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Community and Q&A

Sizing Mini Split Air Handlers for Upstairs Bedrooms

Type2 | Posted in General Questions on
Hello everyone – this website has been a great resource and I have tried to do my homework as best as I can before posting. I want to install mini split units in three upstairs bedrooms that have difficulty maintaining temperature control. I used the website CoolCalc to do room by room and block load Manual J. For the room by room I used two criteria: loose and a calculated ELA based on a blower door test.
 
I had two HVAC companies quote me a Mitsubishi mini split system. Company #1 quoted both a 24k condenser unit and a 30k condenser unit. The respective wall sizes for the 24k unit was 15k/6k/6k and 18k/9k/9k for the 30k unit.
 
Company #2 only quoted a 30k condenser unit. The respective wall sizes for the 30k unit was 12k/9k/9k. 
 
*********
Current HVAC System: Trane XL 14i Model #:2TTX4042B1000AA [14 SEER]
BTU: 42,000 or 3.5 Tons
 
Furnace: Trane XR90 Model #: TUX100C948D3; Input BTUH 100,000
Capacity BTUH (ICS) 93,000
*********
 
Quick background – I live in Kansas in a two story English Tudor style house built in 1933. Stucco siding, 2×4 framing with zero insulation in the walls. It’s a leaky house (which I am working on). Bedrooms are all upstairs. Large south facing wall where two bedrooms are located. The Master BR is located on the North side.
 
Last summer I had the attic spray foamed which helped bring the temperature delta (upstairs vs downstairs) from ~5-7 degrees to about ~2-3 degrees. So it made a difference, but for $5,000 I was hoping for more comfort control. They ran a blower door test: 3,402 CFM @ 50 Pascals 
 
Based on the blower door test I attempted to calculate Effective Leak Area (ELA) and Air Change Per Hour at 50 Pascals (AHC50). I am not 100% certain my numbers are correct which is why I ran two types of Manual J at CoolCalc – one using the “loose” criteria and one using the ELA number I calculated. The ELA number I calculated came in approximately 16% higher than “Loose”, so perhaps my ELA calculations are not completely wrong.
 
Manual J using “loose” and ELA 189
Master Bedroom Loose / ELA 189
Total Cooling BTUH 6,945 / 7,400
Total Heating BTUH 9,525 / 10,146
CFM 324 / 334
Sq ft 198
 
Bedroom #2 Loose / ELA 189
Total Cooling BTUH 4,192 / 4,487
Total Heating BTUH 7,090 / 7,494
CFM 194 / 201
Sq ft 165
 
Bedroom #3 Loose / ELA 189
Total Cooling BTUH 4,236 / 4,509
Total Heating BTUH 6,390 / 6,762
CFM 198 / 204
Sq ft 143
 
My goal is to eventually abandon the central air system completely. So I want to size the units as if there is no backup cooling or heat. In case you are wondering, I’ve done some rough Manual D calculations and to get the CFM required into the bedrooms would require that I add another duct into each room. The cost to demolish the walls and route additional ducting is cost prohibitive. 
 
I could install a 2nd central air system in the attic but that would also require a completely new duct system that is sized properly. The cost of equipment would be less than mini splits, but the cost of labor would easily outstrip the cost of mini splits. So, back to mini splits…
 
Question #1 – the CoolCal Manual J states the following:
Summer Outdoor F 95* 
Winter Outdoor F 10*
Summer Indoor 75*
Winter Indoor 70*
 
Does that mean I should look at the BTU Heat on the spec sheets for the air handlers at that temperature (10*)? If so, here are the specs off the Mitsubishi brochure:
 
BTU HEAT @ 47* / 17* / 5*
MSZ-FH06NA 8,700 / 5,900 / —
MSZ-FH09NA 10,900 / 6,700 / —
MSZ-FH12NA 13,600 / 8,000 / —
MSZ-FH15NA 18,000 / 11,000 / —
MSZ-FH18NA2 20,300 / 13,700 / —
 
*For some reason, the numbers on spec sheet @ 5* only state max capacity @ 47*
 
The 6k & 9k air handlers will modulate heat down to 1,600, the 13k will modulate heat down to 3,700 and both the 15k and 18k units will modulate heat down to 5,150. Pretty impressive range.
 
