Choosing a Water Heater (Boiler vs Tankless): Power and Consumption Calculation Guide

Choosing a water heater is not only about price—it’s about matching hot-water demand to the right technology and correctly calculating power and energy use. In Anaheim, where households often run multiple fixtures, start by estimating your peak demand: list showers, faucets, dishwasher, and laundry, then note how many may run at the same time. Storage (boiler) water heaters are measured by tank volume (gal or liters) and recovery rate. To estimate energy needed to heat water, use: Energy (kWh) ≈ Volume (L) × ΔT (°C) × 0.001163. Example: 80 L heated from 15°C to 55°C (ΔT=40) needs about 3.7 kWh per full heat cycle (plus standby losses). A larger tank improves comfort but increases heat loss if insulation is poor. Tankless (instant) heaters are chosen by flow rate and required temperature rise. Power requirement can be approximated by: Power (kW) ≈ Flow (L/min) × ΔT (°C) × 0.069. Example: 8 L/min with a 25°C rise needs ~13.8 kW. If you want to run a shower and sink together, total flow increases and so does required kW—often beyond typical electrical panel capacity. Gas tankless units can cover higher loads, but venting and gas line sizing matter. Compare real operating cost using your local utility rates: Cost ≈ kWh × rate, and remember that tankless saves standby losses, while storage can be more forgiving for high simultaneous demand. For Anaheim properties, a quick check of panel amperage, fixture flow restrictors, and incoming water temperature will make your final choice accurate.