Pressure gauges

Assuming you're installing a closed-loop, pressurized solar thermal system, a pressure gauge is absolutely essential. You can place it almost anywhere in the loop, but it's best to locate the gauge close to the charging ports.

As a rule, pressure gauges are quite cheap, so go the extra mile and get a high-quality one. The bottom-end gear works fine, but it falls apart very quickly, so it's worth paying more. Combined pressure and temperature gauges are also available and work well but, again, target the high end of the market for durability reasons.

Thermometers

Solar thermal installations do not need thermometers, but they're extremely useful for monitoring performance, can help spot problems and feed the inner geek who wants to see how everything's running inside the pipes!

There's no limit on how many thermometers you can install on your solar thermal system, but most professionals suggest putting them at prime locations – on either side of the heat exchanger on the solar loop (so you can monitor the "before" and "after" levels coming in from the collector and after passing heat to your domestic water) and on the solar storage tank (near the top). Additional gauges can be installed at will.

Modern thermometers come in two flavors: mechanical and electronic. Traditional setups use mechanical thermometers, which provide durability at the expense of planning requirements. These simple models are tough and reliable but typically need a well or chamber within the pipes themselves, so you need to plumb them in when you're installing your solar thermal system. Well thermometers are very accurate and comparatively cheap.

The more expensive option is electronic thermometers. These work from outside the pipes, so they don't need to be planned to the same extent as the mechanical alternative. Electronic thermometers are sensors which are often separate to the readout, so they can be installed in locations that are inconvenient to reach. Some meters will display multiple readings from around the system on one screen while more advanced models interface with your computer for monitoring, logging and analysis.