Introduction
Water heater sizing ensures that a building has sufficient hot water storage and recovery capacity to meet peak demand. Undersized heaters run out of hot water; oversized heaters waste energy. Plumbing Booster uses ASHRAE Handbook methodologies with multiple sizing tables to provide accurate sizing recommendations.
Methodology
Plumbing Booster supports multiple ASHRAE and ASPE sizing methods:
**ASPE 2015 Methods:**
1. **ASPE Method 1: Average Hourly Demand** - Fixture-based average demand calculation.
2. **ASPE Method 2: Occupancy Type (Multifamily)** - Multifamily demand by occupancy class (LMH).
**ASHRAE 2019 Service Water Heating Methods:**
3. **ASHRAE Table 6** - Peak hour and daily demand.
4. **ASHRAE Table 7 (Apartments)** - Apartment sizing by LMH classification.
5. **ASHRAE Example 1 Table 8** - Design time (simplified method).
6. **ASHRAE Example 1 Table 9** - More accurate method.
7. **ASHRAE Table 10** - Fixture-based method.
8. **ASHRAE Tables 11-12** - Food service sizing.
9. **ASHRAE Table 13** - Industrial wash fountains and showers.
10. **ASHRAE Table 14** - Ready-mix concrete plant.
11. **ASHRAE Table 16** - Hot-water demand in fixture units.
12. **ASHRAE Table 17** - Preliminary demand.
For each method:
- Input: Building type, fixture counts, hot water temperature, usage patterns
- Output: Required storage volume (gallons or liters) and recovery rate (GPH or L/h)
- The software selects the appropriate table based on the chosen method and building parameters.
Storage vs Recovery
Water heater capacity has two components:
- **Storage volume**: The tank capacity in gallons/liters. Larger storage handles peak draws without running out.
- **Recovery rate**: How fast the heater can reheat water, in GPH (gallons per hour) or L/h. Higher recovery means less storage needed.
There is a trade-off: high-recovery + low-storage or low-recovery + high-storage both work. The ASHRAE tables optimize this balance for each building type.
How Plumbing Booster Automates It
The Water Heaters module:
1. Select sizing method (ASPE Method 1 or 2, or ASHRAE Tables 6, 7, 8, 9, 10, 11-12, 13, 14, 16, or 17).
2. Enter building parameters (type, fixtures, temperature).
3. The software calculates required storage and recovery.
4. For catalog mode, it matches heaters from the built-in catalog (AO Smith and others) with brand policy (any/prefer/require), hard constraints (recirculation, installation, venting, pressure, temperature, gas/electrical, connections, dimensions, certifications), and scoring weights (oversize, footprint, weight, maintenance, cost, efficiency).
5. For generic mode, it uses B2 auto-staging (choose k units <= maxUnits meeting envelope, optional N+1 redundancy).
6. The Summary page shows sizing results, selected heaters, and compliance status.
