What Size Generator Do I Need for My House?
When the power goes out, most people ask the same question — what size generator do I actually need to keep my house running? Get it wrong and you're either sat in the dark with an overloaded generator tripping out, or you've spent thousands more than you needed to on a unit that's massively oversized.
This guide gives you a straight answer. No jargon, no waffle — just a clear breakdown of what size diesel generator you need for your home based on what you want to keep running.
Quick Answer: What Size Generator for a House?
| What You Want to Power | Generator Size | Typical Home |
|---|---|---|
| Essentials only — lights, fridge, boiler, phone charging, TV | 5–8 kVA | Flat or small house |
| Essentials + cooking — all above plus microwave, oven, kettle | 10–12 kVA | 2–3 bed semi or terrace |
| Most of the house — all above plus washing machine, dishwasher, power tools | 12–15 kVA | 3–4 bed detached |
| Whole house backup — everything including electric heating, immersion, shower | 15–25 kVA | Large detached or rural property |
Most UK households end up buying a 10–15 kVA single phase diesel generator — it covers all the essentials plus a few extras without being oversized.
How to Work Out Your Exact Requirements
The best way to get this right is to list everything you'd want running during a power cut and add up the wattage. Here's what typical UK household items use:
Household Appliance Wattages
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| LED Lighting (whole house, ~15 bulbs) | 150W | 150W |
| Fridge | 100W | 400W |
| Freezer | 100W | 400W |
| Gas Boiler (central heating pump + controls) | 200W | 400W |
| Television | 100W | 100W |
| Wi-Fi Router | 15W | 15W |
| Phone / Laptop Chargers (x4) | 100W | 100W |
| Microwave | 1,000W | 1,500W |
| Kettle | 3,000W | 3,000W |
| Electric Oven | 2,500W | 2,500W |
| Washing Machine | 500W | 2,000W |
| Dishwasher | 1,800W | 1,800W |
| Tumble Dryer | 2,500W | 2,500W |
| Immersion Heater | 3,000W | 3,000W |
| Electric Shower (8.5kW) | 8,500W | 8,500W |
| Portable Electric Heater | 2,000W | 2,000W |
| Hair Dryer | 2,000W | 2,000W |
| Iron | 2,500W | 2,500W |
| Vacuum Cleaner | 1,400W | 1,400W |
Important: You won't be running all of these at once. The key is to add up the items you'd realistically have on at the same time during a power cut. You're not going to be hoovering, running the tumble dryer, and using the electric shower all at once while the power's out.
Example: Typical 3-Bed House During a Power Cut
Let's say you want to keep the following running at the same time:
| Item | Running Watts |
|---|---|
| All house lighting (LED) | 150W |
| Fridge | 100W |
| Freezer | 100W |
| Gas boiler / central heating | 200W |
| TV + Wi-Fi | 115W |
| Phone chargers | 100W |
| Microwave (occasional use) | 1,000W |
| Kettle (occasional use) | 3,000W |
| Total running load | 4,765W (4.8 kW) |
Now convert to kVA: 4.8 kW ÷ 0.8 = 6 kVA. Add a 25% safety margin: 6 × 1.25 = 7.5 kVA.
So for this setup, an 8 kVA generator handles it comfortably. But if you want the option to run the washing machine or electric oven occasionally on top, step up to 10–12 kVA for proper headroom.
What About Starting Watts?
This catches a lot of people out. Your fridge might only use 100W while running, but when the compressor kicks in it draws 400W for a few seconds. Same with your washing machine — 500W running, but up to 2,000W on the initial spin-up.
This is why you need headroom. A generator rated at exactly your running load will trip the second a motor starts. The 25% safety margin we mentioned above helps, but if you've got several large motors (fridge, freezer, washing machine, central heating pump), consider going one size up.
Single Phase — That's What Your House Uses
Almost every UK home runs on single phase 230V power. That's the standard 3-pin plug sockets you use every day. So you need a single phase generator.
The only exception is some larger rural properties or homes with workshops that have a three phase supply installed. If you've got red 3-phase sockets or a 3-phase meter, you'll need a 3-phase generator — but this is rare for domestic homes.
