Tankless RV Water Heaters: What the Specs Mean and What Changes in Use

Can you put a tankless heater in your RV?

In most trailers and motorhomes with a sidewall water heater, yes. Suburban sizes its Advantage tankless heater to replace its own 6, 10, 12 or 16 gallon tanks, or a 6 or 10 gallon aluminum tank from another maker, with a replacement panel and vent cap over the old door opening.

Suburban's ST-42 and ST-60 fit the existing sidewall cutout of a Girard or Furrion 6 gallon or tankless heater. Girard sells door kits so the GSWH-2 fits Suburban and Atwood 6 and 10 gallon openings, and Furrion sells retrofit kits the same way; measure the existing unit first.

Truma sells the AquaGo comfort for retrofit, with mounting frames in three sizes; the comfort plus is listed for new RVs only. Truma also does the swap at its Elkhart, Indiana and Lakeland, Florida service centers. If you are still weighing this against a tank water heater, the deciding factors are below.

This is not a do-it-yourself job. Girard says the GSWH-2 must be installed and serviced by a recommended installer, service agency or gas supplier, and Furrion says the same for its F2GWH. The propane connection and the vent belong to a licensed RV technician.

What the makers rate their units for

The minimum flow is the figure to compare first, because it decides whether a gentle shower keeps the burner lit. No RV maker gives a hot flow at a stated temperature rise, so output reads differently brand to brand.

Sources: Truma AquaGo comfort, Suburban's IW60 operation guide and ST-42/ST-60 manual, the Girard GSWH-2 owner's manual and the Furrion FWH09AFA. Girard gives both 0.8 and 0.9 gpm, hence the range. Furrion's older F2GWH is the Girard design under Lippert, with the same minimum flow and door kits. No tier-one RV supplier sells an electric tankless unit.

What BTU, flow and temperature rise mean

The colder the incoming water, the less hot water you get from the same heater. BTU per hour is the heat the burner puts into the water, and every model above turns the gas up and down to match what you draw. What you feel at the faucet is a rise added to the inlet temperature: spread the same heat over more water and the rise is smaller, which is why 2.4 gallons per minute means little without an inlet temperature.

When several faucets run at once, even a 60,000 BTU/h burner cannot reach the set temperature.

What changes when you use it

Expect a minimum flow, a short wait and a run-time limit. Trickle a faucet below the minimum in the table and the burner does not light, or drops out mid-shower.

Suburban says heated water starts about 3 seconds after ignition on an IW60 and about 7 seconds after a faucet opens on an ST, but it still has to push out the cold water standing in the hot line, so a longer run means a longer wait. Suburban's IW60RL adds recirculation to keep hot water at the faucets.

Girard, Furrion's F2GWH and Suburban's ST models shut off after 20 minutes of running; the IW60RL stops after three hours. Supply pressure matters too, which makes the RV water pump part of the picture: Girard and Furrion want a steady 45 psi or more, and Truma caps the AquaGo at 65 psi, so fit a pressure reducer on a stronger city supply.

Freeze protection and winterizing

Built-in freeze protection works only while the heater has power and propane, so drain it for storage. Girard's and Furrion's F2GWH fire the burner below 38°F, protecting the heat exchanger only. Truma's AquaGo comfort fires below 41°F (5°C) only with constant 12 V, propane and the unit switched on; the AquaGo basic has no protection. Suburban adds a valve that opens in the cold and drains the heater, at thresholds it states variously as 34°F, 39°F or 40°F.

Suburban says to drain before winter, adding RV antifreeze afterward only if the coach maker recommends it. Girard and Furrion need no bypass kit, while Truma requires an installed bypass to winterize with fluid.

Electric units and 12 V power

For an electric tankless heater you have to look beyond the RV brands: Suburban confirms the IW60 uses propane for heat and 12 V only for its components. A 120 V point-of-use heater draws whatever its maker prints, and that has to fit a 30 amp hookup alongside the air conditioner, so check the nameplate first.

The propane units are light 12 V loads: Truma lists under 2.5 A running, Girard under 3 A. Girard's controller draws about 0.20 A all the time, so switch the 12 V off in storage or when dry camping. Suburban's ST models will not run below 10 V.

How long one lasts, and who services it

No maker publishes a service life, so warranty terms are the only guide:

• Suburban IW60 and ST-42/ST-60: two years, parts and labor, with proof of purchase.
• Truma: twelve months, plus twelve more if you register within two months and it was installed to Truma's instructions.
• Furrion FWH09AFA: one year.

There is no anode rod to replace, but scale builds up: Suburban recommends a yearly drain and a flush with a descaling solution, and Truma an annual service by a certified technician. If yours is throwing an error code or refusing to light, that is a separate diagnosis.

Common questions