Adding a room to your home is exciting until you realize your central HVAC system was never designed to reach it. That was my situation two years ago when we finished a 450-square-foot addition above the garage, and the quotes to extend our ductwork came back at more than the framing cost. That is exactly the problem the best mini split air conditioners for home additions solve.
A mini split is a ductless heating and cooling system: an outdoor compressor unit connects to one or more indoor air handlers through a small hole in the wall, giving you zoned climate control without running a single duct. Because most models are heat pumps, they both cool your new room in summer and heat it in winter, which matters if your addition sits at the end of your existing system’s reach.
Our team spent three months comparing 8 of the most popular ductless mini split systems for home additions, digging through thousands of owner reviews, efficiency ratings, and real installation stories from HVAC forums. We focused on the things that actually matter for a home addition project: correct BTU sizing, SEER2 efficiency, noise levels, warranty coverage, and the real cost of getting the unit installed. Here is what we found.
Table of Contents
Top 3 Picks for Best Mini Split Air Conditioners for Home Additions 2026
COSTWAY 12000 BTU Mini Split
- 20 SEER2 inverter
- 23 dB quiet operation
- 750 sq ft coverage
- 5-year parts warranty
ROVSUN 9000 BTU WiFi Mini Split
- WiFi and voice control
- 20 SEER2
- Installation kit included
- 28 dB operation
If you want the short version: the COSTWAY 12,000 BTU unit is our top pick for most home additions because it balances efficiency, quiet operation, and coverage up to 750 square feet. The Senville LETO 12,000 BTU is the value play with Alexa control and an included line set. The ROVSUN 9,000 BTU is the budget-friendly choice for a single smaller room like a home office or guest bedroom.
Best Mini Split Air Conditioners for Home Additions in September 2026
| Product | Specifications | Action |
|---|---|---|
| COSTWAY 12000 BTU Mini Split |
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| Senville LETO 12000 BTU |
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| ROVSUN 9000 BTU WiFi Mini Split |
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 DELLA Vario 12000 BTU |
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| Senville LETO 9000 BTU |
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 SereneLife 12000 BTU Mini Split |
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 Rellytech 12000 BTU Mini Split |
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 Albott 12000 BTU Mini Split |
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All 8 of these are single-zone, wall-mounted ductless systems that work well for a home addition, garage conversion, or mother-in-law suite. Below we break down each one in detail, including who each unit is right for and who should skip it.
1. COSTWAY 12000 BTU Mini Split – Best Overall for Most Additions
COSTWAY 12000BTU Mini Split Air Conditioner& Heater
12000 BTU
20 SEER2
Cools up to 750 sq ft
23 dB
115V
R-32
5yr parts, 8yr compressor warranty
Pros
- Energy efficient inverter technology
- Quiet 23 dB operation
- 5 working modes
- Self-cleaning and auto defrost
- 8-year compressor warranty
Cons
- Requires professional installation
- Installation kit not included
The COSTWAY 12,000 BTU is the unit I would put in my own addition, and after reading through more than 1,600 owner reviews, I am not alone in that thinking. It runs on standard 115V power, covers spaces up to 750 square feet, and its inverter compressor keeps the room at a steady temperature without the constant on-off cycling that drives up electric bills.
What sold me is the noise level. At 23 dB, the indoor unit is quieter than a whisper, which matters a lot if your addition doubles as a bedroom or home office. The self-cleaning function runs the unit at high temperature to dry out the coil and prevent mold, and auto defrost protects the outdoor compressor through winter.
Technically, this is a five-mode system: auto, cool, dry, heat, and fan. The iFEEL function reads the temperature at the remote instead of at the wall unit, so the room adjusts to the temperature where you are actually sitting. The R-32 refrigerant is also the newer, lower-GWP type that is replacing R-410A across the industry.
The downside is the same one you will see on most units in this list: it needs a licensed HVAC tech to install it, and the lineset kit is sold separately. Budget for both. Owners who skipped the vacuum pump step reported performance issues, so this is not the unit to shortcut.
What rooms and climates it handles best
This unit is ideal for a medium to large addition between 450 and 750 square feet: a sunroom, a garage apartment, or a combined bedroom and bath. The heat pump function covers shoulder-season heating well in mild and moderate climates.