I don’t want to oversize and pay for capacity that I don’t need, but it appears if I did slightly over size the units can modulate down adequately.
 
—Quick recap re: Total Heating BTUH @ ELA 189—
Master: 10,146 
BR #2: 7,494 
BR #3: 6,762 
 
Based on my Manual J it appears that the 6k units in BR #2 & #3 might be slightly undersized at 10*, but that the 9k units may be spot on. For the Master BR it appears the 15k unit will provide enough heat at 10*, but the 12k unit may fall short on coldest nights.

My thought was to go with a 15k/9k/9k with a 30k BTUH compressor. But I am absolutely willing to save money and electricity (money) if I don’t need it.

 
I would appreciate any insight / thoughts / opinions.
 
Thanks,
Chris

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Replies

  1. Type2 | | #1

    Okay replying to my own question - apparently the Summer Outdoor 95* and Winter Outdoor 10* is selected by CoolCalc from the local weather station and 99% of the time will not exceed the summer temp or dip below the winter temp.

    https://support.coolcalc.com/hc/en-us/articles/360000845348-Selecting-Design-Conditions

  2. Josh Durston | | #2

    the FH06/09 wall mount heads only modulate down to 1600 btu when installed in a 1:1 config. When you use the multi head outdoor units, there is some modulation but it's much higher than 1600, it's based on the temp control and the fan speed, and the minimum of the outdoor unit (probably at least 6000 split between the zones). So don't size based on a high turn down assumption.

    Another question is what's going on downstairs, your upstairs often gets some assistance from downstairs due to convection.

  3. Type2 | | #3

    Thanks for the response Josh. The central HVAC unit is still operational for the time being - so the split system will be getting a boost but my goal is to eliminate / stop using the central air system. At night in the winter I'd like to reduce the heat downstairs into the mid 60's and just keep it warm upstairs. Opposite for summer at night.

    It would be nice to know what the Mitsubishi numbers are a 5* so I can size to that. Or I guess I can use the 10* and just size about 20% above. But like you mentioned I don't want to rely on turndown as a sizing metric.

    For the 2.5 ton MXZ-3C30NAHZ2 -- the brochure lists capacity heating range at 47*F 7,200 - 36,000 but at 17* the brochure does not list a heating capacity range, just rated capacity 18,000 / 16,500 which I don't quite understand.

  4. Type2 | | #4

    More info on the air handlers
    BTU HEAT @ 47* / 17* / 5*
    MSZ-FH06NA 8,700 / 5,900 / — (1,600 – 14,000)
    MSZ-FH09NA 10,900 / 6,700 / — (1,600 – 18,000)
    MSZ-FH12NA 13,600 / 8,000 / — (3,700 – 21,000)
    MSZ-FH15NA 18,000 / 11,000 / — (5,150 – 24,000)
    MSZ-FH18NA2 20,300 / 13,700 / — (5,150 – 30,000)

    BTU COOL
    MSZ-FH06NA 6,000 (1,700 – 9,000)
    MSZ-FH09NA 9,000 (1,700 – 12,000)
    MSZ-FH12NA 12,000 (2,500 – 13,600)
    MSZ-FH15NA 15,000 (6,450 – 19,000)
    MSZ-FH18NA2 17,200 (6,450 – 21,000)

    Manual J Total Heating BTUH @ ELA 189—
    Master: 10,146
    BR #2: 7,494
    BR #3: 6,762

    Manual J Total Cooling BTUH @ ELA 189—
    Master: 7,400
    BR #2 4,487
    BR #3 4,502

    If turndown is only rated at 1:1 -- is there a source for a multi-unit condenser and the turndown?

  5. Josh Durston | | #5

    Might be a bit overwhelming but the engineering guide has lots of good info including low ambient de-rating.
    https://nonul.mylinkdrive.com/files/M-Series_Engineering_Manual.pdf

    The rated versus is maximum, is the because when the test for the rated capacity they only run the compressor at 60hz, but with the inverter it's possible to run the compressor much faster enabling the higher max capacity value. The heating capacity is shown as non-ducted/ducted indoor units.

