Hi,the size of your chiller can be affected by the amount of temperature "pull down" you'll need,as well as the volume of water.I'd would say that you are going to need a 1/3HP.I prefer an in-line chiller for a couple of reasons.First they are more effecient & second you can(if house layout permits)locate them remote from the tank,so that the excess heat/noise is not in the house.I plumbed mine through the wall into the garage,so I don't have to deal with those issues.I would also look(if you do select in line)for one that has the largest inlet/outlet pipe diameters,as it will save on back pressure/reduced flow from the return pump.HTH.