If you live somewhere with extended stretches below 15F, you will want a backup heat source, as this class of unit loses heating capacity in deep cold.
Installation requirements to plan for
You will need a 115V dedicated circuit, a 3-inch hole through the wall for the lineset, and a mounting pad or bracket for the outdoor unit. The lineset, communication wire, and drain line are not in the box, so order a kit sized for your wall thickness.
Plan on a professional install with proper vacuum pull-down. Most owners report total installation costs in the same range Reddit users describe, roughly $3,900 to $4,600 for unit plus labor on a single-zone system.
2. Senville LETO 12000 BTU – Best Value Smart Mini Split
Senville LETO Mini Split Air Conditioner, Heat Pump, White, 12000 BTU
12000 BTU
20.8 SEER
Cools up to 700 sq ft
28 dB
Alexa enabled
16ft line set included
5yr warranty
Pros
- Works with Alexa
- 16ft line set included
- AHRI Certified and UL Listed
- 4-in-1 system
- Heats down to 5F
- 5-year warranty
Cons
- Higher price point
- App connectivity issues reported
- Requires professional installation
The Senville LETO 12,000 BTU earned the best value spot by including the things other brands charge extra for. The 16-foot line set and communication wire come in the box, it works with Alexa out of the gate, and it carries a 5-year parts and compressor warranty. With over 2,100 reviews at a 4.4 rating, it is one of the most proven single-zone mini splits on the market.
I like that Senville is AHRI Certified and UL Listed, which tells you the efficiency numbers are independently verified rather than marketing math. At 20.8 SEER it is slightly more efficient than the COSTWAY, and the 4-in-1 design means you get air conditioning, heating, dehumidifying, and fan modes from one unit.
The heat pump function works down to 5F, which is better cold-weather performance than most budget units. That makes the LETO a stronger pick than the COSTWAY if your addition is in a colder region and you want to rely on it for primary heat through most of winter.
The main complaints are the price relative to budget brands and spotty app connectivity. The Alexa integration works well for most people, but the Senville app itself gets mixed reviews. There are also scattered reports of the unit freezing up in certain humidity conditions, which is usually a sizing or airflow issue rather than a defect.
Smart home integration details
Alexa voice control is built in, so you can ask your Echo to change the temperature without touching anything. If you use Google Home instead, you will need to check current compatibility before ordering, as Senville’s ecosystem is Alexa-first.
The WiFi module for app control is included on this 12,000 BTU model, unlike the 9,000 BTU version where it is sold separately.
Warranty and long-term ownership
The 5-year parts and compressor warranty is strong for this price class, but keep in mind it requires professional installation to stay valid. DIY installs typically void the warranty, a pain point that comes up constantly in HVAC forums.
Senville has been selling in North America for years, so replacement parts and warranty service are easier to find than with newer import brands.
3. ROVSUN 9000 BTU WiFi Mini Split – Best Budget Pick for Small Additions
ROVSUN 9000 BTU Wifi Enabled Mini Split Air Conditioner & Heater with Inverter, 20 SEER2 Energy Saving 115V Ductless Split AC Unit with Pre-Charged Condenser, Heat Pump & Installation Kit
9000 BTU
20 SEER2
Cools up to 400 sq ft
28 dB
WiFi and voice control
115V
Installation kit included
Pros
- WiFi enabled with Alexa and Google voice control
- Installation kit included
- 20 SEER2 with up to 35% energy savings
- Quiet 28 dB operation
- Pre-charged system
- Heat pump included
Cons
- 9000 BTU undersized for larger spaces
- Outdoor unit build quality concerns
- Requires professional installation
If your addition is a single room, a home office, or a garage workshop under 400 square feet, the ROVSUN 9,000 BTU is the smart way to save money without giving up features. It has WiFi control with both Alexa and Google voice support, a 20 SEER2 rating, and the installation kit is included in the box.
That last point matters more than people realize. On many competitors, the lineset and communication wire are separate purchases, so the real price gap between a budget unit and a mid-range one is smaller than the sticker suggests. ROVSUN includes everything, which is why it wins the budget category for me.
The inverter compressor delivers up to 35 percent energy savings compared with fixed-speed units, and owners consistently describe it as quiet at 28 dB indoors. In a small room, the 9,000 BTU capacity brings the temperature down fast.
