Solar heating and boilers

Solar heating systems can be used with boilers (particularly popular in countries like the UK)... as long as the solar heating system is equipped with an un-vented cylinder and as long as boilers accept the pre-heated hot water from the solar heating system – something that many combi (combination) models do not.

Solar Systems & Regular and Combi boilers

If you have a regular boiler system – often called open vent boiler and heat only boiler – with its typical feed and expansion cistern, cylinder and tanks, it will be easy to link the solar heating system to your boiler. Solar water heating demands a storage tank, and in this case you have it...

However, if you have the typical design of a combination boiler, you must pay attention to compatibility problems and look for models and manufacturers offering that compatibility. Combination boilers heat water on demand and don’t use a storage tank. Besides, a combi boiler provides mains pressure hot water while solar water heaters are often low pressure systems.

See, for details on combi boilers and their advantages: Condensing and combi boilers

Combi boilers and the issue of the storage tank and pressure

If you're going to install a solar water heater and a new combination boiler, then just take into account whether the combi boiler is compatible for use with solar heater (see point below). Some manufacturers offer 'modulating' boilers – a kind of model able to monitor the water temperature in the boiler and to adapt the flame with the solar water heating system demands…

Be aware. Combination boilers and solar heating systems demand compatibility. If you are unsure of that compatibility, you should check the issue with the manufacturer to avoid doing an expensive option.

Manufacturers offering compatibility

He is a list (obviously incomplete) of manufacturers offering combi boilers compatible with solar heating systems:

Atmos
Ariston
Vaillant
Worcester/Bosh
Macdonald Engineers
Mts Group
Newark Copper Cylinder.
Solar Savings

Fitting a solar water system to an existing combi boiler

It’s difficult to fit a solar water system alongside an existing combination boiler. The more common solution is to have the combination boiler and the solar collectors heating a common water tank, and to have a separate outlet (from the combi boiler) leading to the shower or radiators. That will ensure the boiler will fire on full power whenever necessary, and to have mains pressure hot water for showers…

There are, however, peculiarities associated with each system, demanding a professional assessment and resolution.