How to Buy a UPS Without Regret: A 9-Step Checklist From an Office Admin

Who this checklist is for

I'm the office administrator for a 210-person company — two offices, a warehouse, and a network closet in each building that nobody thinks about until it goes dark. I run most of the non-IT procurement here. Over the last five years that's meant somewhere around 40 UPS units, everything from $90 desktop bricks under reception desks to a pair of 30kVA three-phase units we installed during the 2024 build-out.

This is the checklist I actually work from. Nine steps, in order. It's written for the person who buys the thing, gets it invoiced, and then lives with it for a decade — not for an electrical engineer.

Fair warning: if you skip step 3, every decision after it is a guess.

The 9-step checklist

1. Walk the floor yourself and list everything that has to keep running

Don't start from the list IT emails you. Walk it. Open the closets, look behind the desks, check the warehouse office. My first pass five years ago missed the PoE switch running the door badge readers, which is why nobody could get into the building for 40 minutes during an outage back in 2022.

What usually makes the list: workstations, monitors, network switches, PoE switches, the NAS, the phone system, the NVR for the cameras, the warehouse barcode scanners, and whatever the front desk uses to check people in.

What shouldn't: laser printers, space heaters, anything with a heating element. A laser printer's fuser pulls a huge inrush when it wakes up. I've watched a perfectly sized 2kVA UPS drop its whole load because someone sent a 40-page document to print during a brownout. Put printers on the let-it-die list.

2. Sort that list into three tiers

You'll never afford to back up everything for an hour, and you don't need to.

• Tier 1 — has to ride through 10–15 minutes and shut down gracefully: servers, switches, NAS, badge system, phone system.
• Tier 2 — has to survive a flicker or a 30–60 second dip: workstations, POS terminals, scanners.
• Tier 3 — can go down: spare-desk monitors, printers, the coffee situation.

Write the tier next to each item. Now you know how many units you're buying and roughly what shape they need to be.

3. Measure the real load instead of reading the nameplate

This is the step everyone skips, and it's the expensive one.

People add up the wattage printed on the power supplies and buy to that number. That's how you end up with a 2kVA UPS that runs for four minutes, or a hugely oversized unit that never loads above 8% and still eats a battery string every four years.

A nameplate is a maximum, not a draw. A standard office PC with two monitors measured 145 W on our floor — I'd been budgeting 400 W for the same desk. We had been oversizing by about 2.5x. Maybe 2.7x on a few of them, I'd have to go back and check the spreadsheet.

Buy a $30 plug-in power meter, or read the metering on your rack PDU if you have one. Log a full workday. That number is what you size against.

4. Pick the topology before you pick anything else

IEC 62040-3 sorts UPS units into three basic classes, and the class matters more than the brand:

• VFD (standby/passive) — the cheap UPS mini units, 600–900VA. Fine for a router and a modem. Transfer time is typically 6–10 ms and the output is often a stepped approximation of a sine wave.
• VI (line-interactive) — what most "ups for pc" searches actually need. Voltage regulation built in, and usually a true sine wave on anything decent.
• VFI (online double-conversion) — the load always runs off the inverter, so there's zero transfer time. This is what a 1kVA online UPS is (catalogs often list these as a "1kv online ups" — same box, just sloppy unit labeling).

Go online (VFI) when the equipment has an active PFC power supply that's picky about waveform, when you need long holdover, or when the power in the building is genuinely dirty. Go line-interactive for a workstation or a small switch. Use standby units only where a few seconds of downtime is acceptable.

5. Size in watts, then derate

VA and W are not the same number. Modern units are often rated at 0.9 or unity output power factor, so a 2kVA UPS may legitimately deliver 1,800–2,000 W. Older ones at 0.6–0.7 gave you far less. Ask for watts, always.

Then:

• Derate 20–25% for battery aging and future growth.
• Ask for the runtime chart at your measured load, not at half load.
• Plan on roughly two-thirds of the published runtime once the batteries are three years old.

What vendors won't tell you is that the runtime chart was generated at 25°C with brand-new batteries and a resistive test load. Your closet is not 25°C and your load is not resistive.

6. Decide modular versus single-block — honestly

A modular UPS system lets you populate the frame with hot-swappable power modules, add capacity as you grow, and run N+1 without buying a second unit. At 20kVA and above, in a room you expect to fill, it's usually the right call. A failed module becomes a 20-minute swap instead of a service call.

