Can a tankless hot water heater be used as a boiler?

mikehughson

I have a small radiant load 15,000 BTU and a larger hot water demand in my Sugar House. I was hoping to use a Navien or similar tankless unit to feed the radiant and use also as a the DHW unit. Can you cycle water back through a tankless like you would a Boiler? Maybe feed into a buffer tank with 2 coils. One for the radiant and one for the DHW.
Thanks in advance for for any help.

kcopp

CAN you or Should you... you can but you will prob not be happy w/ the results. Why not have a heating contractor design you a set up that will work for you and give you many years of trouble free service?

Barry E. LaDuke

Navien's NCB-E combi separates the waterways between DHW and space-heating with dual temp control. Size for the DHW load. The NCB180E produces 14,000 BTU/h at the lowest firing rate, so your small radiant load is one concern.

DHW load would need to be under 150,000 BTU/h (better defined by simultaneous gpm draw). You'll get two showers out of that unit if your delta-T is 80 degrees or less.

The smallest NCB-E gets the minimum fire rate down to 12,000 on the radiant side, but only 120,000 on the DHW load. MAYBE two showers, but your mileage may vary depending on how cold your inlet water is.

mikehughson

Hi Barry and thanks for the response, I'm thinking of using the the Navien NCB-150E. There is no shower just a kitchen sink for washing maple syrup equipment. The Navien will produce 2.6 GPM and the spray hose I intend on using requires 1.5 GPM.
I plan on running the radiant through a buffer tank, to help create a heat sink. I realize there won't be much hot water when initially heating the slab, but feel it will be fine after the slab in warmed up. The building get used 4 months a year.

Jon_blaney

What are you using to heat your evaporators? Wood, oil, Propane?

mikehughson

Wood