Mike Sanders’ Straight‑Talk Guide: “Mini Split Sizes — What You Really Need to Know”

If you’re shopping for a ductless or “mini‑split” system, one of the first terms you’ll see is “mini split AC sizes” (or “mini split sizes” for short). What do those numbers mean? How do you pick the right size? And how does the sizing of a mini‑split compare to a more standard bundle like the Goodman 3‑Ton bundle above?

I’ve worked on lots of installs, I’ve seen homeowners oversize, undersize, get frustrated with weird performance because the size was off. So let’s walk through everything—from the basics of mini splits to real‑world sizing, to how you compare to a traditional central system.

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What exactly is a “mini split” and why sizing matters

A mini‑split (also called ductless split system) is a system where you typically have an outdoor condenser unit and one or more indoor air‑handlers, with refrigerant lines rather than the traditional full ductwork of a central system. Because they are flexible, often more efficient, and can serve zones, they’re very popular today.

When it comes to sizing, “mini split sizes” typically refer to the system’s capacity—expressed in BTUs (British Thermal Units) or tons (1 ton = 12,000 BTU/h). For example, one sizing guide says:

“6000 BTU Mini Split = 0.5 Ton → covers ~200‑300 sq ft; 9000 BTU = 0.75 Ton → ~300‑450 sq ft; 12000 BTU = 1 Ton → ~500‑600 sq ft” (HVAC Direct)
Another says for larger sizes: 24,000 BTU (~2 tons) covers ~850‑1,100 sq ft. (HVAC Direct)

Why does this matter? Because if you mismatch size you can run into issues: too small = under‑performing, overheating, high electric bills; too large = short‑cycling, poor humidity control, wasted money. One expert says:

“The size of the spaces you want to heat and cool is just one of many factors … you want an HVAC contractor experienced in sizing, designing, and installing these systems.” (Trane)

So “mini split sizes” isn’t just a number—it’s a critical decision.

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How to estimate what mini split size you need

Here’s a walk‑through of how I walk homeowners through this sizing:

1. Measure your space – length × width to get square footage. If the zone is irregular, break it into parts.

2. Reference sizing charts – for example, one guide shows 9,000 BTU for ~300‑450 sq ft; 12,000 BTU for ~400‑550 sq ft. (Senville)

3. Use a rule‑of‑thumb – one rule says ~20 BTU per square foot in average conditions. (GREE Comfort)

4. Adjust for factors – ceiling height >8′, large windows/sun exposure, poor insulation, many occupants, or extreme climate all increase required capacity. For example, one sizing guide says to multiply square footage by 25 for rough BTU estimate. (Carrier)

5. Consider zone vs multi‑zone systems – Many mini splits are single‑zone (one indoor head, one outdoor unit). Others are multi‑zone (one outdoor unit, multiple indoor heads) which complicates sizing because you add up loads across rooms. 

6. Better yet: get a professional load calculation (Manual J) – always better when you’re dealing with custom spaces or non‑standard conditions.

So if you had a 500 sq ft living room with standard 8′ ceilings, average insulation and snow/climate moderate, one might estimate roughly a 12,000 BTU (~1 ton) mini split. But if you had vaulted ceilings, big west‑facing windows, poor insulation – you might bump up to ~15,000‑18,000 BTU (~1.25‑1.5 tons) or more.

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Typical mini split sizes & the square footage they serve

Here’s a quick table to help you see common mini split sizes and what they cover (ballpark) based on current guides:

*Note: These are guidelines only. Actual needed capacity can vary significantly based on all the factors above (insulation, ceilings, climate, etc.)

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How this relates to the Goodman 3‑Ton Bundle

Now you may be looking at the Goodman 3‑Ton 14.5 SEER2 R‑32 bundle (that’s our internal link) and thinking: “Mike, but that’s 3 tons—why are we talking about mini split sizes which often top out at 1–2 tons for many homes?” Good question. Here’s how I break it down:

• The Goodman bundle is designed for a standard ducted central system, 3‑ton capacity (~36,000 BTU). That size makes sense for a larger home with more square footage, ductwork, multiple rooms, multiple zones, etc.

• Mini splits often serve fewer zones (even a single room) and thus the size increments start smaller and scale differently.

