How Long Should the Hot Water Last in Your RV?

There are many reasons why you would want to know how much hot water you will have available in your RV. You may be taking an extra passenger, and want to be sure everybody will get a shower, or maybe you suspect your water heater is broken, and would like some numbers to confirm your suspicion. Whatever your reason, we're here to help. While there are many variables that can affect the amount of hot water your RV water heater provides, a few important pieces of information can help put you in the ballpark.

1.) TANK CAPACITY

RV water heaters come in either six or ten gallon models. Obviously, ten gallon models hold more hot water, but they also take longer to heat up.

2.) RECOVERY RATE

Most water heaters are going to be electric, gas, or a combination of the two. Gas models heat faster than their electric counterparts, with recovery rates in the range of 7.4 - 13.5 gallons per hour, compared to the 5.8 - 6.2 GPH of many electric models. Water heaters that can utilize both electric and gas power have even faster recovery rates, with many models capable of over 16 gallons per hour.

3.) FIRST HOUR DELIVERY

Once you know your water heater's size and recovery rate, you can get a general idea of how much hot water you should have. By multiplying the size of the tank by 0.7 and adding the recovery rate, the water heater's First Hour Delivery can be determined. First Hour Delivery is the amount of hot water that a water heater can provide in one hour of operation, provided it has started fully heated. For example, suppose your RV is equipped with an Atwood G6A-7 water heater, which has a capacity of 6 gallons and a recovery rate of 11.6 gallons per hour.

6 x .7 + 11.6 = 15.8

If your water heater is starting from a fully heated state, you should produce about 15.8 gallons of hot water in the first hour of operation.

So How Long Can I Shower?

How long your hot water lasts is directly related to how fast you are using it. To determine this, you will need to know the flow rate of the device being used. This can be easily determined using a bucket and stopwatch. First, place the bucket under the faucet or shower head, then turn it on for ten seconds. Next, multiply the amount of water by six to determine the flow rate per minute. For example, consider a shower head that emits one quart of water in ten seconds.

One quart x 6 = 6 quarts/minute = 1.5 gallons/minute.

If you don't have the necessary equipment, or don't feel like going through the trouble of measuring your device's output, most newer RV shower heads can be estimated to use about two gallons per minute.

Now it's as easy as dividing the First Hour Delivery by the usage rate. For example, using the same numbers from before, we divide the 15.8 gallon First Hour Delivery by the 1.5 gallons per minute that the shower head uses, and we end up with about 10.5 minutes of hot water. But remember, you don't get this 10.5 minutes all at once. First Hour Delivery means just that; it takes the whole hour for the water heater to provide the entire 15.8 gallons of hot water.

Hopefully, you now have the tools to determine whether or not your RV's hot water heater is working properly, as well as a ballpark figure for just how much hot water you have available.

Here is a link to a PDF article on some of the ins and outs of First Hour Delivery, as well as some tables for recovery rates.