How long does a water heater take to heat up?

Typical heat-up times

Source: A. O. Smith. Lennox gives similar figures: about 30 to 40 minutes for a full 40 gallon gas tank and 60 to 80 minutes or more for a comparable electric one. A. O. Smith's guide to new installations says a gas tank heats from empty in about 30 to 40 minutes and most electric tanks in about 60 to 80 minutes.

Why gas is faster: recovery rates

Manufacturers rate tanks by recovery, the gallons of water a heater can warm per hour by a set amount, usually 90°F. A. O. Smith's sizing guide lists these figures for a 90°F rise:

Two details explain the gap. A. O. Smith figures gas heaters at 75% recovery efficiency, because some heat goes up the flue, and electric at 100%. But a gas burner simply puts in far more heat per hour. And on a typical electric tank with two elements, they don't run at the same time: Rheem's spec sheet bases its recovery on non-simultaneous operation, so a heater with two 4,500 watt elements recovers at about 21 gallons per hour, not double that.

The recovery number and the minutes above measure different things. The table is rated capacity at a 90°F rise; the minutes are A. O. Smith's typical times for a tank to fully recover in normal use.

What changes how long you wait

• Incoming water temperature. A. O. Smith notes the heater works harder in January than in July, so winter recovery is naturally longer. In the sizing guide's table, a 40,000 Btu burner heats 40.4 gallons an hour at a 90°F rise but 60.6 at a 60°F rise.
• Tank size. Bigger tanks take longer to heat but run out later. A. O. Smith says the first-hour rating, which combines stored water with what the heater can make in an hour, matters more than tank size alone (see what size water heater do I need).
• Thermostat setting. Most heaters ship at 120°F. A higher setting takes longer to reach and costs more (see what temperature a water heater should be).
• Element or burner size. A. O. Smith says larger elements heat water faster; a new installation has the right size for that model.

How much hot water a shower uses

EPA WaterSense says a standard showerhead uses 2.5 gallons a minute and a WaterSense model no more than 2.0. That's total flow, hot and cold mixed, so a 20 minute shower runs 40 to 50 gallons through the showerhead, and the hot share depends on how hot you like it. Back-to-back long showers can outrun a 40 or 50 gallon tank, and then you're waiting on recovery. If that happens daily, see hot water runs out fast.

When slow heating means something's wrong

A heater that takes longer every year usually has a problem. A. O. Smith lists the common ones:

• Sediment. Minerals settle on the tank bottom and act like a blanket between the burner or elements and the water. Popping or rumbling while heating is a sign (see why is my water heater making noise and how to flush a water heater).
• A failed electric element. Lose one of the two and A. O. Smith says recovery time doubles (see signs of a bad element).
• A bad thermostat. It won't tell the burner or elements to turn on, leaving lukewarm water or none.
• A broken dip tube. Cold water mixes in at the top of the tank, so hot water turns lukewarm fast (see water heater dip tube).
• A heater that's too small, or too old. A new heater should meet the recovery in its manual; if it doesn't, it may be undersized. On tanks 10 or more years old, A. O. Smith says long recovery times can mean it's time for a replacement.

Electric homes wait longer

Because electric tanks recover more slowly, households that run on electricity feel this more. About 81% of homes in Marsing, Idaho heat with electricity, and about 51% in Elizabethtown, Pennsylvania, according to census estimates on our town pages. If an electric tank has gone from slow to cold, our guide to testing a bad electric water heater element walks through the usual checks.

Local pages mentioned

• Elizabethtown, PA
• Marsing, ID