One of the most common questions Davis Plumbing hears when helping customers replace a water heater is: “What size do I need?” Getting the right size is critical — too small and you’ll run out of hot water; too large and you’re paying to heat water you don’t use. Here’s a straightforward guide for Riverside County homeowners.

Tank Water Heater Sizing (By Number of People)

  • 1-2 people — 30-40 gallon tank
  • 3-4 people — 40-50 gallon tank
  • 5-6 people — 50-80 gallon tank
  • 6+ people or large homes — 80+ gallon tank, or consider a tankless unit

These are guidelines. A household with back-to-back morning showers and high laundry demand may need a size up from the standard recommendation.

The First Hour Rating (FHR): A Better Measure

Tank water heater manufacturers also specify a “First Hour Rating” — how many gallons the unit can deliver in the first hour of use, starting with a full tank. This is a more useful measure than tank size for busy households. The FHR should be at least the hot water demand in your home’s peak hour.

A typical morning hour in a 4-person family household might include 2 showers (20 gallons each), a dishwasher cycle (6 gallons), and hand washing (2-3 gallons) — totaling 48-49 gallons. A 50-gallon tank with a 60+ FHR handles this comfortably.

Tankless Water Heater Sizing (Flow Rate)

Tankless water heaters are rated by flow rate in gallons per minute (GPM) and temperature rise. To size a whole-home tankless unit correctly:

  • Add up the GPM of all fixtures that might run simultaneously in your peak hour (shower: 2 GPM, dishwasher: 1.5 GPM, etc.)
  • Calculate the temperature rise needed: if incoming ground water is 60°F and you want 120°F output, you need a 60°F rise
  • Choose a unit rated for that combined GPM at the required temperature rise

Most properly-sized single-family home installations in Riverside County use a 9-11 GPM unit from brands like Navien, Rinnai, or Noritz.

Gas vs. Electric Water Heater — Size Implications

Gas water heaters recover (reheat) much faster than electric — typically 30-40 gallons per hour vs. 15-20 for electric. This means a gas unit can often get away with a slightly smaller tank than an equivalent electric unit for the same household.

Professional Sizing by Davis Plumbing

When you call Davis Plumbing for a water heater replacement, we ask you about your household size, peak usage, and any plans for future changes (adding family members, ADU). We’ll recommend the right size and type to match your needs.

Call (951) 657-0393 for water heater sizing and installation service in Murrieta, Temecula, Menifee, and all of Riverside County. Or contact us online.