RV Hot Water Calculator: How Long Does a 6 Gallon Water Heater Last?

A 6 gallon RV water heater gives about four and a half minutes of hot shower on typical figures, and closer to six and a half through a 1.8 gal/min head. Answers online range from five minutes to ten, and each is right for someone — because the time depends on your shower head, your water temperatures and your heat source, not on the tank alone.

How long does a 6 gallon RV water heater last?

Longer than 6 gallons of water, which is the part most answers miss. You never shower in tank water. You mix it down with cold, so only part of every gallon through the head comes from the tank.

On the calculator’s defaults — a 130°F tank, 55°F cold water, a 100°F shower — that part is 60%: (100 − 55) ÷ (130 − 55). A 2.5 gal/min head therefore pulls 1.5 gal/min from the tank. Meanwhile the heater is putting water back: Suburban’s 10.1 gallons an hour on propane is about 0.17 gal/min. The tank runs down at the difference, and 6 gallons at 1.33 gal/min is about 4.5 minutes.

What Suburban publishes, and what it does not

Suburban’s tank water heater spec sheet gives the recovery figures the calculator uses:

Tank	Gas input	Recovery on propane	Recovery on electric
4 gallons	9,000 BTU/h	7.6 gal/hr	6.1 gal/hr
6, 10, 12 or 16 gallons	12,000 BTU/h	10.1 gal/hr	6.1 gal/hr

From Suburban’s Porcelain Steel Tank Water Heater specification sheet. The electric figure is for its 1,440 W element.

Notice the burner does not get bigger with the tank. A 16 gallon tank recovers no faster than a 6 gallon one; it simply holds more to start with. That 12,000 BTU/h is also what the propane cylinder supplies for every hour the burner fires — our propane calculator adds it to the furnace and turns both into days per cylinder.

What the sheet leaves out matters as much. It gives no thermostat setting and no temperature rise for either recovery figure. That is why the calculator asks for your tank temperature instead of assuming one, and why it prints the same shower at 120°F and 140°F in the tank — 3.8 minutes against 5.2 on the defaults. That spread is bigger than most of the fixes below, so the first thing worth doing is reading your own heater’s manual.

The free levers first

Before buying anything, the calculator shows what the same tank gives if you change how you use it. On its defaults:

• A shower 5°F cooler — 95°F instead of 100°F — gives about 5.2 minutes, 0.6 more.
• Running propane and electric together gives about 4.9 minutes, 0.4 more, by adding the element’s 6.1 gal/hr to the burner’s 10.1. That needs shore power and a heater that lets both run at once — Suburban’s spec sheet lists the two separately and does not say, so check your heater’s switches and manual.
• Turning the water off while you soap. The calculator cannot put a number on this one, because it depends on how long you stand there — but every paused minute is a minute of hot water still in the tank.

Your shower head is the biggest lever

Federal law caps a shower head made since 1994 at 2.5 gallons a minute, “measured at a flowing pressure of 80 pounds per square inch” (10 CFR 430.32). If you do not know your head’s rating, that is the fair assumption, and it is the calculator’s default.

Drop to a 1.8 gal/min head and the default shower goes from 4.5 minutes to 6.6 — 2.1 more from the same tank, which is more than all the free levers above put together.

Where the hot water goes

A 4.5 minute shower at 2.5 gal/min is about 11 gallons of water, all of it heading for your grey tank. If you are boondocking, that number matters more than the hot water does — our water tank calculator works out which tank fills first.

Tankless is a different question

A tankless heater has no tank to empty, so it never runs out in the way this page describes. Its limit is how much water it can heat, by how many degrees, at once — a flow and temperature-rise figure from its own manual, which this calculator does not work out. Furrion’s tankless, for example, lets you set the output between 95°F and 124°F. If you have a tankless heater and it is winterizing time, note that it is handled differently from a tank — our winterizing calculator covers why.

The heads compared

Model	Rated flow	Flow control	Hose	Buy
Oxygenics Fury RV	1.8 GPM at 80 PSI	A "Flow Control lever" that "quickly adjusts shower pressure". Oxygenics does not describe it as a full pause or shut-off	72 in	Check price(opens in a new tab)
Oxygenics PowerFlow RV	1.8 GPM at 80 PSI	"Flow control lever allows you to reduce water to a trickle right on the shower head"	72 in	Check price(opens in a new tab)
Oxygenics BodySpa Adventure RV	2.0 GPM at 80 PSI	"Design includes a built in SmartPause® setting that preserves water in tanks"	72 in	Check price(opens in a new tab)

Where this goes wrong

1. Assuming the tank temperature. It moves the answer more than most fixes, and Suburban’s spec sheet does not publish one. Check your manual.
2. Using summer cold water in winter. Colder water in means more hot water per shower and fewer minutes.
3. Running a second tap. The calculator assumes the shower is the only thing drawing hot water.
4. Buying a bigger heater for a flow problem. A bigger Suburban tank recovers no faster than a 6 gallon one. A lower-flow head buys more time from the tank you already have.

Questions worth answering