Is a 10 Ton Rooftop Unit Enough for Your Building? Tony’s No-Nonsense Sizing Breakdown
If you’re responsible for a commercial building—office, store, warehouse, restaurant, gym, you name it—you already know HVAC isn’t something you can shrug off. When a rooftop unit is undersized, the building turns into a sauna, people complain, humidity spikes, and equipment gets hammered so hard it dies prematurely. Oversize it and you get short cycling, uneven comfort, mold risks, wasted energy, and replacement bills long before the equipment should’ve aged out.
That brings us to the question every facility manager, building owner, and contractor ends up asking at some point:
“Is a 10-ton rooftop unit enough for my building?”
Here’s my answer as Tony—the guy who has had more roof hours than most people have had hot lunches:
It depends.
It depends on the building, the people inside it, the equipment, the sun, the roof, the insulation, and even the ZIP code.
Commercial HVAC sizing isn’t a guessing game. It’s math, physics, and experience rolled together. And the truth is, 10 tons might be perfect—or it might be laughably small.
Let’s break it down, Tony style.
What “10 Tons” Actually Means
Let’s get the terminology out of the way.
One ton of cooling = 12,000 BTU/hour.
So a 10-ton rooftop unit gives you 120,000 BTU/hour of cooling capacity.
Sounds big. But commercial loads aren’t neat, tidy, or polite. They swing like crazy based on:
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Internal heat generation
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Ventilation rates
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Sun exposure
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Occupancy
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Equipment
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Insulation
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Windows
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Roof type
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Climate zone
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Airflow and static pressure
Anyone who sizes a system using square footage alone is asking for a system that fails when you need it most.
Here’s a helpful reference on cooling capacity basics:
[Cooling Capacity Principles]
Why Square Footage Alone Is Never Enough
Sure, you can use square footage as a rough estimate, but that gets people into trouble more often than not. Commercial buildings are NOT like houses. A warehouse doesn’t act like a restaurant. A gym behaves nothing like an office. A school classroom has completely different ventilation and occupancy needs than a nail salon.
Here’s the general square-foot-per-ton ballpark:
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Offices: 4,000–7,000 sq ft
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Retail: 3,500–6,000 sq ft
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Restaurants: 2,500–4,000 sq ft
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Gyms: 2,500–3,500 sq ft
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Warehouses: 5,000–8,000 sq ft (only if insulated and low occupancy)
But Tony’s rule?
“A building’s cooling load is determined by what happens inside it—not its floor area.”
I’ve seen 3,500 sq ft restaurants that needed 12.5 tons and 6,000 sq ft warehouses that were fine with 7.5 tons.
That’s the range we’re working with.
Internal Heat Loads: The BTUs That Sneak Up on You
If there’s one thing that gets underestimated in commercial HVAC sizing, it’s internal heat load. People assume the space size is the main factor. Nope. The equipment inside the building often generates more heat than the sun.
Let’s break it down.
Occupancy Load
Every human is a little space heater. Depending on activity level:
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Light office work: 200–250 BTU/h per person
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Retail traffic: 250–350 BTU/h per person
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Gym workout: 400+ BTU/h per person
Twenty people create an additional 4,000–8,000 BTU/h.
That’s half a ton to a full ton of additional cooling.
Stick 40–60 people in a room?
Now you're looking at two tons of cooling just to offset warm bodies.
Lighting Load
Even LED lighting still adds heat.
Older fluorescents and metal halide lamps?
They turn your building into a heat lamp.
The higher the wattage, the more cooling you need.
Equipment Load
Commercial equipment produces SERIOUS heat:
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Computers
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Printers
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POS systems
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Refrigeration cases
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Display freezers
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Fryers, ovens, grills
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Fitness equipment
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Air compressors
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Motors
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Vending machines
You’d be amazed at how much heat one open-case cooler can dump into a room.[Commercial Energy Consumption Overview]
Specialty Rooms = Specialty Tonnage
A small server room can need its own mini-split.
A kitchen will always need excess tonnage.
A gym will always need more tonnage PLUS better ventilation.
These loads aren’t “optional add-ons.”
They’re the difference between comfort and chaos.
Climate Zone: The Line Between “Enough” and “Not Even Close”
Your location matters more than you think.
Cooling in Phoenix is not like cooling in Denver.
Cooling in Miami is nothing like cooling in Chicago.
Let me put it bluntly:
“Your climate zone can change your cooling requirement by 20–40%.”
Here’s how different regions behave:
Hot-Dry (Phoenix, Vegas)
You’ll need more sensible cooling because of brutal outdoor temps.
Hot-Humid (Miami, Houston, New Orleans)
Moisture removal becomes the real battle.
Undersize the system and humidity skyrockets.
Mixed-Humid (Atlanta, Charlotte)
You need balanced sensible + latent capacity.
Cold Climates (Minnesota, Michigan, North Dakota)
Cooling needs are lighter, but humidity still matters in shoulder seasons.
[Climate Zone Reference Material]
If you're in a high-heat or high-humidity zone, your 10-ton unit will feel smaller than it looks on paper.
Ventilation and Fresh Air: The Dealbreaker
Ventilation is the #1 reason commercial HVAC systems are undersized.
