FHR vs Tank Size: What Actually Matters
Most Tampa homeowners shop water heaters by gallon count alone, and that is the fastest way to buy the wrong unit. The number that actually predicts whether you run out of hot water during the morning rush is First Hour Rating, or FHR. FHR measures how many gallons of hot water a unit can deliver in the first 60 minutes of heavy use, starting with a full tank. It combines stored capacity plus recovery rate (how fast the unit reheats incoming cold water while you are using it).
Here is why this matters. A 40 gallon gas unit with a strong burner can outperform a 50 gallon electric unit during back to back showers, because gas recovers roughly twice as fast. Two households with the same tank size can have completely different real world hot water experiences based on fuel type, burner BTU, and element wattage.
Rheem FHR by Tank Size (Typical Gas Models)
| Tank Size | First Hour Rating | Best Fit |
|---|
| 40 gallon | 54 GPH | 1 to 2 people, 1 bathroom |
| 50 gallon | 67 GPH | 3 to 4 people, 2 bathrooms |
| 75 gallon | 87 GPH | 5+ people, garden tubs, 3+ bathrooms |
Recovery Rate: Gas vs Electric
Recovery rate is gallons per hour the unit can heat from cold to hot during active use. A 50 gallon Rheem gas unit recovers at roughly 40 to 45 GPH. A 50 gallon Rheem electric unit recovers at only 20 to 22 GPH, less than half the gas speed. If your home has natural gas service, staying with gas almost always gives better hot water at lower operating cost. If you are on electric only, size up one tier beyond what gallon charts suggest, or consider a heat pump water heater.
Household Size Sizing Table
Base Sizing by Occupancy
- 1 to 2 people: 40 gallon tank covers two back to back showers with a small buffer. Fine for a condo or small single family home in St. Petersburg or Carrollwood.
- 3 to 4 people: 50 gallon tank is the Florida standard. Handles a morning routine of two showers plus kitchen sink and a dishwasher cycle without running cold.
- 5 or more people: 75 gallon tank or tankless. Anything smaller will struggle on school day mornings when three people shower within 45 minutes.
Upward Adjustments (Size Up One Tier)
- Garden tubs: A standard 42 gallon garden tub needs 28 to 30 gallons of hot water per fill. A 60+ gallon jetted tub can empty a 50 gallon tank by itself.
- Long showers: Teens and homeowners who run 15+ minute showers draw 25 to 35 gallons per shower.
- Simultaneous fixtures: Two showers running while laundry fills and the dishwasher is on can drain a 50 gallon tank in under 20 minutes.
- Florida humidity factor: Tampa Bay residents tend to take longer, warmer showers during the humid summer months. Plan for 15 to 20 percent higher daily hot water draw from May through September.
Florida Attic-Install Size Limits
A large portion of Tampa Bay homes built between 1985 and 2015 have the water heater installed in the attic above the garage or hallway.
Weight and Platform Restrictions
A full 75 gallon tank weighs roughly 625 pounds. A 50 gallon tank weighs around 420 pounds full, and a 40 gallon weighs about 340 pounds. Most original attic platforms were framed for 40 or 50 gallon loads only. Dropping a 75 gallon unit onto an unreinforced platform is a code violation and a real structural risk. In most Tampa attic installs, 50 gallons is the practical maximum without adding sister joists, a new platform, and a deeper overflow pan.
Pan Sizing and Florida Code
Florida code requires a drain pan with at least 2 inches of clearance around the tank on all sides, with a 3/4 inch drain line routed to an approved termination point. If you are moving from a 50 to a 75 gallon unit, plan on pan replacement plus platform reinforcement plus possibly a new drain line path. In many cases the easier and safer solution is to relocate the new unit to the garage or a utility closet. Relocation adds roughly $400 to $900 depending on pipe rerouting.
Rheem Model Recommendations by Size
40 Gallon: Rheem Performance Platinum XE40M10ST45U0
Installed cost: $1,500 to $2,000. Our go-to for condos, townhomes, and smaller homes in areas like Seminole Heights or Dunedin. 12 year tank warranty, brass drain valve, digital display.
50 Gallon: Rheem Performance Platinum XE50M10ST45U0
Installed cost: $1,800 to $2,400. The volume seller for four person Tampa households. Same 12 year warranty, same digital controls, enough recovery to keep up with two morning showers and a dishwasher cycle.
75 Gallon: Rheem Professional Classic Plus
Installed cost: $2,400 to $3,200. For large families, homes with garden tubs, or properties with a guest suite. Heavier unit and may require platform reinforcement or relocation if currently attic mounted.
Hard Water Upgrade: Rheem Gladiator
For homes in Brandon, Riverview, Lutz, and Wesley Chapel where municipal water runs hard (often 12+ grains per gallon), the Rheem Gladiator line adds a self cleaning dip tube and anti scale system. Worth the $200 to $350 upcharge because it can double tank life in hard water zones from 8 years to 14+ years.
When to Skip Tank Entirely (Tankless)
If you are running out of hot water daily no matter what tank size you pick, the tank is not the problem. Your household hot water demand has outgrown the storage model.
The Rheem RTGH-95DVLN tankless unit installed runs $2,800 to $3,800 and delivers 9.5 gallons per minute of continuous hot water. That is enough for two simultaneous showers plus a running faucet, forever, with no tank to empty. Gas line requirements are the main gotcha. Most tankless units need a 3/4 inch gas line and a 199,000 BTU supply. Many older Tampa homes were plumbed with 1/2 inch gas lines sized for a tank, and the upgrade runs $300 to $700 depending on the run length from the meter.
