Can I still get solar thermal with a combi boiler?

Combi boilers have become increasingly popular in the last 20 years. They are great for smaller properties or those worried about space, because you don’t have a big old hot water cylinder to make room for.

Solar thermal is a growing industry and we have seen a massive surge in interest in this technology since the introduction of the Renewable Heat Incentive (launched in March of last year). The ability to produce hot water from the sun’s energy is obviously a nice idea since not only are you doing your bit for the planet – you also don’t need to fire up the boiler so much. The size of the solar thermal panels also makes it very popular for city dwellers, whose roofs are often too small to accommodate a full solar PV system. The main issue with solar thermal though, despite the fact the panels are relatively small, is that you need a tank to store the hot water that is produced.

For properties with combi boilers – you can probably see the issue here – there is no tank!

Many people therefore think that if you have a combi boiler then solar thermal system is a no go – but this isn’t entirely true though!

If you have a compatible combi boiler, it may be possible to feed pre-heated water from your solar thermal system into the boiler. That means your boiler won’t have to work as hard to heat the water to the required temperature and so you should end up making considerable savings.

Even if it isn’t compatible with your particular boiler, you can essentially turn the combi back into a heat only boiler, using the new solar thermal tank as a new hot water store.

How does solar thermal work with a combi boiler?

If the components allow, the preheated water will enter the boiler and be boosted up to the necessary temperature. Once the water hits 50 degrees or more, the water is diverted so the boiler no longer heats the water.

If the boiler isn’t compatible, the answer is to effectively turn the boiler into a system boiler. This is done by installing a twin coil cylinder and taking a loop off the heating circuit, then connecting it to the higher coil in the cylinder. A valve and timer then control the heating circuit.

How much extra does this setup cost?

A typical solar thermal system will set you back around £4,000, but you will need to install a cylinder and extra pipe work with a combi, so you can expect another £1,000 on top to make the solar thermal work with a combi. As long as you have the required space for the cylinder, there’s no reason why you shouldn’t go ahead, as the payback time is still very reasonable, and you can still claim the RHI payment.

Installing Solar Thermal

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