Most RVs have a 6 or 10 gallon tank water heater that runs on propane, on 120-volt electric power, or on both at the same time. Tankless units heat water as it flows instead of storing any. Which one you have is printed on the heater itself, behind the outside access door.
RV Water Heaters Explained: Tank vs Tankless, Gas vs Electric, 6 vs 10 Gallons
At a glance
- What you probably have: a 6 or 10 gallon tank heater from Suburban or from Dometic, the brand that absorbed Atwood.
- Gas, electric or both: running both together gives Suburban's fastest published reheat rate, 16.2 gallons per hour on its gas/electric models.
- 6 vs 10 gallons: Suburban gives its 6 and 10 gallon heaters the same burner and the same reheat rate, so the bigger tank stores more hot water but does not heat any faster.
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How your RV water heater works
A tank heater holds 6 or 10 gallons of water and heats it with a propane burner under the tank, a 120-volt element inside it, or both. A thermostat cycles the burner or element back on as you draw hot water off.
Older heaters have a pilot that you light by hand behind the outside door. Current models use direct spark ignition, switched from inside the RV, which needs 12-volt power even in propane mode; Dometic asks for a 10 to 14 VDC supply.
If the spark cannot light, the heater gives up: Dometic's WH series makes three attempts, then locks out and lights a red lamp. For faults, see water heater troubleshooting.
Which type do you have?
Your heater is most likely one of these three lines, and the model number is on the data label behind the outside door.
| Line | Fuel | Sizes and output | Tank and anode |
|---|---|---|---|
| Suburban Advantage tank (SW6D, SW10D) | Propane; DE and DEL versions add a 1,440 W electric element | 6, 10 and 12 gallon models all at 12,000 BTU/h; the line runs 4 to 16 gallons | Porcelain-lined steel, replaceable anode rod |
| Dometic WH series, formerly Atwood (WH-6GA, WH-10GEA) | Propane only on WH-6GA, propane plus electric on GEA models | 6 and 10 gallon tanks; WH-6GA 10,000 BTU gas input (Dometic publishes no input for the 10 gallon) | Aluminum, no anode, and Dometic says not to fit one |
| Suburban Advantage tankless (5581A) | Propane | 36,000 BTU/h first stage, 60,000 BTU/h second stage, maximum setpoint 130°F | No tank, no anode |
Figures from Suburban's 2025 product catalog and Dometic's WH-series installation and operation manual.
Gas, electric or both?
Propane works anywhere, including boondocking, as long as the 12-volt system is live. Electric needs shore power or a generator, and both together heat fastest.
Suburban's catalog gives 6 gallons per hour on electric alone against 16.2 gallons per hour on electric plus propane, and Jayco tells owners to leave both switches on for the fastest hot water recovery.
Not every heater has an electric side: Suburban's D models and Dometic's WH-6GA are propane only. Electric-only tank heaters, such as Suburban's SW7EC, have no burner and no venting.
Tip: Hot water on propane but never on shore power? Look for a second switch behind the outside door, in the lower left corner of the control housing. On Suburban DE models it is the only control for the electric element. DEL models add a relay so the interior switch runs both.
Is 6 or 10 gallons enough?
The 10 gallon tank stores about four gallons more hot water, and that is the whole difference. Suburban gives its 6 and 10 gallon Advantage heaters the same 12,000 BTU/h burner and the same recovery, 10.1 gallons per hour on gas and 6.1 gallons per hour on electric.
Suburban says the right size depends on your plumbing and how many people want hot water at once. No maker publishes a shower count per tank size, so treat any such figure as someone's estimate.
Size also decides the hole in the wall. Suburban's 4 and 6 gallon heaters take one exterior door and its 10, 12 and 16 gallon heaters another, so moving up a size is a sidewall job, not a swap.
Tip: A Dometic WH-9GEA is a 6 gallon tank and a WH-16GEA is a 10 gallon tank. The 9 and 16 are "effective" gallons of 130°F water delivered through the built-in mixing valve. Buy a door and a cutout for the real tank size.
Steel tank with an anode, or aluminum without?
Which tank you have decides whether there is an anode to look after. Suburban tanks are glass-fused-to-steel, protected by a magnesium or aluminum anode rod that corrodes in place of the steel. Suburban recommends checking it every 6 to 12 months and replacing it yearly, or whenever more than 75% of it is gone.
Dometic's current WH tanks are aluminum and need no anode, and the manual lists anode rods among the after-market devices not to use with the heater at all.
Tip: This changes how you drain the tank. On a Suburban the anode rod doubles as the drain plug and comes out with a 1-1/16 socket. On a Dometic you pull a plain drain plug, and about two quarts stay in the tank, which Dometic says will not damage it if it freezes.
Tank or tankless?
Tankless units heat water as it passes through, with a much larger burner (Suburban's runs 60,000 BTU/h at second stage), and Furrion now sells tankless models only. Before antifreeze goes in, close a tank heater off with its bypass and drain it; for tankless, makers differ (Jayco says no bypass is needed, Truma requires a bypass kit). The full comparison is on the tankless water heater page.
Replacing one
What matters is the opening, not the brand. A 6 gallon cutout is close to 13 inches square on both Suburban and Dometic, and a 10 gallon cutout close to 16 inches, but depths and tolerances differ, so measure your own opening and use the cutout table in the new heater's installation manual.
Both makers sell a way around a mismatch. Suburban's Advantage Direct Fit SAW6D replaces 6 gallon aluminum tank heaters without sidewall or cabinet changes (door and switch sold separately), and Dometic sells adaptor brackets and matching doors for older openings.
Stop at the connections. The propane line, the vent and the 120-volt wiring are for an RV technician: Suburban states that gas appliances must be installed by a qualified service technician, and Dometic warns that improper installation can produce carbon monoxide, causing death or serious injury.
Common questions
Can I replace my RV water heater with a tankless one?
Yes. Suburban says a Suburban or Atwood-style tank heater can be replaced with its tankless unit, using a replacement panel for the old door plus a vent cap assembly. Buy the kit for your brand style and tank size.
How long does an RV water heater take to heat up?
Neither maker publishes a heat-up time, and Dometic publishes no recovery rate at all. Suburban's gas recovery of 10.1 gallons per hour works out to roughly 36 minutes for a 6 gallon tank and about an hour for a 10 gallon tank (calculated, 6 divided by 10.1 and 10 divided by 10.1), at a temperature rise Suburban does not state.
Can I run my RV water heater on gas and electric at the same time?
Only on a gas/electric model: a Suburban DE or DEL, a Dometic GEA, or an older Atwood combination model with a C in the model number. Do not add an after-market element to a gas-only heater; Dometic warns these can lack critical safety controls and lead to uncontrolled tank heating and tank explosion.
Should I turn off the water heater while driving?
Turn the propane side off. Dometic says to shut the gas off at the LP tank while the vehicle is moving, because wind can cause flame reversal and trip the thermal cut-off, which then has to be replaced. Suburban says the same for all gas appliances.