Water Heater Check · full explanation

Expansion conditions

Expansion worksheet

40°F starting-water reference · arithmetic only

Ranges are this worksheet’s scope, not pressure or temperature recommendations. Use the source guide if a value is unknown. Do not adjust equipment to make a form accept it.

Complete the conditions first

Unknown values stay unknown. No tank model is selected here.

Keep a source-linked summary

40°F starting-water reference, matching pre-charge, fixed 14.7 psia atmosphere. Both expanded-water acceptance and total tank volume need manufacturer verification. No equipment selection is made.

Sources and limits

Reviewed 2026-11-15. The linked method and your model manual take precedence over an explanatory example.

  1. Amtrol MC10007 · sizing and placement (opens source in a new tab)

    03/19. Pages 2–3: 40°F-base factors, DPF, pre-charge example and placement. Manufacturer-specific guidance; local and model requirements still apply.

  2. Watts · potable expansion sizing conditions · source record

    Live tool instructions. Distinct initial/final pressure and temperature conditions. Its 85%-of-relief ceiling and 90°F starting-water note must not be silently mixed with another method.