It is not the right call for a four-person branch office. You'll pay a premium for a frame you'll never fill, and you'll be locked into one vendor's module pricing for ten years. Ask what a spare module costs before you sign, not after.

7. Check the electrical reality of the room

This is where projects slip a month.

A desktop unit plugs into a NEMA 5-15 and you're done. A 30kVA UPS is a different animal — typically three-phase 208V, hardwired, with a dedicated circuit, breaker coordination, and an electrician. It also weighs a few hundred pounds with batteries installed, so you're dealing with floor loading, freight, a liftgate, and possibly rigging.

Get the electrician's quote before you get the UPS quote. I've watched a $14,000 unit turn into a $19,000 project because the panel didn't have room. Don't hold me to this across every market, but I think our last three-phase install ran about $4,500 in labor alone.

If the UPS is going into a dedicated IT equipment room, NEC Article 645 changes some of the rules around disconnects and cabling. Loop in your electrician or AHJ rather than guessing.

8. Buy the monitoring, not just the box

It took me about three years and 40-odd UPS purchases to understand that nobody ever complains about the UPS — until it fails, and then it's the only thing anyone talks about. A UPS that fails silently is just a heavy power strip. Confirm before you order:

• Is there an SNMP card slot, and is the card included or extra? (Usually extra. Budget $200–400.)
• Does it support dry contacts into your building management system?
• Does the auto-shutdown agent actually support your OS and your hypervisor?
• Who gets the alert when the battery self-test fails at 3 a.m.?

That last one is the whole point. In August 2023 we had an outage that took the network down for four hours — not because the UPS failed, but because the battery string had been dead for months and nobody was watching. The unit reported "on battery, 3 minutes remaining," and then it didn't.

9. Do the five-year math, not the purchase-price math

For everything above 1kVA, the batteries will cost more than the unit over its life. Rough numbers from our own recent quotes (early 2025 — verify current pricing before you budget):

• UPS mini (600–900VA): $70–150, disposable, not worth replacing batteries.
• 1kVA online UPS: $250–500.
• UPS 2 kVA: $500–950, with a battery set around $120–200 every 3–5 years.
• 30kVA UPS: $12,000–25,000+ before installation, and a battery string at $3,000–8,000 every 4–5 years.

VRLA batteries are generally rated for a 3–5 year design life at 25°C, and IEEE 1188 covers the maintenance and testing practice behind that number. The commonly cited rule of thumb is that every 8–10°C above 25°C cuts that life roughly in half. Our first closet ran at 31°C in summer and we replaced the batteries at 30 months. Nobody warns you about that at the quoting stage.

Get the battery string price in writing at purchase. Otherwise you'll be negotiating from a standing start in year four with a dead UPS and a purchase order that's already closed.

Where this goes wrong — my scars

A few things I'd hand to anyone doing this for the first time:

• Don't buy on VA alone. The question everyone asks is "how many kVA?" The question they should ask is "how many watts at my load, for how many minutes, with batteries that are three years old?"
• Check that the vendor can invoice you properly. In 2021 I found a great price on a batch of units from a new supplier — about 22% cheaper than our regular vendor. They couldn't produce a proper invoice, only a handwritten receipt. Finance rejected the expense report and I ate $1,900 out of my own department budget. Now I verify tax ID, PO acceptance, and invoicing capability before I place any order, no matter how good the quote looks.
• Ask about lead time on batteries specifically, not just on the unit. The unit ships in a week; the matching battery string can sit on backorder for months.
• Don't oversize "just in case." A UPS running at 5% load is inefficient, wastes budget, and doesn't live longer. Size to your measured load plus 20–25%.
• Write down the model and serial numbers. You will need them in three years and nobody will remember where the purchase order went.

To be fair, this is what works for us. We're a 210-person company with two predictable offices and slow, steady growth. If you're running a clinic, a trading floor, or anything where 30 seconds of downtime is a real event, the calculus is different and you should be talking to someone who does this full time.

But for a normal office, nine steps and an honest look at the real load will get you most of the way there.

Pricing above is from our own early-2025 quotes and is for general reference only — actual prices vary by vendor, capacity, and battery configuration. Verify current rates before you budget.