First Hour Rating combines tank size and recovery rate into one number that estimates how much hot water is available in a busy hour.
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Quick answer
First Hour Rating, or FHR, is a standardized figure that estimates how many gallons of hot water a tank water heater can deliver in one hour of typical use, starting from a full tank. It combines both stored tank volume and recovery rate — how fast the burner reheats water — into a single practical number, which makes it a more useful sizing tool than tank capacity alone, especially for households with a busy morning routine involving multiple showers close together.
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Two water heaters with the same tank capacity can have very different real-world performance if their burners recover at different speeds. A 50-gallon tank with a strong recovery rate might deliver noticeably more hot water in a busy hour than a 50-gallon tank with a weaker burner, because the weaker unit can't reheat depleted water fast enough to keep up with continued draws.
FHR accounts for this by testing how much hot water a unit delivers over a full hour of simulated draws, starting from a completely heated tank, rather than just reporting how many gallons the tank physically holds. This gives homeowners and technicians a more realistic figure to size against actual household routines.
| Household routine | General FHR guidance |
|---|---|
| 1-2 people, staggered showers | Lower FHR generally sufficient |
| 3-4 people, moderate overlap in morning routine | Moderate to higher FHR recommended |
| 4+ people or back-to-back showers with laundry/dishwasher overlap | Higher FHR needed, or consider tankless for unlimited duration |
| Large soaking tub fills | FHR needs to account for the tub's volume as a single large draw |
It's a common assumption that a larger tank automatically means more available hot water per hour, but if the larger tank has a comparatively weak recovery rate, its FHR might not be much higher than a smaller tank with a stronger burner. This is why comparing FHR directly, rather than gallon capacity alone, gives a more accurate picture when choosing between models.
A licensed technician sizing a replacement water heater will typically look at FHR alongside your household's actual peak-hour hot water use, rather than defaulting to matching the old tank's gallon size, since the old tank's actual performance may not have matched its rated capacity by the time it needed replacing.
To roughly estimate what FHR your household needs, a technician will typically ask about your busiest hour — usually mornings — and count up the approximate hot water draws that happen in that window: number of showers, whether laundry or dishwashing typically overlaps, and whether anyone regularly fills a large tub. This gives a working estimate of peak-hour gallons needed, which can then be matched against a water heater's rated FHR.
Because FHR is measured under standardized test conditions, actual real-world performance can vary somewhat based on your home's incoming water temperature (colder in winter) and your desired output temperature, so the rating is a useful guide rather than an exact guarantee.
Households that consistently need a very high FHR to avoid running out of hot water are often good candidates to at least discuss tankless with a licensed technician, since tankless systems aren't limited by a first-hour figure at all — they heat continuously as long as demand stays within the unit's rated flow rate (GPM). As a ballpark, not a quote, tankless installation in Metro Vancouver generally runs $3,500–$7,500, and proper sizing depends on your home's fixture count and how many typically run at once.
Safety note
Gas tank water heater sizing and installation should be handled by a licensed gas fitter to ensure correct venting and gas line sizing for the chosen unit. If you ever smell gas near the water heater, leave the home immediately and call FortisBC at 1-800-663-9911.
No, FHR combines tank capacity with recovery rate into a single figure estimating hot water delivered over one hour, which can differ meaningfully from the tank's raw gallon size.
FHR is typically listed on the manufacturer's spec sheet or energy label for the specific model, and it should be verified against the documentation for your unit rather than assumed from tank size alone.
Not necessarily on its own — FHR reflects delivery capacity, not efficiency, so a high-FHR unit isn't automatically less efficient, though burner size does factor into overall gas consumption during heavy use.
Yes, this is common, since recovery rate (burner strength) varies between models and manufacturers even at the same tank capacity.
Sediment buildup, a weakening burner, or a partially failing component can reduce real-world performance below the original rated FHR over time, which is one reason older units sometimes seem to run out of hot water faster than they used to.
No, FHR is a tank water heater metric. Tankless systems are rated by flow rate (GPM) instead, since they don't rely on stored volume.
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