Propane tank/tankless water heater combo

[Josh josh]

I own a 2020 Columbus 5th wheel with my first on demand tankless water heater. Typically, the system must sense significant water flow to turn on. Once on, you have unlimited hot water until you stop the flow by shutting off the hot water. But due to the design, you always end up with a large volume of ice cold water prior to startup. I’m considering adding a standard Rv propane water heater as the main reservoir, with on-demand behind it. This should reduce the initial ‘cold blast’ volume, as well as allow for low flow hot water via the standard heater, which can’t be provided with an on-demand system. Has anyone attempted this modification? It seems much more efficient and a simple installation as long as there is room.

[NMWildcat]

No need to do any of that.
The perfect companion to an on demand water heater is a Shower Miser. https://www.showermiser.com/rv/
We installed one years ago in our RV. It saves us about 30 gallons a week while boondocking, while also eliminating any cold water bursts when taking a navy shower or warming the water initially. We love it!
Not sure what you are experiencing with your unit in regards to 'high flow necessary' for an on demand. Ours is one of the first generation, and if you turn on the hot water above a trickle, the unit fires. Perhaps your unit needs adjusting or you are still going through the learning curve?
We always turn on the hot water only to full open, and then adjust from there. Newer units have several different methods to set temperature.

[GolfingDave]

Sounds like quite a project. If going to that extremes is there anyway to install a hot water recirculating pump? No messing with propane then.

No idea if it is feasible on a camper but might be easier. As long as it has enough flow to kick on the heater.

[NavyLCDR]

Shower Miser is probably the easiest solution for RV, after it is installed.

[Larry-NC]

Originally Posted by GolfingDave

Sounds like quite a project. If going to that extremes is there anyway to install a hot water recirculating pump? No messing with propane then.

No idea if it is feasible on a camper but might be easier. As long as it has enough flow to kick on the heater.

A pump would continually draw battery current. Not good for boondockers.

In my previous home, I used a convection scheme which worked wonderfully, based on a typical residential 50-gallon vertical-tank water heater. I took off the drain valve and inserted a tee for a 1/4 soft copper line. I ran that line alongside the copper pipe serving the furthest-away sink and insulated each one separately. The thinking is that there is enough convection in the hot water tank to do the circulation.

After I finished the plumbing and refilled the system, I took a break. After about an hour I thought "I wonder if this 3/4" copper pipe is even warm yet." and grasped it with my hand. It was nearly too hot to hold.

The problem with trying this on a camper is that the tank is horizontal. There is only about a foot between the cold water inlet and the hot water outlet. Not sure there is enough distance to get good convection.

[GolfingDave]

Originally Posted by Larry-NC

A pump would continually draw battery current. Not good for boondockers.

Just an fyi, you only run recirculating pumps momentarily until hot water gets to the faucet. Kind of like a ShowerMiser concept. At least that is how I always understood it.

Hot and cold(heater return) are splice together through the pump. Never did it myself as my shower was close to the water heater at home.

https://www.familyhandyman.com/artic...culating-pump/

[Larry-NC]

Originally Posted by GolfingDave

Just an fyi, you only run recirculating pumps momentarily until hot water gets to the faucet. Kind of like a ShowerMiser concept. At least that is how I always understood it.

Hot and cold(heater return) are splice together through the pump. Never did it myself as my shower was close to the water heater at home.

https://www.familyhandyman.com/artic...culating-pump/

I didn't have to run mine at all--no pump! Furthermore, all the other fixtures between the heater and end fixture also got instant hot water. With the scheme you propose, you would need a switch at every fixture to start the pump. And it wouldn't be instant.