How to Choose the Right Emergency Backup Generator
Power cuts in the UK can happen at the worst times—freezers thaw, heating stops, and devices die when you need them most. That’s when an emergency backup generator becomes more than a convenience; it’s peace of mind. It keeps your essentials running and protects your home from sudden blackouts. In this guide, you’ll learn how these generators work, how to choose the right size, and what to check before buying one that fits your household’s needs.
What Is an Emergency Backup Generator? How Does It Work?
An emergency power generator is a self-contained power system designed to supply electricity when the main utility supply fails. It acts as a dedicated backup power source—keeping key appliances such as heating, lighting, refrigeration, or critical systems running during a blackout, so your household remains safe and functional.
When the mains supply drops or goes off:
The ATS monitors the incoming electricity feed and detects a disruption or unacceptable voltage/frequency drop.
As soon as the ATS sees the problem, it signals the generator to start its engine, which runs on fuel (diesel, LPG, or natural gas).
The running engine spins an alternator, turning mechanical motion into the AC electricity that your home uses.
Once the generator is producing stable power, the ATS shifts the connection: it disconnects the house from the grid and connects it to the generator output so your selected circuits receive the backup supply.
When the normal supply returns and stabilises, the ATS switches the house back to the grid and the generator shuts down and returns to standby mode.
Emergency vs Standby Generator: What’s the Difference?
When you’re thinking about a backup power solution for a UK home, it’s worth understanding the difference between what the industry labels as “emergency” and “standby” generator systems.
Emergency Generator System
An “emergency” generator system is designed for situations where power loss would affect safety, life-support or building evacuation. The system reacts very rapidly—typically within 10 seconds after mains supply is lost—so that essential services (emergency lighting, alarms, medical equipment) keep running. These systems are often set up with complete independence from the normal distribution board.
Standby Generator System
A “standby” generator system is intended more for convenience and continuity rather than immediate life-safety. It provides backup power for key household circuits—heating, refrigeration, lights—rather than critical safety infrastructure. The transfer can take up to 60 seconds instead of just a few seconds, and the system may share more of the house’s wiring or mains infrastructure.
Types of Emergency Generators
Selecting a generator isn’t one-size-fits-all. From conventional and inverter technologies to petrol, diesel and gas fuels, understanding each type helps you match the right system to their needs.
By Fuel Type
Petrol Generators
Compact and cost-effective, petrol-powered units are common for smaller or portable setups. They’re easy to refuel and perfect for short outages, but the fuel doesn’t store well for long periods, making them better for occasional rather than continuous use.
Diesel Generators
Diesel models deliver strong, reliable performance for longer blackouts or heavy electrical loads. They’re fuel-efficient and robust but generally louder and pricier to maintain. Diesel remains a solid choice for rural homes or properties needing extended backup.
LPG or Natural Gas Generators
These clean-burning options are popular for fixed home installations. They can connect directly to your property’s gas line or use a tank, offering quieter operation and lower emissions. In the UK, many standby systems now favour LPG or natural gas for convenience and compliance.
Dual-Fuel and Renewable-Compatible Generators
Many newer models combine traditional fuels with renewable or stored energy sources—such as LPG with solar integration or power stations linked to batteries. These hybrid systems lower running costs, extend runtime, and reduce environmental impact, providing a flexible balance between convenience and sustainability.
By Technology Type
Conventional Generators
A conventional generator produces electricity directly from the engine’s rotational speed, delivering alternating current (AC) straight to your circuits. They’re reliable and straightforward, but they run at a constant speed, which means higher noise levels and fuel consumption.
Inverter Generators
Inverter models are quieter, cleaner, and more efficient. They first convert the engine’s output to direct current (DC) and then invert it back to AC power with a steady frequency. This “clean power” makes them ideal for sensitive electronics and entertainment systems. They’re usually compact and portable—perfect for smaller UK homes, flats, or short power cuts.
How to Size an Emergency Backup Generator?
Choosing the right size for an emergency backup generator for home is more than picking the biggest model you can find—it’s about matching capacity to your actual needs so the unit is efficient, reliable and cost-effective.
1. List the Appliances You Want to Power
Start by making a clear list of the electrical items you’ll need to keep running during a power cut—things such as the fridge, freezer, heating system, lights, router, medical equipment or pumps.
2. Determine Running and Starting Wattage
Each appliance will have a “running wattage” (the continuous power it uses) and possibly a higher “starting wattage” (when a motor kicks in). You’ll need both to calculate correctly.
Here are the running watts and starting watts of typical household appliances:
Appliance | Running Watts | Starting Watts |
Dishwasher | 1300 | 1800 |
Washing Machine | 1200 | 2300 |
Refrigerator/Freezer | 700 | 2200 |
Light Bulb | 60-75 | N/A |
Microwave | 600-1000 | N/A |
TV | 500 | N/A |
Toaster | 900 | N/A |
Vacuum | 1440 | 2500 |
Coffee Maker | 1000 | N/A |
Laptop | 50-300 | N/A |
3. Add Up Your Total Load
Add together the running wattage of all appliances you expect to power at the same time, then include the highest single starting wattage. This gives you the minimum size your generator should be able to serve.
4. Apply a Safety Margin
It’s wise to choose a generator with extra capacity—typically 10-20% more than the calculated load—to cover future needs, unforeseen surges and to prevent running the generator at full load constantly.
5. Seek Professional Advice for Complex Loads
If your property has many motors, commercial equipment, three-phase power or unusual loads, it’s best to work with an electrician or installer. Such systems can have large surge currents and require detailed calculation.
