There are many technical terms you need to be familiar with when installing a water heater in your home. This is important to safely use the heater and care for it. The first-hour rating (FHR) of a water heater is one such term you need to understand. Even though water heater brands advertise many great features of their products, the FHR or the amount of water the heater can produce within one hour is one of the most important features to consider when investing in a quality water heater for your home. This article explains what the first-hour rating (FHR) of a water heater is all about.

What Is The FHR Of A Water Heater?

The FHR is the capacity of a water heater to deliver 100% heated water within the first hour of its operation. The maximum capacity and the recovery rate of the heater comes to play in this regard. It’s mandatory for every manufacturer to provide the FHR label on the water heater. In order to get the first-hour rating of a water heater, you should multiply the maximum capacity by 0.70 (70%) and add it to the recovery rate of the heater. The total is the FHR measured by gallons per hour. The 70% is the amount of hot water the heater is capable of delivering on peak hour.

You may wonder why only 70% of the maximum capacity of the heater is taken for the calculation. You need to know how a typical water heater functions to understand this. When you consume hot water, new cold water will start to enter the tank of the heater. This usually happens from the bottom in order to replace the amount of water lost. The overall temperature will drop as a result of the mix of cold water. The rest of the hot water becomes colder as new cold water enters the tank. Once you have used 70% of the heater’s full capacity of hot water, the remaining water will likely become cold.

A typical heater will start to heat water as the hot water in the tank goes out and the cold water comes in. Based on the set temperature level, the thermostat of the heater will sense the loss of heat in the tank. Due to this process, you can expect at least 70% of the water to be at the same temperature that you desire. Most heater brands will allow a 20% drop of temperature from the set point of temperature. For example, if a homeowner sets the heater to warm water at 120 degrees, he or she can expect hot water temperatures that range from 100 to 120 degrees in the 70% amount.

Computing The FHR

The formula for computing the FHR is:

Tank capacity in gallons X 0.70 or 70% + recovery rate = FHR in gph (Gallons per Hour).

For example, the tank capacity is 50 gallons and the recovery rate of the heater is 40 gph. Applying the above formula to this, you will get the following answer.

50 gallons X 0.70 + 40 gph = 75 gph (this is the FHR of the heater).

How To Determine The Right FHR For Your Home

Each family may have their own hot water requirements. You can estimate the use of hot water in your home for various activities during peak hours for this calculation. Peak hour means the times when your family uses hot water. For example, let’s say you have three members in the family (father, mother, and daughter), and you use approximately 74 gallons of hot water per peak hour. With 74 gph of usage, you should opt for a water heater with a first-hour rating of 74 gph or something close to that figure. But if your family uses a lot of hot water each day, you should opt for a water heater with a fast recovery rate. These are important factors to consider when shopping for a quality water heater for your home.

Household water heaters play an important part in your home, especially during the cold season. There are many features to look for when buying a water heater. The first-hour rate or FHR is one of the most important features to consider when investing in a quality water heater for your home.