Mitchell-DIY-Guy
Well-Known Member
To do it right you have to size a tankless based off the coldest input water temp the heater will ever see and how many GPM you need at a selected output temp if you want it to work everyday of every year.
Most homes require two tankless heaters here to meet a busy homes demand, some need 3. Our city water temps are usually no colder than 55 degree, or haven’t been in n at least 30 yrs, I check.
In the 6 months out of the year incoming cold temps are around 75
Right. A typical Delta-T would be 70; 125 set point minus 55 cold water temp. Your location (like mine) sees lukewarm water in the summer months. That doesn't happen in places where the water mains are 5' below grade.
I can only imagine two or three tankless when the house is designed and plumbed for it from the start. Most of the time people are simply trying to catch the trendy wave, and replacing one tank in one place with one tankless and even that can be a PIA with changing venting requirements and upsizing a gas line.