Single Boost SP2B or Double Boost SP21S
At ShowerPowerBooster we try to give the best advice to our customers and many customers get away with a single boost for electric showers, for gravity systems, combi boilers, megaflows, and the like. A single boost SP2B is normally good enough to stop showers fluctuating due to low water pressure or to get a decent flow on a gravity system, so we know that most people will get away with a single boost.
We cannot always be right and we have in the past recommended a double boost when a single boost would have been good enough or a single boost when a double boost is needed.
The cost of a single boost SP21S is £155 and a single boost SP2B is £125. In recent times we tend to play it safe and recommend the SP21S rather than a SP2B for all mixed flow systems.
For downstairs taps and showers we will always recommend a SP21S double boost .
If you do buy a single boost you can upgrade to a double boost by buying a SP1U.
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Double Boost with the SP21S to get the equivalent of mains pressure on the hot.