  6. Expert Member
    Akos | | #6

    Generally multi splits with dedicated wall mounts for each bedroom are a bad idea (I have this at home). It can result in terrible efficiency and comfort.

    The problem is that multi splits don't modulate as well as 1:1 units, in most cases the wall mount is either running at rated capacity or it is off, there is no modulation on the indoor units. This means that even a 6k wall mount is probably at least 3x oversized for a typical bedroom cooling load. Coolcalc tends to overestimate cooling load, so I wouldn't trust it much. There is no way a bedroom in an un-insulated house has a 7k cooling load. Maybe during the peak of the day with sun beating through the windows, definitely not at night time.

    Almost always the best solution for multi story min split installs is to install a ducted air handler upstairs to feed multiple rooms and a wall/floor/ceiling mount downstairs. Provided you size each correctly for the load, this can be made to work even on a multi split.

    If you have some runtime numbers for your existing 3.5 ton unit, you can get an idea of the overall outdoor unit cooling capacity needed. I would also do a wintertime heating load calculation based on your current heating cost to double check the results of any online calculators. Run through the steps here:
    https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new

    Once you have some realistic numbers, you can see which setup works best.

    P.S. Around me (hot and muggy summers) it is no problem to cool a 4 bedroom 100 year old uninsulated all brick house with original windows with a 2 ton multi split with a 9k wall mount on the main floor and a 18k ducted unit upstairs.

  7. Type2 | | #7

    Good morning Akos - I have attached a JPG image from my IotaWatt meter for the hottest day of the year in my location - July 18, 2020 (95*). With humidity the heat index was around 110*. The two longest cycles were at 3pm - 5pm (2 hours) and 5:10 pm - 7:40 pm (2.5 hours).

    The blue represents the outdoor air condenser unit and the green is the air handler. Obviously they track each other.

    We have our thermostat set to 74* - we'd like to have it around 72* but the AC would basically not stop running and we'd have a $400+ power bill, so we settle for ~74* and a $300 power bill.

    Temp upstairs last summer on the hottest day prior to the spray foam would hit about 82* with 40% + humidity. I have four thermostats that I put around the house. Prior to locating the thermostats I sat them all in the same room to make sure they all had the same readings. The deviation was under .1* - so pretty consistent. Can't guarantee accuracy.

    After the spray foam, this year we were ~77* while the downstairs was around 75* - so the spray foam helped but I was measuring the temperature upstairs in the hallway so it doesn't represent the southern facing walls which were likely 2-3* higher than that (easy). The two southern facing rooms both have very large single pane windows (old glass with that wavy look). You could fit a fridge through them.

    In July 2020 I installed an 8,000 BTU Midea U inverter A/C for the master bedroom (North side of house) which modulates down to ~1,600 BTU. You can see my comments and power numbers / cycling here: https://www.greenbuildingadvisor.com/question/new-midea-u-shaped-inverter-window-ac

    The 8,000 BTU was the perfect size as a backup to the central air. It modulated well at night and during the day kept the room dry and cool around 72* while not consuming much power. Our 6 year old slept in our bedroom all summer with us because her room (south side) was an oven that kept radiating heat during the evening and it simply could not shed the heat the concrete exterior had soaked up during the day.

    With no backup central air unit I can't imagine a 6k wall unit being 3x oversized based on our experience living in the house.

    Any thoughts?

  8. Type2 | | #8

    Akos - follow up - I read that link you posted. I also read this one: https://www.greenbuildingadvisor.com/question/mitsubishi-vs-fujitsu#0

    Incredibly incredibly helpful and informative. Thank you.

    I am still going to go with the mini split, but I have decided to run three 1:1 systems. Two 6,000 BTU MSZ-FH06NA 33.1 SEER units in the bedrooms and one 9,000 BTU Mitsubishi MSZ-FH09NA 30.5 SEER unit in the Master Bedroom.

    From my Manual J the Master BR should require - based on the 99% temperature of 10* F a total heating of 10,146 BTUH. The square footage is 198 sq ft. Even using the grossly simplified 25 x sq ft formula that everyone on her rails against - that would result in 4,950 BTUH.

