Hot Water Replacement

wildtoad wrote:
I’ve never understood how a small OD wh can provide adequately (subjective I know) hot water for a high flow requirements of a shower, especially during the colder months.

With modern day water standards there is no such thing as a "high flow" shower.. 1.5 to 2.5 GPM is pretty much the water flow standard unless you have done something to modify the shower head for full flow..

FLOW RATES

"Flow Rate Restrictions

Since 1994, federal regulations have limited shower head manufacturers to a maximum flow rate of 2.5 gallons per minute (gpm). California has enacted its own legislation limiting the flow rate to 2.0, which will be reduced even further, to 1.8 gpm, in July 2018. Water flow regulations save billions of gallons of water each year while the latest technologies help preserve or even enhance your shower experience. There’s no need to suffer a substandard showering experience just because of regulations.

The engineers at Delta Faucet believe that environmentally friendly design shouldn’t compromise optimal performance. Before the restrictions, shower heads typically used 5.5 gpm. Restricting the flow to 2.5 gpm led to a new generation of water-saving shower heads. The change in flow rate is particularly noticeable if you go from a shower head produced before 1994 to a modern model. With consumer satisfaction in mind and knowing how important a good showering experience is to customers, the Delta Faucet engineers got to work."

2.5 GPM is nothing, my water well at 45 PSI supplies 11 GPM but the restrictive regulations the shower and faucet manufacturers must follow prevents my shower head from supplying more than 2 GPM at 45 PSI.. Perhaps at 60 PSI (city water pressures) I might get 2.5 GPM.. I would not call 2.5GPM or less to be "high flow" by any means.