Water Heater Size Calculator
Answer four questions and get the size a licensed plumber would recommend — tank gallons or tankless flow rate — plus realistic installed-cost context for the San Antonio metro.
Your recommendation
Hard-water note for the NE San Antonio metro: at 14–15+ grains per gallon, plan on an annual flush (tank) or scheduled descaling (tankless) — or pair the install with awater softener to protect the investment.
Water Heater Sizing FAQs
How accurate is this water heater size calculator?
It uses the same first-hour-rating logic plumbers use for sizing: household size, bathroom count, and peak-usage overlap. It gets you to the right size class; a quick phone call confirms the exact model for your home’s gas line, venting, and space.
Does hard water change what size I should buy?
Not the size — but it changes the plan. In the northeast San Antonio metro (14–15+ grains per gallon), sediment eats capacity over time, so an annual flush or a softener matters more than upsizing. Tankless units here need scheduled descaling.
Should I switch from tank to tankless?
Tankless shines for larger households that keep running out of hot water, and for garages where space matters. It costs more upfront and needs a bigger gas line in many homes. Our tankless vs tank guide walks through the honest math.
What does installation cost in the San Antonio area?
Typical installed cost runs about $1,400–$3,300 for a standard tank and $3,500–$6,500 for tankless, depending on size, venting, code updates, and permits. Your city may require a permit and inspection — we handle that.
Want it sized by a pro?
Free phone assessment — we'll confirm size, venting, and code items in five minutes.