What size condensate pump do I need?

Match the pump's flow rate to the unit's condensate output and ensure the max head exceeds the required lift by at least 20%. Check the indoor unit's technical data sheet for condensate production figures.

Aspen vs Sauermann — which condensate pump is better?

Aspen is the preferred choice for residential splits and cassettes where compact size and low noise are priorities. Sauermann suits commercial and multi-unit installations requiring higher flow rates. Both are reliable, F-gas-compatible brands widely used by UK trade installers.

Can a condensate pump be used externally?

Most standard condensate pumps are rated for indoor use only. For external or exposed installations, check the IP rating and operating temperature range. Specialist pumps with IP44 or higher ratings are available for semi-exposed locations.

Choosing the Right Condensate Pump: A Trade Buyer's Guide

June 15, 2026

When Do You Need a Condensate Pump?

Most split and cassette AC units produce condensate that must be drained away. Where gravity drainage isn't possible — concealed ceiling voids, internal walls, or below-floor-level units — a condensate pump is required.

Key Selection Criteria

Before specifying a pump, confirm:

Max head (lift): Vertical distance the pump must push condensate — always add 20% safety margin
Flow rate: Match to the unit's condensate output (check manufacturer data)
Noise level: Critical for bedrooms, boardrooms, and noise-sensitive environments
Tank vs mini: Mini pumps clip directly to the unit; tank pumps suit higher flow or multiple units
Voltage: 230V standard; confirm supply availability at installation point

Brand Comparison

	Aspen Pumps	Sauermann	Blue Diamond
Range	Mini Lime, Mini Orange, Hi-Lime	SI-30, SI-1800, SI-2200	Micro, Maxi, Pluto
Max head	Up to 10m	Up to 10m	Up to 10m
Noise	Ultra-quiet (Mini Lime)	Low noise	Ultra-quiet (Micro)
Best for	Residential splits, cassettes	Commercial, multi-unit	Residential, light commercial
Notable feature	Compact clip-on design	High flow rate options	Compact, reliable float switch

Browse: Aspen Pumps | Sauermann Pumps | Blue Diamond Pumps

Application Scenarios

Cassette units: Mini pump clipped to unit tray — Aspen Mini Lime or Blue Diamond Micro
Concealed FCUs (ceiling void): Tank pump with high max head — Sauermann SI-1800 or SI-2200
Commercial VRF/VRV: Multiple indoor units draining to one pump — Sauermann high-flow range
Noise-sensitive rooms: Aspen Mini Lime or Blue Diamond Micro (both rated ultra-quiet)

Installation Tips & Common Mistakes

Never reduce pipe diameter on the discharge side — maintain manufacturer-specified bore throughout
Ensure float switch is accessible for maintenance without dismantling the unit
Test lift height under load before signing off — not just bench-tested max head
Check alarm output is wired to unit — pump failure should trigger unit shutdown
See our Condensate Pump Selection Guide for further sizing guidance