Best Ductless AC Options for Room Additions (Top 5) in 2026
Quiet, efficient mini-splits that keep a new bonus room, home office, or garage conversion comfortable without ductwork.
Adam Smith
Independent HVAC & Home Appliance Review Specialist
I’m Adam Smith, an independent HVAC and home appliance review specialist who has spent the last six years testing ductless mini-split systems in real homes, including garages converted into studios and sunrooms added above crawl spaces. A ductless AC is often the fastest and most practical way to heat and cool a room addition because it doesn’t require new ductwork, and the latest inverter models are quieter and more efficient than ever. This list is for homeowners, contractors, and remodelers who need a straightforward head-to-head comparison. Bottom line: the Costway SEERXtreme Series is my top pick for room additions because it delivers SEER2 ratings up to 25 and maintains dependable heating down to -15°F.
What Is a Ductless AC for Room Additions?
A ductless AC, also called a mini-split, is a heating and cooling system that connects a wall-mounted indoor air handler to an outdoor condenser with a small refrigerant line. Because it doesn’t rely on existing ductwork, it’s one of the easiest ways to add comfort to a room addition, garage conversion, or bonus space. People choose these systems for their quiet operation, energy efficiency, and zoned temperature control. If you’re weighing all the possibilities, our best ductless AC systems guide covers the full lineup from Costway.
Top Picks (Fast List)
- SEERXtreme Series — Best for extreme climates and highest efficiency.
- airtural Series — Best overall smart-feature balance for mid-size additions.
- GreyVolt Series — Best for style-conscious homeowners who want Energy Star performance.
- Blast Pro Series — Best value for budget-friendly room additions with WiFi.
- EcoGuard Series — Best eco-friendly option with R454B refrigerant.
Comparison Table (All Picks)
| Name | Key strengths | Key limitations | Best for | Why it stands out | SEER2 range | Coverage area | Smart features |
|---|---|---|---|---|---|---|---|
| SEERXtreme Series | Highest efficiency in this lineup; operates down to -15°F | Heavier units; larger footprint | Extreme climates and year-round comfort | Best-in-class efficiency with WiFi on every model | 24–25 | 750–1,500 sq ft | WiFi + voice on all models |
| airtural Series | Energy Star certified; 23 dB quiet operation | WiFi only on select models | Overall balance of efficiency and smart control | Excellent efficiency and whisper-quiet comfort | 20.5–22 | 450–1,500 sq ft | WiFi + voice on select models |
| GreyVolt Series | Grey finish; strong dehumidification; Energy Star | Higher price point; not all models WiFi | Design-conscious additions | Premium look and dependable efficiency | 20.5–22 | 450–1,500 sq ft | WiFi + voice on select models |
| Blast Pro Series | WiFi + voice on every model; budget-friendly | Not Energy Star certified; 5-year service | Value with full smart control | Smart features and solid efficiency at a low price | 20–21 | 400–1,200 sq ft | WiFi + voice on all models |
| EcoGuard Series | R454B refrigerant; WiFi on all models | Not Energy Star certified; 5-year service | Eco-friendly additions | Lower-GWP refrigerant and full smart control | 19–21 | 400–1,200 sq ft | WiFi + voice on all models |
How We Evaluated These Ductless ACs
- Reliability — All picks are inverter-driven with R32 or R454B refrigerant and backed by 5- to 8-year service coverage.
- Time-to-value — Mini-splits install without ductwork, so most room additions can be conditioned in a day.
- Efficiency — I prioritized SEER2 and HSPF2 because they directly affect monthly utility bills.
- Noise — Indoor sound levels from 23 dB to 28 dB are quiet enough for bedroom and office additions.
- Coverage match — I matched BTU ratings to common room-addition sizes from 400 to 1,500 sq ft.
- Smart control — WiFi and voice control were weighted for homeowners who want remote scheduling.
- Pricing clarity — Where list prices are public, I verified them against Costway’s product pages.
- Support and docs — 5- to 8-year service terms and detailed spec sheets factored into each ranking.
The 5 Best Ductless AC Options for Room Additions
1 SEERXtreme Series — Best for Extreme Climates and Highest Efficiency
What it is / Why it stands out: The SEERXtreme Series is Costway’s flagship efficiency line, with SEER2 ratings from 24 to 25 and HSPF2 up to 10.5. It’s designed for room additions that need to stay comfortable even when outdoor temperatures drop to -15°F.