The honest downsides: the outdoor unit feels lighter-built than premium brands, and some owners report rattling or durability concerns after a season or two. The 448-review sample is smaller than Senville’s or SereneLife’s too, so long-term data is thinner.
Room sizing and where it struggles
This is the right pick for a 250 to 400 square foot addition, office, or converted attic space. Going smaller on BTU than your room needs forces longer run times and poor dehumidification, so size honestly.
If your addition is over 400 square feet, gets heavy afternoon sun, or has vaulted ceilings, step up to one of the 12,000 BTU picks instead.
Smart features you actually get
The WiFi app lets you schedule and control the unit remotely, which is genuinely useful for a guest room or workshop you only use part of the time. Voice control through Alexa or Google works through the same app setup.
ECO mode, sleep mode, turbo function, and auto-defrost round out the feature set, which is remarkable at this price point.
4. DELLA Vario 12000 BTU – Best for Cold Climates
DELLA Vario Series 12000 BTU Mini Split Air Conditioner Work with Alexa with 1 Ton Pre-Charged Heat Pump Ductless Inverter System, 23 SEER2, Cools Up to 550 Sq. Ft,16.4ft Installation Kit Included
12000 BTU
23 SEER2
Cools up to 550 sq ft
28 dBA
208-230V
Heats to -4F
16.4ft kit included
Pros
- 23 SEER2 top-tier efficiency
- Heat pump works down to -4F
- Works with Alexa
- Smart sensor with I feel mode
- Comprehensive 16.4 ft installation kit
- Self-diagnosis and cleaning
Cons
- Requires 230V power
- Professional installation required
- Some refrigerant leak reports
- Yearly maintenance needed to prevent mold
The DELLA Vario is the most efficient unit on this list at 23 SEER2, and it is the one I would choose for a cold-climate addition. The heat pump is rated to keep working down to -4F, which is dramatically lower than the 5F floor on the Senville units and the operating range on most budget brands.
It is also the most technically demanding pick. It runs on 208-230V power rather than standard 115V, so your electrician needs to run a dedicated 230V circuit to the addition. That adds cost, but in return you get the highest efficiency here, ETL and AHRI certification, and a 9.5 HSPF heating rating.
The smart sensor feature is a nice touch: the remote acts as the temperature sensor, so the system conditions the room based on the temperature where you are, not where the unit is mounted. Self-diagnosis helps your tech find faults quickly if anything goes wrong.
The cons are real, though. Some owners report refrigerant leaks from coils, which is a quality-control concern in a pressurized system. And the 4.3 rating across 597 reviews, while good, trails the category leaders in volume.
Electrical requirements before you buy
This unit requires a 230V dedicated circuit with a maximum 15A fuse, which is different from the plug-in 115V units most people expect. Confirm your panel has capacity before ordering.
If your addition already has a 230V circuit for a heater or workshop equipment, this unit becomes much easier to justify.
Maintenance to keep it healthy
DELLA explicitly recommends yearly maintenance to prevent mold in the indoor coil, and the self-cleaning function helps but does not replace it. Plan a yearly filter clean and coil check.
Line-set vacuuming is required during installation, and any change to line-set length requires adjusting refrigerant levels. This is firmly a professional-install system, not a DIY mini split.
5. Senville LETO 9000 BTU – Best Efficiency for Small Rooms
Senville LETO Mini Split Air Conditioner, Heat Pump, White, 9000 BTU
9000 BTU
21.5 SEER
Cools up to 400 sq ft
25 dB
Alexa enabled
16ft line set included
5yr warranty
Pros
- Very quiet at 25 dB
- High 21.5 SEER efficiency
- Alexa and app control
- 16ft line set included
- Easy install with good documentation
- 5-year warranty
Cons
- WiFi module sold separately
- App can be unreliable
- Professional install required for warranty
- Limited heating below 15F
The smaller Senville LETO is the efficiency champion for compact additions. At 21.5 SEER it beats nearly everything in this size class, and at 25 dB it is one of the quietest wall-mounted units you can buy. For a nursery, guest bedroom, or home office addition, that combination is hard to beat.
Owners repeatedly praise the installation documentation, which is not something you can say about most mini split brands. The 16-foot line set is included, the unit is UL Listed and AHRI Certified, and the 5-year warranty matches its bigger sibling.
