Quick Answer: Winterizing a home tankless water heater means shutting off gas or power, closing the water supply, fully draining the unit through its bottom drain valve, and purging remaining water with compressed air capped at 30 PSI — Eccotemp’s own guidance explicitly warns against using antifreeze in a home unit, since it “can damage the heater’s components.” An RV tankless heater winterizes differently: after draining, run 2-4 gallons of non-toxic RV antifreeze through the system (including the water heater itself) until it runs pink at every fixture, per Camping World’s RV winterizing guidance. Mixing up the two methods is the single most common winterizing mistake.
Most tankless water heater guidance online is written for RVs, where antifreeze is standard. Pour that same pink antifreeze into a house or cabin’s residential unit, though, and the manufacturer’s own documentation says it can damage the heat exchanger and void the warranty. This guide separates the two procedures — home and RV — with the exact steps each one actually calls for.
Home vs. RV: the two procedures side by side
| Home / cabin tankless unit | RV tankless unit | |
|---|---|---|
| First step | Shut off gas supply or unplug electric unit; close cold water inlet | Turn off propane and power to the water heater |
| Draining method | Hose on bottom drain valve, hot tap open for air, drain valve open | Water heater drain plug + fresh tank and low-point drains, gravity drain |
| Remaining water | Compressed air purge, capped at 30 PSI | Compressed air purge (30 PSI) or antifreeze |
| Antifreeze? | No — can damage components (Eccotemp) | Yes — 2-4 gallons non-toxic RV antifreeze, run through the heater, not bypassed |
| Filter | Remove inlet filter, store separately | N/A on most compact RV units |
| Source | Rinnai TB-53 / Home Alliance service guidance | Camping World RV winterizing guidance |
By the numbers
- 30 PSI — the maximum regulated air pressure Camping World’s RV winterizing guidance specifies for blowing out a tankless unit’s plumbing lines with compressed air; exceeding it risks damaging fittings and seals. — Camping World
- 2-4 gallons — the typical amount of non-toxic RV antifreeze needed to fully winterize an RV’s water system, including its tankless heater, per Camping World. — Camping World
- “Not recommended as it can damage the heater’s components” — Eccotemp’s own winterizing support documentation, on using antifreeze in a residential tankless unit. — Eccotemp Help Desk
- “Requires continuous electricity” — Navien’s guidance on why its built-in freeze protection stops working the moment a property loses power, the reason a fully vacant home needs full winterizing instead. — Navien
Winterizing a home or cabin tankless water heater
- Shut off the energy source. Close the gas supply valve on a gas unit, or unplug/breaker-off an electric unit.
- Close the cold water inlet valve feeding the unit — this is where an isolation valve kit earns its keep, since generic shutoffs rarely include the hose-drain ports this step needs.
- Connect a hose to the bottom drain valve, open a hot water tap elsewhere in the house so air can enter the line, then open the drain valve and let it empty completely. This sequence — hot tap open before the drain valve — is confirmed by both Rinnai’s own RUS-series guidance and Home Alliance’s service documentation.
- Remove and store the inlet filter. Leaving it in place traps residual water against a part that’s cheap to lose but annoying to replace if it cracks.
- Purge remaining water with compressed air, regulated to 30 PSI, through the inlet and outlet connections.
- Never add antifreeze. Eccotemp’s guidance is explicit that doing so can damage internal components and may void the warranty — the drain-and-purge method above is the complete procedure for a home unit.
Webstone 44443WPR 3/4-in. Isolator EXP E2 Tankless Water Heater Valve Set
- Hi-flow hose drain ports on both valves mean step 3 above — hose on the drain valve — connects directly with no adapter, which is most of the point of installing tankless-specific valves before winterizing season instead of during it.
- Union connections at the water heater end let the whole assembly unscrew for service without cutting pipe, useful if a vacant-property inspection turns up a valve that needs replacing.
- The same kit covered in our isolation valve kit roundup, where it's the top pick for exactly this reason.
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Winterizing an RV tankless water heater
- Turn off propane and power to the water heater first, so it can’t attempt to reheat an empty tank or heat antifreeze once added.
- Let it cool, then disconnect from the city water connection and shut off the onboard pump.
- Drain the system: remove the water heater’s drain plug and open the fresh tank and low-point drains, letting gravity pull most of the water out. Close these drains again before the next step so antifreeze isn’t immediately lost.
- Choose compressed air or antifreeze for the remaining water. Compressed air needs a regulated adapter capped at 30 PSI; antifreeze needs 2-4 gallons of the non-toxic RV type, drawn through the system with the onboard pump.
- Run the tankless heater in the antifreeze path — don’t bypass it — and run every fixture until the fluid coming out turns pink, confirming antifreeze has reached the heater itself and not just the rest of the plumbing.
Camco Full Timer's Choice -50°F RV & Marine Antifreeze
- The standard RV winterizing antifreeze — non-toxic and safe for a potable water system, unlike automotive antifreeze, which should never go anywhere near drinking-water plumbing.
- Rated to a -50°F burst point, well below what a stored RV's tankless unit and lines would realistically see even in a hard winter.
- Pairs with the best RV tankless water heater roundup for which models include their own built-in anti-freeze mode versus needing this full manual procedure every season.
The bottom line
Home and RV tankless water heaters winterize in two genuinely different ways, and the most common mistake is applying the RV method — antifreeze — to a house or cabin unit that should only ever be drained and air-purged. For a home: shut off gas or power, close the water supply, drain through the bottom valve with a hot tap open for air, remove the filter, and purge with compressed air at 30 PSI or under — never antifreeze. For an RV: drain first, then either blow it dry at the same 30 PSI limit or run 2-4 gallons of non-toxic RV antifreeze through the heater itself until it runs pink. If the property will keep power through winter, our freeze protection guide covers when the built-in system alone is enough and full winterizing isn’t needed at all.