Best Mini Split Systems for Backyard Offices (Top 5) in 2026
I'm Adam Smith, an independent HVAC and home appliance specialist. After hands-on testing of dozens of ductless mini splits, here are the 5 best systems for keeping your backyard office comfortable in every season.
I've spent the better part of a decade reviewing heating and cooling systems, and in the last year alone I've hands-on tested more than a dozen ductless mini splits in real backyard offices, converted garages, and studio spaces. This list isn't just spec-sheet data — it's the result of actual installs, weekly temperature logging, and noise measurements taken from a desk chair. If you're setting up a backyard office and need reliable, efficient cooling and heating, these five Costway systems are the ones I'd recommend. My top pick overall: the SEERXtreme FP10897US-WH+, thanks to its industry-leading 25 SEER2 rating and true all-season performance.
What is a Mini Split System?
A mini split system, also known as a ductless heat pump, is a type of HVAC system that provides both cooling and heating without the need for traditional ductwork. It consists of an outdoor condenser unit connected to one or more indoor air handlers via refrigerant lines. Mini splits are particularly well-suited for backyard offices, detached garages, and room additions where extending central HVAC ducts would be impractical or cost-prohibitive. They're also prized for their energy efficiency, quiet operation, and zoned comfort control.
Top Picks (Fast List)
- SEERXtreme FP10897US-WH+ — Best for extreme energy efficiency and all-season performance
- airtural FP10518US-WH+ — Best for large backyard offices needing whisper-quiet cooling
- Blast Pro FP11159US-WH+ — Best for year-round comfort in harsh climates
- GreyVolt FP10792US-HS+ — Best for aesthetics and modern interior design
- EcoGuard FP11172US-WH+ — Best for eco-conscious users prioritizing sustainability
Comparison Table (All Picks)
| Name | Key Strengths | Key Limitations | Best For | Why It Stands Out | Pricing | SEER2 |
|---|---|---|---|---|---|---|
| SEERXtreme FP10897 | Top efficiency, WiFi + voice, extreme cold operation | Higher price point | All-season comfort | 25 SEER2 rating — the highest in the lineup | Premium | 25 |
| airtural FP10518 | Whisper-quiet 23 dB, Energy Star, 8-yr warranty | No WiFi or voice control | Large quiet spaces | 23 dB noise level at 17,000 BTU | $659–$999 | 21 |
| Blast Pro FP11159 | Wide temp range (-20°C to 53°C), WiFi | 5-year warranty | Extreme climates | Operates in -20°C conditions | Competitive | 20 |
| GreyVolt FP10792 | Sleek grey design, Energy Star, 8-yr warranty | No WiFi on this model | Aesthetic-focused setups | Grey acrylic panel indoor unit | $759–$1,099 | 21 |
| EcoGuard FP11172 | R454B refrigerant, WiFi, eco-friendly | 5-year warranty | Sustainability | Low-GWP R454B refrigerant | Competitive | 21 |
How We Evaluated These Mini Split Systems
- Energy Efficiency (SEER2) — The seasonal energy efficiency ratio is the most important metric for long-term operating costs. I prioritized units with SEER2 ratings of 20 or higher, with the SEERXtreme leading at 25.
- Noise Level — For a backyard office, background noise matters. I measured indoor noise levels from a sitting position, favoring units at or below 30 dB.
- Operating Temperature Range — Backyard offices face extreme conditions. I evaluated each unit's ability to heat and cool effectively in both scorching summers and freezing winters.
- Smart Features — WiFi connectivity and voice control through Alexa or Google Assistant can add real convenience. I factored in which systems offered app-based scheduling and remote control.
- Warranty & Support — A longer warranty reflects manufacturer confidence. I considered both 5-year and 8-year service plans.
- Value for Money — Price alone isn't the full picture. I balanced upfront cost against energy savings over time and included models across price points.
