How To Wire A 12V DC Tankless Water Heater In An RV That Previously Had A 120V Water Heater

Updated 08/21/2025 | Published 02/17/2021

Question:

I currently have a gas electric hot water heater. The electric is 120 volt. The tankless units are gas and 12V DC. Will I need to find or run a 12V DC source from somewhere or should there already be a 12V DC source at the present unit.?

asked by: Michael H

Expert Reply:

For your new tankless water heat that runs on 12V DC, such as Furrion RV Tankless Water Heater - Gas - Automatic Pilot - 60,000 BTU - 16" x 16" Door # FR98SR, you will need to wire this to your RV 12V DC battery and it's not likely there's already any 12 volt wring near your current heater and a 12 volt heater cannot run using 120VAC

I have attached a detailed installation video showing this process.

expert reply by: Andrew N

Ray V.

7/11/2024

Could you send me the video ...need to connect my Figatti RV water heater to my 12v battery

Andrew N.

7/11/2024

@RayV You can see it here https://www.etrailer.com/tv-install-fogatti-rv-tankless-water-heater-2007-starcraft-homestead-lite-fifth-wheel-lsb64fr.aspx

Helpful Links

tv-install-fogatti-rv-tankless-water-heater-2007-starcraft-homestead-lite-fifth-wheel-lsb64fr.aspx

Abby

8/31/2024

@AndrewN Does this video show installing a new 12v power supply for the hot water heater. I currently only have a gas hot water heater and I’m trying to install the tankless and need the 12v power

Lou

3/11/2025

@Abby no it does not, I can’t seem to find anything online about new wiring to a water heater that didn’t have electricity before… let me know if you found something so I can figure it out also, thanks

Bradley

5/30/2025

What do I do if main power is shut off during winter months and then when camping season comes around and power is back on, but battery is so dead for a trickle charger to bring it back to life? To clarify, I permanently installed a trickle charger to battery to keep it charged but didn't count on the fact that main power being off and battery getting dead dead from that.

Andrew N.

6/2/2025

@Bradley Hey there, good question. So that is actually a very common issue during the off season; lots of batteries getting drained or even ruined from being brought to such a low voltage for several months. You really only have 2 options. 1: pull the batteries for winter and keep them in your garage or basement on trickle charger. 2: install an off-grid low wattage solar panel to keep a trickle charge on them. A possible 3rd option is to go over to the batteries a few times during winter with a generator or something to give them some juice during off season.

Erald

8/20/2025

I have removed a 120vac RV water heater and replacing it with a 12vdc tankless water heater and need to power the 12volt gnighter Is it possible to connect the 120vac source that was available at the old heater to the line side of a bridge rectifier for the 12vdc output to power the ignition circuit for the new LP gas heater as well as a new 12 volt DC water pump that is protected via 10 amp blade type fuse?? Thank you much

Andrew N.

8/21/2025

@Erald Hey Erald, You definitely don’t want to feed 120VAC into a bridge rectifier and expect safe 12VDC out, that could fry the controls or pump. The right way is to tie the new tankless heater and pump into your RV’s existing 12V DC system (what powers your lights, fans, etc.), each on its own fused circuit. If your rig doesn’t already have a 12V system handy, you’ll want a AC-to-12VDC power supply like a converter.