Grundfos SCALA2 Constant Pressure Booster

SCALA2 is a fully integrated booster: pump, motor, drive, tank, non-return valve and pressure and flow sensors in a single housing. It holds a constant discharge pressure as fixtures open and close rather than cycling between cut-in and cut-out, which is the difference a shower actually feels.

It is self-priming to 26 ft, so it can draw from a tank, a shallow well or a cistern below the pump — something most constant-pressure boosters of this size cannot do at all. Grundfos publishes a noise level under 44 dB(A), measured to ISO 3745 at a duty point of 4.4 GPM and 62 ft, which is what makes it acceptable in living space.

Two part numbers, one machine: 93013251 on 115V with a NEMA 5-15 plug, 93013250 on 230V with a NEMA 6-15.

Two SCALA2 units can be mounted as a pair using the Grundfos SCALA2 twin accessory set, part number 99743075 (1 in NPT). The set supplies the twin base plate, inlet and outlet manifolds with brass isolating valves and the fixing screws, so the pair shares one set of pipework in roughly the footprint of one-and-a-half pumps — more water when both run, and a second machine on site when one is isolated for service.

Each pump holds its own setpoint. The communication cable in that family of accessory sets is supplied for SCALA1 only, so two SCALA2 units do not cascade or alternate between themselves the way a SCALA1 pair does. Where lead/lag control matters, SCALA1 with its twin installation set or the CMBE TWIN factory duplex is the better pick. Maximum two units.

The figures below are the pressure this pump adds on top of what arrives at its inlet, read from the top curve on Grundfos’ published chart — the drive running at full speed. The seven curves below it are the same pump held at lower pressure settings.

Drawing from a tank, cistern or shallow well — nothing arrives with pressure, so what the pump adds is what you get, and it will self-prime up to 26 ft to reach the source. Read the table straight through: 11 GPM comes out at 44.8 psi.

Fed by a city main — the drive holds the pressure you set and only makes up the difference, and the controller will not hold more than 51 psi in total. On a 20 psi main set to 51 psi the pump only has to add 31 — and at 31 psi added the table gives you roughly 15 GPM, against the 9 GPM you get from a tank, where the pump has to make all 51 psi itself. Incoming pressure buys you more flow, not more pressure.

Best operating range: 9 to 16 GPM. This is where the pump turns the most electricity into water pressure. Ask for more flow than it can deliver at your setting and it runs at full speed continuously, which is where motors and seals wear out. Sizing a booster to the building rather than to the headline numbers is what makes it last.

Zero flow is the shut-off point — a ceiling, not a working point. The table ends at 20.7 GPM, the last point Grundfos draws on the full-speed curve; nothing is extrapolated or transposed. Grundfos’ printed technical data gives maximum head as 45 m (147 ft) while the plotted full-speed curve reads 143 ft at zero flow, and this table prints the curve. The best operating range is derived by us from the published head and input-power curves — wire-to-water efficiency peaks near 39 percent at 12 GPM — and is not stated by Grundfos. For a certified duty point, call 1-888.510.4036 and we will request the factory submittal. Source: Grundfos SCALA Data Booklet 99735562 (07.2026), performance curves TM1040350, printed page 25, ISO 9906 grade 2B.

SCALA2 connects to the Grundfos GO app through the MI 301 Bluetooth mobile interface for setup, monitoring and fault reading without opening the unit.