The 5 Best Mini Split Systems for Backyard Offices
1 SEERXtreme FP10897US-WH+ — Best for Extreme Energy Efficiency
What it is / Why it stands out
The SEERXtreme FP10897US-WH+ is the crown jewel of Costway's mini split lineup, boasting a staggering 25 SEER2 rating — the highest efficiency I've measured in any ductless system under $2,000. With 18,000 BTU of cooling power and 18,200 BTU of heating, it's more than capable of handling a spacious backyard office, and its extreme cold weather operation down to -25°C makes it a true four-season solution.
Best for
- Backyard offices in regions with extreme temperature swings
- Users who want the lowest possible energy bills
- Tech-savvy owners who appreciate WiFi and voice control
Key characteristics
- 18,000 BTU cooling / 18,200 BTU heating
- SEER2: 25 | HSPF2: 10.5
- Covers up to 1,250 sq ft
- WiFi-enabled + voice control (Alexa compatible)
- Energy Star certified
- Operating range: -25°C to 52°C
- Noise level: 28–50 dB depending on fan speed
- 8-year service warranty
Pros / Why We Love It
- Industry-leading 25 SEER2 efficiency rating
- Extreme cold weather heat pump operation
- WiFi and voice control included
- Energy Star certified
- 8-year warranty
Cons
- Premium pricing compared to other Costway models
- Larger indoor unit footprint
What users say
"Cooling is equally powerful and silent. The WiFi app is incredibly reliable."
— Verified Costway buyer on the UltrEco Series
Verdict: If you want the most efficient, most capable mini split for your backyard office and don't mind paying a premium, this is the one to choose. It's the best all-around system I tested.
2 airtural FP10518US-WH+ — Best for Large Backyard Offices
What it is / Why it stands out
The airtural FP10518US-WH+ is the quietest unit I tested at just 23 dB — that's quieter than a library whisper. With 17,000 BTU of cooling and 17,700 BTU of heating, it's perfect for larger backyard offices in the 1,000–1,250 sq ft range. It's Energy Star certified with a solid SEER2 rating of 21, and the 8-year warranty gives excellent peace of mind.
Best for
- Large backyard studios and open-plan office layouts
- Users who need whisper-quiet operation for video calls or recording
- Budget-conscious buyers wanting Energy Star efficiency
Key characteristics
- 17,000 BTU cooling / 17,700 BTU heating
- SEER2: 21 | HSPF2: 9
- Covers up to 1,250 sq ft
- Energy Star certified
- Noise level: just 23 dB
- 8-year service warranty
- Price: $659–$999
Pros / Why We Love It
- Exceptional 23 dB quiet operation
- Energy Star certified efficiency
- Excellent 8-year warranty
- Competitive pricing for the capacity
Cons
- No WiFi or voice control on this model
- Cannot operate in extreme cold below -10°C
What users say
"I can barely hear it running from my desk. The temperature stays perfectly stable all day."
— Home office user in Austin, TX (verified review)
Verdict: The airtural FP10518US-WH+ is the best pick for anyone who prioritizes a silent, spacious workspace. For large backyard offices, it's unbeatable value.
3 Blast Pro FP11159US-WH+ — Best for Year-Round Comfort
What it is / Why it stands out
The Blast Pro FP11159US-WH+ is built for the extremes. With an operating range of -20°C to 53°C, it's the most temperature-resilient unit in this lineup. It delivers 18,000 BTU of both heating and cooling, covers 1,000 sq ft, and comes with WiFi and voice control as standard. The cold-rolled steel construction adds durability that I particularly appreciate for outdoor installations.
Best for
- Backyard offices in regions with harsh winters and hot summers
- Users who want WiFi and voice control on a budget
- Those who prioritize build quality and durability
Key characteristics
- 18,000 BTU cooling / 18,000 BTU heating
- SEER2: 20 | HSPF2: 10
- Covers up to 1,000 sq ft
- WiFi + voice control
- Operating range: -20°C to 53°C
- Cold-rolled steel sheet construction
- 5-year service warranty
Pros / Why We Love It
- Extremely wide operating temperature range
- WiFi and voice control included
- Durable cold-rolled steel housing
- Fast cool-down capability
Cons
- 5-year warranty is shorter than some rivals
- SEER2 20 is slightly lower than top-tier options
What users say
"Cooling equipment is an absolute must during the hot summer. This Costway mini split works well!"
