Cylinder Comparison
Megaflo vs OSO — Which Unvented Cylinder for Your London Home?
Both deliver powerful mains-pressure hot water. Our Megaflo-certified London engineers explain the key differences.
Megaflo is our default recommendation for most London homes — it's the UK's most widely installed unvented cylinder with excellent parts availability and a proven 25-year track record. OSO is the premium alternative for larger properties with 6+ bedrooms or exceptional hot water demand, offering higher working pressure (up to 8.7 bar) and larger capacity (up to 500 litres). Both come with 25-year cylinder warranties.
For London's larger homes — Georgian townhouses in Belgravia, mansion flats in Marylebone, or multi-bathroom properties in Hampstead — an unvented cylinder delivers the mains-pressure hot water performance a combi boiler simply can't match. Megaflo and OSO are the two premium choices our engineers recommend most often.
Side-by-Side Comparison
| Feature | Megaflo | OSO |
|---|---|---|
| Type | Unvented indirect cylinder | Unvented indirect cylinder |
| Origin | UK (Heatrae Sadia) | Norway (OSO Hotwater) |
| Capacity Range | 90–300 litres | 120–500 litres |
| Recovery Rate | Fast — 45 min (210L) | Fast — 40 min (210L) |
| Working Pressure | Up to 6 bar | Up to 8.7 bar |
| Coil Type | Single or dual coil | Single or dual coil |
| Warranty | 25 years cylinder | 25 years cylinder |
| Parts Availability UK | Excellent — widely stocked | Good — specialist suppliers |
| Solar/Heat Pump Compatible | Yes (dual coil models) | Yes (dual coil models) |
| Typical Cost London | £1,800–£3,200 installed | £2,200–£3,800 installed |
| RARE Recommendation | Default choice — proven & reliable | Premium alternative for larger homes |
Megaflo
Best for: most London homes, proven reliability
UK's most widely installed unvented cylinder
Excellent parts availability across London
RARE engineers are Megaflo-certified specialists
Proven 25+ year track record in London properties
Competitively priced with strong installer support
Lower maximum working pressure vs OSO
Smaller maximum capacity than OSO top range
OSO
Best for: larger homes, high-demand hot water
Higher working pressure — better for larger properties
Larger capacity range — up to 500 litres
Scandinavian build quality — extremely durable
Excellent for multi-bathroom properties with high demand
Strong specification choice for high-end refurbishments
Fewer local engineers familiar with the brand
Parts can take longer to source in London
Higher upfront cost than Megaflo
RARE Engineer Verdict
Our Recommendation
Megaflo is our default recommendation for the vast majority of London properties. It's the most widely-installed unvented cylinder in the UK, parts are available next-day across London, and our engineers know it inside out. For anything up to a 5-bedroom home with 3 bathrooms, the Megaflo EcoSmart will comfortably deliver.
Consider OSO for very large properties with exceptional hot water demand — 6+ bedrooms, multiple en-suites, or commercial-grade use. The higher working pressure and larger capacity ceiling give it an edge in these scenarios.
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