I'm setting up a wood boiler\oil burner parallel system. I have an unpressurized storage tank with both space, and dhw heat exchangers. This post is about the dhw plumbing. So, starting at my current mixing valve... Cold water comes in the top, directly from my well. At the bottom of the mixing valve is hot water from my oil boiler. Out the back of the mixing valve is a copper pipe that turns ninety degrees vertical, goes straight up about about 8 feet or so, and converts to red pex which goes out to all the areas of my house that require dhw. My initial plan was to put a tee in the copper pipe that has the mixed dhw a foot or so before where it converts to pex. I would then connect that tee to the hot water output of my storage dhw exchanger. Here's my question. Let's say it is summer and the oil burner is essentially basement temperature. The tank is heated. It seems to me, when there is a call for dhw, cold water from the well is going to be pushed into both the oil furnace, and the cold water input to my dhw heat exchanger in storage. Hot water (that has already come through an anti scald valve on the storage exchanger) is going to go into the tee I described in the previous paragraph, and mix with unheated water coming through the oil burner. Am I over thinking this, or do I need to incorporate a zone valve below the tee that I am planning to add? The zone valve would only open when the oil furnace was running. Thank you for your time.