a minimum, so between that and the supply air box, etc... the idea is to now build out the ceiling into the attic, remove the ceiling drywall entirely and install direct mount ceiling tiles.
possibly reframe a 16 oc joist to 32" for a larger filter if i really want to chase a super low static pressure.
solves all of the problems the other locations have -- cramped space, future maintenance issues, loss of cabinet space, loss of ceiling height.
and "started to do the math" means i asked chatgpt. ill check the work before committing to anything.
https://i.ibb.co/kJ8gmL6/image.png
That filter clac looks off. I've used a 16x25x2 on low static unit without issues.
Attic cubby can work, just make sure you size it big enough. You'll need much more than 3' to fit refrigerant lines, plenum and ducting.
For the intake, I've done simple return by converting the unit into a bottom intake and mounting a filter grill with a 1" spacer directly to the bottom of the unit, basically using the unit as the return. Since the fan is directly in view, it is a bit louder though.
>That filter clac looks off. I've used a 16x25x2 on low static unit without issues.
chatgpt has never been wrong in its life : )
going for bigger is more of an "easy" way reduce pressure to make up for my potentially poor elbows.
>Attic cubby can work, just make sure you size it big enough. You'll need much more than 3' to fit refrigerant lines, plenum and ducting.
the hall dimension is 8x3', the expansion in the attic can be be a bit wider. height is tbd.
i just put a lot of work into insulating the knee wall where the ceiling changes from 8' to 10'...
https://i.ibb.co/98cSV0Y/image.png
.... which is right above the hallway x)
re-work is always fun.
about to order something i think. these tariffs got me worried. saw this today https://i.ibb.co/Xfs3dK4V/qj4j0s7ghzge1.jpg
anyone have objections to https://ashp.neep.org/#!/product/155834/7/25000/95/7500/0///0 ? can do up to .6 static pressure, so plenty of room for error. i hope.
with a load calculation https://i.ibb.co/nsTPdyz7/image.png
i will still have a ductless 18k btu minisplit, which will eventually be replaced with a ducted unit.
decently accurate input on my part. with what i know was leaking in the initial blower door test and what i've done, i think the near 3.0 ach50 is actually realistic.
not sure how i should calculate a future ERV. that website has an input for ventilation CFM. if i have an ERV that is 70% efficient and is operating at 100 cfm, should i input 30 cfm into the load calculation?
the cooling loads for the office, bedroom, bathroom total around 9k, while the unit will modulate down to 3k for cooling. i haven't fully calculated the duct static pressure, but depending on how the numbers are, i would like to get a register in the laundry room. thats another ~1200 for the cooling load.
*some* of the ducts will technically be in the attic. but will build a net around them to hold cellulose and/or spray foam as needed.
seems like the 9k unit would possibly be pushing it, and an 18k unit minimum capacity isn't as great.
ty everyone for the help so far.
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hell yeah, love me some tote bags.
well, went with the gree.
more second guessing myself:
if i need 90-120 cfm/~2200 btus for the rooms, will possibly use some flex, and i won't be obtaining any super nice wide 90 elbows(idk what they are called).
will a 10x8x8 register probably be fine?
trying to avoid duct board, or having to go to a fab shop for anything.
https://www.homedepot.com/p/Master-Flow-GreenBoot-10-in-x-8-in-to-8-in-Pre-Sealed-and-Pre-Insulated-R-6-Register-Box-with-Installations-Rails-DTB10X8X8/202865430 seems like the easiest/cheapest option.
its a bit of a premium over an uninsulated box, but no duct board and ill only have to mastic & spray foam the joints/seams instead of the entire box.