A 9 GPM system can work when peak demand stays modest. If two showers plus other fixtures can push above roughly 7–9 GPM, a 15 GPM-class system gives safer treatment margin.
Why 9 GPM may be enough
Low-flow showers and staggered use can keep a three-bathroom home under the smaller system’s validated flow.
Why 15 GPM can be the better buy
A larger UV unit preserves dose when several fixtures run together and reduces the risk of exceeding the validated flow during peak use.
VIQUA reference points
The Arros family is offered in 9, 15 and 22 GPM classes at the manufacturer’s 30 mJ/cm² standard condition.
Do not ignore upstream flow restrictions
Sediment filters, iron filters and softeners can all reduce available flow. Size the UV from the actual treated-water flow reaching the chamber.
How to size and install What Size UV Water System for 3 Bathrooms?
Equipment performance depends on matching capacity to the load rather than choosing the largest model. For pumps and heaters, that means required flow, pressure or temperature rise. For dehumidifiers and pool equipment, it means the environmental or hydraulic load. For UV treatment, it means validated flow at the required dose with appropriate upstream water quality.
Check electrical service, drainage, plumbing connections, clearance and ambient operating limits before purchase. A system can look ideal on a specification table but become expensive when the installation requires a new circuit, condensate pump, larger plumbing, structural changes or professional labor that was not included in the hardware price.
Operating cost, maintenance and failure points
Compare energy use and consumables over several years. Pumps, heaters, dehumidifiers and UV systems add electricity cost; pool and spa equipment may add filter or chemical maintenance; leak-detection devices may require batteries, valves or hub hardware. A lower purchase price can lose its advantage when operating cost or replacement parts are materially higher.
Look for serviceable components, warranty terms, replacement-part availability and the maintenance tasks the owner will actually perform. Equipment that depends on inaccessible proprietary parts or frequent neglected maintenance carries more long-term risk than a slightly more expensive system with clear service support.