A 1500VA UPS for your home server is really a 900W UPS
Key takeaways
- VA is not watts. A 1500VA UPS is typically rated 900W, and the watt figure is the only one that decides whether your kit fits.
- Measure your real draw at the wall, multiply by 1.5, then buy the nearest tier up. Most home NAS boxes pull 30 to 60W, far less than people assume.
- Aim for 10 to 30 minutes of runtime, not hours. A UPS exists to shut the server down cleanly, not to keep it running through the outage.
- Budget for a battery replacement every three to five years. That recurring cost usually exceeds the difference between the cheap unit and the good one.
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1500VA. It is printed on the box in the largest font the marketing team could get away with, and it is not the number that matters. The same unit is rated 900W, and watts are what decides whether your kit actually fits.
That gap is where most people overspend or, worse, undersize. A UPS for a home server is one of the few purchases where the spec sheet openly tells you two different things and lets you pick the flattering one.
VA is not watts, and the gap is where the money goes
Volt-amps measure apparent power. Watts measure the real work. On a UPS the ratio between them sits somewhere around 0.6, which is why a 1500VA unit carries a 900W rating and a 1600VA unit carries 960W.
Your gear is quoted in watts. So the conversion you want runs the other way: take your measured draw in watts, multiply by roughly 1.6 to reach volt-amps, then add about 30 percent so the UPS is not living at its limit. A 60W load becomes about 96VA, then about 125VA with headroom. That is a long way below the 1500VA box everybody reaches for by default.
One thing worth flagging before you shop: these figures are for 230V units sold in the UK, EU, Australia and most of Asia. North American 120V models carry different wattage ratings and different socket types for the same VA number, so check the regional SKU rather than the family name.
How to size a UPS for a home server in three steps
Step one: measure, do not estimate
Plug the NAS or server into a socket energy monitor and read it. Idle, then during a parity check or a big transfer, because the peak is what you are buying for.
People consistently guess high. Typical real numbers:
- A two-bay NAS plus a small switch: around 30W
- A four-bay NAS with four large drives: around 50W
- An eight-bay DIY build on a Ryzen 5 with eight drives: around 110W
A Raspberry Pi 5 running as a home server is a rounding error next to any of those, well under 15W with a drive attached. A Beelink Mini S12 Pro sits in similar territory. Spinning disks are what drive the number up, and NAS drives like the Seagate IronWolf Pro draw most heavily during spin-up rather than at rest.
Step two: multiply by 1.5
Take the measured peak watts and multiply by 1.5. That covers spin-up surges, whatever you add to the rack next year, and the fact that a UPS running near capacity has a miserable runtime curve.
Fifty watts measured becomes a 75W design target. One hundred and ten becomes 165W. Both sit comfortably inside a mid-range unit, which is the point.
Step three: pick a runtime target, not a big battery
Here is where the budget usually goes wrong. A UPS for a home server is not there to keep the server running. It is there to hold the lights on long enough for the server to shut itself down properly.
Ten to thirty minutes is plenty. A clean shutdown on a NAS takes two to four minutes. Everything beyond that is margin for short flickers, which are the most common outage type anyway.
The runtime curve is steeply non-linear. The APC BR1600SI, for example, is quoted at 1 hour 18 minutes with a 100W load and around 13 minutes at 50 percent of its rated capacity. Loading a UPS lightly buys disproportionately more time than buying a larger unit and loading it heavily.
Pure sine wave, and when your PSU actually cares
Cheaper line-interactive units output a stepped approximation of a sine wave when running on battery. Most kit tolerates it. Some does not.
The dividing line is active power factor correction. Active PFC power supplies, which means nearly every modern desktop and DIY server PSU, can read a stepped waveform as a fault and either shut down or run hot and noisy. The exact device that most needs to survive the outage is the one most likely to object.
So: a synology-style appliance NAS with an external brick is usually fine on a stepped unit. A self-built server with an active PFC ATX supply wants pure sine wave, and this is not a place to gamble with an array mid-write. If you are still planning that build, our 2026 home server build guide covers the PSU side in more detail.
The best UPS for a NAS or home server in 2026
Five units, sized from a router shelf up to a full rack-adjacent build. Prices move constantly, so check the current figure rather than trusting a number in an article.
