Originally Posted by richard5933
The downside to tankless water heaters is the increased flow necessary to trigger the burner/heater to turn on. When dry camping this can result is going through your water much more quickly than you would with a tanked water heater.
Yeah the water waste while you wait for the water to heat up is one issue. Another issue is the dreaded "cold water sandwich" when you are trying to take a Navy shower to conserve water.
For those not familiar with this, in a Navy style shower you wet down quickly, shut the water off, soap up, then turn the water on for as short a time as possible to rinse off. This minimizes water consumption on a Naval vessel at sea and for an RV'er when boondocking.
So, what is the "cold water sandwich"? With tankless water heaters, when you turn off the water flow for a few minutes while soaping up during a Navy style shower, the tankless shuts off almost immediately in order to avoid overheating. Of course, when you restart the flow again, it takes the tankless heater another 30-40 seconds to fire up again for the second time. Meanwhile, you can hear the screams of your wife echoing up and down the mountain valley as the cold water sitting in your water hose hits her body for up to 40 seconds or so while waiting for the tankless to kick on and make a dent in the water temperature (40 seconds seems like an eternity for the poor soul in the shower). That blast of cold water in between the episodes of hot water is referred to as the "cold water sandwich" between the two slices of hot water, lol.
Other than point of use water heaters with small buffer tanks, you can take a look at the Truma tankless heater. It has a built-in small (1 liter or so) water tank that it preheats in order to provide instant hot water at even "trickle" levels of hot water flow rates and to provide a buffer to absorb the cold water coming into the tankless before the tankless unit has had a chance to fire up and heat the water adequately.