    So - I am concerned that my Manual J numbers are higher than they should be. That also makes me comfortable going with a 9k unit as opposed to my original thought to run a 12k unit.

    The Mitsubishi MSZ-FH09NA 30.5 SEER will heat to 6,700 @ 5*, and will modulate in a 1:1 configuration between 1,700 - 12,000 BTU. So even if I overshoot by quite a bit, the modulation characteristics would indicate it would run at partial capacity and probably get close to the rated SEER numbers quoted.

  9. Expert Member
    Akos | | #9

    If your existing 3.5 ton unit is getting that much run time, you have some serious low hanging fruit. Based on the size of the bedrooms, my guess your place is around 1600 to 1800 sqft total. With ~500sqft/ton and the AC is barely keeping up means time for a bit of envelope upgrades.

    Generally vindow replacments are not worth it but in your case with large south facing windows it would pay in energy savings. I would look at some double pane units with low SHGC coating or at least install a set of coated storm windows.

    If you can add some shading to the south side, the lack of insulations in the walls will matter much less.

    If your walls could be dense packed, it definitely would make a big difference both for heat gain and air leakage. Problem is insulating old stucco houses has its challenges, more of a last resort unless you are doing major interior/exterior work.

    As for the mini splits, as long as you don't mind the extra outdoor units, the setup you propose would definitely work. Since you have a the power trace from the Midea unit, you can get a good idea of your actual bedroom cooling load. AcPower*AcSeer would get you into the ballpark.

    Most of the wall mounts can do a fair bit more cooling than their rated capacity. You can take a look here:
    https://ashp.neep.org/#!/product/25906
    https://ashp.neep.org/#!/product/25894

    Except for the max capacity, the specs on both are pretty close, so there is really nothing wrong with going for the larger unit.

    The combination of the 3 units upstairs, provided you leave the bedroom doors open, could probably do most of the cooling for your house, so it definitely would save a fair bit over the seer 14 unit.

    One thing to watch is the higher SEER rating on lot of the wall mounts comes at the cost of humidity removal. They modulate down the 1700 BTU but the CFM/ton there is very high, you won't get much dehumidification from the unit during shoulder season.

  10. Expert Member
    Deleted | | #13

    Deleted

  11. Type2 | | #10

    Hi Akos - I went back to the drawing board on the Manual J and took your advice re: wintertime heating load calculation. I followed Dana's instructions line by line and came up with a total house load based on my real world actual fuel usage:

    65 DEGREE BALANCE POINT 43,659 BTU/hr
    60 DEGREE BALANCE POINT 45,640 BTU/hr

    I also ran CoolCalc again taking Dana's advice to use parameters that assume much better insulation and a tighter envelope (I used tight with R11 insulation in wall cavities). The Manual J numbers for the whole house (room-by-room) are almost the exact average between the 65 & 60 degree balance point:

    Heating BTUH: 44,429
    Cooling BTUH: 38,431

    So, I think I can trust the new CoolCalc Manual J room by room data:

    Manual J Total Heating BTUH
    Master BR: 4,977
    BR #2: 4,294
    BR #3: 3,785

    Manual J Total Cooling BTUH
    Master BR: 4,861
    BR #2 2,925
    BR #3 3,054

    Other 2nd Floor Loads from CoolCalc Manual J *Total Heating / Cooling BTUH*Bath 1,801 / 1,445
    Hall 808 / 638
    Master BR: Closet 777 / 361
    BR #2 Closet 572 / 409  
    BR #3 Closet 70 / 31
    Linen Closet 4 / 24

    Additional 2nd floor Heating BTUH 4,032
    Additional 2nd floor Cooling BTUH 2,908

    Total 2nd floor Heating BTUH 17,088 (38% of total house heating load)Total 2nd floor Cooling BTUH 13,758 (35% of total house cooling load)

    This leads me to believe that the largest per-room air handler I would want to use is the Mitsubishi MSZ-FH06NA, and even that is oversized by 1.3x. So this certainly illustrates why a low/mid static single zone ducted mini split would be much easier to size for a single upstairs zone because you only have to take into account the 2nd floor as a whole and not by the room. With the modulation in a single zone ducted mini split it will always run at its most efficient. Once you start adding zones you really screw things up.

