I am purchasing a replacement Grundfos pump. Grundfos pump you certainly don't need to purchase flanges again. We know of no finer made pump. Having said that we do want you to realize that every pump has a specific function. Meaning, for example, a circulating cast iron pump isn't generally for domestic drinking water.
Every pump also has a specific flow rate, etc.
They are an excellent choice for drinking water. I want to install a hot water circulation loop so that I can get hot water quickly at my taps. Just make sure to get rid of ALL of air in your return line and design your system so that no air will be in your line. Click here for other questions Typical hot water system before a recirculation pump. Common recirculation pump installation.