Warming RO water?

[Black Phantom]

Your pressure loss using a 1/4 inch line versus 1/2 should be almost the same. Being that friction loss is directly tied to flow rate it seems to me that the flow rate for an RO unit is very small. A 50 gallon per day RO unit delivers about .03472 gallons a minute. This translates to a very small pressure loss regardless of the size of your line.