    That being said, despite all the evidence pointing towards installing a single mid-static unit, I am a little bit intimidated with the process of running a Manual D, calculating friction losses, fabricating ductwork, adjusting air dampers to get a consistent static pressure, cutting holes in my ceiling for load and return air and finding a place to put the air filter so I don't have to climb in the attic to change the air filter every couple of months. 

    The wife is strongly against the three 1:1 min split condensers mounted on our house. Perhaps I can come up with a design to conceal the condensers. So, in the meantime, I am back to looking at 3 zone multi-splits.

    The smallest Mitsubishi 3 Zone mini split that I am aware of is the Mitsubishi MXZ-3C24NAHZ2 -- a 24,000 BTU unit. From what I understand, it will "modulate" in 1/2 ton / 6,000 BTU/hr increments. Split among three heads, that means the lowest modulated cooling output would be 2,000 BTU/hr per head (2,400 for heat) and is pretty close to the 1:1 modulation of the Mitsubishi MSZ-FH06NA which is around 1,600 BTU/hr. 

    What I am curious about is if the Mitsubishi MXZ-3C24NAHZ2 will spend most of its time cycling on and off, or will it mostly run at the lowest 6,000 BTU/hr (2k per head). 

    Are there any 18,000 BTU 3 Zone condenser units out there I missed? 

    I am approaching paralysis by analysis so any thoughts / opinions would be appreciated.
    Thanks 

  12. Expert Member
    Akos | | #11

    The MXZ-3C24NAHZ2 is still way oversized. The min on it is 12000BTU, which is still above your design load for combination of the 3 bedrooms. This means that it will be cycling a fair bit on anything but the hottest/coldest days.

    You larger bedroom is within the size of a 6k head, so you are fine there, the issue is the rest.

    Could you find space for a slim ducted unit in a closet that is within easy access of the rest of the spaces? This would let you go down to a two zone multi split which would be closer match. Ducting is no problem as long as you make it large. Typical bedroom needs a 6" duct plus you can get pre-made plenum adapters such as:

    https://www.minisplitwarehouse.com/product/midea-front-board-duct-adapter-supply-plenum

    You never want the air handler in the attic. If all other options are exhausted, you can run some ducting there, but you need to be extra diligent about air sealing any holes through your ceiling. The air handler should always stay within conditioned space.

    Fujitsu and Midea also make ducted units that can be mounted vertically and almost all manufacturers make a high static unit that is pretty close to a standard furnace type air handler. These are a bit easier to work with as it is closer to standard ducting.

    For example, this unit with a 7k wall mount and 9k slim ducted unit would be a pretty close:
    https://ashp.neep.org/#!/product/33668

  13. Type2 | | #12

    Hi Akos - thank you for your response. I was looking at the Mitsubishi Product Catalog page 31/41 and under capacity range it lists 6,000 - 23,600 for Cooling non-ducted / ducted. So I was under the assumption that it could modulate down to 6,000 BTU, which is a far cry from 12,000 BTU. Not like I'm asking you to do my research for me, but do you have a link that shows the modulation limit is 12,000 BTU? That certainly changes everything.

    I will just remind (and anyone else) that my attic is foam sprayed and is essentially the same temperature as my upstairs within a few degrees. So it's not your typical attic.

    I will attach pictures of my attic.

    It's a long thread so I will also point out that I do have 3"x10" ducts (2 in Master BR and 1 ea in each other room). The problem is that the air trickles out right now and cannot keep up with the heat / cool load. I was initially thinking of putting the mid static units in the basement and running them up through the current ducts but they are super leaky. I excavated my kitchen ceiling (I replaced 3 compromised ceiling joists) and in doing so I noticed there are huge gaps between the ducts coming from the basement to the individual rooms.

    There is a linen closet in the upstairs hallway I could use but the wife would murder me if I got rid of the closet.

    There is a ton of space in the attic but I don't know how it would work logistically. That is why the wall mounted air handlers were so appealing.

    Thoughts?

