Logic of chiller sizing

[Notophthalmus]

I am looking into getting my first chiller. This is for a freshwater, cool stream setup. I came here for advice because freshwater hobbyists don't use chillers for the most part.

As I understand it, the chiller should be sized based on heat input. However, the manufacturers base chiller recommendations on tank volume. How does water volume interact with chiller effectiveness?

I have the idea that a large, insulated sump, though it will increase system volume, will not increase demand on the chiller. So the chiller just needs to account for heat input from ambient air, pumps, and lights, whether the system volume is 100 gallons or 1000 gallons. Is this correct?

[jmoney]

also the amount of water they can process is important, for example a 1/15 hp chiller probably wont be effective on a 1000 gallon tank as most have water rates of 125 gph. However I run a 1/15 hp chiller rated for only 45-50 gallons just fine on a 100 gallon system. The small one will work of course eventually, but it might be on a long long time, which could cause your electricity bills to spike, but if you don't care about that..then its not an issue.

[Notophthalmus]

Thanks, J Money, that makes sense.