I replaced my water heater a couple of weeks ago and noticed the cold water side was leaking a bit still. So I loosened the union and tightened the offending connection. Unfortunately, this moved the water expansion tank very close to the exhaust vent and am curious if it's considered too close? If it was simple,I'd just readjust it,but I'll have to re solder the T connection which will be annoying to say the least but doable. Here are some pics.