On Friday, July 10, 2015 at 1:38:25 AM UTC-4, HerHusband wrote:


Does any tankless hot water heater monitor the flow rate and output
temperature and then adjust the flame to keep the temperature constant
regardless of the flow?

I have no idea, but a standard tank model doesn't do this either. You set
a maximum temperature and the heater heats the water to that level
(typically 120 degrees). A tankless heater isn't really all that different.
It's just heating the water as it comes in instead of preheating it in a
big tank. Either way the water should always be 120 degrees when it leaves
the heater.


There is a big difference. The tank type has most of a tank of hot
water at close to the same temperature. When you start drawing
water, you can pull a lot of water at whatever rate you want and
the temp is not going to vary much. If you pull enough, eventually
the temp will drop as the cold water entering the bottom of the tank
starts to effect the hot water leaving the top.

With a tankless, the burn rate of fuel has to be adjusted to
the flow rate. Otherwise you'd get steam at .1 gal an hour
and the temp would vary wildly based on flow rate. How exactly
they do that, IDK, but I'd suspect they use some kind of
modulating gas valve.