    1. Expert Member
      Akos | | #14

      The 12000BTU is the min for the outdoor unit. You can find all the engineering data here:

      https://nonul.mylinkdrive.com/item/MXZ-3C24NAHZ2.html

      With an SPF attic, putting your air handler up there is a no brainer.

      You won't have to do fancy ductwork as everything is easily accessible, you can probably get away with a low static unit. Put the unit in spot where the bottom of if is above your 2nd floor hallway. Most units can be converted to bottom inlet and you can cut a slot in the ceiling bellow and use a large filter grill with a very small length of ducting as your return plenum. For the supply plenum it is best to get one of those pre-fab ones with round takeoffs. Ballpark would be to run two 5" (or one 7") ducts to your master, one 6" one to each bedroom and a 4" to the bathrooms.

      Make sure to run a small supply to your attic as well as it also needs a bit of conditioning.

  14. Type2 | | #15

    Thank you for the link to the submittal sheets. I dug through the single zone submittal sheets. From what I can see with Mitsubishi there is a PEAD series and KD series. The PEAD has the ability to operate a wider range of static pressure. It's also the most expensive.

    The Fujitsu surprised me. What I was shocked by was the huge turndown available on the Fujitsu unit. It also has the highest SEER & HSPF ratings. It's also significantly less expensive than the Mitsubishi unit.

    I am thinking with the wide turndown ratio that comfort may be better than with the Mitsubishi. The Fujitsu is only rated down to -5 vs the Mitsubishi -13. I don't think I will make my decision based on 9* for that .01% of time that may occur. The Fujitsu has what appears to be a more powerful fan than the Mitsubishi KD series, but not as powerful as the PEAD series air handler.

    I won't post prices, but I will say the Fujitsu 18RLFCD is $1,466 less than SE-KA18NAH (at ecomfort website).

    Is it just me or is the Fujitsu the most obvious choice for ducted mini split?

    Mitsubishi SE-KA18NAH $Most Expensive
    Condenser: SUZ-KA18NAHZ.TH
    Air Handler: PEAD-A18AA7 600 CFM (0.14-0.60 in. WG)
    SEER 18.9
    EER 12.8
    HSPF 10.8
    Heat -13 F
    95* Cool Rated 18,000 (Min / Max 9,320 - 18,000)
    47* Heat Rated 21,600 (Min / Max 8,800 - 28,000)
    17* Heat Rated 14,200

    Mitsubishi SE-KD18NAH
    Condenser: SUZ-KA18NAHZ.TH
    Air Handler: SEZ-KD18NA4R1.TH 635 CFM (0 to 0.2 in.WG)
    SEER 19.1
    EER 13.1
    HSPF 10.9
    Heat -13 F
    95* Cool Rated 18,000 (Min / Max 9,200 - 18,000)
    47* Heat Rated 21,600 (Min / Max 8,800 - 28,000)
    17* Heat Rated 14,200

    Mitsubishi SE-KD15NAH
    Condenser: SUZ-KA15NAHZ.TH
    Air Handler: SEZ-KD15NA4R1.TH 529 CFM (0 to 0.2 in.WG)
    15,000 / 18,000
    SEER 17.3
    EER 12.5
    HSPF 9.5
    Heat -13 F
    95* Cool Rated 15,000 (Min / Max 9,000 - 15,000)
    47* Heat Rated 18,000 (Min / Max 8,600 - 22,400)
    17* Heat Rated 12,200

    Fujitsu 18RLFCD
    Condenser: AOU18RLFC
    Air Handler: ARU18RLF 554 CFM (0 to 0.36 in.WG) [4spd]
    18,000 / 21,600
    SEER 19.7
    EER 12.0
    HSPF 11.3
    Heat -5 F
    Cool Rated 18,000 (Min / Max 3,100 - 20,100)
    Heat Rated 21,600 (Min / Max 3,100 - 25,600)

  15. Expert Member
    Akos | | #16

    In reality the efficiency difference between any of these will be noise for your overall energy costs.

    Any of the options above can work well for your application. Lot of times it comes down to which brand is better supported locally. For Mitsubishi it is always better to design for the KD series, the price difference is not worth it unless you are doing complicated multi-story ducting.

