Water Heaters
Water Heater Selection Methodology
After sizing determines the required capacity, selection methodology chooses the right heater configuration: single unit, multiple staged units, or tankless. Here is how.
Introduction
Water heater selection goes beyond sizing - it involves choosing the right type (storage, tankless, boiler, heat pump), the right configuration (single vs staged), and the right model from a catalog. Plumbing Booster supports both generic and catalog-based selection modes.
Generic Mode (B2 Auto-Staging)
In generic mode, the software uses B2 auto-staging:
1. Calculate the required envelope (storage + recovery).
2. Find the minimum number of units (k) that meet the envelope, where k <= maxUnits.
3. Optionally apply N+1 redundancy (add one standby unit).
4. Each unit is sized for envelope/k.
Example: Required = 200 gallons storage, 100 GPH recovery. Max units = 4.
- 1 unit: 200 gal, 100 GPH (may exceed available model sizes)
- 2 units: 100 gal, 50 GPH each (more practical)
- With N+1: 3 units installed, 2 operating
The user can adjust maxUnits and toggle N+1.
Catalog Mode
In catalog mode, the software matches actual products:
1. Filter catalog by heater type (storage, tankless, boiler, heat pump).
2. Match units to the required envelope.
3. Preferred manufacturer/brand is a soft preference (boost score) but does not hard-filter.
4. Other brands appear as alternatives.
5. Select the best match based on capacity, efficiency, and preference score.
The built-in catalog includes AO Smith/AOSmith specifications. Additional manufacturer catalogs can be imported.
Tankless Sizing
Tankless (instantaneous) water heaters are sized differently:
- No storage - heated on demand
- Sized by peak flow rate (GPM) at the required temperature rise
- Temperature rise = Hot water temp - Cold water inlet temp
- Must meet peak instantaneous demand, not daily usage
Plumbing Booster handles tankless sizing in both generic and catalog modes.
How Plumbing Booster Automates It
The Water Heaters module supports per-heater sizing method, selection constraints, and peak-window analysis (Method 2). The Summary page shows:
- Sizing method and results
- Selected heater type and configuration
- Selection status (enabled/disabled)
- Per-heater details (capacity, recovery, efficiency)
- Issues and validation warnings
Related Articles
Water Heater Sizing Guide
Water heater sizing determines the storage capacity and recovery rate needed to meet peak hot water demand. Here is the ASHRAE-based methodology Plumbing Booster uses.
Domestic Water Demand Calculation
Domestic water demand calculation is the foundation of plumbing system design. This guide covers WSFU summation, diversity factors, and code-specific flow conversion.
Want to try these calculations yourself?
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