Combi vs System Boiler: Which Is Right for Your Home?

2 October 2026 · 6 min read

Choosing the right type of boiler matters more than the brand. The wrong type can leave you short of hot water or paying for capacity you never use.

Combi boilers

A combination (combi) boiler heats water on demand straight from the mains. There is no hot water cylinder and no tank in the loft, which frees up space. Combis suit most flats and houses with one bathroom, and are the most common choice in Glasgow homes.

System boilers

A system boiler heats water and stores it in a cylinder. This lets several taps and showers run at once, which suits larger homes with two or more bathrooms.

Quick guide

One bathroom and good mains pressure: a combi is usually best. Two or more bathrooms used at the same time: consider a system boiler with a cylinder. Already have a cylinder you want to keep: a system or regular boiler avoids extra work.

Getting the size right

Boiler output is measured in kilowatts (kW). Bigger is not always better — an oversized boiler cycles on and off and wastes energy. Our online quote asks about your home so we can recommend a suitable size.