    You can also look at the 18K version of this, for some reason its not in the NEEP site. Excellent performance and price.

    https://ashp.neep.org/#!/product/30346

    Midea OEMs the mini splits for lot of domestic manufacturers, I think this might be the 18k unit:

    https://ashp.neep.org/#!/product/26057

  16. Type2 | | #17

    Well, then I should really go with Mitsubishi. Both of the biggest HVAC companies in town install and service Mitsubishi. One of them is less than a 5 minute drive. The closest Fujitsu is 26 miles. LG is about 30 miles away. Daikin is 31 miles away. Bryant has one in town (I think). Lennox / Gree in town but I don't know a lot about Lennox/Gree mini splits. I don't know if Midea is in town - they don't have a search function - I have to contact them directly. Carrier website says one in town works on them.

    When I got two quotes a few months ago I asked about getting parts. The guy told me that Mitsubishi has a stash of parts here in town and wait times are in the hours or next day.

    BTW he quoted me a grossly oversized kit:
    Condenser: MXZ-3C30NAHZ2 30,000 BTU
    Master BR: MSZ-FH12NA 12,000 BTU
    BR#2 MSZ-FH09NA 9000 BTU
    BR#3 MSZ-FH09NA 9000 BTU

    He also sold me a 3.5 ton unit for my old 1,400 sq ft house a few years ago. This was before I started doing any research and assumed bigger was always better...

    So, I think it really boils down to the Mitsubishi SE-KD18NAH vs Mitsubishi SE-KD15NAH

    The SE-KD18NAH has better SEER, EER, HSPF and can modulate to almost the same level as the SE-KD15NAH. I'd have a little more punch for the 99% cold weather.

    Thoughts?

  17. Type2 | | #18

    Akos, so I did a deep dive into the 18k Midea unit. It appears to have a significant price / performance advantage on the Mitsubishi & Fujitsu units ($436 less than Fujitsu @ hvacwholesaledirect. It claims to also heat down to -22* while maintaining 69% of rated capacity. The modulation range is also pretty decent. Like the Fujitsu it does horizontal or vertical installation.

    Midea Ductless DLFSDA/DLCSRA Single Zone Advantage Series Ducted System 18,000 Btu/h
    Condenser: DLCSRAH18AAK
    Air Handler: DLFSDAH18XAK 300/400/480 CFM (up to 0.4 in.WG) [3 speeds]
    SEER 20.0
    EER 12.5
    HSPF 10.8
    Heat -22 F
    95* Cool Rated 16,500 (Min / Max 6,000 - 18,700)
    47* Heat Rated 19,000
    17* Heat Rated 12,400
    100% heating capacity at 5° F
    69% of rated capacity down to -22°
    Heating Capacity Range (Min / Max 8,900 - 21,400)

    Air Handler info: http://woe.woeimages.com/webimages/DLFSDA_ducted_LS_9_24k.pdf
    Condenser info: http://woe.woeimages.com/webimages/DLCSRA_ODU_9_36k.pdf

    I'm going to call around to see if HVAC companies service these units.

  18. Expert Member
    Akos | | #19

    When it comes to installed cost the price difference between any of these units won't matter. Find an installer you can trust and install the equipment they are familiar with. This will get you a much better system in the long run than trying to save a couple of bucks.

    The items you want to watch with a ducted install:
    -make sure the drain is hard piped
    -outdoor unit mounted on masonry walls or ground. Never wall mount of wood walls.
    -hvac tech do both a pressure and vacuum decay test. R410 systems are very sensitive to moisture, lot of issues come from not doing proper purging of lines.
    -if they are doing the ducting, most likely it will be with flex. Make sure they install it properly (ie pull it straight, no tight bends).
    -make sure the return ducting between the filter and the unit are extra sealed. A good filter+no leaks means clean AC coil and blower for many years to come. The filter should be about 1.5x times larger than a standard HVAC unit.

  19. Type2 | | #20

    I don't know if I can trust anyone, honestly. The two HVAC companies in town tried to sell me oversized mini splits for $12,000. There are a couple more I may try. I suppose I could have them requote just the ducted air handler.

