How to Choose the Right Water Heater Size for Your LA Home

March 25, 2026  |  Buying Guide

Choosing the wrong size water heater is one of the most common installation mistakes. An undersized unit means cold showers. An oversized one means you're paying to heat water you don't use. Here's how to get the sizing right for your Los Angeles home.

Sizing a Tank Water Heater

Tank water heaters are sized in gallons. The key number is "First Hour Rating" (FHR) — how many gallons of hot water the unit can deliver in the first hour of use, starting with a full tank. Here's a general guide:

Note: Add 1 size category if you have a large soaking tub, spa, or frequently run multiple showers simultaneously.

Sizing a Tankless Water Heater

Tankless units are sized by flow rate (gallons per minute) and temperature rise. The formula:

1. Determine peak simultaneous demand: What hot water fixtures will run at the same time? A shower uses ~2 GPM, a kitchen faucet ~1.5 GPM, a dishwasher ~1.5 GPM.
2. Calculate temperature rise: LA groundwater is around 65°F. If you want 120°F output, that's a 55°F rise.
3. Select a unit that meets your GPM at that temperature rise.

Here are general guidelines for LA homes:

• Smaller homes / 1–2 people (1–2 bathrooms): 6–8 GPM
• Medium homes / 2–4 people (2–3 bathrooms): 8–9 GPM
• Larger homes / 4+ people (3–4 bathrooms): 9–11 GPM
• High demand / multiple simultaneous fixtures (4+ bathrooms): Multiple units or a commercial-grade unit above 11 GPM

LA-Specific Considerations

• Cold water temperature: At 65°F inlet (typical for LA), tankless units perform better than in colder climates. You can use a slightly smaller BTU unit than you'd need in a colder state.
• Hard water: Scale reduces effective flow rate over time. Size up slightly if you won't be doing annual descaling.
• Gas pressure: LA has consistent SoCal Gas pressure, which supports high-BTU tankless units without issues.

Not sure what size you need? Call Simple Water Heater & Filtration. We assess your home's specific hot water demand as part of every installation quote — no guesswork, no overselling.