A Real-life Case Study
Step 1: List the Appliances You Want to Power
Let’s say you have a UK house and you want backup power for:
Freezer
6 light bulbs
Laptop
Step 2: Determine Running and Starting Wattage
Estimate typical wattages:
Appliance | Running Watts | Starting Watts |
Freezer | 700 W | 2200 W |
6 light bulbs | 6 × 60 W = 360 W | 0 |
Laptop | 300 W | 0 W |
Step 3: Add Up Your Total Load
Running total: 700 + 360 + 300 = 1,360 W
Highest single starting surge: of the list above the freezer surge at ~2,200 W is the highest.
Required minimum wattage: 1,360 + 2,200 = 3,500 W
Step 4: Apply a Safety Margin
Add ~10-20% buffer:
3,500 × 1.10 ≈ 3,850 W 3,500 × 1.20 ≈ 4,200 W
So you’d aim for a generator able to handle ~3,800-4,200 watts continuous plus surges.
Step 5: Compare With EcoFlow DELTA Pro 3 Portable Power Station
Continuous output: 4,000 W
Surge / “X-Boost” capacity: up to 6,000 W
The total load requirement came to approximately 3,500 W, with a recommended generator size of 3,800–4,200 W to include a safety margin.
The EcoFlow DELTA Pro 3 Portable Power Station offers a continuous output of 4,000 W and surge capability up to 6,000 W, which means it meets the necessary performance for this scenario.
EcoFlow DELTA Pro 3 Portable Power Station
What to Look for When Choosing the Best Emergency Generator
When selecting best generator for home backup power, here are key factors to check. These will help you make a practical, well-informed choice that keeps your household running smoothly during an outage.
Capacity: Aim for continuous output that covers your running appliances plus the biggest start-up surge. For a typical 3-bed home, something offering around 4 kW + surge is a good baseline.
Fuel Type: Choose a fuel you can reliably source, store safely and afford to run. For most UK homes, petrol or LPG works for smaller units; for regular use consider diesel or gas-line models. If you’d like to cut down on fuel reliance, you might also consider how to build a home battery backup system, offering a cleaner and more flexible power solution.
Fuel Efficiency: Look for models with high efficiency and low fuel consumption at partial load (e.g., running at 50–70% load). That saves money and extends runtime during longer outages.
Portability: If your property has limited exterior space or you plan to move the unit, pick one that’s compact, wheel-mounted or easy to relocate. If it’s fixed-install, weight and size matter less.
Noise Level: In a residential UK setting, target around 50-65 dB at typical loading for minimal disruption. If a conventional generator seems too loud, you might prefer a portable power station.
For example, the EcoFlow DELTA Pro 3 Portable Power Station + Smart Extra Battery delivers sound levels as low as 30 dB at 2,000 W — even quieter than a running fridge.
EcoFlow DELTA Pro 3 Portable Power Station + Smart Extra Battery
Emergency Backup Generator Maintenance Tips
Having a backup generator is only part of being prepared — maintaining it properly is what keeps it reliable when you need it most. Here are key tips to help you keep your system in top shape:
Check oil and coolant levels at least once a week. Top up if needed and look for signs of leakage.
Inspect the battery terminals and measure voltage monthly to ensure the starter system is ready.
Clear debris, dust or blockages from the exhaust, vents and surrounding area—especially after storms or when the generator is idle.
Run the generator under load (or at least no-load for 10 mins) every month to confirm it starts reliably and handles demand.
Replace oil, fuel and air filters annually (or as per manufacturer) and record the date to track maintenance intervals.
Conclusion
When the lights go out, a well-sized emergency backup generator can make all the difference—or you might complement it with home battery storage for even greater resilience. Pairing a generator with battery storage reduces fuel use and runtime, smooths switchover for sensitive electronics, and lets you run key loads silently and more efficiently during extended outages.
FAQs
How long will an emergency generator run?
The runtime of an emergency generator depends on its type, fuel supply, how much power it’s drawing, and the size of the fuel tank or reserve. A typical portable petrol/gasoline generator might operate for 6 to 18 hours on a full tank under moderate load. A large standby generator, especially one fed by natural gas or with a large diesel tank, can run for 24 to 72 hours or more—provided fuel supply and maintenance are managed. For residential use, aim to size your system not only for how long it can run, but how much load you’ll place on it and whether you can easily refuel or recharge during prolonged outages.
Will a gas-powered generator survive an EMP?
Possibly — but not guaranteed. An EMP (or a strong geomagnetic event) mainly damages sensitive electronics. A purely mechanical petrol generator with a simple magneto or recoil starter and no electronic control is much more likely to keep running. Modern generators with electronic ignition, engine management, inverters, controllers or digital displays are vulnerable because those electronics can be fried. If you’re worried, practical steps are: keep a simple, mechanically started unit as a backup; store spare electronic control modules in a Faraday cage; and fit surge/protection devices and isolation switches so you can disconnect vulnerable kit quickly. Remember that weaponised EMP events are rare; solar storms (CME) are a more realistic risk to grid electronics.
What should you not plug into an inverter?
Avoid anything that either: (a) draws more continuous or surge power than the inverter can supply, or (b) is very sensitive to waveform or frequency. Typical items to avoid include:
Large motor compressors and pumps (central heating pumps, well pumps, large AC units) with high start-up current unless the inverter/generator is rated to handle the surge.
EV chargers or anything hard-wired that expects a dedicated supply.
Induction cookers and some kettles if their wattage exceeds the inverter rating.
Medical equipment that requires guaranteed UPS/clean power unless the inverter is a certified pure-sine UPS.
Devices specified as “pure sine wave required” if your inverter is modified-sine.