The cold shower problem
Most RVs leave the factory with a 6 or 10 gallon tank heater. That is enough for one quick shower, or dishes and a hand wash. On a rainy weekend at a Northwest campground, when everyone wants to warm up at once, it runs out fast. Then you wait, often 20 minutes or more, for the next batch.
On-demand heaters, often called tankless, promise to end that wait. They can be a great upgrade, but they are not right for every rig or every camper.
How on-demand heating works
A tank heater keeps a set amount of water hot all the time. An on-demand unit has no storage. When you open a hot tap, water flows through the unit, a sensor detects the flow, and a propane burner fires to heat the water as it passes through a heat exchanger. Close the tap and the burner shuts off.
Because nothing is stored, you are only limited by your fresh water supply and propane, not by the size of a tank. That is the main appeal.
Tank versus on-demand at a glance
- Hot water supply: a tank runs out, on-demand keeps going while water and propane last
- Wait time: a tank needs time to recover, on-demand needs a few seconds to fire up
- Propane: a tank burns fuel to keep water hot even when you are not using it, on-demand only burns while water flows
- Power: both usually need 12 volt power for controls, and on-demand units need it for ignition every time
- Flow: on-demand units need a minimum flow rate to stay lit, so a very low trickle may not trigger the burner
Will one fit your rig?
Many on-demand units are made to drop into the same outside opening as a standard 6 or 10 gallon tank. That makes the swap simpler, but it is not automatic. The opening size, the gas line, the 12 volt supply and the venting all need to match what the new unit expects.
Some older rigs have unusual compartments or framing. It is worth measuring the opening and noting the make and model of your current heater before you buy anything.
How they handle a damp Northwest winter
Output temperature depends on how cold the incoming water is. In summer, fresh water might come in fairly mild. On a January morning, water from a hose or a cold fresh tank can be close to freezing. The unit has to raise that water a lot further, so you may notice the hot water is a little less hot at high flow.
On-demand units also hold water inside a compact heat exchanger. If that freezes it can crack. If you camp through winter, you need to keep the unit protected, and if you store the rig, it has to be drained or bypassed properly during winterizing.
Who it makes sense for
- Families or couples who shower back to back
- Full time or long trip campers who hate waiting on hot water
- Owners whose old tank heater is near the end of its life anyway
- People who mostly camp hooked up to water or carry plenty of fresh water
Who might want to wait
- Weekend campers who rarely run out of hot water
- Boondockers who are careful with every gallon, since endless hot water can drain a fresh tank quickly
- Rigs with unusual heater openings where the swap would need major changes
Things to ask before you buy
Before you commit, find out whether the unit is designed for RV use, what opening size it needs, how it is controlled from inside, and how you drain it for winter. Also check how you will reach it for maintenance, because on-demand units benefit from periodic flushing to keep scale out of the heat exchanger.
Thinking about the upgrade?
Call or text J&L Mobile RV Repair at (855) 936-1457. Tell us about your rig and current heater, and we will talk through whether on-demand is a good fit.
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