Every cubic foot of outdoor air has to be:
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Cooled
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Dehumidified
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Filtered
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Pushed through ductwork
Ventilation requirements are based on ASHRAE 62.1 standards, and they vary by building type:
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Gyms: extremely high ventilation
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Restaurants: very high
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Classrooms: high
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Retail: moderate
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Offices: moderate
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Warehouses: low
Boosting your outdoor air intake from 10% to 25% can require another 1–2 tons instantly.
This is where 10 tons often stops being enough.
Roof Conditions: The Overlooked Heat Source
Commercial rooftops get hit HARD by sunlight.
A dark roof can hit 150–170°F in summer.
Your roof materials determine how much heat transfers into the building.
Reflective Roof (white TPO)
Reduces cooling load significantly.
Old black EPDM roof
Acts like a skillet.
Adds tons of load.
Poor roof insulation
Also adds major sensible heat.
A reflective roof can literally allow the same 10-ton unit to cool a space that would need 12.5 tons otherwise.
Ductwork & Static Pressure: The Silent Capacity Thief
You can have all the tonnage in the world, but if your ductwork is undersized, leaking, poorly routed, or full of sharp turns, your airflow drops.
Low airflow = low capacity.
It doesn’t matter that the unit is 10 tons.
If your static pressure is high, the rooftop unit simply can’t move enough air.
Buildings that “won’t cool down” often don’t have a tonnage problem—they have an airflow problem.
[Ductwork & Static Pressure Fundamentals]
Building Type: What a 10-Ton Unit Can Actually Handle
Here’s the truth about which buildings match which loads.
Offices (4,000–7,000 sq ft)
A 10-ton unit works for MOST offices if:
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Moderate occupancy
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Normal equipment load
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Decent insulation
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Reasonable window area
Office buildings are the most predictable load type.
Retail (3,500–6,000 sq ft)
Retail stores often need more tonnage because:
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Lighting loads
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Door opening frequency
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Weekend traffic
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Display equipment
10 tons may work, but only for smaller spaces with low plug loads.
Restaurants (2,500–4,000 sq ft)
Restaurants create heat like nobody’s business:
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Grills
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Fryers
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Ovens
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Hood systems
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Dishwashers
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Foot traffic
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Outdoor air demand
A 10-ton unit will NOT cover a typical restaurant unless it's exceptionally small.
Gyms (2,500–3,500 sq ft)
Gyms need:
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More cooling
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More ventilation
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More humidity control
If you're trying to cool 3,000 sq ft of sweaty humans with a single 10-ton RTU, prepare for complaints.
Warehouses (5,000–8,000 sq ft)
If they’re insulated and lightly occupied, a 10-ton system has shocking range.
But add machinery, forklifts, or big bay doors, and that range collapses quickly.
Mixed Use
Never try to cover mixed-use spaces with one rooftop unit.
Each use type has a different load profile.
One RTU will always underserve at least one area.
What Happens When You Undersize a 10-Ton Unit
People think “the worst that can happen is the space will be warm.”
Incorrect.
Here’s the real list:
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Compressor overheating
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Reduced compressor lifespan
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Frozen coils
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Long runtimes
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Soaring utility bills
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Humidity problems
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Hot spots
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Constant complaints
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Premature equipment failure
Undersizing is more expensive than buying the right size upfront.
What Happens When You Oversize a 10-Ton Unit
Oversizing creates its own nightmare:
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Short cycling
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Poor dehumidification
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Temperature swings
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Mold growth
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Noise
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Higher maintenance
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Early unit death
People love to say “bigger is better,” but in HVAC?
Bigger is usually worse.
When a 10-Ton Unit Is Enough (Tony’s Green Light)
A 10-ton rooftop unit is probably correct if:
✔ Your building is 4,000–7,000 sq ft
✔ Occupancy is moderate
✔ Equipment load is average
✔ You have decent insulation
✔ You’re not in a brutal climate zone
✔ Ventilation needs are standard
✔ Your ductwork supports the airflow
✔ The space is ONE type of use
If all of that is true, 10 tons is a solid, efficient, cost-effective choice.
When a 10-Ton Unit Is Not Enough (Tony’s Red Flags)
A 10-ton unit is NOT enough if:
✘ Your building has high occupancy
✘ You have kitchens or heavy equipment
✘ You’re in a hot-humid climate
✘ You have poor roof insulation
✘ You need above-average ventilation
✘ You’re cooling multiple use types
✘ You have large west-facing windows
If even one of these applies, you need to recheck the load.
If two or more apply?
Forget 10 tons.
Wrapping It Up: Tony’s Final Verdict
A 10-ton rooftop unit is a great system size—if it matches the building. Too often, people size by square footage alone without accounting for:
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Occupancy
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Ventilation
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Internal equipment load
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Climate
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Sun exposure
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Airflow
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Roof conditions
Do that, and you’re asking for big trouble.
My advice?
If you want comfort, longevity, efficiency, and fewer 2 a.m. phone calls, do the load calculation.
Do it right.
No guessing.
No shortcuts.
A properly sized system is cheaper than a broken one—every single time.
In the next blog, we will know what makes this unit a smart commercial upgrade in 2025.