• If you were comparing “should I do a mini split or a central system like the Goodman bundle?” you’d need to consider your home size, your ductwork, your budget, your efficiency goals.

• So talking about “mini split sizes” is helpful to put perspective around smaller zones, retrofits, or areas where you might not need a full 3‑ton central system. The size you pick matters just as much (if not more) than the brand or SEER rating.

In short: if your home is large and you need a full 3‑ton system like the Goodman, then yes, you’re in the right ballpark for that capacity. But if you’re simply considering a mini split for a specific zone or smaller space, the sizing will likely fall lower and you’ll want to use the charts we described above.

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Mistakes I see homeowners make with mini split sizing

As Mike Sanders, I’ve seen many folks stumble in this area. Here are the most common mistakes—and how to avoid them:

1. Assuming bigger is better
   Many people think “Let’s get the largest size so it handles anything.” But with mini splits, oversizing leads to short‑cycling, excess wear, poor humidity control, and waste. One guide warns: “For each room, calculate BTU then consult professional — sizing chart is for guidance only.” (Senville)

2. Relying only on square footage and not adjusting
   It’s common to see someone take “500 sq ft → assume 12,000 BTU” and stop there. But if you have high ceilings, poor insulation, lots of sun – you might need more. Ignoring those factors can lead to under‑performance.

3. Using the same size for multi‑zone without balancing
   With multi‑zone mini splits, you cannot just add up square footage blindly; each zone has different load. One source notes: “For multiple rooms/zones, calculate each room’s BTU need, then ensure the outdoor unit supports the sum.” (Senville)

4. Installing a mini split when a full central system is more appropriate (or vice‑versa)
   If your home has full ductwork and you need to condition multiple rooms and zones, a system like the Goodman 3‑ton bundle might make more sense than several mini splits (or a mini split sized incorrectly).

5. Ignoring the future expansion
   If you plan to finish a basement, add rooms, or expand conditioned space, sizing up a bit makes sense—but it must be justified by actual load, not guesswork.

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How to decide between mini split sizing and a central system size

Here’s how I would advise a homeowner considering whether to go with a properly sized mini split vs. stepping up to a system like the Goodman 3‑ton bundle:

Step A – Assess your minimal zone or area

• Are you conditioning one room, a basement, an ADU, or the entire house?

• What’s the square footage of that zone?

• What’s the insulation condition, ceiling height, windows, sun exposure, ductwork?

• If you find the size falls in the ~6,000–18,000 BTU range (~0.5‑1.5 tons) then a single‑zone mini split might make sense.

Step B – Evaluate your whole‑home or multi‑room needs

• If you’re looking at conditioning multiple rooms, whole‑home, or central system with ductwork, you might be in the 24,000–36,000 BTU (~2‑3 tons) range which aligns to a system like the Goodman 3‑ton bundle.

• Consider whether you already have ductwork—if yes, central system is viable; if no, mini splits may be more cost‑effective.

Step C – Compare costs, complexity, and flexibility

• Mini splits: generally more flexible, easier to zone, can install in retrofit spaces without major ductwork.

• Central systems/bundles: better for full‑home conditioning, may have lower per‑ton cost, may tie into existing ducts.

• Consider installation cost difference, and long‑term operation cost (efficiency, maintenance, lifecycle).

Step D – Perform or request a professional load calculation
The best way to avoid size‑mistakes is a Manual J calculation done by a qualified HVAC contractor. This will tell you the actual BTU needs and help you match to appropriate size rather than guessing.

Step E – Make your choice

• If the load calculation says you need ~12,000–18,000 BTU (~1–1.5 tons) and you’re conditioning a single space: choose a mini split sized accordingly.

• If it says you need ~36,000 BTU (~3 tons) for the space (or multiple rooms) then a full system like the Goodman 3‑ton bundle becomes the right choice.

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Real‑world example (Mike Sanders case study)

Let’s say you have a 1,200 sq ft open floor living/dining/kitchen area, with 9′ ceilings and large west‑facing windows, in a moderate climate. You’re considering a mini split or central system.

• Square footage alone: 1,200 sq ft × 20 BTU/sq ft ≈ 24,000 BTU (≈2 tons) based on general rule.

