System design
Hot water planning for two-bathroom homes
The moment a house has two showers that might run together, hot water design stops being an afterthought. This is where combi limitations show up most clearly — and where oversizing a combi is the wrong fix.
For: Families with more than one bathroom
Flow rate, not kilowatts
A combi delivers hot water at a rate limited by the incoming mains. If the main can only give 15 litres per minute, a bigger boiler doesn't produce more water — it just heats what's there. Two simultaneous showers need either a strong main plus a high-output combi, or stored hot water from an unvented cylinder.
How we decide
- Measured mains flow rate and static pressure at the property
- Realistic simultaneous demand — showers, baths, en suites
- Cylinder space and reheat time if stored water is the answer
- Whether a future loft conversion will add a third bathroom
Frequently asked
- Can a combi ever do two showers?
- With a strong mains supply and a high-output model, sometimes acceptably. With average flow, no — and we'll show you the measurement.
- Is an unvented cylinder better?
- For simultaneous demand, generally yes. It needs space, an annual check and a G3-qualified installer.
- What if I might add a bathroom later?
- Say so at survey. Designing for it now costs little; retrofitting costs a lot.
Measure before you choose
Flow-rate measurement takes ten minutes and settles an argument that otherwise runs on opinion. It's the first thing we do on these surveys.
Related solutions
Core services
Where we cover
Further reading
Worcester Bosch Accredited · 10 Year Guarantee*
New Worcester boiler with a 10 year guarantee*
Free no-obligation quotes for installation, servicing & repairs across BA & BS postcodes.