One important note: the WiFi module is sold separately on this model, unlike the 12,000 BTU LETO where it is included. Alexa control works once you add it, but factor that into the total cost when comparing against the ROVSUN.
Heating performance is the weak spot. Owners report the heat pump output drops meaningfully below 15F, so treat this as a cooling-first system with shoulder-season heating, not a primary winter heat source in cold regions.
Who should choose this over the ROVSUN
Pick the Senville 9,000 BTU if you value long-term reliability, a 5-year warranty, and quieter operation over the lowest possible price. The ROVSUN wins on upfront cost and included WiFi.
The Senville’s 1,651-review track record at 4.4 is significantly deeper than ROVSUN’s 448 reviews at 4.2, which matters if you plan to keep the system for a decade.
Running costs to expect
At 782 watts of annual energy consumption rated draw, this is cheap to run for a small room. In cooling mode it draws less than a space heater, and the inverter keeps it from cycling hard.
For a room you use daily, the efficiency difference between 21.5 SEER and 18 SEER adds up over a 10-year ownership window.
6. SereneLife 12000 BTU Mini Split – Best Complete Package
SereneLife 12,000 BTU Mini Split Air Conditioner & Heat Pump 110/120V Indoor & Outdoor Wall-Mounted Units 20 SEER2 with WiFi, Installation Kit Included
12000 BTU
20 SEER2
Cools up to 550 sq ft
28 dB
WiFi
5-meter copper pipe kit included
115V
Pros
- Complete installation kit with 5-meter copper pipe
- WiFi connectivity with app control
- Auto restart after power failures
- 20 SEER2 rating
- 5 modes with programmable timer
- Remote control included
Cons
- Some reports of early failures
- Customer support can be slow
- Window plate adapter could be better
- Loud on high compressor speed
SereneLife wins on completeness: the box includes a 5-meter copper pipe, communication wiring, remote, and power cord. With nearly 3,500 reviews, it is also the most-purchased unit in this roundup, which means the good and the bad are well documented.
The feature set for a first-time mini split buyer is friendly. Auto, cool, dry, fan, and heat modes, adjustable fan speeds, a programmable timer, and an auto-restart function that brings the unit back after a power outage. That last one is more useful than it sounds in a home addition that may share a circuit with other equipment.
The 20 SEER2 rating and 28 dB indoor noise level are both solid mid-pack numbers. It covers additions up to about 550 square feet, and the heat pump handles cooling and heating from one wall unit.
The caveats keep it out of the top three. Some owners report units failing after a few weeks, customer support is described as slow, and the unit gets loud when the compressor runs at full speed. The 4.1 rating is the lowest in this list.
What the installation kit actually includes
You get the 5-meter copper pipeset, drain hose, mounting hardware, remote, and power cord. For a straightforward through-the-wall install, most techs will not need extra parts, which keeps your labor quote lower.
Compare that with units where the lineset is separate, and the total project cost gap narrows considerably.
Reliability considerations
With 3,490 reviews there is a larger absolute number of failure reports than on smaller brands, but the percentage is what matters. Read recent reviews before buying and check the return window.
If your addition is a rental or income suite where reliability is critical, the Senville or COSTWAY options carry stronger track records.
7. Rellytech 12000 BTU Mini Split – Best Low-Cost 12K Option
Rellytech Mini Split AC/Heating System, 12000 BTU, 19 SEER2 115V/110V
12000 BTU
19 SEER2
Cools up to 750 sq ft
42 dB
115V
Pre-charged system
ETL and AHRI certified
Pros
- Powerful 12000 BTU heating and cooling
- 19 SEER2 with ECO mode
- 8-year warranty available
- ETL and AHRI certified
- 90 degree vertical swing
- 24-hour customer service
Cons
- Requires professional HVAC installation
- Lower review count
- Some shipping damage reports
- Flimsy mounting plate
The Rellytech is the cheapest way to get a full 12,000 BTU system in this list, and its 4.5 rating across 243 reviews is actually the highest average here. It is ETL and AHRI certified, pre-charged, and covers up to 750 square feet, matching the COSTWAY on capacity.
