What size drain pan do I need for a 50 gallon water heater?

Most 50 gallon tanks are 20 to 24 inches in diameter, so a 26 inch pan suits the majority. Measure across the jacket at its widest point and add at least two inches. Heat pump water heaters are wider than resistance tanks of the same capacity, so a 30 inch pan is often the right answer for those.

Is a drain pan required by code?

Wherever a leak would damage the building, which covers attics, upper floors and finished spaces, and in many jurisdictions everywhere. The pan has to extend beyond the heater and drain through a line of at least 3/4 inch to an approved point. Even where it is not required, it is a few dollars against a tank that will eventually fail by leaking.

Does the pan depth matter?

It matters for how long a slow leak stays contained. A standard two inch pan holds a few gallons, while a six inch pan holds close to ten times that, which is the difference between a damp floor and a finished ceiling below. In a finished space the deeper pan is worth the extra money, and in a garage on concrete it usually is not.

Should I fit a leak detector as well as a pan?

Yes, and it is inexpensive. A pan and drain handle water that arrives slowly. An alarm in the pan tells you a leak has started, and a version with an automatic shutoff valve closes the cold inlet so the tank can only release what it already holds. On an upper floor that combination is the single best value protection available.

Install calculator

Water Heater Drain Pan Size Calculator

Quick answer

A drain pan should be at least two inches larger in inside diameter than the tank. A typical 50 gallon tank at 22 inches diameter needs a 24 inch minimum, which in practice means a 26 inch pan, drained through at least a 3/4 inch line.

Result

Pan size to buy 24 in Convention

Minimum inside diameter 24 in Convention

Minimum drain line 0.75 in Published standard

A pan with no drain line is a bucket that overflows onto the same floor. If there is no practical drain point, fit a leak detector with an automatic shutoff valve instead, which closes the cold inlet when the pan wets so the tank can only release what it already holds.

The formula

Minimum pan inside diameter = tank diameter + 2 inches. Then round up to a pan size that is actually sold.

The code requirement is that a pan is fitted wherever a leak would damage the structure, that it extends beyond the heater, and that it drains through a line of at least 3/4 inch to an approved point. The "plus two inches" figure is a convention for how far beyond. Note that pans are sold by INSIDE diameter, and some listings quote the outside, which is how people end up with a pan the tank will not sit in.

The figures above are computed with these exact inputs: Tank diameter 22 in.

What this calculator assumes

Some of these are published test procedures or code tables and some are planning conventions. They are not the same kind of number, so each one is labeled.

Assumption	Kind	Where it comes from
Pan Clearance: 2	Convention	Pan inside diameter taken as the tank diameter plus two inches. The code requirement is that the pan extends beyond the heater and drains through at least 3/4 inch

Best for: Lowboy and small electric tanks

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Intermediate

SUPPLYGIANT

Everflow AWHP26 26 in Aluminum Pan

$47.99

The 26 inch aluminium pan with the 1 inch to 1.5 inch PVC fitting, which is the size the drain line usually needs.

Best for: The standard 50 gallon tank

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Frequently asked questions

What size drain pan do I need for a 50 gallon water heater?: Most 50 gallon tanks are 20 to 24 inches in diameter, so a 26 inch pan suits the majority. Measure across the jacket at its widest point and add at least two inches. Heat pump water heaters are wider than resistance tanks of the same capacity, so a 30 inch pan is often the right answer for those.
Is a drain pan required by code?: Wherever a leak would damage the building, which covers attics, upper floors and finished spaces, and in many jurisdictions everywhere. The pan has to extend beyond the heater and drain through a line of at least 3/4 inch to an approved point. Even where it is not required, it is a few dollars against a tank that will eventually fail by leaking.
Does the pan depth matter?: It matters for how long a slow leak stays contained. A standard two inch pan holds a few gallons, while a six inch pan holds close to ten times that, which is the difference between a damp floor and a finished ceiling below. In a finished space the deeper pan is worth the extra money, and in a garage on concrete it usually is not.
Should I fit a leak detector as well as a pan?: Yes, and it is inexpensive. A pan and drain handle water that arrives slowly. An alarm in the pan tells you a leak has started, and a version with an automatic shutoff valve closes the cold inlet so the tank can only release what it already holds. On an upper floor that combination is the single best value protection available.

Researched guidance, not professional advice. These results are planning figures from published test procedures, code tables and manufacturer specifications, and they do not replace a sizing done by the person who will sign the permit. A water heater is a pressure vessel: never cap, plug or remove the temperature and pressure relief valve, and replace one that will not open when the test lever is lifted. Gas line, flue and vent work belongs to a licensed plumber or gas fitter, because improper venting produces carbon monoxide. Water at 140 F scalds a child in seconds. Turn off the breaker before touching an element, and never energise an element that is not submerged.