A hot water tank’s size is crucial to provide an adequate and efficient hot water supply for your household. The right tank size depends primarily on the number of people in your home, your peak water usage patterns, and the types of appliances and fixtures you have.
Hot Water Tank Size Calculator
Here is a comprehensive guide covering the key considerations and tank size recommendations to help you decide on the appropriate hot water tank size:
1. Household Size and Usage Needs
The most straightforward factor is the number of household members, as more people naturally require more hot water for showers, dishwashing, laundry, and bathing.
- 1 to 2 people: A tank of about 30 to 40 gallons (115 to 150 liters) is usually sufficient.
- 3 to 4 people: Tanks ranging from 50 to 60 gallons (190 to 230 liters) are recommended.
- 5 or more people: A larger tank, typically 70 to 80 gallons or more (265 to 300+ liters), is needed to accommodate simultaneous usage.
An approximate guideline is to add roughly 10 gallons (about 38 liters) per additional person beyond four members.
2. Peak Hour Water Demand (Peak Usage)
Peak water demand refers to the maximum hot water needed during your household’s busiest times, usually mornings or evenings when showers and appliances are used simultaneously.
- The First Hour Rating (FHR) is an essential metric. It indicates how many gallons of hot water the tank can deliver per hour starting with a full tank.
- Average hot water use per person during peak times is roughly 12 gallons, but this varies by habits and fixture types.
For example, a family of five with a high peak usage might require a tank size of about 340 to 400 liters for gas or electric systems depending on water consumption rates.
3. Types of Hot Water Systems and Size Considerations
- Electric Hot Water Tanks: Usually sized between 125 to 400 liters depending on family size and usage intensity.
- Gas or LPG Tanks: Slightly smaller sizing may suffice; for instance, a 90 to 200-liter gas tank covers 1 to 6 people, respectively.
- Solar Systems: These tanks tend to be larger to store daytime heated water, e.g., 180 liters for 1-2 people, 300 liters for 3-4 people, and up to 440 liters for 5-6 people, often coupled with electric or gas boosters.
- Tankless Systems: Unlike tanked systems, sizing depends on maximum flow rate (gallons per minute) of fixtures used simultaneously and the temperature rise required. For example, simultaneous use of a dishwasher, shower, and washing machine might require 7 to 11 GPM capacity.
4. Physical Dimensions and Installation Space
Hot water tanks generally range in height from about 50 to 70 inches (127 to 178 cm) and diameter between 20 to 30 inches (50 to 76 cm). Larger tanks occupy more space and require proper placement in basements, garages, or roof spaces with adequate clearance.
5. Sample Tank Size Recommendations by Household Size and Usage
| Household Size (People) | Peak Usage Level | Electric Tank Size (Liters) | Gas Tank Size (Liters) | Approximate Gallons (US) |
|---|---|---|---|---|
| 1 – 2 | Low | 80 – 125 | 90 | 30 – 35 |
| 1 – 2 | High | 125 – 150 | 135 | 40 – 45 |
| 3 – 4 | Low | 160 | 130 – 160 | 40 – 46 |
| 3 – 4 | High | 250 – 315 | 170 – 260 | 65 – 85 |
| 5 – 8 | Low | 250 | 170 | 65 |
| 5 – 8 | High | 315 – 400 | 340 | 85 – 100 |
Source: Australian hot water system sizing guide, Pure Plumbing Professionals
6. Factors Impacting Hot Water Tank Size Choice
- Number and Type of Fixtures: Multiple showers or high-flow showerheads increase water demand.
- Simultaneous Usage: More outlets running at the same time require larger tanks.
- Daily Routines: Families with clustered shower times have higher peak demand.
- Energy Efficiency and Recovery Rates: Some systems recover heat faster, which can offset the need for very large tanks.
- Available Space: Physical size may limit tank options.
7. Special Considerations
- For Larger Homes: Multiple tanks or combination systems may be necessary.
- Solar Hot Water Systems: Larger storage needed due to reliance on daytime heating.
- Instant or Tankless Systems: Require calculation of flow rates and temperature rise rather than just volume.
Practical Steps to Choose Your Hot Water Tank Size
- Assess Household Size: Count the number of occupants.
- Estimate Peak Hour Demand: Consider simultaneous hot water needs.
- Check Fixture Flow Rates: Include showers, dishwashers, washers.
- Consult First Hour Rating (FHR): Find a tank meeting or exceeding your peak demand volume.
- Consider Space: Measure installation area to ensure fit.
- Choose Energy Type: Electric, gas, solar, or tankless impact sizing.
- Factor in Future Growth: Include margin for additional family members or usage change.
This detailed overview should help you select the most suitable hot water tank size to meet your household’s hot water needs efficiently and economically. The key is balancing capacity with peak usage to avoid running out of hot water during high-demand periods while not overspending on unnecessarily large systems. Always consult professional guidelines and installers for accurate sizing tailored to your specific conditions.