How to Choose a UPS – a Practical Guide

An uninterruptible power supply (UPS) protects your equipment from power cuts, voltage drops and surges. The right UPS keeps a computer, server, router, video surveillance system or heating boiler running; the wrong one either overloads or runs for only a few minutes. Here is how to choose, step by step.

1. Add up your load in watts (W)

List every device that will be connected to the UPS and add up its real power consumption in watts. Typical values:

• Office computer – 60–150 W
• Monitor – 20–40 W
• Router or Wi-Fi access point – 10–20 W
• Video recorder (NVR) with disks – 20–50 W, PoE camera – 5–12 W each
• Gas boiler pump and controls – 80–150 W
• Server – 200–600 W

Add a 20–30% reserve to the total. Running a UPS close to its maximum shortens both battery runtime and UPS life.

2. VA and W – check both numbers

A UPS has two ratings: apparent power in VA and real power in W. For example, a 1000VA/600W UPS can carry at most 600 W. Choose by watts. More in our article VA vs W – what is the difference.

3. Choose the UPS type

• Line-interactive – with automatic voltage regulation (AVR) at an affordable price. Good for computers, routers, video recorders and point-of-sale systems.
• Online (double conversion) – the load always runs from the UPS inverter, with zero transfer time. Best for servers, medical and laboratory equipment, boilers, unstable mains and generator backup.

The differences in detail: Line-interactive vs online UPS.

4. How long should it run?

With built-in batteries a UPS usually runs 5–15 minutes at half load – enough to save files and shut down properly. If you need hours of backup (for a boiler, cameras or a network), choose a UPS for external battery packs.

Work out how many batteries you need with our UPS calculator, or read how many batteries does a UPS need.

5. Output waveform

Budget UPS units produce an approximated (modified) sine wave on battery. Power supplies with active PFC, pumps, motors and heating boilers may not work properly on it. For these loads choose a UPS with a pure sine wave – every online UPS has one.

6. Form factor, outlets and management

• Tower or rack – for a server rack choose a rack or convertible (rack/tower) model.
• Outlet type and count – Schuko (standard) or IEC C13/C19 (server style).
• Management – USB or an SNMP card lets servers shut down automatically and safely during a long outage and lets you monitor the UPS over the network.

7. Battery care

A UPS lead-acid battery lasts about 3–5 years at 20–25°C. Every 10 degrees hotter roughly halves its life, so keep the UPS in a cool, ventilated place. Replacing old batteries is inexpensive – see batteries.

Quick selection table

See all UPS systems with prices.