I have a single bath in my shop and the plumber put the DHW tank in a little room above the shower (above all other fixtures in the bath). The tank is a lowboy 30 gallon tank. With one shower the water is cold within a couple minutes. I asked the plumber he said he can install a 2nd tank. I think my hot water is migrating out of my DHW tank or cold water is migrating into the tank. Any thought or direction would be great a 30 gallon tank should last for a 10 min shower my shower head is rated at 1.75 gpm