How to Drain a Water Heater (Tank or Tankless) — Step by Step

Draining a water heater is needed for three reasons: (1) removing the old unit during replacement, (2) routine sediment flushing during maintenance, or (3) winterizing a tankless or vacation home. The procedure differs slightly for each. This page covers all three.

Tools needed

• Garden hose (¾", 25-50 feet, depending on distance to a floor drain or outside)
• Bucket (5-gallon) — for testing water clarity during a flush
• Channel-lock pliers — for stubborn drain valves
• Towels for the area around the heater
• Flashlight

Full drain — for replacement

1. Shut off power. Gas: turn the gas control to "Pilot" or "Off." Electric: flip the breaker
2. Shut off cold water supply at the cold-inlet valve on top of the heater
3. Open a hot tap somewhere in the house (kitchen sink, bathtub) — this lets air in and prevents vacuum that slows draining
4. Connect the garden hose to the drain valve at the bottom of the tank. Route the other end to a floor drain, a bathtub, or outside (downhill from the heater)
5. Open the drain valve (lever or knob)
6. Wait. A 50-gallon tank takes 30-90 minutes to drain depending on water pressure and drain valve diameter. Hot water draining slowly is normal
7. When flow stops, briefly open the cold-inlet valve to flush remaining sediment, then close again
8. Close the drain valve and disconnect the hose when the tank is empty

If the drain valve clogs partway (sediment block), close it, wait a few minutes for sediment to settle, reopen. If completely stuck, the original brass drain valve can be replaced with a ball valve ($15-30, requires a wrench and possibly a wet/dry vacuum to remove residual water).

Partial drain — sediment flush

For routine maintenance to remove sediment without fully draining and refilling. Cleaner approach than the full drain:

1. Turn the gas to "Pilot" or flip electric breaker
2. Leave the cold-inlet OPEN (this is the key difference from full drain — pressure pushes sediment out)
3. Don't open hot taps
4. Connect the hose to the drain valve
5. Open the drain valve — water flows out, cold water continues to fill, creating a flushing action
6. Run for 5-10 minutes until the water exiting the hose runs clear (catch some in a bucket to verify)
7. Close the drain valve
8. Disconnect the hose after the heater pressurizes
9. Restore gas/electric

This is the easier method for annual flushing — no waiting for the tank to refill before turning power back on. See how to flush a water heater for the full annual maintenance walkthrough.

Draining a tankless water heater

Tankless units don't have a tank to drain in the conventional sense — only the heat exchanger holds water (typically less than 1 gallon). Draining is needed for:

• Descaling — connect a pump to the isolation valves and circulate vinegar/descaler. See brand-specific guides: Rinnai, Navien
• Winterizing — for vacation homes or cabins in freezing climates. Drain the unit to prevent heat exchanger freeze damage

Tankless winterizing

1. Shut off gas at the unit
2. Shut off cold and hot isolation valves on the service kit
3. Connect a hose to the cold isolation valve service port; drain to a bucket
4. Open the hot isolation valve service port; air enters, allowing remaining water to drain
5. Use a shop vac on the inlet to pull residual water from the heat exchanger
6. Leave the service ports open during winter storage
7. To restart: close service ports, open isolation valves, restore gas, power on, verify normal operation

Refilling after a drain

Critical for electric units: never apply power to a dry electric water heater. The heating element burns out within seconds without water around it. Always refill fully before energizing.

1. Verify the drain valve is closed
2. Close the hot tap you opened earlier
3. Open the cold-inlet valve fully
4. Wait until water pours from the hot tap (open a faucet) with no air bubbles — this means the tank is full and air is purged
5. Close the hot tap
6. Restore power (electric: breaker) or relight gas pilot
7. Allow 30-60 minutes (gas) or 90-120 minutes (electric) for water to reach setpoint

Drain-related troubleshooting

• Drain valve won't close fully (drips): sediment trapped under the seat. Open briefly to flush, then close. If still drips, drain valve needs replacement
• Drain water is dirty/rusty: normal for an unflushed tank with sediment. Continue flushing until clear. If the water continues to be heavily discolored, the tank's interior may be corroding — see lifespan
• Drain valve clogs: close, wait 5 min, reopen. If still clogged, use a thin wire to dislodge the blockage
• Sounds like air sucking but no water: hot tap not open. Air-lock prevents flow

Related guides

• How to flush a water heater
• Annual maintenance
• Replacement
• Anode rod (often inspected during drain)

Bottom line

For sediment flushing, use the "leave cold supply open" method — faster and cleaner. For full drain before removal, follow the closed-supply procedure. Never re-energize an electric heater before it's fully refilled. Annual drain-and-flush adds years to the unit's lifespan and is the highest-ROI maintenance task you can do.