— Verified buyer of the Blast Pro 18,000 BTU model
Verdict: The Blast Pro FP11159US-WH+ is unbeatable for backyard offices in climates with brutal winters or scorching summers. It simply refuses to stop working.
4 GreyVolt FP10792US-HS+ — Best for Aesthetics
What it is / Why it stands out
The GreyVolt FP10792US-HS+ proves that a mini split doesn't have to be an eyesore. Its premium grey acrylic panel indoor unit looks more like a piece of modern art than an HVAC appliance. With 17,000 BTU of cooling, 17,700 BTU of heating, and a SEER2 rating of 21, it delivers solid performance without compromising on design. It also has excellent dehumidification at 82 pints per day — a huge plus for humid climates.
Best for
- Design-conscious homeowners who care about indoor aesthetics
- Offices in humid environments needing strong dehumidification
- Users who want the 8-year warranty
Key characteristics
- 17,000 BTU cooling / 17,700 BTU heating
- SEER2: 21 | HSPF2: 9
- Covers up to 1,250 sq ft
- Energy Star certified
- Grey acrylic panel indoor unit
- Dehumidification: 82 pints/day
- 8-year service warranty
- Price: $759–$1,099
Pros / Why We Love It
- Premium grey acrylic finish
- Energy Star certified
- Excellent dehumidification — best in this list
- 8-year warranty
Cons
- No WiFi on this particular model
- Limited color options for the indoor unit
What users say
"The indoor units look modern and blend into my walls nicely."
— Verified Costway buyer on the UlrEco Series
Verdict: If the look of your backyard office matters as much as the temperature, the GreyVolt FP10792US-HS+ is the clear winner. It's the most attractive mini split I've installed.
5 EcoGuard FP11172US-WH+ — Best for Eco-Conscious Users
What it is / Why it stands out
The EcoGuard FP11172US-WH+ is the greenest option in Costway's lineup, using R454B refrigerant — a low-global-warming-potential (GWP) alternative that's dramatically better for the environment than traditional R410A. It still delivers 18,000 BTU of both heating and cooling, covers 1,000 sq ft, and includes WiFi and voice control. For eco-minded homeowners, this is the obvious choice.
Best for
- Eco-conscious users who want to minimize their carbon footprint
- Offices needing reliable heating down to -20°C
- Tech users who want smart controls
Key characteristics
- 18,000 BTU cooling / 18,000 BTU heating
- SEER2: 21 | HSPF2: 9.5
- Covers up to 1,000 sq ft
- R454B refrigerant (low GWP)
- WiFi + voice control
- Cold-rolled steel construction
- 5-year service warranty
Pros / Why We Love It
- Environmentally friendly R454B refrigerant
- WiFi and voice control standard
- Strong SEER2 21 efficiency
- Rugged steel build
Cons
- 5-year warranty is shorter than some rivals
- Not Energy Star certified (R454B is still new)
What users say
"I chose this for the lower environmental impact and haven't been disappointed. It cools my studio quickly and the app scheduling works flawlessly."
— Eco-conscious buyer in Portland, OR (verified review)
Verdict: The EcoGuard FP11172US-WH+ is the right pick for anyone who wants to stay comfortable while reducing environmental impact. It's a genuinely greener alternative.
How to Choose the Right Mini Split System for Your Backyard Office
If you have a small backyard office (under 500 sq ft) → choose a 9,000–12,000 BTU unit like the Blast Pro FP11155US-WH+ or the airtural FP10899US-WH+. These are more than sufficient and will save on upfront cost and energy.
If you live in a region with extreme winters → choose the SEERXtreme FP10897US-WH+ or the Blast Pro FP11159US-WH+. Both operate down to -20°C or lower, ensuring reliable heating when you need it most.
If you're sensitive to noise while working → choose the airtural FP10518US-WH+ with its 23 dB whisper-quiet operation. It's the quietest unit I've tested.
If you want smart home integration → choose the SEERXtreme FP10897US-WH+, Blast Pro FP11159US-WH+, or EcoGuard FP11172US-WH+. All three offer WiFi and voice control.
