Undersize the air conditioner in a telecom equipment shelter and you get thermal shutdowns. Oversize it and you get short-cycling, poor humidity control, and wasted equipment cost. Getting the tonnage right the first time is one of the most important decisions in a shelter build-out — and it's simpler than most people expect once you know what actually drives the load.
Why Telecom Shelters Are Different From Ordinary Buildings
A typical office or home is sized around occupancy and solar gain. A telecom shelter is sized almost entirely around internal heat load — the electronics inside generating heat around the clock, regardless of outside temperature. That's why shelters often need cooling even in the dead of winter, and why the sizing math looks different from a residential load calculation.
The core inputs you need:
- Total electronics heat load (in watts or BTUH) — sum the heat dissipation of every rack, battery cabinet, and piece of equipment in the shelter. Most manufacturer spec sheets list this directly; if not, a rough rule of thumb is that nearly all the electrical power consumed by the equipment converts to heat.
- Building envelope gain/loss — wall, roof, and door insulation values, plus shelter square footage and exposure.
- Design ambient temperature — the extreme high (and sometimes low) outdoor temperature for your site's climate zone.
- Redundancy requirements — many carrier-grade sites run N+1 cooling, meaning two units each sized to carry the full load independently.
Matching Heat Load to Tonnage
Once you have total BTUH from the electronics load plus envelope gain, match it against nominal cooling capacity:
| Nominal Capacity | Tonnage |
|---|---|
| 24,000 BTUH | 2 ton |
| 36,000 BTUH | 3 ton |
| 48,000 BTUH | 4 ton |
| 60,000 BTUH | 5 ton |
| 72,000 BTUH | 6 ton |
A good rule of thumb: build in a small margin (5-10%) above your calculated load rather than sizing to the exact number, since real-world conditions and future equipment additions rarely trend downward.
Standard vs. Economizer: It Affects More Than Comfort
Once tonnage is settled, the next decision is standard (non-economizer) vs. factory-installed economizer. An economizer brings in cool outside air for "free cooling" whenever ambient conditions allow, locking out the compressor entirely during those hours. In most US climates that means thousands of hours a year where the compressor simply isn't running — lower energy bills and less mechanical wear over the life of the unit.
The tradeoff is upfront cost and a small amount of added complexity (a damper and enthalpy sensor). For unattended, energy-cost-sensitive sites — which describes most telecom shelters — the economizer usually pays for itself.
Don't Forget Electric Heat
Even in warm climates, most wall mount shelter units ship with electric heat as backup, since electronics still need protection during equipment downtime or in extreme cold snaps. Heat kW options typically range from 5kW up through 15kW depending on unit size — sized to the shelter's heat-loss calculation, not the cooling load.
A Quick Sizing Checklist
- Add up electronics heat load (watts → BTUH: multiply by 3.412)
- Add estimated envelope gain for your shelter size and insulation level
- Match total BTUH to the nearest tonnage, rounding up
- Decide standard vs. economizer based on run-hours and energy cost sensitivity
- Confirm voltage/phase availability at the site
- Account for redundancy (N+1) if the application requires it
Ready-to-Ship Options
Every wall mount unit we carry — 2 through 6 ton, standard or economizer-equipped — ships with ground freight included and is in stock now. Browse the full lineup, including electric heat kW and refrigerant details for each model, on the Wall Mount HVAC Units page.
Have a specific shelter or heat load you're trying to size? Contact us with your numbers and we'll help you land on the right model before you order.