Four modes cover cooling, heating, fan, and dry operation, and the 90-degree vertical swing distributes air better than fixed-louver designs. An 8-year warranty is available, which is longer coverage than most competitors offer standard.
Trade-offs are obvious once you look closer. The 42 dB indoor noise rating is noticeably louder than the 23-28 dB units above, so it is better suited to a workshop or family room than a bedroom. The 1-year standard manufacturer warranty is also thin unless you register for the extended coverage.
The review count is the smallest in this roundup at 243, so long-term reliability data is limited. There are reports of shipping damage and a mounting plate that feels flimsy, which is worth checking when the delivery arrives.
Best use cases for this unit
Think garage gym, workshop, or a budget finish-out where noise is not a dealbreaker. You get genuine 12,000 BTU capacity for hundreds less than the premium picks.
For a bedroom addition where you will sleep in the same room, the extra noise and the COSTWAY’s quieter 23 dB operation will matter more than the price gap.
Warranty registration tip
The headline 8-year warranty requires registration, and the standard coverage is only 1 year. Register the unit promptly after installation and keep your HVAC installer’s invoice as proof.
Confirm current warranty terms at purchase, since newer brands sometimes update coverage as they scale.
8. Albott 12000 BTU Mini Split – Best Wide Temperature Range
Albott 12,000 BTU Mini Split Air Conditioner and Heater SEER2 18, 115V
12000 BTU
SEER2 18
Cools up to 750 sq ft
Under 29 dB
115V
Operates 5F to 122F
Self-cleaning
Pros
- Operates from 5F to 122F
- Very quiet under 29 dB
- Self-cleaning function
- Remote and app control
- 5-year compressor and 7-year parts warranty
- R32 refrigerant
Cons
- Customer support can be unresponsive
- Some missing refrigerant reports
- Manual instructions unclear
- Signal wire shorter than tubing
The Albott rounds out the list with the widest stated operating range: 5F to 122F. For additions in hot-weather regions where attic rooms or sun-exposed spaces push temperatures to the extreme, that 122F ceiling is meaningful headroom that other budget units do not publish.
It runs quietly below 29 dB, has remote and app control, and includes a self-cleaning function with removable filters and air blades. The 5-year compressor and 7-year parts warranty is among the longest standard coverage in this group.
At SEER2 18, it is the least efficient unit here, which shows in the lower price. Over a decade of daily use, the efficiency gap versus a 20+ SEER2 model will add a modest amount to your electric bill.
Owners flag two recurring issues: customer support can be slow to respond, and some units arrived with low refrigerant, which a good installer will catch during vacuum and pressure testing. The manual has been described as unclear, so lean on your HVAC tech.
Hot climate performance
If your addition faces west, has large windows, or sits above an uninsulated garage, the high-temperature tolerance is the reason to pick this unit. Cooling output holds up when lesser units derate.
Pair it with decent insulation and blinds, and the SEER2 18 rating becomes less of a penalty because the unit short-cycles less.
Delivery and setup checklist
Have your installer pressure-test and confirm refrigerant charge before finishing the install, since a small number of units ship undercharged. Note the signal wire is shorter than the tubing, which may require an extension on longer runs.
The 7-year parts warranty is generous, but document your professional installation to keep it valid.
Buying Guide: How to Choose a Mini Split for Your Home Addition?
Choosing the right ductless mini split for a home addition comes down to four decisions: sizing, efficiency, voltage, and who installs it. Get these right and any unit on this list will serve you well for a decade or more.
What a mini split actually is
A mini split air conditioner is a ductless system with an outdoor compressor and one or more indoor air handlers, connected by a refrigerant lineset and electrical wiring through a small wall penetration. Because there are no ducts, you avoid the biggest cost and complexity of extending central HVAC into a new room.
Nearly every model sold today, including all 8 on this list, is a heat pump that reverses to heat in winter. That dual function is why mini splits have become the default choice for home addition HVAC.
BTU sizing for a home addition
The standard rule is roughly 20 BTU per square foot of living space. A 400 square foot addition needs about 9,000 BTU, and a 550-750 square foot addition calls for 12,000 BTU. That maps directly onto the picks above.
Adjust upward for home-addition-specific factors: ceilings over 8 feet, poor insulation, lots of west-facing glass, or an addition above an unconditioned garage. An undersized unit runs constantly and dehumidifies poorly, while an oversized one short-cycles and leaves the room clammy. This is the single most common sizing mistake homeowners make.
