Share Pin If your old water heater met your capacity needs, then there may not be a reason to change. But before you purchase another, you may want to consider the different options available. The best time to make changes to your water heater set-up is when you're buying a new one! Here's some questions to ask: What types of water heaters are on the market to choose from? What size tankless water heater do I need? How do I even calculate what my household uses or needs? Read on to learn more! Quick NavigationTank-Style Water HeatersTankless Water HeatersPoint-of-Use Water HeatersMobile Home Water HeatersRV Water HeatersReplacing Your Water HeaterReplacing your water heater is rarely how you want to spend your time or money, and there's many things to consider beyond how you'll dispose of your old unit. For instance, you may want to consider transitioning to a tankless system, or even, if it makes sense, switching fuel types.Do You Have the Right Size Heater?Another thing to consider is how well your old water heater met your household hot water demands. Did your showers run cold during peak periods? If so, you may want to consider purchasing a unit that'll better meet your family's needs. We'll show you how to select the right size below.Water Heater Style Type OptionsTank-Style Water HeatersTank-style is the most common type of water heater. They're very versatile and come in models that can operate on electricity, natural gas, and liquid propane. Some are even designed to use solar panels.Tank-style heaters have an insulated tank where the water is heated and stored until there's a hot water demand within the house. When a faucet is opened, hot water flows from the tank to the faucet. Cold water then fills the tank back up to capacity where it's then heated and held until another hot water faucet is opened. Tank capacity sizes vary from 28 gallons to over 100 gallons. If your old water heater wasn't able to keep up with your household hot water demands, there's a good chance that you either out grew your water heater, or it was incorrectly sized from the beginning.A correctly sized water heater will provide a nice balance between delivering enough hot water and operating in an energy efficient manner. Sizing is simply determining your household's hot water needs. It sounds hard, but it's actually not. How to Size a Tank-Style Water HeaterThe simplest method is to follow this rule-of-thumb chart. Remember, this is not an exact science and you should adjust accordingly to account for your family's individual hot water needs. Household MembersTank Size Needed2 People45 to 55 gallons3 People55 to 65 gallons4 People65 to 75 gallons5 People75 to 85 gallons6 People85 to 100 gallons7 People100+ gallonsRecovery RateWhen selecting a tank-style water heater it's important to consider the rate at which the unit is capable of recovering. Recovery rate = Number of gallons of water heated in an hourThe recovery rate is frequently overlooked when choosing a water heater, however, it plays a big role in the unit's performance. If your household has a high demand for hot water, you'll want to select a water heater with a high recovery rate. Tankless Water HeatersA tankless water heater actually doesn't store water, but rather heats the water when there's a demand. This is why they are frequently called on-demand or instantaneous water heaters. The cold incoming water runs through a heat exchanger and within seconds the water leaves the unit hot. Tankless water heaters are capable of delivering a seemingly endless flow of hot water since they're not limited by the size of a storage tank.They're also more energy-efficient than their tank-style cousins because they're not holding and heating hot water. In fact, the electric tankless models frequently achieve an efficiency score of 99%!However, there's also less margin for error when sizing a tankless water heater. Without a storage tank to draw from, if you exceed the units capacity, the tankless unit may not be able to deliver enough hot water.How to Size a Tankless Water HeaterWhat size tankless water heater do I need? To answer this question you need to know two things: Flow rate and temperature rise.Flow rate is basically the amount of hot water the heater is capable of delivering each minute, measured in gallons per minute (GPM). Temperature rise is the difference between the incoming cold water temperature and the outgoing hot water temperature.To determine the flow rate you'll need to figure out how many fixtures will be used during your peak demand. Peak demand is frequently in the morning when the household is showering. FixtureAverage GPMBathroom Sink1.5 GPMShower2.5 - 3.0 GPMDishwasher1.5 GPMBathtub4.0 GPMWashing Machine2.0 GPMAdd each fixture used during the peak demand period. As an example: If your household typically uses the shower (2.5 GPM) and washes clothes (2.0 GPM) during peak demand, your flow rate requirement will be 4.5 GPM.When sizing a tankless unit, there are 2 factors that you should consider: The temperature rise is not the same year around. In the winter, the temperature rise will be higher than in the summer. The flow rate is impacted by the temperature rise. In the winter, when the temperature rise is higher, your flow rate will be lower.The most common tankless water heaters deliver 3.5 gallons per minute, which is generally enough hot water to service 2 points simultaneously. In other words, a shower and a faucet.Tankless units are designed to operate on electricity, natural gas, or liquid propane. Although the electric units are far more energy efficient, there are often electrical upgrades that need to take place to the home in order to provide the amount of electricity necessary. Check out our detailed buyer’s guide where we look at our favorite tankless systems.Point-of-Use Water HeatersPoint-of-use units are sometimes called utility water heaters. They are small tank-style water heaters that are frequently used in shops, garages or outbuildings, and they range in size from 2.5 to 19 gallons and come in various power sizes from high wattage models down to plugin 110V heaters.A common use for these types of water heaters is to provide hot water to a secondary bathroom that is located too far from the main water heater, and therefore is poorly serviced. If a point-of-use water heater is installed, the bathroom will have near instantaneous hot water since the heater will be so close.Mobile Home Water HeatersMobile homes have special requirements for water heaters. A traditional tank-style water heater is usually not an option, although, some tankless models are rated for mobile homes.A mobile home water heater is designed to specifically be used in mobile homes. They are also available in both gas and electric models. RV Water HeatersRecreational vehicles require a specially designed water heater to fit their limited space. There are many different types of water heaters for RV's. They range from a basic design to the sophisticated. RV's are frequently used for extended periods of time. Many "snowbirds" live in their RV's 6 to 8 months a year, so RV water heater's are designed to be compact and yet meet the hot water demand. Check out our article on RV Water Heaters.