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Madison Co. Virginia | I found a used Navien npe240s2 on FB marketplace for $400, and it came with the three-way flush valves. I had the propane tanks sitting here already, but nothing else. I completed the full installation for under $1k, including the heater purchase price, high and low pressure regulators, all the piping, the venting, and quite a few mistakes along the way. I did need to buy Navien's NG to Propane conversion kit for $20 or so. That just switches the orifice size inside the burner.
It's very slow. If it's heating from well-water temp up to 180f, it's flowing around 3 gpm. That's simply all the faster that a 200k btu heater can go. 3 gallons per minute X 8 pounds per gallon = 1440 pounds per hour. 50f to 180f is 130f temp rise. 1440 X 130 = 187,200 btu/hr.
If I had a full tank of free-heater water each time I used it, it would flow much faster, since it's not heating as high. But for the year that I continued milking after installing that heater, my cow numbers were low enough that I didn't get a lot of help from free-heater water.
Diagnostics are interesting. The unit malfunctioned a few months after I installed it. Chasing down manuals online, going through one diagnostic menu after another, swapping thermistors to try to narrow down the problem, etc. I learned a lot about what was inside those heaters in the process, but ultimately I had to call tech support. They won't talk to the homeowner, so I called back claiming that I was a licensed plumber. He ran me through a few more diagnostic questions, then sent me a replacement control board for no charge.
I'm working on rebuilding the herd, with a goal of restarting milk shipments. When I do, I will prioritize finding a second Navien npe heater to gang with this one using the special cord that Navien sells for the purpose. The install should be cheaper, since not all the parts need to be duplicated. That will give me redundancy if one goes down, and will increase the flow rate with no increase in operating cost.
Within the Navien npe lineup, the number approximately denotes the btu/hr size. 240 = 200k btu/hr. 180 = 150k btu/hr. Etc. 'A' denotes an advanced model. That has a small reservoir and recirc pump inside the heater for instant hot water and low flow rates. The 'S', or standard model is missing those features; the flow rate needs to hit 1/2 gpm before the heater turns on. S works well for milk house use; A would be a little nicer for handwashing. The older models just end in 'A' or 'S'. The newer models tack a '2' on the end of the model number. From what I could figure out, most of the guts of the heater are the same between the older and newer models; the control panel is easier to use on the newer models.
Edit: I have very soft water, and the heater came from a region that has even softer water than mine. Don't buy a used heater from a hard water region, unless you personally know its history. Flushing them isn't bad at all if the three-way valves are installed.
Edited by kipps 11/4/2025 06:49
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Milk house water heater
