🚿 Water Heater First Hour Rating Calculator
Calculate the exact First Hour Rating (FHR) your household needs for reliable hot water supply
| Household Size | Recommended FHR (gal) | Recommended FHR (L) | Suggested Tank Size | Heater Type |
|---|---|---|---|---|
| 1 Person | 30–40 gal | 114–151 L | 20–30 gal | Electric / Gas Tank |
| 2 People | 40–50 gal | 151–189 L | 30–40 gal | Electric / Gas Tank |
| 3–4 People | 55–70 gal | 208–265 L | 40–50 gal | Gas Tank / Hybrid |
| 4–5 People | 70–85 gal | 265–322 L | 50–60 gal | Gas Tank / Hybrid |
| 6+ People | 85–100+ gal | 322–379+ L | 60–80 gal | Large Gas / Tankless |
| Tank Size (gal) | Gas FHR (gal) | Electric FHR (gal) | Hybrid FHR (gal) | Recovery Rate |
|---|---|---|---|---|
| 30 gal / 114 L | 60–70 | 42–50 | 55–65 | Gas fastest |
| 40 gal / 151 L | 70–84 | 52–64 | 65–78 | Gas fastest |
| 50 gal / 189 L | 87–98 | 60–76 | 78–92 | Gas fastest |
| 60 gal / 227 L | 98–115 | 70–88 | 90–108 | Gas fastest |
| 80 gal / 303 L | 120–140 | 90–110 | 110–130 | Gas fastest |
| Shower Type | Flow Rate (gal/min) | Flow Rate (L/min) | 8-Min Usage (gal) | 8-Min Usage (L) |
|---|---|---|---|---|
| Low-flow / WaterSense | 1.5 gal/min | 5.7 L/min | 12 gal | 45 L |
| Standard (post-1992) | 2.0 gal/min | 7.6 L/min | 16 gal | 61 L |
| Average modern | 2.5 gal/min | 9.5 L/min | 20 gal | 76 L |
| High-pressure / rain | 3.0 gal/min | 11.4 L/min | 24 gal | 91 L |
| Old / pre-1992 | 3.5–4.0 gal/min | 13–15 L/min | 28–32 gal | 106–121 L |
The first hour delivery, or first hour rating, show the skill of water heater produce warm water. It points the biggest amount of warm water that keeping water heater deliver during one hour. The calculation starts with fully heated device or full tank warm water.
That indication helps to estimate how many warm water a tank heater give during continuous use one hour long. It depends on the store content and on the recovery rate, so how quickly the water in the tank heats back up.
First Hour Rating for Water Heaters
The first hour rating informs exactly as far as warm water the system delivers in most needed moments. Recovery time points as far as quickly warm water becomes available after intensive use. For count it, you takes the store size in gallons and multiply by means of 0.70.
Later you adds the recovery indication to that result. The amount gives the first hour rating, measured in gallons for hour. For instance, device with 80 gallons first hour rating delivers 80 gallons warm water during one hour.
Find that date are easy. The EnergyGuide label shows the first hour rating in the upper left-hand part. It is marked as “Capacity (first hour rating)”.
The Federal Trade Commission forces this label for all new traditional storage water heaters, but no for heat pump water heaters. Maker pamphlet commonly also points it. The rating is in gallons and should not mingle with BTU indication.
Storage tank heaters one dimension according to that rating. A bit more small tank occasionally has higher first hour rating than big. That happens although the small has different capacity but same recovery indication.
Bigger heater can have slow recovery. Other causes, as isolation of the tank and water loss through pipes, also affect the output. Aging device commonly recovers more slowly and produce less warm water during the first hour.
Wrong sensors or aging thermostats prevent to keep ideal temperatures. Such problems limit the amount of warm water during high needs.
