Wash water amount versus temp

[smilingcalico]

I do gouda in a large vat.  I add wash water via a hose, so it's a little at a time versus a full dumping of hot water at once.  The make calls for raising the temp to 37°C. Depending on the season, I may not fully replace the whey before reaching my target temp.  How important is the amount of water replaced?  Should I consider adding some cold water to regulate hitting target temp and full water replacement at the same time?