Originally Posted by Montanaandy
Unless you have a recirc pump either internally in the TWH (which is usually a small HP pump) or preferably externally (a 3 HP is good) you will bleed off a good deal of water getting from 45' to 180' as well as energy to heat that water that is going down the drain. The energy savings if any is negligible. Montanaandy.
Sorry if I have added any confusion. I (or anyone else) was not talking about generating 180 degree water in anything but a completely diverted mode to dump the water directly from the tank. God forbid anyone tries to recirculate 180 degree water, that's insane.
As for the recirc pumps, some models actually use March pumps in the same 1/25th HP range! 3 HP would be WAY overkill for low flow rate recirculation (unless you live at the Vanderbilt Mansion)
The Navien models have the hot water return to the tank from the far end loop and use that for maintaining a "hot water" temp in the hot water supply line (so you'd be wanting to insulate your hot water pipes) but it takes advantage of the 3-stage burner and bypasses the cold water inlet to re-heat the water already in the hot water pipes.