Single vs. Multi-Unit Setup: Is One 20 Ton AC Enough for Your Building?

When I started planning for a new Daikin 20 Ton 14.2 IEER2 packaged rooftop unit, one big question kept me up at night:

👉 Should I go with one big 20 Ton system, or split the load across multiple smaller units?

It’s not an easy decision. Both setups have pros and cons when it comes to cost, comfort, redundancy, and long-term savings. In this guide, I’ll walk you through what I learned while weighing a single 20 Ton unit against a multi-unit setup, so you can make the right call for your building.

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🏢 Why the Question Matters

Commercial spaces vary — from single-tenant warehouses to multi-tenant office buildings. Both might need 20 Tons of cooling capacity (240,000 BTU/hr).

But you can achieve that capacity in different ways:

• One big packaged unit (like the Daikin 20 Ton 14.2 IEER2)

• Two smaller packaged units (e.g., 2 × 10 Ton)

• Four even smaller ones (e.g., 4 × 5 Ton)

This choice affects:

• Upfront equipment and installation cost

• Reliability if something breaks

• How easy it is to zone for tenants

• Utility bills and long-term ROI

📎 DOE – Commercial HVAC Standards

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⚖️ Pros of a Single 20 Ton Rooftop Unit

1. Lower Equipment Cost

Buying one unit is usually cheaper than buying multiple smaller units. Manufacturers build large systems like the Daikin 20 Ton to handle big loads efficiently.

2. Simpler Installation

• One crane lift

• One electrical disconnect

• One curb and duct transition
  All of this reduces labor hours compared to coordinating multiple units.

3. Compact Footprint

Rooftop space can be limited, especially in downtown or strip mall settings. A single 20 Ton unit takes up less space than multiple curbs and pads.

4. High Efficiency in One Package

Daikin’s 14.2 IEER2 exceeds the federal minimum. With a single unit, you know exactly what your building is drawing.

👉 For my install, one unit simplified everything. The crane only had to make a single lift, and my electrician only had to set up one disconnect.

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🧩 Cons of a Single Unit

1. No Redundancy

If the unit goes down, the whole building loses cooling. For mission-critical spaces (like data centers or medical offices), that’s a big risk.

2. Higher Installation Complexity

A 20 Ton unit weighs over 2,000 lbs. That means:

• A larger crane

• Stronger roof structure

• Bigger street closure permits (if rooftop)

3. Zoning Limitations

One unit = one thermostat. Yes, you can add VAV boxes or zoning controls, but it’s more complex and costly than just running multiple small units.

4. Peak Demand Charges

One large unit hitting full load can spike your demand charges with the utility company, depending on your rate structure.

📎 ASHRAE Guidelines on Zoning & Load Management

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🔀 Pros of a Multi-Unit Setup

1. Redundancy

With multiple units, if one goes down, the others keep the building livable. Tenants might not even notice if capacity loss is partial.

2. Flexible Zoning

Each unit can serve a different zone, tenant, or floor. That’s ideal for multi-tenant properties or office buildings with varying cooling needs.

3. Easier Crane Lifts

A 5 or 10 Ton unit weighs much less than a 20 Ton. Smaller cranes = lower lift costs, and in some cases, you may not need a crane at all (forklift works).

4. Staged Load for Efficiency

Running multiple units allows you to stage the cooling load. On mild days, one or two small units can handle the demand, keeping part-load efficiency high.

👉 In fact, a properly staged multi-unit setup can outperform a single large unit on mild days.

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⚡ Cons of Multi-Unit Setup

1. Higher Equipment Cost

Buying multiple units almost always costs more upfront. Manufacturers don’t scale pricing linearly — one 20 Ton unit is usually cheaper than two 10 Tons.

2. More Complex Install

• Multiple curbs

• More duct transitions

• More electrical disconnects

This adds to labor hours.

3. Ongoing Maintenance

More units = more filters, belts, and coils to service. That means higher maintenance contracts.

4. Rooftop Space Required

Some buildings don’t have the square footage to support multiple curbs without crowding service clearances.

📎 Energy.gov – Rooftop vs. Multi-Unit Considerations

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📊 Cost Comparison: One 20 Ton vs. Multiple Smaller Units

Here’s how the numbers shook out when I priced both options for my building:

👉 My single Daikin 20 Ton install came in around $55,800 all-in. The multi-unit options would have added $5,000–$20,000 to the project cost.

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🏢 Case Study: Mark’s Building

I went with one Daikin 20 Ton 14.2 IEER2 packaged unit for three reasons:

1. Single tenant — My building isn’t multi-tenant, so zoning wasn’t critical.

2. Budget — The upfront savings compared to multiple units was significant.

3. Space constraints — My rooftop didn’t have the footprint for multiple curbs.

But I know the risks:

• If my unit fails, cooling is gone until it’s repaired.

• I’ll have to budget carefully for preventive maintenance.

If I owned a multi-tenant property, I’d strongly consider two 10 Ton units instead for redundancy and tenant comfort.

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💡 Mark’s Recommendation

Here’s how I’d simplify the decision:

• ✅ One 20 Ton Daikin rooftop unit if:

  • Single-tenant building

  • Budget is tight

  • Rooftop space is limited

• ✅ Multiple smaller units if:

  • Multi-tenant property

  • Can’t afford downtime

  • Need precise zoning control

  • Willing to pay more upfront for redundancy

👉 At the end of the day, the “right” answer depends on your building use, tenant needs, and tolerance for downtime.

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In the next topic we will know more about: How Daikin’s Commercial Warranty Works (and What Mark Learned Reading the Fine Print)