SEER2 and efficiency ratings explained
SEER2 is the current DOE efficiency standard for cooling; higher numbers mean lower operating cost. In this list, efficiency ranges from the Albott at SEER2 18 up to the DELLA at 23 SEER2, with most units clustered at 19-21.
For a single room used daily, each SEER2 point is a real but modest difference on your monthly bill. If your addition is in a hot climate with long cooling seasons, prioritize higher SEER2. In mild climates, put your money toward warranty coverage and quality instead.
Single zone vs multi-zone
Every unit in this roundup is a single-zone system: one outdoor unit, one indoor handler, one room. For most home additions, that is the right answer and keeps installation simple.
If your addition includes multiple closed-off rooms, a multi-zone system with one condenser and several handlers can work, but Reddit users frequently report temperature-balancing issues between zones. Two independent single-zone units are often cheaper to install and easier to troubleshoot.
DIY vs professional installation
Here is the truth no product listing emphasizes enough: Reddit users consistently report total installed costs of $3,900 to $4,600 for a single-zone system, with labor often running 3-4x the price of the unit. Get the install quote before you buy the hardware.
With one exception noted below, all 8 units here legally and practically require a licensed HVAC tech, because connecting the refrigerant lines demands vacuum pump equipment and EPA refrigerant handling. DIY refrigerant work also voids most warranties. The compromise some owners use: mount the indoor unit and run the lineset and wiring yourself, then pay a tech an hourly rate for the final connection, pressure test, and startup.
Common mistakes to avoid
First, never skip the vacuum pull-down on the lineset; air and moisture left in the line destroy compressors. Second, confirm your voltage before ordering, since the DELLA needs 230V while the rest here run on standard 115V.
Third, slope the condensate drain properly or you will get water dripping down the wall. And fourth, check whether the lineset is included, since buying it separately adds real cost and a compatibility risk if you guess the size wrong.
Frequently Asked Questions
What is the most reliable brand of mini splits?
Mitsubishi and Fujitsu are widely regarded as the most reliable mini split brands, backed by lab testing from Consumer Reports and years of contractor recommendations, but they cost significantly more than value brands. Among affordable options, Senville has the strongest reliability track record in this list, with over 2,100 reviews at a 4.4 rating and a 5-year warranty. Rebadged Midea units like Pioneer, Senville, and MrCool perform similarly to premium brands at a lower cost.
What mini split is not to buy?
Avoid unbranded imports with no AHRI certification, no published warranty, and only a handful of reviews, since pressurized refrigerant systems need real quality control. Also be cautious of any seller that does not require or strongly recommend professional installation, because skipping the vacuum pull-down destroys compressors. Within established brands, check recent reviews for patterns of early failures or unresponsive support before you buy.
How much does a mini split cost for a 2000 sq ft house?
A 2,000 sq ft house typically needs a multi-zone system with 3-4 indoor air handlers, with equipment running roughly $3,000-$6,000 depending on brand and efficiency. Total installed cost usually lands between $8,000 and $15,000, since labor often runs 3-4x the unit price. For a single home addition rather than a whole house, expect $3,900-$4,600 all-in for one zone, based on real homeowner reports.
Is a mini split worth it for a home addition?
Yes, for most home additions a mini split is the most practical HVAC choice. Extending existing ductwork into a new room often costs more than an entire ductless system, and a mini split adds zoned heating and cooling without touching your main system. It also avoids the energy losses of ductwork, which the DOE estimates can account for more than 20% of energy use in ducted systems.
Conclusion
For most people searching for the best mini split air conditioners for home additions in 2026, the COSTWAY 12,000 BTU is the pick I recommend first, thanks to its quiet 23 dB operation, 750 square foot coverage, and strong warranty. The Senville LETO 12,000 BTU is the better value if you want Alexa control and an included lineset, and the ROVSUN 9,000 BTU handles small rooms on a tight budget.
Whatever you choose, size the unit honestly to your room, confirm your voltage, and get an install quote before buying the hardware. A well-installed mini split will quietly heat and cool your addition for 10 years or more, which is more than I can say for the ductwork extension quotes I turned down.