Having two or more bathrooms can make choosing a new boiler more complicated.
The key question isn’t simply “How many bathrooms do I have?” but “How much hot water am I likely to need at the same time?”
If only one bathroom is normally used at a time, a suitably sized combi boiler may be able to meet your needs.
If several showers or hot taps are likely to run simultaneously, a system boiler with a hot water cylinder may be a better solution.
Yes, a combi boiler can supply hot water to more than one bathroom.
The problem occurs when multiple outlets are used at the same time.
A combi heats water as it passes through the boiler. Its available hot water flow is therefore limited by the boiler’s output and the incoming mains water supply.
For example, running two powerful showers simultaneously can divide the available water flow between them.
This is why simply choosing a larger combi isn’t always the answer.
For a home with two bathrooms, there are two main possibilities.
A combi may work well if:
A system boiler can be more suitable where:
Energy Saving Trust specifically identifies multiple bathrooms and higher hot water demand as situations where a combi may be less suitable.
A combi boiler takes its hot water supply directly from the mains.
That means the amount of water available at your taps and showers depends partly on the property’s incoming water supply.
A high-output combi cannot compensate for poor mains flow.
Before installing a combi, an installer should therefore assess the incoming water pressure and flow rate.
Not necessarily.
A higher-output combi can produce more hot water, but there are limits to how much water the property’s mains supply can provide.
If the property has multiple bathrooms and high simultaneous demand, a cylinder-based system may provide a more appropriate solution.
A system boiler heats water and stores it in a hot water cylinder.
When you turn on a tap or shower, the stored hot water can be supplied without the boiler having to heat the entire flow instantly.
A correctly sized cylinder can therefore provide substantial hot water capacity.
However, the cylinder is not unlimited. Once the stored hot water has been used, it needs to be reheated.
Not automatically.
Two bathrooms do not automatically mean you need a system boiler.
The important questions are:
These questions are much more useful than simply counting bathrooms.
The short answer
If you have multiple bathrooms but usually use one at a time, a combi boiler may be suitable.
If you regularly use several showers or hot taps simultaneously, a system boiler with a suitably sized hot water cylinder is often worth considering.
The mains water supply and household hot water demand should be assessed before making the decision.
It can, but performance depends on the boiler’s hot water output and the property’s mains water flow and pressure. The available flow will be divided between outlets.
There is no single answer. A system boiler and cylinder may suit a larger household with high simultaneous hot water demand, while a combi may be suitable where demand is lower.
It may be, depending on how the bathrooms are used and the mains water supply. Boiler output alone doesn’t determine shower performance.
Often, yes, particularly where there is simultaneous hot water demand. A suitable cylinder provides stored hot water that can supply multiple outlets.
Yes, technically, but the important consideration is whether the system can provide the hot water performance your household needs. Multiple simultaneous showers may make a cylinder-based system more appropriate.