    I should be able to put in a Mitsubishi unit for under $5k by myself. The Midea unit I could probably do for about $3k. I plan on installing the air handler, all metal ductwork w/ mastic and tape, wall mount condenser to stucco siding, and run the disconnect / box. I will make a decision on whether to try to pull vacuum and flush the lines myself or have an HVAC tech come out.

    Great YouTube video showing a Fujitsu ducted mini split install: https://www.youtube.com/watch?v=ItYoS9Zp498&t=618s

    I appreciate you guiding me towards the ducted minisplits. I just need to make a table of all the HVAC contractors in town that can service Fujitsu, Mitsubishi & Midea.

  20. Type2 | | #21

    Hi Akos - in terms of condenser placement, when you mention masonry walls I am assuming that does NOT include stucco? I have a 1933 English Tudor style house and it's a stick built 2x4 frame with about an inch of stucco on the side. My research leads me to believe this is considered non-structural masonry veneer since it's not actually holding up the walls, etc --- and I would be wise to mount the condenser on the ground.

    Much appreciated

    1. Expert Member
      Akos | | #22

      You don't want to mount it on that wall. Stucco is not the same as solid masonry, chances are vibration from the unit will couple into the structure, very hard to deal with once there. I have tried to wall mount once on stud wall, spent a couple of days trying to get the noise down to acceptable levels, gave up and built a ground mount under the unit.

      Your best bet is ground mount. Make sure to keep it high enough off the ground to stay above max expected snow cover. The unit will make a fair bit of ice from defrost, so keep it downslope from any walkway/driveway.

  21. saltbox1771 | | #23

    Akos, ( and anyone else)what's your opinion pf LG equipment? I have a contact at a supply house that exclusively sells LG, so I can get a better price there - but not interested in that if the quality and efficiency suffers. I'm looking for cooling only on my 300 year old restored saltbox colonial which I restored 5 years ago, and I need some guidance on this situation.

    The house is 2 story (800 sq ft per floor) with a conditioned 400 sq ft space in the 3rd floor attic under the roof. It has R26 walls (R32 on new South facing wall) as well as R52 -58 on the roof - a combination of 6" foam over the entire roof plus additional polyiso on the inside as well as fiberglass between the new dormer rafters.

    My attic is thus conditioned so the air handler can go there (over the hall in the center of the 2nd floor), but because the house is a saltbox with dormer, the attic space is located above the 2 north facing rooms (on the front of the house). The 2nd floor center hall has a chase above it adjacent to the south side of the attic area. This seems ideal as the chase is between all of the north and south facing rooms of the 2nd floor.
    However, because the attic is actually used for storage and an office I MAY have specific challenges with routing ducts to the north side bedrooms. MUST the cooling output registers, routed through the attic, be located over windows along the outside(north) walls?The attic walkway runs between the BIG (8' square) center chimney and the kneewall on the north wall, while the air handler is on the south side of the attic. Since the house is 300 year old post/beam, the roof rafters are too shallow for overhead ducts. And, 2nd floor ceiling beams are below the attic floor, so duct runs are not possible there either. Routing ducts around the attic perimeter at floor level works, but results in longer runs. So what is the acceptable practice for the register locations and lengths of duct? Though the attic width is only 15', routing around the perimeter would require 13'+15'+13'=41' of duct to the center of the north wall registers - would that be too long? Placing the ceiling register in the center of the bedroom along the chimney wall would prevent that long duct run - so what's the norm for how far the register should be from the center hallway return plenum?
    From reading all of the GBA articles /comments/recommendations about mounting a single ductless minisplit in the 2nd floor hallway , you now see why I was excited to see that. But after subsequent reading, the slim ducted minisplit is more suitable for 2nd floor bedrooms with closed doors.. so once I can sort out the physical issues with ducting, the rest should be easier. I've already done the cooling load, so help with the above questions would be greatly appreciated.

    Note: After rethinking the duct question above, it may be possible to place 3" x 10" rectangular ducts to hug the roof after transitioning from the plenum - does that make sense? Though I'd have to remove polyiso to do that, there's still R39 on the outside of the roof.. and 3x10 is the same volume as 6" round.. Thoughts?

    Thank you in advance - Gary

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