Choosing the right water heater size is crucial. Too small and you'll run out of hot water. Too large and you'll waste energy heating water you don't use. Here's how Mount Pleasant, Charleston, and Daniel Island homeowners can determine the perfect size.
Quick Sizing Guide
| Household Size | Bathrooms | Recommended Size |
|---|---|---|
| 1-2 people | 1-1.5 | 30-40 gallons |
| 2-3 people | 1.5-2 | 40-50 gallons |
| 3-4 people | 2-2.5 | 50 gallons |
| 4-5 people | 2.5-3 | 50-65 gallons |
| 5+ people | 3+ | 65-80 gallons or tankless |
40-Gallon vs 50-Gallon: Direct Comparison
| Factor | 40 Gallon | 50 Gallon |
|---|---|---|
| Best For | 2-3 people | 3-4 people |
| First Hour Rating* | 50-60 gallons | 60-80 gallons |
| Recovery Time | 45-60 min | 50-70 min |
| Equipment Cost | $50-$100 less | $50-$100 more |
| Operating Cost | ~5% less | ~5% more |
| Physical Size | Slightly smaller | Slightly larger |
*First Hour Rating (FHR) = gallons of hot water delivered in the first hour of use
Understanding First Hour Rating
Tank size alone doesn't tell the whole story. First Hour Rating (FHR) is often more important.
What is FHR? The number of gallons of hot water a water heater can deliver in one hour, starting with a full tank.
Why it matters: A 40-gallon tank with a high FHR may outperform a 50-gallon tank with a low FHR during peak use times.
FHR Examples:
- Basic 40-gal electric: FHR 50-55 gallons
- Premium 40-gal gas: FHR 65-75 gallons
- Basic 50-gal electric: FHR 60-65 gallons
- Premium 50-gal gas: FHR 80-90 gallons
Takeaway: Gas water heaters have higher FHRs because they heat water faster.
Calculating Your Hot Water Needs
Step 1: Identify Peak Hour Usage
When does your household use the most hot water? For most families, it's morning (showers, getting ready) or evening (baths, laundry, dishes).
Step 2: Add Up Peak Hour Demand
| Activity | Gallons Used |
|---|---|
| Shower | 10-15 |
| Bath | 15-20 |
| Shaving | 2 |
| Hand washing | 2 |
| Dishwasher | 6-10 |
| Clothes washer (hot) | 7-10 |
Example - Family of 4, Morning Rush:
- 2 showers: 25 gallons
- 1 shave: 2 gallons
- Hand washing: 4 gallons
- Total: 31 gallons
This family needs an FHR of at least 31 gallons. A 40-gallon tank would work, but a 50-gallon provides buffer.
Step 3: Consider Simultaneous Use
Do you run multiple hot water fixtures at once? If someone showers while the dishwasher runs, you need more capacity.
High simultaneous use: Add 20-30% to your calculation
When 40 Gallons Is Enough
A 40-gallon water heater works well for:
- 1-2 person households
- Couples without children
- Small apartments or condos
- Vacation homes with limited use (Sullivan's Island, Isle of Palms rentals)
- Secondary water heaters for detached suites
Advantages of 40 Gallon:
- Lower purchase price ($50-$100 less)
- Slightly lower energy costs
- Fits in tighter spaces
- Adequate for low-demand households
Disadvantages:
- May run out during heavy use
- Not ideal for families with children
- Less buffer for guests
When You Need 50 Gallons
A 50-gallon water heater is better for:
- Families with 3-4 people
- Homes with 2+ bathrooms
- Households with teenagers (long showers!)
- Frequent entertaining or guests
- Multiple simultaneous users
Advantages of 50 Gallon:
- More hot water for peak demand
- Better buffer for unexpected use
- Handles multiple showers back-to-back
- Room for growth (new baby, etc.)
Disadvantages:
- Higher purchase and operating costs
- Requires more space
- Heats water you may not use
When to Go Bigger (65-80 Gallons)
Consider larger tanks for:
- 5+ person households
- Large homes with 3+ bathrooms (common in Mount Pleasant, Daniel Island)
- Jetted tubs or soaking tubs
- Heavy hot water use (hot tub fill, etc.)
- Multi-generational households
Alternatively, consider tankless for unlimited hot water without a larger footprint.
Special Considerations for Charleston Homes
Large New Construction (Daniel Island, Park West)
Many new homes in the Charleston area are 3,000+ square feet with:
- 3-4+ bathrooms
- Master suites with soaking tubs
- High-end appliances
These homes often need 65-80 gallon tanks or tankless systems.
Historic Homes (Downtown Charleston)
Older homes may have:
- Space constraints (small utility areas)
- Fewer bathrooms but longer pipe runs
- Older plumbing with slower flow
A right-sized tank with good FHR often works better than oversizing.
Vacation Properties (Sullivan's Island, Isle of Palms)
Vacation homes have unique patterns:
- Unused for long periods
- Full capacity when occupied
- Multiple guests during peak season
Options:
- Standard 50-gallon for typical vacation home
- Tankless for variable occupancy
- Timer-controlled heating to save energy when vacant
Rental Properties
For investment properties, consider:
- Tenant habits vary widely
- 50-gallon is standard for families
- Durability matters as much as size
Gas vs Electric Sizing Differences
Gas water heaters:
- Heat water faster (higher recovery rate)
- Can often use smaller tank for same output
- Higher FHR ratings
Electric water heaters:
- Slower recovery
- May need larger tank for same household
- Consider hybrid for better performance
Example: A family comfortable with a 50-gal gas tank might need a 65-gal electric tank for equivalent performance.
Upgrading vs Staying Same Size
Reasons to Upgrade Size:
- Family has grown
- Added bathroom
- Current tank runs out regularly
- Planning to stay long-term
Reasons to Stay Same:
- Current size works fine
- Space limitations
- Keeping costs down
- Household is shrinking
Physical Size Comparison
| Tank Size | Height | Diameter |
|---|---|---|
| 40 gallon | 50-52" | 20-22" |
| 50 gallon | 54-56" | 22-24" |
| 65 gallon | 58-62" | 24-26" |
| 80 gallon | 60-65" | 26-28" |
Make sure your water heater location can accommodate the size you need. Measure before purchasing.
Service Areas
Water Heater Doctors helps Charleston area homeowners choose the right size:
Mount Pleasant - All neighborhoods. Daniel Island - Residential and commercial. Charleston - Downtown, West Ashley, James Island. Sullivan's Island - Full service. Isle of Palms - Including Wild Dunes.
FAQ: Water Heater Sizing
Is bigger always better? No. Oversized water heaters waste energy heating water you don't use. Right-sizing saves money.
Can I replace a 50-gallon with a 40-gallon to save money? Only if your household has shrunk or usage has decreased. Otherwise you'll run out of hot water.
What if I'm between sizes? Go with the larger size. The price difference is small, and you'll appreciate the extra capacity.
Do tankless water heaters eliminate sizing concerns? Largely yes. Tankless heats on demand, so you never run out. But you still need proper flow rate (GPM) sizing.
How do I know my current water heater size? Check the label on your water heater. Tank capacity is listed prominently.
Not sure what size water heater you need? Water Heater Doctors provides free assessments throughout Charleston, Mount Pleasant, Daniel Island, Sullivan's Island, and Isle of Palms. Call (843) 990-6524 for expert sizing advice.