Whether it’s sooner or later, every water heater eventually needs replacing. There are numerous factors to consider, and one of the most critical is the size of the equipment. If the water heater is too small, you won't have enough hot water and could get stuck in a cold shower. If it's too big, you're wasting energy. Follow these tips to make sure you correctly match the size of your hot water heater to your houme and your needs.
Find Your First Hour Rating
Efficiency is the name of the game. You want to heat up just the amount of water you use, no more, no less. Fortunately, hot water heaters come with capacity ratings that make it easy to figure out which one is right for you. For standard storage water heaters, i.e. those that have a tank, look for a label that bears the “first hour rating.” That tells you how many gallons of hot water the appliance can provide per hour when starting with a full tank.
You then need to calculate roughly how many gallons your household uses during your peak hour of consumption. For many families, that comes in the morning when multiple people take a shower, but it could be other times, depending on your personal habits.
The U.S. Department of Energy provides a chart to help you figure out your total:
Worksheet for Estimating Peak Hour Demand/First Hour Rating
One you determine your total peak hour demand, you can refine your water heater search to those models with a similar first hour rating.
Sizing Your Instant Water Heater
Choosing an instant or tankless hot water heater can be a little more complicated. You need to add up the flow rate for all the hot water devices you could reasonably expect to be using at the same time. For example, that could mean two sinks, a shower and a washing machine. Add up the gallons per minute for all of those water sources, and you’ve found your total peak hour demand.
Those are the basics – but things could change depending on your specific circumstances, and getting expert advice is recommended. A qualified professional plumber can help you choose the right size water heater and perform the installation.