Router and modem only
APC Back-UPS BE1050G2-UK. 1050VA, 600W, eight UK three-pin sockets and two USB charging ports. Stepped output, which is irrelevant for a router and an ONT. Keeping the internet alive through a short cut is worth more than most people expect, especially if the doorbell, cameras and heating all route through it.
Small NAS or a Pi-based setup
APC Back-UPS BX950MI. 950VA, roughly 520W real. IEC outlets, AVR, cheap. Right for a two-bay NAS, a Pi, a switch, and nothing with an active PFC supply attached.
Two to four bay NAS, the sweet spot
CyberPower CP1500EPFCLCD-UK. 1500VA, 900W, pure sine wave, AVR, two UK sockets plus four IEC, and a tilting LCD showing live load and estimated runtime. The USB interface maps cleanly to the standard NUT driver, which matters more than the specs once you get to the software step below.
This is the default recommendation for most readers. Pure sine wave at a price that does not require justifying to anybody.
Eight bay NAS or a real home server
APC Back-UPS Pro BR1600SI. 1600VA, 960W, pure sine wave, eight IEC C13 outlets, AVR, USB-A and USB-C, LCD, and a user-replaceable battery. That last point is the one to weigh: swapping a cell in four years is far cheaper than replacing the whole unit, and plenty of budget models seal the battery in.
Most capacity per pound
APC Back-UPS BX1600MI. 1600VA, 900W, six IEC outlets, AVR. Stepped output, so appliance NAS and network gear only. If the load is all external power bricks, it is the most headroom you can buy at this price.
The part everyone skips: telling the server to shut down
A UPS that nobody has configured is a surge protector with a heavy battery in it. The whole point is the data link.
Network UPS Tools is the standard on Linux, TrueNAS and Unraid. Connect the USB cable, enable the NUT service, confirm it detects the model, then set a shutdown threshold. Twenty percent remaining or five minutes left, whichever your platform prefers. Synology and QNAP have this built into the control panel under a UPS heading.
Then test it. Pull the mains plug and watch what happens. Doing this on a Saturday afternoon is vastly better than discovering the threshold was never saved during an actual outage.
A UPS is also not a backup. It protects against an unclean shutdown, not against a failed drive, a bad write, or ransomware. Those need the 3-2-1 backup rule and offsite copies, which is a separate and more important project.
Batteries die in three to five years, and that is the real cost
Sealed lead acid cells in a home UPS last three to five years, less in a warm cupboard. Heat is the main killer, so a well-ventilated spot buys real months.
Replacement cells typically run a third to a half of the unit's original price. Over a decade that recurring cost dwarfs the gap between a cheap UPS and a good one, which is the strongest argument for buying a model with a user-replaceable battery and a widely stocked cell format.
Set a calendar reminder for three years out. Most units will not tell you the battery is tired until it fails a self-test at the worst moment, and self-tests are easy to ignore.
Frequently asked questions
Do I really need a UPS for a NAS?
If the NAS holds anything you would be upset to lose, yes. Unclean shutdowns during a write are how filesystems get corrupted and how RAID arrays end up rebuilding. Given what NAS drives now cost, the UPS is a small fraction of what it protects.
How long will a UPS run a NAS?
At a typical 50W draw, a 900W-class unit lightly loaded gives roughly 30 to 60 minutes. That is more than enough, and you should be shutting down well before the battery empties anyway.
Can a UPS keep my router and modem online in a power cut?
Yes, and it is one of the better uses for one. Routers and ONTs draw single-digit to low double-digit watts, so even a modest unit runs them for hours. Whether your internet actually stays up depends on whether your provider's street cabinet has its own backup, which varies enormously by region and technology.
Is a pure sine wave UPS worth the extra?
If anything on the UPS has an active PFC power supply, yes without hesitation. If everything runs off external bricks, no.
Can I run a UPS from a Raspberry Pi setup?
Absolutely, and NUT runs fine on a Pi. A common homelab pattern is one UPS with a Pi acting as the NUT master, telling everything else on the network to shut down. Our Raspberry Pi home server guide covers the base setup.
Does it matter that storage prices are climbing?
It matters for the arithmetic. With drive and memory pricing where it is in 2026, as covered in our memory and SSD price analysis, the replacement cost of a corrupted array has gone up while UPS prices have stayed flat. The case for one is stronger than it was two years ago. If you are still choosing between local storage and a subscription, the NAS versus cloud five-year cost comparison has the full numbers.
Last updated: 19 September 2026.
