Rinnai Tankless Hot Water Heater with Well Pump

General Tech
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I’ve had the Rinnai tankless for about 1 month. I did a lot of research before replacing the hot water tank (which was on borrowed time) with a tankless unit (RU160iP). Some comments were that it didn’t work with a well water due to fluctuating pressure. This was disputed by others, and the company that installed it stated many other customers had well water and there have been no issues. I have not had any issues with water pressure of varying water temperatures due to tankless and a well pump. Of course it is true that the water pressure in my house will fluctuate, it’s not really noticeable, since having the tankless installed no one has complained the water goes from too cold then too hot when taking a shower. Maybe Sense can give some insight to how Rinnai maintains the temperature?

My well is set pretty standard, cut in when the tank pressure reaches 40psi and shut off at 60psi.
The Rinnai unit knows the incoming water temperature which is between 48 and 50 degrees right now, the water flow into the unit and the required output temperature. It will burn the gas it needs to reach and maintain temperature. The speed of fan in the unit seems to relate to amount of BTUs it needs to heat the water, because of this Sense can get a picture of what’s happening.

Left side is the well pump cycling,on the right side Rinnai with someone is taking a shower from 12:13pm - 12:27pm. At 12:15pm the Rinnai energy use is going up, this is because the well pump kicked on and the water flow has increased so more heat is needed to maintain 125 degrees, when the pump kicks off at 60psi, the water flow starts decreasing so less heat is needed to maintain 125 degrees, then the cycle starts over about 5-6 minutes later. The big spike at the end is the water being shut off, the purge fan does max power then does a 3 minute post use purge before shutting down. When taking a shower you don’t notice any change in water flow or temperature since the Rinnai is constantly making adjustments to the flame and tempering servo position based on the incoming water flow and temperature to maintain output temperature. Who knew a water heater could be so interesting!

Regarding the tempering valve- In addition to a the amount of BTUs to heat the water, there is a tempering valve in the unit that mixes cold water into the heated water to maintain the temperature. Its a servo type valve that reacts quickly,in addition to increasing/decreasing flame, to meet needs for hot water such as someone turning on a tap while one is running - or the opposite 2-3 taps running and someone shutting off taps.

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I’ve never liked those instant hot will using a lot in even in high rise their electric but they’re also a problematic
I compare those instant hot like if you have a 500 horsepower car and you going to drive it to the corner and high speed you don’t save anything It is not efficient
I’ve been on the well before so I know all the prones about Wells and pressure tanks
I would add a secondary pressure tank and I would also increase the pressure on the blatters And upon pressure to 80 pounds
The secondary pressure tank could be install in the attic so you work with gravity pressure And the pressure from the Tank
You could add a Booster pump after The pressure tank That keeps the pressure at 60 pounds at all times
You could do like major apartments and hotels do is convert your rene to a circulating heating system where the water is stored in a Insulated storage tank, It stays on until the hot water tank is Heated up to a 120ﾟ~ 160° and then shuts off.

Water heaters are so efficient these days Did you a great jobIf you size it right 40 John is good 50 if you have a larger family
it’s OK if you have a large house And a large family and you need the extra hot water In addition to a large Capacity water heater because you have a large large family and you run out of hot water Because everybody’s taking showers at the same time.
Also with a hot water heater you can install an aftermarket circulating system that cost around $200 at lowes and Is easy to install
This way you always have hot water and you don’t waste any.

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Just a note on tempering valve a lot of cities Have passed codes to remove those And make it that you could not use Those type of Systems Anymore because the Tempering Valve Would go bad and people Would get Badly burned with those.
that’s why They made Multi apartments and hotels switch where there is a heater that circulates and heats the water properly in A large Insulated Water holding tank.