What size water heater do I need?

Choosing the right water heater size for your home is pretty basic. Depending on what your needs are will determine if a traditional tank water heater or an electric one will be right for your home. You’ll also have to consider what style you prefer. Tankless water heaters are all the rage while traditional tank models are still much more common and won’t be going away anytime soon. So how do you know which one is the best fit? It’s simple. Just start with the basics.

Storage Tank Water Heater Sizes

The first thing you want to consider is the size of the tank if you’re going with a traditional storage tank water heater. An average family of four would use somewhere around 200-400 gallons of water per day for dishwashing, showering, washing laundry, etc. A couple living in an apartment might use half of that whereas a family of six might use up to 600 gallons per day or more. The size of the tank really depends on how much water you use per day not so much on family size. Distance from the water heater to the outlet also plays a role so someone with a large house who’s master bath is on the opposite end of the house as the water heater, will need a larger tank than the same size family that lives in a home where the most commonly used water outlets are close to the water heater.

Stored water tank heaters are great for saving money on usage (about half as much as tankless designs) and are perfect if you need to draw hot or warm water from two or more sources at a time. To be certain you have a water heater that’s the right size for your home you’ll have to do some math. Add up all of the hot water devices in your home that you assume you’d be using at the same exact time (someone takes a shower, you’re doing dishes while the washing machine is going, etc). Add the flow rates of these devices. For example, say the faucet is 0.75, the washing machine is 43 gallons, the shower head 2.5 gallons. Together they’d equal 46.25 gallons. A 50-gallon storage tank water heater would probably be the best choice for you and that other person, however if your activities are not simultaneous you could get away with a smaller tank.

Tankless Water Heaters Sizes

Tankless water heaters are actually rated in gallons-per-minute. When all you want to know is what size tankless water heater do I need, calculating the right size for your home can be accomplished in three easy steps.

  • Add up all of the hot water you’ll be using simultaneously. Say you want to jump in the shower and you need to run the dishwasher at the same time. Average usage rates for each would be: 1.5 – 3.0 gallons per minute for a shower and 1.0 – 3.0 for a dishwasher. On the high end that’s 6 gallons per minute.
  • Depending on what side of the US you live in will determine the average groundwater temperature. In general, if you live in the northern areas, you will need a stronger tankless model than someone in a warmer climate as it takes more work to heat up cooler groundwater.
  • Once you have figured out the gallons per minute and the appropriate groundwater temperature you can determine which tankless water heater is the right size for your home. It’s more tricky than a storage tank model to find the correct size. Fortunately, most every tankless water heater manufacturers will have a water heater size calculator on their site along with their model recommendations once you decide on a brand. Be sure to think longer term and possibly get the next size up in case your family grows unexpectedly (or if single you decide to get married).

Choosing the right size water heater and type doesn’t have to be a long and drawn out process. With a bit of math and personal choice you’ll have the perfect water heater for your home in no time.


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