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wingless' Tankless Water Heater

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The major remodel of a rental home includes elimination of the 35 gallon water heater and replacing it with a 18kW tankless water heater mounted on an interior closet wall. This change will permit a later update to add an additional bedroom and bathroom.


The 18kW Rinkmo heater I purchased for my southern Florida home appears to be well made and well designed. The usage of a tankless water heater requires proper selection, based on expected water consumption and based on inlet water temperature. The southern Florida application is best / easiest because the cold water never gets really cold. 18kW Tankless Heater


These are some issues I have with the product and the documentation.


The printed and web documentation has zero mention about external valves that may be required or appropriate for the installation. For my installation I incorporated a 3/4” tankless isolation valve kit w/ a 3/4” over pressure / over temperature valve, per the local requirements. Isolation valve


The copper plumbing for the 3/4” safety valve slopes downhill to the exterior of the structure, w/o any valves, w/o any reduction in size, w/o any trap, ending at the specified height above ground, all per the local code.


The tankless heater parts included four sheetrock wall anchors w/ screws for mounting. There was no way I was going to attach using wall anchors. My installation in the closet next to the unfinished bathroom permitted me to add horizontal 2x4 boards between the vertical studs. Those horizontal boards accepted the right side mounting screws and the vertical stud accepted both left side mounting screws. This is a very solid mounting method. This placement permits the plumbing to enter the walls w/o jogs.


The wiring design was a big disappointment. The 18kW heater has a single 3/4” wiring knock out w/ double flats and includes an appropriate cable clamp. My installation within an interior closet led me to not want to place jacketed NM-B cable so it exists within the living space. My solution was to instead use a 3/4” Schedule 40 conduit and 90° elbow. The problem is that 3/4” conduit is too small for four 8 AWG stranded conductors (with two ground wires). The only wiring option is 8/2 NM-B, unless using individual conductors in conduit, like THHN, because there is no 8/4 NB-B wire available.


A much better wiring solution would be to have a rear entry, through the wall. That was not possible for me to implement, if I were inclined to modify this UL-approved enclosure, because the only space available for placement of this hole is obstructed by a  horizontal mounting stud. If the wire were permitted to enter from the rear, then there would be no wiring exposure to the living space and no issue w/ the 3/4" conduit being too small.


My two 8/2 NM-B wires are routed to the main exterior panel, run through 1” Schedule 40 electrical conduit, attached to the exterior wall on the side of the house, then into that exterior panel. The 1” conduit size is great for two of the 8/2 NM-B wires.


A pair of 240VAC / 40A THQP240 breakers is used to supply power to the wiring. These are the smaller 240 VAC breakers, using only one panel space, straddling the barrier between phases, instead of the full size THQL breakers where the 240V breaker uses two panel spaces. Note that 1/2 size knock out filler cover panels are required when transitioning to and from THQP and THQL breakers. At least two fillers are required to properly close the dead front panel when using any of the smaller THQP240 breakers. For safety never leave any openings in the dead front panel.


The tankless water heater has a small internal “paddle wheel” to detect water flow. The device includes a screen to filter crud from clogging that flow sensor. My solution was instead to place a cartridge filter in the cold water plumbing supplying the tankless heater. If that wheel ever clogs, then no hot water. Water Filter


The valve kit I used permits periodic usage of a tankless water heater cleaning kit, to run vinegar through the tankless heater, to remove scale. There is zero mention of cleaning in the tankless manual or the web page.


My “old school” installation uses 3/4” Type L copper pipe. I run the pipe to within the wall as soon as possible for proper routing / spacing. The hot pipe is insulated w/ snap on foam pipe insulation. The insulation is used to maintain whatever margin exists for making enough hot water. The safety valve output points directly into the wall making that part very clean.




















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