A central heating system is comprised of a gas or oil boiler and a 'wet system' of radiators. Heat is transferred to the home by heating up the water in the radiators, as oppose to a system that blows warm air into the rooms via ducts. The central heating boiler will also supply hot water, either via a cylinder or directly from the boiler. Central heating systems are either ‘open vented’ or ‘sealed’ systems. (NB not to be confused with open vented and unvented hot water tanks, which are explained in our Guide to Hot Water Cylinders.) Many homes in the UK still have an open vented system. We explain the advantages and disadvantages of each system and give guidance on when the circumstances are right to change.
Central Heating a Guide | Open Vented & Sealed Systems
Overview of open vented and sealed central heating systems
Advantages to retaining an open vented system:
- They comprise very few fittings and devices to operate, compared to a sealed systems, which means lower maintenance costs
- Where older radiators are present, that are not to be replaced, changing to a sealed system can put it under pressure and cause leaks
- It is much to cheaper to swap the boiler and leave all other components in place
Disadvantages to retaining an open vented system:
- You can only have a Heat Only boiler, as they cannot work with Combi and System boilers
- Debris can enter the system via the F&E tanks
- Less efficient as there is greater potential for heat loss via the F&E tanks
Advantages to moving to a sealed system:
- Greater flexibility in siting the boiler and other system components
- Options to change to a Combi or System boiler set up
- Can free up space in the roof space
- It keeps the system cleaner at its sealed off. Debris can enter the system via F&E tanks
- More efficient as there is less potential for heat loss, e.g. evaporation via the F&E tank.
Disadvantages to a sealed system
- May cause leaks in old radiator systems and buried pipework
- More components to go wrong, although for combi and system boilers the components that are integral to the boiler, which will be most of them, will be covered by the manufacturer’s warranty.
- When there are older radiators that could lead under pressure
- Where there are pipes buried in screed that may also leak under pressure
- You are on a tight budget
- If you are happy with your heat-only boiler