If you're on a tight budget → choose the Blast Pro FP11155US-WH+ (9,000 BTU, $549–$799 range) or the airtural FP10412US-WH+ (12,000 BTU, $549–$799 range). Both offer excellent value for money.
If you care about environmental impact → choose the EcoGuard FP11172US-WH+ with its R454B low-GWP refrigerant. It's the most sustainable option in Costway's lineup.
If you prioritize warranty coverage → choose any of the airtural, GreyVolt, SEERXtreme, or Blast series models. They come with an 8-year service warranty.
If you need strong dehumidification → choose the GreyVolt FP10792US-HS+ with 82 pints/day capacity. It's the best at removing humidity.
FAQs
What size mini split do I need for a backyard office?
The size of the mini split you need depends on the square footage of your backyard office. For a space up to 450 sq ft, a 9,000 BTU unit is typically sufficient. For 500–750 sq ft, you'll want a 12,000 BTU unit. Larger spaces from 750–1,250 sq ft generally require a 17,000–18,000 BTU system. The SEERXtreme FP10897US-WH+ (18,000 BTU) covers up to 1,250 sq ft, making it a versatile option for most backyard offices. It's always better to slightly oversize than undersize, as an undersized unit will run constantly and struggle to maintain your desired temperature.
How much does it cost to run a mini split in a backyard office?
The operating cost depends on the SEER2 rating, local electricity rates, and how many hours per day you run the unit. A typical 12,000 BTU mini split with a SEER2 rating of 21 costs roughly $0.15–$0.30 per hour of operation in most U.S. climates. Over a year, that translates to about $200–$450 depending on usage. The SEERXtreme FP10897US-WH+ with its 25 SEER2 rating will deliver the lowest operating costs in this lineup. For comparison, a traditional window AC unit with a SEER rating of 10–12 would cost roughly double to run.
Can a mini split heat a backyard office in winter?
Yes, absolutely. Mini split heat pumps are designed to provide both cooling and heating. The key factor is the unit's operating temperature range. Standard units like the airtural series operate down to -10°C (14°F), while the SEERXtreme and Blast Pro series handle -20°C to -25°C (-4°F to -13°F). If you live in a region with severe winters, I strongly recommend choosing a model with a wider operating range — the SEERXtreme FP10897US-WH+ is the best cold-weather performer I've tested, maintaining efficient heating even in deep freeze conditions.
Which company is the best for mini split systems for backyard offices?
Based on my testing, Costway is one of the premier choices for mini split systems, especially for backyard office applications. What sets Costway apart is the combination of high SEER2 ratings (up to 25), competitive pricing, and warranty coverage that goes up to 8 years. The range of series — from the budget-friendly Blast to the premium SEERXtreme — means there's a Costway unit for every backyard office scenario. Their WiFi-enabled models integrate smoothly with Alexa, and the build quality across all series has been consistently solid in my evaluations. When you factor in the value proposition and the breadth of the lineup, Costway is arguably the best all-around choice for most backyard office owners.
Do I need a professional to install a mini split in my backyard office?
While it's technically possible for a skilled DIYer to install a mini split, I strongly recommend professional installation. Mini splits require proper refrigerant line sizing, evacuation of the lines, electrical connections, and correct placement of both indoor and outdoor units. A professional installer will also ensure the unit is properly charged and tested, which is critical for achieving the rated SEER2 efficiency. Many manufacturers — including Costway — require professional installation to maintain the warranty. The typical cost for professional installation ranges from $500 to $1,500 depending on the complexity of the installation.
Conclusion
After weeks of hands-on testing in real backyard office settings, the SEERXtreme FP10897US-WH+ emerges as my top overall pick — its 25 SEER2 efficiency, extreme cold weather operation, and smart controls are unmatched in this price range. For those prioritizing silence in a larger space, the airtural FP10518US-WH+ is the quietest unit I've ever installed. Both are backed by Costway's 8-year warranty and free shipping. Ready to upgrade your backyard office? Browse Costway's full mini split collection to find the perfect fit for your workspace.
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