• But adjustment: 9′ ceilings (+10 % load), large windows/sun (+10 %), moderate insulation maybe standard → say +20‑25 %. So effective load ≈ 24,000 × 1.25 = ~30,000 BTU (≈2.5 tons).

• So if you aimed at a mini split, you’d choose ~24,000–30,000 BTU (~2–2.5 tons) for that zone. That means one of the larger capacity mini splits (or multi‑zone).

• On the other hand, if you already have ducts and condition full home, you might pick the Goodman 3‑ton (~36,000 BTU) bundle, which offers a bit of head‑room and works with the duct system.

In this case you might conclude: “Yes, go with the 3‑ton Goodman bundle since it matches the calculated load (~30,000 BTU) and I have full‑home ducts.” If you didn’t have ducts and only planned to condition the living area, a large mini split might be more efficient and cost‑effective.

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Sizing checklist for mini split systems

Here’s my checklist (Mike Sanders style) to bring to your HVAC contractor or to use when you’re planning a mini split:

• [ ] Measure each room/zone (length, width), note ceiling height.

• [ ] Note insulation levels (attic, walls), window types/quantity/orientation, sun exposure.

• [ ] Check how many rooms will be served by that one indoor head or multiple heads (zones).

• [ ] Check existing ductwork (if any) or plan non‑ducted solution.

• [ ] Identify internal heat loads (number of occupants, electronics, lighting).

• [ ] Use sizing chart / rule‑of‑thumb (e.g., 20‐25 BTU per sq ft) for estimate.

• [ ] Adjust for supplementary factors (ceiling height, sun, insulation, open plan).

• [ ] Consider future expansion or additional zones.

• [ ] Ask for a professional Manual J load calculation and ensure the proposal matches that result.

• [ ] Compare system options: mini split vs central system (like the Goodman 3‑Ton bundle) based on load, ducts, cost.

• [ ] Make sure the installer quotes both capacity and efficiency (SEER, HSPF), installation, warranty, and zoning/controls.

• [ ] Plan for installation logistics: refrigerant piping lengths, indoor unit mounting, outdoor unit clearances, wiring, condensate handling, remote controls.

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Why sizing matters so much for performance & comfort

Let me highlight some consequences of getting sizing wrong—because this is where folks often get frustrated even though they bought the “right brand”.

• Undersized unit → runs constantly, still struggles to cool, higher electric bills, possibly hot spots, premature wear.

• Oversized unit → cools too quickly, short‑cycles (turns on/off too frequently), doesn’t remove humidity properly (especially in cooling mode), may cause comfort issues like clammy rooms.

• Poor zone/room matching → you may choose a capacity that works for one space but the system struggles or overworks for another zone.

• Efficiency penalty → systems operate most efficiently when sized and installed properly. If you oversize, you may compromise efficiency and lifespan.

• Comfort problems → even if the temperature is met, humidity and air distribution may be off, resulting in “feels hot/cold/uncomfortable” even though thermostat says correct temp.

So when we talk about “mini split sizes” we’re really talking about right sized mini splits. The size isn’t the only factor, but it’s among the most critical.

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Final thoughts from Mike Sanders

Alright, to wrap it all up—if you’re in the market and you’ve landed on seeing “mini split AC sizes / mini split sizes” you’re asking the right questions. Let me leave you with the key takeaways:

• Size matters. Don’t pick based purely on marketing or price.

• Use square footage as a starting point (e.g., ~20 BTU per sq ft) but then adjust for ceiling height, insulation, windows, climate, etc.

• For many rooms, mini splits will fall in the range of ~6,000‑18,000 BTU (~0.5 to 1.5 tons) based on common sizing charts.

• If your load calculation shows you need ~24,000‑36,000 BTU (~2‑3 tons) or you have full‑home ductwork, then a system like the Goodman 3‑Ton bundle comes into play.

• Never skip the professional load calculation. It’s the surest way to avoid costly mistakes.

• Work with a licensed, experienced installer who understands both mini splits and conventional systems.

• Don’t assume oversizing means “better”. A properly sized system trumps a too‑large one in performance, comfort, and long term cost.

• Consider your future plans (expansion/zoning) so you can install a system today that still works in 5‑10 years.