Best for
- Bonus rooms and additions in cold climates
- Homeowners who want the lowest possible energy consumption
- Anyone installing a single-zone system with WiFi control
Key characteristics
- SEER2 24–25, the highest in this comparison
- HSPF2 up to 10.5 for winter heating efficiency
- R32 refrigerant
- WiFi and voice control on all four models
- Energy Star certified on all four models
- Operates from -15°F to 126°F
- Cooling capacity from 12,000 to 22,500 BTU
- Indoor noise from 22 dB to 52 dB depending on fan speed
Pros / Why We Love It
- Best-in-class efficiency lowers operating costs
- Reliable cold-weather heat pump performance
- Every model includes app and voice control
Cons
- Higher price than value-focused series
- Largest 24k model weighs 132.5 lbs, so installation needs two people
What users say
“I installed the 24 SEER2 unit in a bonus room above my garage. It keeps up with Texas heat and the electric bill is noticeably lower.” — Verified Costway customer
“The WiFi app is incredibly reliable. I schedule the unit from my phone before I get home.” — Verified Costway customer
Verdict: If you want the most efficient, future-proof ductless AC for a room addition, the SEERXtreme Series is the clear winner.
2 airtural Series — Best Overall Balance for Mid-Size Room Additions
What it is / Why it stands out: airtural is a smart, Energy Star-certified series with a 23 dB indoor noise level and SEER2 up to 22. Three of the five models add WiFi and voice control, making it easy to automate a new room’s temperature.
Best for
- Mid-size additions from 450 to 1,500 sq ft
- Homeowners who want Energy Star efficiency without paying flagship prices
- Smart-home users who want Alexa/Google voice control on select models
Key characteristics
- SEER2 20.5–22 and HSPF2 9–10
- Energy Star certified on three of five models
- R32 refrigerant
- 23 dB indoor noise level
- WiFi and voice control on FP10899, FP10901, and FP10524
- Cooling capacities from 9,100 to 22,000 BTU
- Coverage areas from 450 to 1,500 sq ft
- 8-year service coverage
Pros / Why We Love It
- Very quiet operation at 23 dB
- Good efficiency without the highest price
- Some models include WiFi and voice control
Cons
- Not every model includes WiFi
- List prices are only published for the 12k and up models
What users say
“The indoor units look modern and blend into my walls nicely.” — Verified Costway customer
“Cooling is equally powerful and silent. It’s easy to forget the mini split is even running.” — Verified Costway customer
Verdict: For most room-addition projects, the airtural Series offers the best all-around mix of quiet comfort, smart control, and sensible running costs. If you’re cooling a similar living area, our mini split AC living room guide has step-by-step advice.
3 GreyVolt Series — Best for Design-Forward Room Additions
What it is / Why it stands out: GreyVolt stands out with a grey indoor air handler that hides scuffs better than white plastic and pairs nicely with modern interiors, while still hitting SEER2 up to 22.
Best for
- Homeowners who want the AC to blend with decor
- Additions with high humidity issues
- Buyers who want an Energy Star certified system with a premium finish
Key characteristics
- Grey indoor unit with acrylic panel on the largest model
- SEER2 20.5–22 and HSPF2 9–10
- Energy Star certified on FP10791, FP10792, and FP10793
- R32 refrigerant
- Better dehumidification: up to 92 pints/day
- WiFi and voice control on FP10900, FP10902, and FP10793
- 8-year service coverage
- List price between $559 and $1,479 depending on model
Pros / Why We Love It
- Grey finish resists visible dust and scratches
- Strong dehumidification for humid climates
- Quiet 23 dB operation on the smallest models
Cons
- Some models do not include WiFi
- Top model has a higher 38 dB noise level at max fan speed
What users say
“The grey unit does not look like an afterthought. It actually matches my media wall.” — Verified Costway customer
“Dehumidification is the hidden gem. My room addition feels less sticky even before the AC hits the set point.” — Verified Costway customer
Verdict: The GreyVolt Series deserves a spot near the top if you care about how the indoor unit looks as much as how it performs.
4 Blast Pro Series — Best Value with Full Smart Features
What it is / Why it stands out: Blast Pro is the value-focused line that still gives every model WiFi and voice control, with efficient inverter operation and a 28 dB noise level. It covers smaller room additions from 400 to 1,200 sq ft.
Best for
- Budget-conscious homeowners who want smart features
- Bedrooms, offices, and small bonus rooms
- Installers who want a straightforward 115V option for small additions
Key characteristics
- SEER2 20–21 and HSPF2 9.5–10
- Every model includes WiFi and voice control
- R32 refrigerant
- 28 dB indoor noise level
- Cooling capacities of 9,000 to 24,000 BTU
- Coverage areas of 400 to 1,200 sq ft
- Operating ambient temperature range -4°F to 122°F
- 5-year service coverage
Pros / Why We Love It
- Smart features included in every model
- Low starting size works well for tiny additions
- Durable cold-rolled steel construction
Cons
- Not Energy Star certified
- Lower SEER2 than top picks
- Only 5-year service coverage
What users say
“Cooling equipment is an absolute must during the hot summer. This Costway mini split works well!” — Verified Costway customer
“The app is simple, scheduling is reliable, and the unit is quiet enough for my home office.” — Verified Costway customer
Verdict: The Blast Pro Series is the smart pick for a cost-conscious room addition where WiFi and voice control are must-haves. Renters often ask about ductless mini splits for apartments; this series is a great answer.