If in doubt, look at your electricity meter or consumer unit. Single phase has one main cable coming in. Three phase has three.
Diesel vs Petrol for a House Generator
For home backup, diesel wins every time. Here's why:
- Fuel efficiency — diesel generators use roughly 30–40% less fuel than petrol for the same output
- Longevity — diesel engines last significantly longer, often 3–5 times the lifespan of a petrol generator
- Safety — diesel fuel is less flammable than petrol, making storage safer
- Torque — diesel engines handle varying loads better, which matters when fridges and motors kick in and out
- Availability — diesel is easier to source and store long-term than petrol
Petrol generators are fine for occasional light use like camping or powering a single tool. But for serious home backup power, diesel is the only sensible choice.
How to Connect a Generator to Your House
Important: Never plug a generator directly into a wall socket or wire it into your consumer unit yourself. This is illegal and extremely dangerous — it can backfeed into the grid and kill someone working on the power lines.
The proper way to connect a generator to your house is:
- Extension leads — the simplest option. Run extension leads from the generator to the appliances you need. No electrician required.
- Manual changeover switch — installed by a qualified electrician, this lets you safely switch your house circuits between the grid and the generator.
- Automatic Transfer Switch (ATS) — the premium option. Detects when the grid goes down and automatically starts the generator and switches over. Your power comes back without you lifting a finger.
For most homeowners, extension leads are the practical solution. If you want a permanent installation with automatic switchover, budget for an electrician to fit a changeover switch or ATS panel.
Where to Put a Generator at Home
- Never run a generator indoors — exhaust fumes contain carbon monoxide which is lethal in enclosed spaces
- Keep it outside in a well-ventilated area, at least 2 metres from windows, doors, and air vents
- Place it on a firm, level surface — concrete, paving slabs, or compacted gravel
- Shelter from rain — a silent canopy generator is already weatherproof, but keep it out of standing water
- Consider your neighbours — a silent generator at 65–75 dB is about the volume of a normal conversation at 7 metres. Position it away from neighbouring bedrooms if possible
How Long Will a Generator Run My House?
Runtime depends on fuel tank size and load. At 75% load, typical diesel generator runtimes are:
| Generator Size | Typical Tank | Approx Runtime at 75% Load |
|---|---|---|
| 6–8 kVA (air cooled) | 15–20 litres | 8–12 hours |
| 10–15 kVA (water cooled) | 40–60 litres | 12–20 hours |
| 20–25 kVA (water cooled) | 60–100 litres | 14–24 hours |
For extended outages, you can connect an external fuel tank to increase runtime significantly. We supply bunded diesel tanks from 240 litres upward.
What Size Generator Do We Recommend for Most Homes?
For the average UK home wanting reliable backup power during outages, we recommend a 10–15 kVA single phase silent diesel generator. This covers all your essentials plus enough headroom to run heavier appliances like the oven or washing machine when needed.
It's the sweet spot — not so small that you're constantly managing what's plugged in, and not so large that you've overspent on a generator that's barely loaded.
Our Home Generator Range
We stock the following single phase diesel generators suitable for homes:
- 6.5kW / 8kVA Air Cooled — entry level home backup, covers essentials
- 10kW Silent Generator — popular choice for mid-size homes
- 15kVA Single Phase Silent — whole house backup for larger homes
- 20kVA Single Phase WEICHAI — large home or home with workshop
All come with silent canopy, electric start, AVR voltage regulation, and 12 months warranty. UK stock, fast delivery.
Get the Right Generator for Your House
Not sure which one fits your home? Tell us what you need to power and we'll recommend the right unit. Takes two minutes and saves you buying the wrong size.
Call us: 01254 476 679
WhatsApp: 07484 413 610
Email: info@affordablegenerators.co.uk
Related Guides
- What Size Generator Do I Need? Complete UK Guide
- Single Phase vs 3 Phase Generator: Which Do You Need?
- Diesel Generator Fuel Consumption Guide by kVA
- How to Connect a Generator to Your House UK
- Power Outages UK: How a Generator Protects Your Home