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What Size Water Heater Is Right for My Home?

Water heaters play a crucial role in our daily lives, providing the convenience of warm water for bathing, cooking, and cleaning. Yet, choosing the right water heater size for your home can be a daunting task. Whether you’re considering a traditional tank water heater or a modern tankless unit, getting the size right is essential to ensure a consistent supply of hot water while avoiding unnecessary energy costs.

In this blog, we’ll explore the benefits of both kinds of water heaters and explain how a professional plumber can perfectly determine what size water heater is right for your home.

Tank vs. Tankless Water Heaters: Pros and Cons

Before we start talking about sizing considerations, it’s important to understand the fundamental differences between tank and tankless water heaters.

Tank Water Heaters

A tank water heater, also known as a storage water heater, is a type of water heating system that uses a large tank to store and heat a specific amount of water. These tanks typically range in size from 20 to 120 gallons, and they are insulated to help maintain the water’s temperature.


  • Affordability: Tank water heaters are generally more affordable to purchase and install compared to tankless alternatives.
  • Simple Operation: They have a straightforward operation, making them easy to understand and use.
  • Readily Available: Tank water heaters are widely available and can be found in most stores.
  • Reliable: Tank hot water heaters consistently deliver hot water, which is important for households with high water demands.


  • Energy Loss: Tank water heaters may experience standby heat loss, meaning they continually reheat the stored water even when not in use, resulting in energy inefficiency.
  • Limited Hot Water: The amount of hot water is limited by the tank’s size, which can be a drawback for large households with high hot water demands.
  • Space Requirements: The physical size of the water tank may require a dedicated space in your home, which can be a limitation for smaller residences.
  • Shorter Lifespan: Tank water heaters tend to have a shorter lifespan compared to tankless water heaters.

Tankless Water Heaters

A tankless water heater, also known as an on-demand water heater, is a type of water heating system that heats water directly without the need for a storage tank. 


  • Improved Energy Efficiency: Tankless water heaters are more energy efficient since they exclusively heat water when required, substantially diminishing energy usage and decreasing utility expenses.
  • Endless Hot Water: You won’t run out of hot water with a tankless system as it provides a continuous supply.
  • Space-Saving: Tankless units are compact and wall-mounted, freeing up valuable space in your home.
  • Longer Lifespan: Tankless hot water heaters can last up to 20 years or more with proper maintenance, while traditional tank water heaters typically wear out after 10 to 15 years.
  • Reduced Environmental Impact: The lower energy use of tankless heaters reduces your carbon footprint.


  • Higher Initial Cost: Tankless water heaters can be more expensive to purchase and install upfront compared to tank systems.
  • Limited Flow Rate: The hot water flow rate of tankless systems may be limited, which can be a disadvantage if multiple hot water sources are used simultaneously.
  • Required Ventilation: Proper ventilation and gas supply may be necessary, adding to installation costs.
  • Potential Lag: There can be a slight delay in hot water delivery, especially in homes with long pipe runs, which might not be ideal for some users.
  • Regular Maintenance: Tankless water heaters require regular maintenance to ensure optimal performance.

Water Heater Sizing for Tank and Tankless Water Heaters

Whether you opt for a tank or tankless water heater for your Birmingham, AL home, the size plays a pivotal role in its efficiency and effectiveness. 

Tank water heaters are sized based on their storage tank capacity, typically measured in gallons. To determine the right size for your home, consider your daily hot water needs. A family of four, for example, may require a larger tank, like a 40 to 50 gallon water heater.

Tankless water heaters are sized by their flow rate, typically measured in gallons per minute (GPM). Calculate the GPM needed by considering the number of fixtures that may be using hot water simultaneously. For instance, if you anticipate running multiple showers and a dishwasher at the same time, you’ll need a higher GPM rating.

How a Plumber Decides What Size Water Heater is Right For You

Still wondering what size heater do I need? A professional plumber will help you find the answer. Professional plumbing technicians use various calculations to determine the appropriate water heater size for your home. These calculations consider your household’s hot water usage and patterns. Some of the key aspects they assess include:

  1. Peak Demand: Plumbers evaluate your water heater’s needs, paying close attention to when your home has its peak hour of hot water demand. This might be in the morning when family members are showering or in the evening when dishes are being washed.
  2. Fixture Flow Rates: They measure the flow rates of fixtures like showers, faucets, and appliances to gauge how much hot water is needed.
  3. Temperature Rise: Plumbers calculate the difference between your incoming water temperature and the desired hot water temperature. This difference impacts the unit’s capacity requirements.
  4. First-Hour Rating (FHR): FHR represents the total gallons of hot water the unit can deliver during the first hour. It’s a critical factor for tank water heaters and large households.

Get the Water Heater You Need Today

At Douglas Cooling & Heating, we recognize the importance of correctly sizing and skillfully installing water heaters. Our team of experienced plumbing technicians excels in selecting the properly sized water heater for your home and the number of people in it.

In addition to installation, we offer repair and maintenance services for a variety of water heater models including:

  • Natural gas water heaters
  • Electric water heaters
  • Propane gas water heaters
  • Power vent water heaters

Don’t let your home suffer from the inconvenience of cold showers and other water heater issues. Contact Douglas Cooling & Heating today for a free estimate or to schedule service. Our team is here to keep your Birmingham area home comfortable and your hot water running reliably.

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