Message: Aloha, I'm going to install an MTI Ofuro in a remodel project. Have you ever heard of reheating the water with a natural gas tankless heater? The idea is to recirculate the water slowly, rather than with high velocity pumps, like a jacuzzi. Perhaps a 5 gpm pump with a Rinnai 5gpm tankless heater. Manual operation. What do think? FYI, I live in Hawaii, so an outdoor heater is possible. Unlike in snow country. Thank you, Gen Boyer.

Dated on : 11-07-2012

Replies :

Hello,   I am an engineer with Northern Lights Cedar Tubs.  Yes, I have thought about exactly that  concept and never pursued it, because of a number of concerns: 1) the inlet water temperature for the tankless heater will now be variable, being the hot tub water temperature ,up to 104F.  Is the tankless heater designed to work with such high inlet temperatures? 2) the outlet temperature will be correspondingly high also?  Will the internal high limits, stop operation 3) Can the tankless heater take the hot tub water chemistry? 4) What do you do about filtering? Typically you need more than 5gpm flow for good filtering, and even if that was enough how do you continue to filter when the water is hot enough an the heat needs to be turned off?  Possibly a Belimo 3-way valve could be deployed, keeping the pump running 24/7 and then the temperature controller just controls the 3-way valve,  5) Lastly cost - this is not cheaper than using say a Pentair MiniMax natural gas heater with a standard hot tub circulation pump.   Dieter

Post By : Dieter Jung Dated On : 11-07-2012