RV Water Heater Options: Tank, Tankless & Hydronic

An RV water heater must add enough heat at the real flow while staying within fuel, battery, water, pressure and installation limits. “Endless hot water” is irrelevant when the fresh or gray tank is empty after one shower.

Calculate shower demand

mixed gallons = shower GPM × minutes

A 1.0 GPM shower for four minutes uses 4 gallons; two showers use 8. Add that demand to the fresh-water and gray-water calculation.

Heating energy is approximately:

kWh = gallons × temperature rise °F × 0.00244

Raising 2.6 gallons by 72°F requires about 0.46kWh before losses. That is roughly 38Ah from an idealized 12V source, with real battery draw higher. A small 12V label does not mean low energy.

Compare the main systems

Total installed cost includes vent/cutout, propane or fuel labor, valves, relief discharge, bypass, mixing, electrical feed, control panel, drainage and service clearance.

Electric tank heaters

Check element watts, tank gallons, recovery and dry-fire protection. A 500W element requires about an hour in an ideal calculation to add 0.5kWh; real recovery is longer. A 1,500W element run through an inverter can draw well over 125A from a nominal 12V battery once losses are included.

They fit shore-power-heavy use or a deliberately designed high-capacity electrical system. Put the real element and inverter load into the US electrical calculator before selecting it. Never energize a tank element until the heater is confirmed full. Install every required temperature-pressure relief component and route discharge safely.

Propane tank heaters

Traditional 6- or 10-gallon RV heaters store hot water and may offer propane, electric or both. They have known recovery and can work at low fixture flow, but use exterior wall volume and require tank draining, anode/scale service where applicable and winter bypass.

Use only listed RV equipment and qualified service. Follow the exact manual for gas pressure, combustion air, exterior door, clearances and ignition wiring.

Tankless propane heaters

Tankless equipment heats only during flow. Performance depends on inlet temperature and GPM. A unit that supplies a comfortable outlet from 70°F incoming water may produce less flow when the inlet is 40°F.

Suburban's ST-series product sheet explicitly distinguishes models by cold-inlet performance and lists safety/freeze features. Those features may require propane and 12V power; “freeze protection” is not a substitute for storage winterization.

Confirm:

• minimum activation GPM;
• rated temperature rise at your shower flow;
• maximum inlet PSI;
• required 12V current and propane supply;
• listed exterior vent/cutout;
• altitude limitations or derating;
• bypass and winterization steps.

Also compare performance when the RV switches between its onboard pump and a regulated campground connection. City pressure must remain within the heater and plumbing limits, while the onboard pump must still provide the heater's minimum activation flow. A heater that feels stable on a high-flow hookup can cycle or run cool from a restricted tank circuit. Test both supplies during commissioning, check the inlet screen and document the regulator setting. If the appliance lists altitude limits or a high-altitude mode, follow that guidance before mountain travel rather than changing gas components or combustion settings yourself.

Do not install an unvented portable propane shower heater inside any vehicle.

Engine and hydronic heat

An engine calorifier transfers coolant energy into domestic water while driving. It can reduce fuel/electric use but introduces critical work on the base-vehicle cooling loop. Use approved heat exchangers, hoses, isolation and professional integration; a leak can overheat the engine.

Hydronic fuel heaters can provide cabin heat and domestic hot water through separated circuits. They suit cold climates but add pumps, expansion, valves, electrical draw and service expertise. Plan component replacement access from the beginning.

Pump, pressure and temperature

The RV water-pump guide should be completed alongside heater selection. Pump shutoff PSI must remain below the heater and every downstream rating. Tankless heaters also need enough flow to activate and remain stable.

Stored hot water can scald. Install manufacturer-required mixing, check, bypass and pressure-relief devices. Keep hot tubing short and rated for its actual temperature. Long branches waste scarce water while occupants wait for heat.

Freeze and storage design

Water heaters contain small passages that are expensive to freeze. The correct process differs sharply by product. Some tankless heat exchangers must be drained through a cartridge; some hydronic domestic coils cannot be winterized with compressed air; tank heaters may need bypass and a removed drain plug/anode.

Winnebago's Truma maintenance and winterization guide shows distinct AquaGo and Combi procedures and repeatedly directs owners to the exact manual. Build the system with:

• reachable bypass valves;
• an unobstructed drain and air-admission path;
• hot and cold low-point drains;
• removable filter cartridges;
• model-specific RV winterization instructions.

Decision worksheet

1. Is hot water for dishes, showers or both?
2. What mixed GPM and gallons does each use require?
3. What is the coldest inlet-water temperature?
4. How quickly must the heater recover?
5. Is shore power, propane, engine heat or diesel reliably available?
6. Does pump GPM/PSI match the heater operating envelope?
7. Where are exterior vent, relief discharge and service opening?
8. Who will install and commission gas or fuel equipment?
9. Can the exact unit be completely winterized?
10. What do heater water, hardware and energy system add to payload?

Resolve all ten before ordering. The best RV water heater is the one that safely delivers the measured wash demand without forcing an oversized battery, tank or propane system.