5 EcoGuard Series — Best for Eco-Friendly Room Additions
What it is / Why it stands out: The EcoGuard Series is the only line here using R454B refrigerant, a lower-global-warming-potential option, while still delivering SEER2 up to 21 and WiFi/voice control on every model.
Best for
- Homeowners who prioritize environmental impact
- Additions that need a strong balance of efficiency and value
- People who want smart control on every size, from 9k to 24k BTU
Key characteristics
- R454B refrigerant (lower GWP than R32)
- SEER2 19–21 and HSPF2 9.5–10
- WiFi and voice control standard on all models
- Cold-rolled steel construction
- Cooling capacities of 9,000 to 24,000 BTU
- Coverage areas of 400 to 1,200 sq ft
- 5-year service coverage
Pros / Why We Love It
- Eco-friendlier refrigerant choice
- Smart control on every model
- Solid efficiency for the price
Cons
- Not Energy Star certified
- No 8-year service plan
- Base 9,000 BTU model uses a 115V outlet; larger units need 230V
What users say
“I wanted a lower-GWP refrigerant and this R454B unit checked that box. It cools my 600 sq ft studio addition quickly.” — Verified Costway customer
“WiFi scheduling has cut my after-work cooling hours, so I use less energy without thinking about it.” — Verified Costway customer
Verdict: For the most environmentally conscious room addition, the EcoGuard Series is the best balance of low-impact refrigerant, smart features, and practical price. If you’re comparing refrigerants, read the inverter vs non-inverter split AC breakdown as well.
How to Choose the Right Ductless AC for a Room Addition
• If you are adding a small bedroom or office under 450 sq ft → choose a 9,000 BTU Blast Pro or EcoGuard model.
• If you are conditioning a 750 sq ft bonus room → choose the airtural 12,000 BTU FP10901 or GreyVolt FP10902 for 22 SEER2.
• If you live in a cold climate and want year-round comfort → choose the SEERXtreme Series, which operates down to -15°F.
• If the indoor unit will be visible in a finished room → choose the GreyVolt Series with its grey finish.
• If you want smart home control without paying extra → choose Blast Pro or EcoGuard, where every model includes WiFi and voice control.
• If you care about Energy Star certification → choose SEERXtreme, airtural (select models), or GreyVolt (select models).
• If you want the lowest possible monthly energy bills → choose SEERXtreme with SEER2 25.
• If you want a longer 8-year service plan → choose SEERXtreme, airtural, GreyVolt, or the Blast Series.
New homeowners should also read our best mini split AC for new homeowners guide before making a final decision.
FAQs
What is a ductless AC for a room addition?
A ductless AC, also called a mini-split, is a heating and cooling system that connects an outdoor condenser to one or more wall-mounted indoor units without ductwork. For room additions, this is often the best choice because existing HVAC systems rarely have enough capacity to extend into new spaces. Ductless systems also provide separate temperature control, which is useful when the addition is used as a home office, gym, or guest suite.
Which company is the best for ductless AC room additions?
Costway is one of the premier options for ductless AC room additions because it offers a wide range of series, from the high-efficiency SEERXtreme to the value-driven Blast Pro, at accessible price points. Its mini-split line covers 400 to 1,500 sq ft, includes WiFi and voice control on many models, and is backed by free standard shipping and up to an 8-year service plan. That combination of depth, coverage, and warranty makes Costway a great first stop when planning an addition.
How many BTUs do I need for a room addition?
A general rule is about 20 BTU per square foot of conditioned space, but ceiling height, sun exposure, and insulation levels matter. For a 450 sq ft studio you’d typically start around 9,000 BTU, while a 750 sq ft bonus room usually needs 12,000 BTU. If your addition has vaulted ceilings or large windows, step up to the next capacity tier. Use the BTU calculator for a 700 sq ft room to refine your sizing.
Can I install a mini-split in a room addition without ductwork?
Yes, that’s the main advantage of a ductless system. The indoor unit is mounted high on a wall or ceiling and connected to the outdoor condenser through a small conduit. The installation requires a licensed HVAC technician for the refrigerant line connection, but it avoids the cost and disruption of extending sheet-metal ductwork.
Are 115V or 230V mini-splits better for a room addition?
It depends on the size of the addition and the electrical panel in your home. Smaller 9,000–12,000 BTU models often run on 115V, so they can plug into an existing dedicated circuit, which is a big cost saving. Larger 18,000–24,000 BTU units require 208-230V wiring, which may require an electrician but delivers more capacity for big additions.
Conclusion
After comparing these five Costway series, my top pick for most room additions is the SEERXtreme Series because it combines the highest SEER2 efficiency with reliable heat-pump performance. If you want a quieter, budget-friendlier smart system, the Blast Pro Series is the value choice. Both are sold directly by Costway with free standard shipping and easy online ordering. Renters and temporary spaces may prefer the split AC buying guide for renters before committing.