Hello,
I asked myself this question when setting up my basement system, which had a 4.5m lift (from the basement floor to the top of the tank). I needed 4,500 L/h (1 200 Gl/h) for my 900 L (240 G) in the living room.
I had considered using two pumps for safety, but in fact, I use only one, the second is spare cause the flow rate is very high with one.
The problem was finding a pump with sufficient flow at 4.5 meters. And I didn't want 'RD' pump because I had already used them on skimmers and had been bothered by their reliability. For their price… I could find two for one.
I first found a Jebao 18000 which was able to push water at more than 4 500 l/h at this height (9m max).
This was mesurements I made on my system.
After few months of use, I realized that the 18 000 was oversized and bought the 15 000 Jebao (7m max), which is currently running at 90W to bring my water flow up to 3000 L/h. The 18 000 is in spare in the sump, ready to be restarted.
For me, the most important thing is to limit pressure losses in the pipes and bends. These pumps run 24/7. Every watt saved is important. My riser and fall pipes have a nominal diameter of DN50 (2").
The riser pipe, as straight as possible.
Both pumps are extremely quiet (it’s not a problem in basement). And given the price, even if they break down after 4 or 5 years, I won't have any qualms.
My basement
If it can help